"Voicing" an amp for harp.
Hi, Skip.
The Kalamazoo and the MA17 you did for me are treasures. People ask me about them all the time, and I would like to sound smarter when I answer some of their questions.
I know that (tube) amps that are designed for guitar and as PA heads are often "modded" when they are to be used for harmonica. But could you explain, generally and in terms that harp players might understand (and without giving away any trade secrets, unless you are so inclined), what the main goals of "voicing the amp for harp" are?
Are the modifications mostly to the "tone circuit?" Are they designed to boost certain frequency ranges and/or to reduce others? Which ones?
Are there important modifications to other parts of the amp? I am aware of the idea of changing preamp tubes for different amounts of gain, but are there "hard" modifications as well?
Thanks for your time and you willingness to share.
Mark Heffington
Hello Mark- Thanks for writing. The first thing to remember is that amp design is like cooking. You can change or even "improve" a recipe, but not everyone will agree with you!
Another thing I feel can be overlooked is that most musicians of the past would never have dreamed of changing speakers, tubes, capacitors etc. to voice an amp. Of course there were people who experimented a lot (Bo Diddley!) but in general most players would have worked with the amp they had and gotten another if they didn't like it (and could afford it!).
Most classic guitar amps were made with the ability to get a bright cutting sound, but don't forget that all the gods played with these same Fender amps. The Super Reverb and tweed Bassman amps were very popular for many years with pros and got a darn good tone without mods or voicing.
Vintage PA heads like the Mascos were originally made for a person speaking through a microphone from at least a few inches in front of the mike. Compare that to a harp-dog blasting away with a harp cupped right on to the mike. Now you're putting way more signal into the amp, which is why most stock PA amps can be very sensitive and feedback prone.
Yes, it's true that on Mascos I reduce the gain of the preamp and make sure that they aren't too bright, but I what I really did was experiment on my own followed by giving the amp to people who could really blow. When they liked it, I liked it. I also have a lot of customers who are not pros, and as a side-benefit the amps are "easier" to play for people without years of experience playing amplified.
So, if you want to "voice" an amp for harp, you will generally start by reducing the gain and brightness of the amp. But the actual way you go about it is just like cooking - there are lots of options and everybody has their own idea of "best." Most of the old pros voiced their amps by turning the knobs and by adjusting their technique, which is still a good skill to have today. Of course if your amp uses 12AX7 preamp tubes, it's easy to reduce gain by substituting lower-gain tubes like 12AU7s.
Skip Simmons