The Hundred-Buck Amp Challenge

[TheGimp]

I keep my upper frequency -3dB limit below 10KHz for my guitar amps.

I suggest reducing you coupling cap values.

[TheGimp]

Since the fundimentals are at or below 1Khz, the tenth harmonic will only be at 10KHz, so no sense having a greater bandwidth as it adds to noise.

This was an earlier version.

[PB2]

Originally Posted by TheGimp

I keep my upper frequency -3dB limit below 10KHz for my guitar amps.

I suggest reducing you coupling cap values.

Coupling caps alter the low end and I suggest increasing them to reach the lowest note on a standard tuned 6 string of the low 80s or the low 40s if the plan is for a bass amp. Drop tunings are popular with lead guitar so 60 Hz might be a good compromise. I've simulated several popular guitar amps and most have a LF rolloff at ten Hz that compares to his 100 Hz referring to the curve in post #480.

HF rolloff is usually accomplished in guitar amps with the 68K grid stopper at the input jack forming a LP filter with the first tube's Miller capacitance. All the grid stoppers contribute to the HF rolloff.

[TheGimp]

My bad, sorry about that.

[ChrisA]

Originally Posted by TheGimp

It will be interesting to see how people approach the distortion aspect.

I've got mine to the point where one can dial the power from below 0.1W up to 3W with the distortion staying at about the same level, although the noise floor comes up with power.
First is distortion mode at 0.1W, second is same at 3W before clipping and the third is in clean mode at 1W.

What does it SOUND like? Not many people could figure out the sound from your graph. I think it measures the wrong thing

It is hard to be objective when describing sound. So I think it's best to make objective comments about what can and can not be heard. Examples might be

1) "It cleans up to sound like a Fender champ." (This sound, I think is do to the tone stack even if on a Champ the pots are replaced with fixed resistors but the standard TMB stack is still in there)

2) Distorted power chords sound good but triads and other "normal" chords sound like mud. (this is typical of most "rock" type heavy clipping type distortion.)

3) It's "touch sensitive". Force in the pick controls distortion without effecting loudness so much. (I think amps need to compress the dynamics to make this happen but that's just my theory)

4) the bass strings tend to distort before the others. (or vice versa) Or "tone changes as you move up the neck." I've heard it both ways but I think a lot of people wold go for crystal clear highs and a "crunchy" bass. (It has to do with the freq. response of the first gain stage because it is typically the second gain stage that is driven into distortion.)

5) This amp is design to be a clean tube sound and to by very "pedal friendly".

Those are all objective things one could say or not say. None of them are good or bad, just observations


I don't think the spectra of a 1K signal says anything at all about a guitar amp. 1K is not realistic. try a sweep of the four octave sweep from 80Hz up. That is the range that is used. No point is showing those higher harmonics either as a typical guitar speaker has very little output above about 5KHz

There is absolutely no "correct" answer to how a guitar amp should sound. My preference would be for one to go from "Champ-like" clean to a blues-overdriven sound and use pedals for anything else. In an ultra low power $100 amp I'd also want it to be a combo.

[Wavebourn]

I am going to record some video to show how it works.

Also, I will bring some on BAF in San Francisco. We may need some room for guitar amps, I believe.

Also, I have unfinished bass guitar prototype, but I don't have bass guitar. Anyone?

[Trout]

Originally Posted by Wavebourn

I am going to record some video to show how it works.

Also, I will bring some on BAF in San Francisco. We may need some room for guitar amps, I believe.

Also, I have unfinished bass guitar prototype, but I don't have bass guitar. Anyone?

Bass? Man, mine has been in the case under my bed for at least 7 years now, think I should get new strings?

[Trout]

Since we are on guitar amps,

Does anyone have a copy of the schematics to mod a Gibson GA-5 to the spec as seen in this video?

3:00 minutes in
Viddler.com - Back to the Future Opening Scene - Uploaded by heyuguys

[Wavebourn]

Originally Posted by Trout

Bass? Man, mine has been in the case under my bed for at least 7 years now, think I should get new strings?

You have to!

I took my Ibanez from closet where it was standing last 5 years...

Meanwhile, I created Youtube account, uploading movies there. The first one shows parts, the second one oscilloscope screen and sounds. It is a dirty compressor; you can play from clean to super-dirty without touching any knob, on almost the same SPL.

However, I'm not a guitarist, but I played good enough to show how the amp works.

[wdcw]

Gday Wavebourn,

Do you have a link to your Youtube videos?

Cheers