Updated 20 NOV 2004
| THD Electronics |
| Andy Marshall and the folks at THD Electronics have offered some of the finest amplifiers over the years, and their construction and design is as top rate as anything I have seen. These days, they are full of new ideas and products, pushing the envelope with new products that are innovative and are of interest to a lot of folks. The Univalve amplifier received rave reviews at the 2001 NAMM show. Every article that has been written about this amplifier glow even more than if a publicity agent for THD had written them. This year, at the 2002 NAMM, they had their new BiValve 30 at the show. Another hit. It seemed that people wanted even more power for live performances, and the folks at THD responded with their latest offering. Also shown at the NAMM show was a great 2x12 ported cabinet, and the cabinets for the Univalve and Bivalve, which turn either of these amps into a combo amp in a matter of minutes, with a vintage look and a great sound. If you have not heard this pure class A amplifier, you might want to give a listen. If you have not read the reviews in the various music publications, try to find the time, or go to Harmony Central on the web, and read the reviews in the amplifier section, or head off to the amp forum and just search past forum topics for "Univalve". THD's hotplate is just the ticket for the over the top sound without the complaints of the neighbors ... their 2 x12 speaker cabinet has the output that exceeds a Marshall 4 x 12 half stack at less weight and with more response. Their Yellow Jackets will let you change your current amplifer into something quite different in a matter of moments, and right back again when you are ready, and their Reactive Rectifer is another product of their's which shows Andy's thinking outside the envelope. If you already own a UniValve, look further below for some information you may find of interest showing some of the aspects of various types of output tubes. Something to remember, try a 12AT7 in the driver position (V2) for more of a blues tone, and a 12AX7 in this position for more of a Marshall or higher front end gain tone. You might also want to try the line out of the UniValve to feed the instrument input of your current amplifier. The UniValve is one of the most impressive recording tools available, as well as a superb front end for amplifiers in a performance venue. Mic'd up with its own cabinet and mixed with a signal into the house system is something to be heard ... you won't forget the experience. This is one of the biggest features of this amp. It is overlooked by too many folks. If you have a clean amp that you thought was rather one dimensional (as an example, a clean Fender Twin), using the UV as a preamp will yield fantastic results. Plug your guitar into the UV, and take the line out from the UV using the instrument setting, plug into the Fender Twin input. Now you can set your volume on the Fender Twin to the desired loudness level, set the UV's volume to the desired clean, crunch, or distortion taste, and then balance the overall level using the UV line out level pot as to keep from overdriving (unless you want to) the front end of the Fender. The UV sits quite nicely on the top of most amps. You do not need to even have a speaker hooked up to the Univalve, it has built in protection when a speaker is not connected. I do not think of the Univalve as a guitar amp. I do not try to compare it with other amps. It is a great amp of course, and is quite loud in spite of it's published ratings, but this amp is a MUST HAVE tool for the studio. It is a fantastic unit to use with ProTools or other direct recording Digital Work Stations. If you have a budget for amps and another for studio gear, maybe take a little out of each for a Univalve. This amp is also a great live amp. It can actually cover pretty nice sized clubs. Mic it and you can cover any venue. It is small enough to be used in a simple A/B rig ... the UV as a second amp dialed in for a particular tone. Take a look at the THD website at: www.thdelectronics.com |
It is one of the things in life that all guitarists have to do
these days .... that is ... head over to the THD website and
listen to the Univalve soundclips, and if the 6L6 example is
not what a guitar amp should sound like, well, then I don't
know what else to say! I know, I am a blues player, but this
sound clip is a tone that is quite a benchmark.
these days .... that is ... head over to the THD website and
listen to the Univalve soundclips, and if the 6L6 example is
not what a guitar amp should sound like, well, then I don't
know what else to say! I know, I am a blues player, but this
sound clip is a tone that is quite a benchmark.
My currently used
Univalve setting and
configuration can be
found in my "past info"
section in the area of
soem of my equipment.
You can get there by
clicking here
Univalve setting and
configuration can be
found in my "past info"
section in the area of
soem of my equipment.
You can get there by
clicking here
A great link for Univalve, which is a very nice website, also has
information and links to some other great sites. It is the site of Bob
Savage and it is located below if you click on the link:
http://members.cox.net/bsavage/univalve/univalve.htm
information and links to some other great sites. It is the site of Bob
Savage and it is located below if you click on the link:
http://members.cox.net/bsavage/univalve/univalve.htm
| THD Univalve Information |
In regard to the chart above, this was done quite a while ago, using a 4 ohm cabinet, but also using what was not a
calibrated watt meter. Recently, in July of 2003, new tests were run, with high power levels shown in an 8 ohm
cabinet. The chart above is good for to compare various tubes, but should not be used as a reference for actual data.
In July of 2003, using a 5751 in V1, a 12AX7 in V2, and a 6L6 GE and a 5881 Tung Sol in V3, the clean power output
measured with calibrated equipment was 14.6-15.1 clean watts out (8 ohm load), and 23 watts peak output. This amp
had more clean output than my Tweed Deluxe (cathode biased) , and was very close to my Fender Deluxe Reverb (A/B)
rated higher.
The Univalve deploys no NFB, so just like the Vox AC30 (30 watts rated) compares in levels to many as close to the 85
watt Fender Twin reverb, the use or lack of use of NFB is one large aspect of loudness overall.
calibrated watt meter. Recently, in July of 2003, new tests were run, with high power levels shown in an 8 ohm
cabinet. The chart above is good for to compare various tubes, but should not be used as a reference for actual data.
In July of 2003, using a 5751 in V1, a 12AX7 in V2, and a 6L6 GE and a 5881 Tung Sol in V3, the clean power output
measured with calibrated equipment was 14.6-15.1 clean watts out (8 ohm load), and 23 watts peak output. This amp
had more clean output than my Tweed Deluxe (cathode biased) , and was very close to my Fender Deluxe Reverb (A/B)
rated higher.
The Univalve deploys no NFB, so just like the Vox AC30 (30 watts rated) compares in levels to many as close to the 85
watt Fender Twin reverb, the use or lack of use of NFB is one large aspect of loudness overall.
Written by Andy Marshall, the President of THD Electronics ( www.thdelectronics.com)
in response to a forum article I wrote in a response to one of the comments by a member
of the forum.
Doug, you've got a pretty good handle on most things on the whole, though I find you a bit bold in some of your
sweeping statements. You clearly do not understand PCB layout or assembly techniques and sound like
someone terribly afraid of going out of business due to competition.
Not all manufacturers choose to use PC boards just to save money. We use them for consistency more than for
price, but making a somewhat affordable amplifier is a nice benefit. I don't think that someone should have to be
a lawyer or Microsoft Millionaire to be able to afford a new amplifier that is hand-built, reliable and sounds and
feels good to play.
If a PC board is designed correctly and the correct components are used, the amplifier production should be
absolutely consistent from one unit to the next. No re-routing of traces should ever be necessary to make an
amp function or sound right. If you find it necessary to change and re-rout wires in your amps, then you are not
in production, but are just making a series of unstable prototypes. Treble reduction to the point where it reduces
the clarity of the amplifier is not an acceptable stabilizing technique for either a PTP or PCB amplifier.
Recently, we got a call from a tech complimenting us on our old Plexi model amplifier (that we built between
1990 and 1995), but he said that it was just a little bit "stiff in the high-end" compared to a real Marshall Plexi. To
back up his point, he told us that he had a real Marshall Plexi on the bench next to ours and was comparing the
two side by side. What he did not seem to realize was that no two Marshall Plexis sound the same. They were
terribly inconsistent with their component sources and values, not to mention the inconsistencies in wire routing.
Taking a point to point or a turret-board amplifier, if one moves the wires around, the entire sound and
character of the amplifier can change, often dramatically. This is a well-recognized phenomenon.
If you understand these interactions well, you can design a PC board to sound and feel any way you want it to.
Furthermore, every one will sound the same. How many times have you plugged into an old Marshall-50 watt
head, only to be terribly disappointed by the sound and feel of the amplifier? While this may be caused by poor
tubes, at least in part, inconsistencies in the internal layout of the amplifier often play a significant role.
If you understand how one component affects the component next to it and how one trace affects the trace next
to it, then you should be able lay out a circuit board correctly the first time, not by building 10 and picking the
best one. Mind you, it takes many years of experience to develop the sort of understanding of the capacitive
and inductive interrelations involved. In the old days, I did this for a living for other companies, designing circuit
boards for the audio sections of amplifiers, mixing consoles, signal processing equipment, etc... While I am
under confidentiality agreements with almost all of my former clients, I can tell you that there is hardly a
professional recording studio in the US or Europe that does not have some audio circuit board with my layout in
some piece of equipment.
After a few hundred such projects, one develops an intricate understanding of how traces and components
interact
A number of years ago, Guitar Player magazine did a review of one of our amplifiers. They stated that they, as a
general rule, do not care for circuit board amplifiers, but also said that I had addressed every one of their
concerns, and that they had nothing bad to say regarding our use of circuit boards. It felt good to see someone
start to understand what it is that we do and why.
Certain components throw a rather large field. Others do not. Some components are very susceptible to the
fields from other components, while some are not. Components can affect the signal passing through traces,
and traces can affect the signal passing through components. It ends up being an enormous network of positive
and negative feedback between components within each other's sway. This is why the distance between specific
components on the board and the physical orientation of the components relative to one another (rotational
orientation, as well as lateral placement) cannot be ignored. Furthermore, which traces are parallel to one
another and at what distance, which traces are perpendicular to one another and that what distance, and the
amount of ground plane in-between them can seriously affect the overall sound and feel of the finished amplifier.
Most people design circuit boards either haphazardly or for the greatest parts density/easiest and least
expensive manufacture. Neither of these methods belongs in a high-end amplifier, and such approaches give
PC Board designs a bad name.
If you know what you are doing, a thicker board is better than a thinner board (ours are .093" or 3/32", most are
.062? or 1/16?) and that thick copper is a good idea (ours is 4 oz, most use 1/2 oz or 1 oz). One of the greatest
problems facing most circuit board amplifiers is board flex. Board flex creates metal fatigue in the copper. As the
copper cannot really "break", it just crystallizes and makes tons of noise. This is much worse in combo amps, of
course. We go to the trouble to support our boards ever few inches. Our design standard is that 100 pounds of
force on a 1/4" diameter probe should not be able to flex the board more than 20 thousandths of an inch at any
point on the board. All of our amps designs must pass this test. For comparison, most Marshall and Fender
circuit boards would break under such force, and would flex more than 3/8 of an inch just before breaking.
Through-plated holes are an absolute must, with solder pads on both sides. This makes it much harder for a
repairman to inadvertently lift a pad or a trace by overheating or from poor technique. The way that we have
addressed this is to start with boards that are clad with 2 oz copper, and in the through-hole plating process we
add another 2 ounces. This leaves us with traces and ground planes of 4 ounces, and through plated holes with
2 oz copper in the holes themselves. I have seen some other people start with 3 oz copper, plating on an
additional 1 oz, and I have not like the results I have seen. The through-holes pull out too easily.
Contrary to popular belief, "Orange Drop" film capacitors are far from great. They are OK for certain position in
certain circuits, but their consistency from one to the next is atrocious. Maybe this is part of why so many people
who use them in PTP amps find the need to make wire adjustments. This is a big part of what I mean by using
the right components.
As for PCB solder joints becoming problematic with time, this is no more a problem than on PTP. A good solder
joint with absolute minimum stress on it (using the right component with the right lead length and the right
mounting technique) will yield the longest and most consistent life. Assuming that the flow-solder machine is
correctly set up, the right solder, right flux, right solder temperature, right flux temperature, right pre-heat, right
cooling, etc? are done, a flow-soldered board will last longer and have higher quality solder joints than a
hand-soldered board. If you doubt this, ask yourself the following questions: How do you decide what solder to
use? Do you choose SN60, SN63, SN96, Savebit or some other? How do you decide what flux to use in your
solder and how much? How do you decide what temperature to set your iron at? It all makes a HUGE difference
in the quality and consistency of your solder joints. If you cannot answer all of these questions, then you cannot
even have a clue about the long-term consistency and life expectancy of your products. This, along with
countless other points, is part of what separates the hobbyist from the professional.
In a PTP amp, the entire surface of the solder joint is exposed to air, and thus, to corrosion. In a through-plated
PCB amp, only the top and bottom surfaces of the solder joint are exposed to corrosion, not the majority of the
joint, which is within the through-hole, which is where most of the contact is made.
We use only FAA-approved aircraft assemblers in every stage of our manufacturing. They have to understand
all of these points completely. The FAA is even more stringent than the military. Also, the aircraft industry is just
about the only industry left that uses PCBs for the electronic components wired to chassis-mounted
electro-mechanical components like the controls and connectors. They do this because countless FAA tests
have shown that devices built this way last longer and are more reliable and consistent than any other method,
even taking cost out of the picture entirely. This is, of course, why we use the exact same methods.
In closing, I absolutely believe that circuit boards, when they are well-designed and laid out, are in all ways
superior to other manufacturing techniques when one is building amplifiers in quantities. If I did not believe this
firmly, I would not be doing it. This said, I think it is a terribly expensive and cumbersome method for hobbyists to
attempt. If you don't have a great deal of experience under your belt designing circuit boards, you won't like the
results. Point to point and turret-board techniques offer the hobbyist and the small-scale amp shop the
opportunity to easily tweak their designs, as is so often necessary. So, unless you're going to be building 50
amps a month or more, it is probably best to stay away from circuit boards.
in response to a forum article I wrote in a response to one of the comments by a member
of the forum.
Doug, you've got a pretty good handle on most things on the whole, though I find you a bit bold in some of your
sweeping statements. You clearly do not understand PCB layout or assembly techniques and sound like
someone terribly afraid of going out of business due to competition.
Not all manufacturers choose to use PC boards just to save money. We use them for consistency more than for
price, but making a somewhat affordable amplifier is a nice benefit. I don't think that someone should have to be
a lawyer or Microsoft Millionaire to be able to afford a new amplifier that is hand-built, reliable and sounds and
feels good to play.
If a PC board is designed correctly and the correct components are used, the amplifier production should be
absolutely consistent from one unit to the next. No re-routing of traces should ever be necessary to make an
amp function or sound right. If you find it necessary to change and re-rout wires in your amps, then you are not
in production, but are just making a series of unstable prototypes. Treble reduction to the point where it reduces
the clarity of the amplifier is not an acceptable stabilizing technique for either a PTP or PCB amplifier.
Recently, we got a call from a tech complimenting us on our old Plexi model amplifier (that we built between
1990 and 1995), but he said that it was just a little bit "stiff in the high-end" compared to a real Marshall Plexi. To
back up his point, he told us that he had a real Marshall Plexi on the bench next to ours and was comparing the
two side by side. What he did not seem to realize was that no two Marshall Plexis sound the same. They were
terribly inconsistent with their component sources and values, not to mention the inconsistencies in wire routing.
Taking a point to point or a turret-board amplifier, if one moves the wires around, the entire sound and
character of the amplifier can change, often dramatically. This is a well-recognized phenomenon.
If you understand these interactions well, you can design a PC board to sound and feel any way you want it to.
Furthermore, every one will sound the same. How many times have you plugged into an old Marshall-50 watt
head, only to be terribly disappointed by the sound and feel of the amplifier? While this may be caused by poor
tubes, at least in part, inconsistencies in the internal layout of the amplifier often play a significant role.
If you understand how one component affects the component next to it and how one trace affects the trace next
to it, then you should be able lay out a circuit board correctly the first time, not by building 10 and picking the
best one. Mind you, it takes many years of experience to develop the sort of understanding of the capacitive
and inductive interrelations involved. In the old days, I did this for a living for other companies, designing circuit
boards for the audio sections of amplifiers, mixing consoles, signal processing equipment, etc... While I am
under confidentiality agreements with almost all of my former clients, I can tell you that there is hardly a
professional recording studio in the US or Europe that does not have some audio circuit board with my layout in
some piece of equipment.
After a few hundred such projects, one develops an intricate understanding of how traces and components
interact
A number of years ago, Guitar Player magazine did a review of one of our amplifiers. They stated that they, as a
general rule, do not care for circuit board amplifiers, but also said that I had addressed every one of their
concerns, and that they had nothing bad to say regarding our use of circuit boards. It felt good to see someone
start to understand what it is that we do and why.
Certain components throw a rather large field. Others do not. Some components are very susceptible to the
fields from other components, while some are not. Components can affect the signal passing through traces,
and traces can affect the signal passing through components. It ends up being an enormous network of positive
and negative feedback between components within each other's sway. This is why the distance between specific
components on the board and the physical orientation of the components relative to one another (rotational
orientation, as well as lateral placement) cannot be ignored. Furthermore, which traces are parallel to one
another and at what distance, which traces are perpendicular to one another and that what distance, and the
amount of ground plane in-between them can seriously affect the overall sound and feel of the finished amplifier.
Most people design circuit boards either haphazardly or for the greatest parts density/easiest and least
expensive manufacture. Neither of these methods belongs in a high-end amplifier, and such approaches give
PC Board designs a bad name.
If you know what you are doing, a thicker board is better than a thinner board (ours are .093" or 3/32", most are
.062? or 1/16?) and that thick copper is a good idea (ours is 4 oz, most use 1/2 oz or 1 oz). One of the greatest
problems facing most circuit board amplifiers is board flex. Board flex creates metal fatigue in the copper. As the
copper cannot really "break", it just crystallizes and makes tons of noise. This is much worse in combo amps, of
course. We go to the trouble to support our boards ever few inches. Our design standard is that 100 pounds of
force on a 1/4" diameter probe should not be able to flex the board more than 20 thousandths of an inch at any
point on the board. All of our amps designs must pass this test. For comparison, most Marshall and Fender
circuit boards would break under such force, and would flex more than 3/8 of an inch just before breaking.
Through-plated holes are an absolute must, with solder pads on both sides. This makes it much harder for a
repairman to inadvertently lift a pad or a trace by overheating or from poor technique. The way that we have
addressed this is to start with boards that are clad with 2 oz copper, and in the through-hole plating process we
add another 2 ounces. This leaves us with traces and ground planes of 4 ounces, and through plated holes with
2 oz copper in the holes themselves. I have seen some other people start with 3 oz copper, plating on an
additional 1 oz, and I have not like the results I have seen. The through-holes pull out too easily.
Contrary to popular belief, "Orange Drop" film capacitors are far from great. They are OK for certain position in
certain circuits, but their consistency from one to the next is atrocious. Maybe this is part of why so many people
who use them in PTP amps find the need to make wire adjustments. This is a big part of what I mean by using
the right components.
As for PCB solder joints becoming problematic with time, this is no more a problem than on PTP. A good solder
joint with absolute minimum stress on it (using the right component with the right lead length and the right
mounting technique) will yield the longest and most consistent life. Assuming that the flow-solder machine is
correctly set up, the right solder, right flux, right solder temperature, right flux temperature, right pre-heat, right
cooling, etc? are done, a flow-soldered board will last longer and have higher quality solder joints than a
hand-soldered board. If you doubt this, ask yourself the following questions: How do you decide what solder to
use? Do you choose SN60, SN63, SN96, Savebit or some other? How do you decide what flux to use in your
solder and how much? How do you decide what temperature to set your iron at? It all makes a HUGE difference
in the quality and consistency of your solder joints. If you cannot answer all of these questions, then you cannot
even have a clue about the long-term consistency and life expectancy of your products. This, along with
countless other points, is part of what separates the hobbyist from the professional.
In a PTP amp, the entire surface of the solder joint is exposed to air, and thus, to corrosion. In a through-plated
PCB amp, only the top and bottom surfaces of the solder joint are exposed to corrosion, not the majority of the
joint, which is within the through-hole, which is where most of the contact is made.
We use only FAA-approved aircraft assemblers in every stage of our manufacturing. They have to understand
all of these points completely. The FAA is even more stringent than the military. Also, the aircraft industry is just
about the only industry left that uses PCBs for the electronic components wired to chassis-mounted
electro-mechanical components like the controls and connectors. They do this because countless FAA tests
have shown that devices built this way last longer and are more reliable and consistent than any other method,
even taking cost out of the picture entirely. This is, of course, why we use the exact same methods.
In closing, I absolutely believe that circuit boards, when they are well-designed and laid out, are in all ways
superior to other manufacturing techniques when one is building amplifiers in quantities. If I did not believe this
firmly, I would not be doing it. This said, I think it is a terribly expensive and cumbersome method for hobbyists to
attempt. If you don't have a great deal of experience under your belt designing circuit boards, you won't like the
results. Point to point and turret-board techniques offer the hobbyist and the small-scale amp shop the
opportunity to easily tweak their designs, as is so often necessary. So, unless you're going to be building 50
amps a month or more, it is probably best to stay away from circuit boards.
From my amps section area of this website:
THD Flexi 50 - This amp was purchased in November of 2004. There is more detail on this amp in a review I
wrote on Harmony Central which I also copied and included in the THD area of this website below here. The
reason for the acquisition of this amp was due to be impressed by a few of these that had crossed my path. I
wanted a mid power amp that could cover many tonal requirements and this amp did the job better than any
other amp I had seen. The transformer isolated line out is perfect for the largest venues to augment a mic'd
cab. THD may have the best line out in the business, bar none. The front end of this amp is articulate and
defined at any setting, the tone stack is one of the most impressive I have ever used and the amp has a very
extensive feature set that is described elsewhere. The amp was delivered with a fine set of NOS 1990's
12AX7C tubes and the great Ruby EL-34B-STR. I have amps that cover the EL-34 tones and this amp
covered them just as nicely, or more so but I was looking for more of a darker tone set and this amp gave me
ability to have whatever I wanted for the most part. The tube set was changed to 3 GT-12AX7M tubes, V3
being an SAG-AX7-MPI built off a 12AX7M. The output set is a GT-6L6GE duet biased as per THD
instructions which are right on the money and may be a bit different than many folks are used to. Thie name
"Flexi" should mean "flexible" when you think of this amp. This may be the nicest playing, most versatile,
greatest sounding 50 watter than I have seen in a long long time. The last thing I needed to explain to my wife
on spending more "amp money" was the logic for yet one more amp.
THD Flexi 50 - This amp was purchased in November of 2004. There is more detail on this amp in a review I
wrote on Harmony Central which I also copied and included in the THD area of this website below here. The
reason for the acquisition of this amp was due to be impressed by a few of these that had crossed my path. I
wanted a mid power amp that could cover many tonal requirements and this amp did the job better than any
other amp I had seen. The transformer isolated line out is perfect for the largest venues to augment a mic'd
cab. THD may have the best line out in the business, bar none. The front end of this amp is articulate and
defined at any setting, the tone stack is one of the most impressive I have ever used and the amp has a very
extensive feature set that is described elsewhere. The amp was delivered with a fine set of NOS 1990's
12AX7C tubes and the great Ruby EL-34B-STR. I have amps that cover the EL-34 tones and this amp
covered them just as nicely, or more so but I was looking for more of a darker tone set and this amp gave me
ability to have whatever I wanted for the most part. The tube set was changed to 3 GT-12AX7M tubes, V3
being an SAG-AX7-MPI built off a 12AX7M. The output set is a GT-6L6GE duet biased as per THD
instructions which are right on the money and may be a bit different than many folks are used to. Thie name
"Flexi" should mean "flexible" when you think of this amp. This may be the nicest playing, most versatile,
greatest sounding 50 watter than I have seen in a long long time. The last thing I needed to explain to my wife
on spending more "amp money" was the logic for yet one more amp.
This is a review that I posted on Harmony-Central. I actually made a few changes, mostly
corrections for typing errors, but I thought I could also stray a bit from the 1-10 scale that
you are limited to on Harmony-Central.
Features: 10
My amp has not arrived yet, it is on order but I have had a number of these cross my bench and have spent
many hours with them. These come across the bench for tube kits and ideas, not for service of any nature.
Most if the features have been mentioned here in other reviews. I will take a moment to approach things from a
bit of a different angle.
The late 1980s saw some great amp builders come on the scene. Matchless, Dr. Z and THD were a few of
them.
THD came to my attention though a friend, Aspen Pittman, founder of Groove Tubes. Now you may love or
hate GT but the point here is that Aspen has one of the most extensive amp collections around and he does
have a great ear. When THD came out with their tweed bassman reproduction Aspen commented that is was
perhaps the best sounding and playing tweed bassman he had ever heard.
Years later I saw an amp called a Univalve. I am involved with tubes in my line of work and this amp seemed to
be just the thing to actually compare tubes easily. Too often we rely on tests, traces and specs where these
things differ more in the actual tone aspects of the tube. I bought a Univalve from The Amp Shop in So. Cal.
My UV was one of the earliest. I met with Andy Marshall from THD to perform a change to make the amp more
reliable. The amp had been 100% reliable for months and this change was something that would fix something
"that could happen" but rarely did. It never happened to me. In the process of making the change an etch had
to be cut. This opened my eyes quite a bit. You cannot tell all that easily the thickness of etches visually. Once
you try to cut one of these THD traces and realize you need a power grinder you realize how thick the etches
and substrate are. The construction of these amps is about as perfect as it gets. THD uses proper technology
to it's best advantage where it is best applied. Chassis mount sockets with flying hand wired leads to the
board. Modern resistors rather than carbon comps which are not as stable and are more noisy.
The Univalve became a primary studio tool. One feature overlooked by far too many folks was the great
transformer isolated line out. I use the UV as a preamp quite often. Get the gain and tone from the UV and
take it's line out to a Fender Twin Reverb and you can have a pretty amazing rig.
The Flexi 50 - No surprises here. I first saw and heard this amp at the 2003 NAMM. I was very impressed. I told
the THD folks I wanted to get on the list for one. They were not going to be shipping for a while as the tone
stack was not finalized. Andy and Ed at THD don't let things out until they are completely satisfied with the end
result.
The amps has the features most people would want and that most folks would find useful. I am a big fan of the
THD line outs. They are one of the few folks that seem to know how to do this in a way where it works for the
applications I need. I have used the UV in very large live environments. Mic the cab and run to one channel
and take the line out to a second channel and you can cover a lot of arena area.
The dual voltage is a great feature for 6V6 use.
The amplifier is fully featured yet not messy or complex.
Sound Quality: 10
I have used the Flexi 50 amps in a number of environments - live work, studio work, etc.
This amps is not trying to replicate a specific amp. I guess when folks hear Flexi they think Plexi. This is sort of
a yes and no. This amp covers the tones and bases of the early era Marshall amps really nicely. BUT >>>> it
can also cover bases other than just the "Marshall" tones. With a 12AY7 in V1 and a nice set of 6L6 output
tubes and a 4x10 cab you can hear tweed bassman tones and character. With a 12AX7 in V1 and V2 and
12AT7 in V3 with those same 6L6 tubes and an open back 2x12 you can cover Fender tones pretty darn
nicely.
This amp does not "copy" other amps. It is a very versatile amp that lets you move to the character of other
amp types due to it's design and architecture, tube change ability, etc.
On cabinets by the way, I have used these amps with 1x12, 2x12, 2x10, 4x10, ported, open backed and closed
back cabs. Some of you know the other amps and cabs I have and most of those cabs have been used. I have
strong personal preferences, and I think Ed at THD has made comments that I am more a "Fender guy" than a
high gain guy. Yup, I grew up on Fender, Marshall, Vox in the 60s and have sort of stayed that way but I work
with a lot of folks that are quite "over the top" when it comes to gain or walls of cabs. These days the walls of
cabinets are going away due to the "Nashville backline" where control and tone are important in live
performances. Now one needs a great cab that may be out of sight. I want to just take a second here to say
that my two favorite cabinets in the universe are the Dr. Z Z-Best and THD 2x12 cabs.
This amp is very versatile in the "sound" area and covers more bases due to it's tube swappage ability than
most any other amp. Many folks think that you can switch 6L6 to EL34 in other amps with a rebias. Well, sort of
yes and no. Technically yes, but the amp's output transformer was generally optimized for a specific tube and
these two tubes are different. So how can this be done by THD? They have their own design transformers and
these are quite different than convention iron. When you move a convention speaker tap from the 4-8-16 ohm
positions, you are using a smaller portion of the transformer and the winding setup is not the same. THD
transformers use the full core at any setting. Perhaps this should be mentioned as a "feature" but it does affect
the sound.
THD also makes transformers that you can buy for your non THD amp. They also make something called the
reactive rectifier which is a very cool piece of gear that many folks do not know about. Their Hot Plate and
Yellow Jackets are already well known.
If you do want over the top metal sounds just grab an Extreme III pedal and have at it. The amp is very pedal
friendly.
Reliability of THD products overall: 11
I expect this amp to give the same reliability as my Univalve. My UV goes to many gigs, concerts, and studio
sessions. The UV has been used from day one many times per week, has been flown over most of this planet,
used as a stand alone amp and as a preamp. It has ingested more "suspect" tubes as a test device without
problems. It has never had a single problem - EVER.
If there are folks thinking that only a PTP amp can be reliable think about a Navy F-18 pilot crashing onto a
carrier flight deck every day. These pilots are surrounded with PCBs that are lighter surface mount technology
with micro etch work. Basically, a well built amp is a well built amp and a badly executed PTP amp or PCB amp
is going to be a nightmare.
Customer Support: 15
THD support is legendary. Ed at THD is also a killer player and is more than happy to offer his
advice on just about anything even if it is not a THD product. Ed is also pretty terrific on recording
techniques and live rigs. Andy Marshall is a super fellow too and seems to surround himself with
great folks from the receptionist outward in their staff.
Overall Rating: 12
I have been playing since I was eight. I am now 55. On my other gear it is basically Fender, Marshall, GT, THD,
Victoria, Mesa, Dr. Z, and more. A lot of this is on my business website at Guitar Amplifier Blueprinting. When I
am not at GAB I am at GT (Groove Tubes) where I run the SAG (special applications group). I see a lot of
amps cross my path, maybe a bit more than the average fellow out there.
Submitted by Myles S. Rose at 11/19/2004 08:47
corrections for typing errors, but I thought I could also stray a bit from the 1-10 scale that
you are limited to on Harmony-Central.
Features: 10
My amp has not arrived yet, it is on order but I have had a number of these cross my bench and have spent
many hours with them. These come across the bench for tube kits and ideas, not for service of any nature.
Most if the features have been mentioned here in other reviews. I will take a moment to approach things from a
bit of a different angle.
The late 1980s saw some great amp builders come on the scene. Matchless, Dr. Z and THD were a few of
them.
THD came to my attention though a friend, Aspen Pittman, founder of Groove Tubes. Now you may love or
hate GT but the point here is that Aspen has one of the most extensive amp collections around and he does
have a great ear. When THD came out with their tweed bassman reproduction Aspen commented that is was
perhaps the best sounding and playing tweed bassman he had ever heard.
Years later I saw an amp called a Univalve. I am involved with tubes in my line of work and this amp seemed to
be just the thing to actually compare tubes easily. Too often we rely on tests, traces and specs where these
things differ more in the actual tone aspects of the tube. I bought a Univalve from The Amp Shop in So. Cal.
My UV was one of the earliest. I met with Andy Marshall from THD to perform a change to make the amp more
reliable. The amp had been 100% reliable for months and this change was something that would fix something
"that could happen" but rarely did. It never happened to me. In the process of making the change an etch had
to be cut. This opened my eyes quite a bit. You cannot tell all that easily the thickness of etches visually. Once
you try to cut one of these THD traces and realize you need a power grinder you realize how thick the etches
and substrate are. The construction of these amps is about as perfect as it gets. THD uses proper technology
to it's best advantage where it is best applied. Chassis mount sockets with flying hand wired leads to the
board. Modern resistors rather than carbon comps which are not as stable and are more noisy.
The Univalve became a primary studio tool. One feature overlooked by far too many folks was the great
transformer isolated line out. I use the UV as a preamp quite often. Get the gain and tone from the UV and
take it's line out to a Fender Twin Reverb and you can have a pretty amazing rig.
The Flexi 50 - No surprises here. I first saw and heard this amp at the 2003 NAMM. I was very impressed. I told
the THD folks I wanted to get on the list for one. They were not going to be shipping for a while as the tone
stack was not finalized. Andy and Ed at THD don't let things out until they are completely satisfied with the end
result.
The amps has the features most people would want and that most folks would find useful. I am a big fan of the
THD line outs. They are one of the few folks that seem to know how to do this in a way where it works for the
applications I need. I have used the UV in very large live environments. Mic the cab and run to one channel
and take the line out to a second channel and you can cover a lot of arena area.
The dual voltage is a great feature for 6V6 use.
The amplifier is fully featured yet not messy or complex.
Sound Quality: 10
I have used the Flexi 50 amps in a number of environments - live work, studio work, etc.
This amps is not trying to replicate a specific amp. I guess when folks hear Flexi they think Plexi. This is sort of
a yes and no. This amp covers the tones and bases of the early era Marshall amps really nicely. BUT >>>> it
can also cover bases other than just the "Marshall" tones. With a 12AY7 in V1 and a nice set of 6L6 output
tubes and a 4x10 cab you can hear tweed bassman tones and character. With a 12AX7 in V1 and V2 and
12AT7 in V3 with those same 6L6 tubes and an open back 2x12 you can cover Fender tones pretty darn
nicely.
This amp does not "copy" other amps. It is a very versatile amp that lets you move to the character of other
amp types due to it's design and architecture, tube change ability, etc.
On cabinets by the way, I have used these amps with 1x12, 2x12, 2x10, 4x10, ported, open backed and closed
back cabs. Some of you know the other amps and cabs I have and most of those cabs have been used. I have
strong personal preferences, and I think Ed at THD has made comments that I am more a "Fender guy" than a
high gain guy. Yup, I grew up on Fender, Marshall, Vox in the 60s and have sort of stayed that way but I work
with a lot of folks that are quite "over the top" when it comes to gain or walls of cabs. These days the walls of
cabinets are going away due to the "Nashville backline" where control and tone are important in live
performances. Now one needs a great cab that may be out of sight. I want to just take a second here to say
that my two favorite cabinets in the universe are the Dr. Z Z-Best and THD 2x12 cabs.
This amp is very versatile in the "sound" area and covers more bases due to it's tube swappage ability than
most any other amp. Many folks think that you can switch 6L6 to EL34 in other amps with a rebias. Well, sort of
yes and no. Technically yes, but the amp's output transformer was generally optimized for a specific tube and
these two tubes are different. So how can this be done by THD? They have their own design transformers and
these are quite different than convention iron. When you move a convention speaker tap from the 4-8-16 ohm
positions, you are using a smaller portion of the transformer and the winding setup is not the same. THD
transformers use the full core at any setting. Perhaps this should be mentioned as a "feature" but it does affect
the sound.
THD also makes transformers that you can buy for your non THD amp. They also make something called the
reactive rectifier which is a very cool piece of gear that many folks do not know about. Their Hot Plate and
Yellow Jackets are already well known.
If you do want over the top metal sounds just grab an Extreme III pedal and have at it. The amp is very pedal
friendly.
Reliability of THD products overall: 11
I expect this amp to give the same reliability as my Univalve. My UV goes to many gigs, concerts, and studio
sessions. The UV has been used from day one many times per week, has been flown over most of this planet,
used as a stand alone amp and as a preamp. It has ingested more "suspect" tubes as a test device without
problems. It has never had a single problem - EVER.
If there are folks thinking that only a PTP amp can be reliable think about a Navy F-18 pilot crashing onto a
carrier flight deck every day. These pilots are surrounded with PCBs that are lighter surface mount technology
with micro etch work. Basically, a well built amp is a well built amp and a badly executed PTP amp or PCB amp
is going to be a nightmare.
Customer Support: 15
THD support is legendary. Ed at THD is also a killer player and is more than happy to offer his
advice on just about anything even if it is not a THD product. Ed is also pretty terrific on recording
techniques and live rigs. Andy Marshall is a super fellow too and seems to surround himself with
great folks from the receptionist outward in their staff.
Overall Rating: 12
I have been playing since I was eight. I am now 55. On my other gear it is basically Fender, Marshall, GT, THD,
Victoria, Mesa, Dr. Z, and more. A lot of this is on my business website at Guitar Amplifier Blueprinting. When I
am not at GAB I am at GT (Groove Tubes) where I run the SAG (special applications group). I see a lot of
amps cross my path, maybe a bit more than the average fellow out there.
Submitted by Myles S. Rose at 11/19/2004 08:47