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Topic: Low reverb signal? |
Dennis Detweiler
From:
Solon, Iowa, US
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Posted 2 Sep 2021 3:29 pm |
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I have a Session 400 Limited that has a low output signal. The pan is NOS. I replaced the reverb chip and that eliminated the hum problem, but the signal output is still weak. The reverb control has to be full on to get a signal that should be happening at less than half way on. Which weak component would cause this?
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 2 Sep 2021 8:24 pm
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| How much reverb did you have before you changed the chip? If the output was low then too, it's probably a bad tank. |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 3 Sep 2021 5:39 am
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When I bought the amp, it didn't have a tank. I just bought a new tank for it. It's the correct tank. I'm thinking it must be a capacitor or transistor. The Limited has a few transistors. Two of them are in the area of the reverb circuit, but I'd have to look at the schematic to be sure. There is a cap on each side of the reverb chip.
I replaced the reverb upgrade (Burr-Brown) chip with the original 4558 and it made no difference with the gain, but did eliminate the hum.
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Michael Brebes
From:
Northridge CA
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Posted 3 Sep 2021 6:00 am
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It could also be the reverb drive circuit that has the problem.
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Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Jack Stoner
From:
Kansas City, MO
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Posted 3 Sep 2021 6:31 am
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Incorrect model reverb pan will also cause this.
Peavey reverbs tend to be "weak" compared to a Fender reverb.
The hum could be a bad ground in one of the reverb leads. If its got the typical "Molex" connector that's the first place to look. The difference in gain (volume) between the Burr Brown chip and the OEM chip could be why the hum is gone.
Many possibilities, but my first thought is the Molex connector/connections. |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 3 Sep 2021 7:07 am
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Since it came without a pan, I didn't have the molex. I hardwired new shielded cables with new connectors. I tested each for continuity afterwards. Tried reversing the inputs. The hum is gone since I installed the original chip back into it. But, the low reverb signal is still there. A quick glance at the schematic, it doesn't look like a large circuit. I could just replace each component?
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Jack Stoner
From:
Kansas City, MO
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Posted 3 Sep 2021 9:08 am
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Reverb Pan. Are you sure this is the correct one? One with the wrong impedance (ohms) would cause low signal.
I don't have a schematic. Assuming the chip you installed is not defective I would first look at capacitors.
Another area to look at is the printed circuit between the Molex pins and the other components in the reverb circuit. I had a similar problem on a Nashville 400. I found a "hairline" break in one of the printed circuit leads. |
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Ken Fox
From:
Nashville GA USA
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Posted 6 Sep 2021 8:07 am Reverb
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 6 Sep 2021 8:14 pm
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4EB2C1B is the NOS pan that I installed.
Problem must be in the circuitry, but not the chip?
If I bounce the amp enough to rattle the pan, it's very loud. So, the pan output is loud. The guitar signal getting to the pan is very weak. Maybe that narrows down the problem?
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Jack Stoner
From:
Kansas City, MO
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Posted 7 Sep 2021 2:19 am
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| Can't rule out the reverb pan, either |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Sep 2021 3:44 am Reverb drive
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It does sound as if the problem is not in the the reverb output stage.
However a bad pan is still possible. Also the reverb drive circuit needs to be checked for proper voltage supply to the transistors in the drive stage. Also could be defective transistors or capacitors. Also the signal to the drive stage transistors could be degraded as well.
Without proper testing and diagnosis all you can do is “shotgun†parts at it. |
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