Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ajeffcote on February 14, 2012, 06:02:04 am
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The amp I'm working on is an Allen Accomplice. Bass is too boomy. Tried replacing the tone stack standard values of .1 and .047 with two .022s. Still too much bass. The post-phase-inverter master-volume uses 4 ,.1 caps to couple to the output tubes. Two before and two after the MV. Cathode by-pass caps are standard 22uf. If I want to re-voice there can I just replace the last two caps, or do I need to replace all four?
OR, maybe I should change the second stage coupler, an .02 to maybe a .01?
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Cathode by-pass caps are standard 22nf.
You mean 22μF, right? If so, change those to something under 5μF and see if that gets where you want to be. 0.68μF and 2.2μF are popular values.
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OK, if I change the cathode bypass caps do I leave the other values stock?
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cathode resistor and cap act as a shelving eq and will not change that much the overall tone. It is like adding pepper to a meal. It won't turn a bad meal into a good one.
I would rather go for a high pass filter just b 4 the PI or right after the tone stack. The signal being routed to two resistors in series to ground, the FIRST resistor being by passed with a cap ( to taste ).
Colas
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we see usually high value resistors with low value cap or the opposite eg: 2k7 with .68uF, or 820 ohm ( shared ) with a 330uF
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OK, if I change the cathode bypass caps do I leave the other values stock?
You may want to change coupling caps too, but I suggest not changing too much at the same time.
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Have you tried other speakers before taking a soldering iron to an Allen amp ?
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maybe just the first gain stage output coupling cap to .002
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cathode resistor and cap act as a shelving eq and will not change that much the overall tone. It is like adding pepper to a meal. It won't turn a bad meal into a good one.
I would rather go for a high pass filter just b 4 the PI or right after the tone stack. The signal being routed to two resistors in series to ground, the FIRST resistor being by passed with a cap ( to taste ).
Colas
Thanks. I did think of that, sort of, but I don't want more highs. I just want less lows.
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OK, if I change the cathode bypass caps do I leave the other values stock?
You may want to change coupling caps too, but I suggest not changing too much at the same time.
Take it slow, huh? That's a good point. If I change too much at once it might get confusing. And I'm already confused! :icon_biggrin: :icon_biggrin::icon_biggrin:
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Have you tried other speakers before taking a soldering iron to an Allen amp ?
It's the third speaker I have tried, although I may still need another change. About the soldering iron, I'm the one who messed it up in the first place. When I built it. :icon_biggrin:
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maybe just the first gain stage output coupling cap to .002
If I understand the way things work, which I may not at all, the first stage coupling cap is actually the tone stack. Is it not? If so I have already reduced the bass and mids caps. The second stage coupler is an .02 cap.
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Made a mistake in the first post. I fixed it. I KNOW somebody caught it, huh? :icon_biggrin:
Back to a previous question. If I want to make a change at the PI output, should I change all four .1 caps? If I just change the final two, smaller, won't that shift the frequency response up a bit? Does the MV need the balance of all four caps being equal? :think1:
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Why not call David Allen ? His circuit differs from a stock Deluxe Reverb, ( I know because I'm looking at the Accomplice layout right now ).
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There's still a mistake in your first post.
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Try a .0045 coupling cap before the PI. Why not call David Allen ? His circuit differs from a stock Deluxe Reverb, ( I know because I'm looking at the Accomplice layout right now ).
That does make sense, but this is more fun. OK, I may have to do that.
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There's still a mistake in your first post.
OK,I :laugh: fixed it AGAIN. :laugh:
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Forget the .0045 cap... I was thinking of Allens Sweet Spot, ( Princeton Reverb ), but call Dave.. he'll answer your questions , even if your not buying his amps.
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I have owned many Allen amps. They are fender inspired, close, but not clones.
Where are you setting your bass control? AB763 amps in all of their variations have mucho bass available. It isn't uncommon for players to have the bass at nearly zero when playing at volume. Also, if you haven't already done so, turn the "raw" pot off. That helps a lot.
You may change the PI input cap from .001 to 500pf, that will shave some boominess from the overall tone.
You could also try a 2.7k/.68uf cathode resistor/cap on the second stage of V1.
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OK. I take it that I was on the wrong track with the MV caps. I'll try the phase-inverter input reduction first only because I have that cap available. Don't have a .68 laying around.
About the volume control settings, I turn it down more as I turn the volume up. Volume past 6 and the bass is all the way down. I don't see that the raw adds bass, it adds all frequencies. I like it!