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Amp Insider: Getting Amped with Brandon Montgomery PDF Print E-mail
Thursday, 17 July 2008 22:39
brandon.jpgGJD: What are the biggest challenges from an amp design standpoint?

BM: Wow, that is a huge question. I think the first and most obvious is to produce an amp that sounds good and that is pleasing to the ears. Beyond that, you have many technical challenges, like lead dress for example.

GJD: What is lead dress?

BM: Lead dress is the arrangement of wires through out the amp. How and where the wires are routed is huge. It has a big affect on the sound and the overall noise level. You have to keep in mind, not to have certain wires too close to each other. But that can get complex as well. For example, AC signal creates stray fields and sometimes coupling can occur. Many times this is not desired but at times it is desired. Just dealing with that can drive you a bit batty.

Also, the destination of certain wires and the grounding scheme is very complex. A lot of times something may sound great but be noisy. The builder has to decide about those kinds of trade offs. Keep in mind that this sort of thing exists through the circuit in many places and the variables can get out of hand. I always go back to high school science class. The one thing that the teacher always spoke about was keeping a constant, so you had a reference point to measure parameters.

GJD: What are some other technical challenges?

BM: Well, component choice is huge. Specific so called perfect capacitors and resistors
don't always translate to good tone. I have various ways of testing these components. I test for ESR... this stands for equivalent series resistance. Without getting too technical, the ESR reading allows you to know the internal heating of the cap due to AC current, and can act like a resistor at certain AC frequencies. So, at times having more accurate info can help you to achieve the tone that you are after.

GJD: Brandon can you expound on this a bit more?

BM: Some caps and resistors are perfect for a specific part of the circuit and others are not. I don't get always crazy about a components measurement; I just try to tune the amp around that individual part. In other words, I don't get obsessed with finding the perfect part. Parts have tolerances and many times there is no real reason why something sounds good. I guess that is where experience comes into play.

GJD: Can you give our readers a specific example or two?

BM: Sure, maybe you have a cap that is .01 mf but that actual spec is .0112 mf, but that might be what I am looking for at the time. A below spec part might thin out your sound in a good way and that might be best for that part of the circuit. Another example would be a smaller cap gives you a more pronounced sound with the mid range control. Look, guitar amps are supposed to be colored. It is a matter of what kind of coloration is the best for the results that you are trying to achieve.

GJD: So what can you do to use your time in an effective manner with parts testing, etc?

BM: Like I said before, the old high school science class idea is on my mind. Also, keeping track of testing through trial and error. Both mental and written notes help. The more organized you are, the better you productivity will be. Also, not getting too obsessive about thousands of details that don't really matter. Ultimately, it is about how good your ears are and you have to also really take care of your ears. They are an amp designer's best friend.

GJD: What about tube mounting and transformers?

BM: Yes, how and where you mount your tubes is huge. Noise, tube life, tone, etc. All that stuff is really important. The angle and distance of how tube sockets and transformers are mounted really matters. How close tubes are mounted to transformers. Also, the direction of how the transformers are mounted can have affect on the phasing and frequency response. Later on we can get more into tube and transformer details.

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