60 watt 6l6 tube amp, too muddy...why? - diyAudio
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Old 9th October 2011, 08:54 PM   #1
rotagen is offline rotagen  United States
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Default 60 watt 6l6 tube amp, too muddy...why?

OK, I've got a couple of old Acoustic 60 watt guitar tube amps. Actually I find the tone very unique and warm, that's why I bought a backup.

But here's the deal, I'm always playing through pedals that boost the signal in a clean fashion. The tone is decent when I do this, but less "tubey" and more solid-state sounding. But the pedals (specifically my "treble booster" pedal) clean up the tone tremendously and get rid of a major problem: the bass while boomy is very very muddy and indistinct, not punchy at all...sloppy would be a good term.

When I go direct from guitar into amp this sloppy muddy bass is intolerable, even when I increase treble with my tone knobs. I've tried everything on amp and guitar but this never goes away.

I have replaced the tubes in the past but no dice, its still there.

I guess my big question is this: what do you think is the culprit here? Could it be that my transformers are low grade, too weak or something. Guess I just need to know some likely suspects in the circuit of the amp.

Tubes havent been changed in a few years, I ordered some new ones that should be an upgrade, but I'm skeptical they will remove the problem.

Thanks for any help I really want to "fix" this amp.
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Old 9th October 2011, 10:00 PM   #2
kevinkr is offline kevinkr  United States
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Per FORUM policy since this post relates to an acoustic instrument amplifier it belongs in I&A.
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Old 9th October 2011, 10:02 PM   #3
kevinkr is offline kevinkr  United States
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Additional information such as who made your amps, the specific model and an out of copyright (or hand redrawn) schematic would really help a lot.

Have the power supply capacitors or any other components in these presumably old amps been replaced?

The fact that your pedals make it sound better point to a possible interaction between the guitar and the input electronics in these amps, again having a schematic or something more to go on would help..
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Old 9th October 2011, 10:08 PM   #4
rotagen is offline rotagen  United States
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I do have the schematic on a cd somewhere, will post soon after band practice, thanks for those ideas. No caps have been replaced, it is an Acoustic tube-60 Collaboration Series made in 1987 or thereabouts, thanks again.

Could a weak output transformer cause this problem?
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Old 9th October 2011, 10:09 PM   #5
rotagen is offline rotagen  United States
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Just a quick note "Acoustic" is the Brand name , it is an electric guitar amp. thanks.
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Old 9th October 2011, 11:13 PM   #6
kevinkr is offline kevinkr  United States
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Very unlikely to be an output transformer, I suspect a combination of design and old components - particularly the electrolytic capacitors in the power supply which are way overdue for replacement.
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Old 10th October 2011, 12:17 AM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by rotagen View Post
But the pedals (specifically my "treble booster" pedal) clean up the tone tremendously and get rid of a major problem: the bass while boomy is very very muddy and indistinct, not punchy at all...sloppy would be a good term.

When I go direct from guitar into amp this sloppy muddy bass is intolerable,
Kevin is your tube amp master
I won't mess with him

but that your pedals change the 'issue', and sounds better
it could indicate impedance problems

I wonder if some owner before you lowered input impedance

that you got a couple, maybe tells that they might have been used fore hifi/stereo
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Old 10th October 2011, 03:27 AM   #8
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Note that he's using treble boost pedals to overcome boomy bass. (As I recall, Acoustic was known for bass amps.)


Have you tried a different speaker?
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Old 10th October 2011, 06:17 PM   #9
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sounds like a power supply problem, is it valve or diopde rectified? switching to diode rectification might help and as kevin said, the caps probably could do with replacement. as for impedance problems, i doubt this is the case, although it can contribute, i cant see it making a significant difference. also, if any bypass caps are electrolytic then it probably wouldnt be a bad idea replacing them either, and if theyre relatively big, making them slightly smaller wont hurt.
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Old 10th October 2011, 06:54 PM   #10
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It could be the input impedance to the amp being too sucking highs off the guitar, power capacitors being old, cathode bias amp with small cap, a whole host of things. Just guessing without a schematic.
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