|Guitar amplifier blueprinting? What the heck is that all about?
"Blueprinting" sets up and tunes an amplifier much in the same way as blueprinting the
engine and suspension for a car. Using proprietary methods, we match the amplifier to
the guitarist or bass player, for his particular playing style.
A guitar amplifier can be compared in some ways, to a production automobile. When it
comes off the assembly line, it must meet basic requirements which are within a broad
range of specifications. An amplifier can be "tuned", much in the same way that a race
car is set up for a certain driver on a certain track ... suspension, engine tuning, etc.
We do not "hot rod" an amplifier, that is not the purpose here. The amplifier is
specifically set up for a particular guitar player's style and musical tastes.
The best amplifier manufacturers in the world, even if they had the time, cannot set up
an amplifier in this manner. There is no direct contact between the player and the
manufacturer in most cases. Sometimes you will hear of amp builders that do this, such
as Dumble, but in most cases, this is not the norm.
Amplifiers are also shipped with various styles and brands of tubes. An amplifier using
6L6 style tubes, may be shipped with Sovtek, Svetlana, Tesla, or others. Each are very
different in sound. A "6L6" amp may use 5881, 6L6B, 6L6C, KT-66, tubes also... all
different. During the process, we may swap tubes many times, working with the client
to capture his "sound". Preamp tubes are especially critical in this area.
After the tube types are chosen, we move on to the second objective in this area;
matching the output section of the amplifier.
Mis-matched tubes work against each other. Your notes will not "sing". Some notes
will die a quick death of decay. Sustain is reduced dramatically and even absent at
some frequencies. It is very important in a class A/B design, to have a close match in
the output section. Any difference in waveform will be cancelled out in the NFB loop as
used in Marshall and Fender style amplifiers.
Many times a player will have some notes "sing" and others sound lifeless. They
usually explain to me, that it is "a dead spot in the neck" of their particular guitar. At this
point, I have them try another guitar, if available, of the same type. About 90% of the
time, they are surprised. The other guitar shows the same "dead spots" on the same
notes. It is not the guitar ... it is the amp. I also show them why this is happening on
a scope with a signal generator. This is one of the reasons that the player must be
present when we go through this process for the first time. This is not a procedure
where you can drop off your amp and pick it up a few weeks later.
Another common source of these "dead spots", is an imbalanced 12AT7 or 12AX7
phase inverter or driver. Very few people match the two sides of a preamp triode.
Some of the vendors selected to be shown in our tube vendor section can do this.
When it comes to preamp tubes, most vendors check that the tube "works". They will
also sometimes check that it is not microphonic. That's usually the end of the story. It
is not practical to expect that any tube seller would match the two sides of a dual triode
as a general practice. This is time consuming, and requires specialized equipment. It
involves going through a LOT of tubes and FINDING the pick of the batches. You
cannot make matched triodes, you have to find them. This would easily double the cost
of existing preamp tubes from suppliers. Some folks that sell tubes for high end audio
and hi-fi applications will perform this matching at additional cost. The cost is money
well spent. Less the 5% of preamp tubes are matched within the range we use for our
phase inverters. Typically on a good day you will find 1 in 20 ... on an average day it
can be 1 in 50.
A mismatched output section - If one puts the amp on the scope with a lower frequency
input waveform, it is easy to see the non-linear waveform between the upper and lower
sides of the sine wave. Even the most non-technically involved person can "SEE" the
problem as well as hear the problem. This test is done during the blueprinting
process. THIS IS EXTREMELY CRITICAL FOR GUITARS USING DROPPED
TUNINGS OR 7 STRING GUITARS WHICH TAX THE LOWER FREQUENCIES.
The first stage of gain, or the first preamp tube (usually called V1), is a very important
and tube in your amplifier. It sets the initial gain, tonal qualties, and noise floor for the
amplifier. If you follow the link in the tube reviews to the 12AX7 section, there is a
technical paper on this subject, along with some tips and hints.
Bias has a great impact on the way an amplifier sounds, distorts, and compresses.
Most amps are set to a specific value as the norm. If one sets bias in a conventional
manner, the amp will generally have good tube life overall, and work fairly well.
Bias can be set to other values, which can change sound and feel. It will also change
power, tube life, and where the amps output section starts to distort. Amps that have a
grainy character as a design (such as Mesa Rectifiers), can also have their output
section adjusted, even if you wish to maintain the fixed bias feature of these amps.
Marshall amps with a crunch character can have this "moved" to lower or higher volume
ranges in the amp. In a class A amplifier, there are other methods of producing the
same results and even fixed bias amps such as these have tricks that can be done.
Once we know what you want, what you like, and we have made it happen ...all of this
is recorded and documented. This makes it possible in the future to have your amp
serviced if you cannot be available.
Once your amp has been blueprinted, you are one of our clients. If you are in the local
area, you will be given a phone number to call for help, or be met at the studio or
performing venue to fine tune or change things before a session or performance.
The service of blueprinting an amplifier generally takes about three hours, although in
some cases, can take longer. Email me if you would like additional information.
|As of May 2005 I am now taking blueprinting appointments for evenings and weekends.
|Amplifier blueprinting consists of the following operations and quite a bit more:
1. Scope the amplifier for clean output before work is started. Record output in watts.
2. Scope the amplifier for maximum output in watts before work is started. Record output.
3. Measure and record B+ Voltage, idle current, bias voltage.
4. Check Bias / current draw on existing output section. Record results.
5. Record percentage of current draw of output section. Record results.
6. Check match of side A and B, and microphonics of all tubes in preamp section of amplifier.
Discuss various qualities of different preamp tubes and reach a target objective. All preamp tube
characteristics will be documented.
7. Check the dynamic match of the phase inverter. If not matched, this will be replaced, whether
the amp is blueprinted or not, with a matched phase inverter.
8. Have Musician play amplifier and discuss qualities they would prefer if any.
9. Install new output tubes if desired and re-bias amplifier, or if non-adjustable bias or class A,
replace the current tubes with tubes of the best optimum range for the player's style, taste, and
10. Work with musician changing idle dissapation as to focus in on their particular needs, style,
primary guitar, etc. Adjust as required.
11. Check phase inverter and match of output section using LF waveform to check for optimum
phase balance. If necessary, replace phase inverter again. The phase inverter at this point is
optimized to compliment the rise time of the output tubes.
12. Measure and record the final current draw.
13. Measure and record the final percent plate dissapation.
14. Scope the amplifier for clean output. Record output in watts.
15. Scope the amplifier for maximum output in watts. Record output.
If the musician wishes, he may supply his own tubes of his preference. I will test and classify these
tubes as part of the process. I am not in the "tube selling" business, and there are perhaps better
avenues for tube purchasing than using me as a tube salesman. I will be happy to advise in any