peavey classic 30 reverb driver and recovery issue

[severthee]

Good day,

I have a 20year old peavey classic 30 it started to give me frying bacon sound. So I re-cap all the big caps. the frying sound was gone and it played like new! except that I seem to have lost the reverb.
i checked the tank, I don't see any broken wires. I checked the resistance on the output about 200ohms and 60ohms in the input.

I tried the tank on my Fender Blues Deluxe. it uses the same accutronics tank but with a 20ohm input instead. still it (classic 30 accutronics tank) worked fine with the blues deluxe.

I plugged the tank again in the classic30. double checked input and output reverb cables to make sure i didnt reverse them. checked cables for continuity and they do.
still no reverb. I tried to tap the tank, usually it gives a boing, but it did not. instead it gave a thud static sputtery sound like plugging/unplugging your guitar cable on a cranked amp.

just for kicks, and to check if the return is working, I fed music by iPhone's headphone out to the reverb's return circuit. well i heard the music coming out of the classic30, but I have to crank the iphone's volume otherwise when it's below 80% volume, it gives me that same sputtery sound like tapping the tank previously.
I am stumped. last trick up my sleeve was to change the IC 4558. i have lots of jrc4558 from the od builds. still no go.

I'm about to feed a reverb pedal in the effects loop but as much as possible I'd like to have the builtin reverb working. what else do I need to check on the reverb circuit? all I can see in the recovery are some electrolytic caps, a big 1 watt resistor and a j202 fet right before the reverb pot. anyone knows where else to look?


Thanks!

[52 Bill]

It sounds like you have a broken connection in the return circuit input, probably the ground.

It's very easy to break a jumper wire in a chassis that is so compacted like that one is. Follow the signal from the return input and see if you can find broken connection.

[nevetslab]

Following IC1 4558 is a series FET (a J231) Perhaps it's bad. Though I agree with 52 Bill ^^^^^^ as it sounds like you did have Reverb before pulling the amp apart, and now you don't.

[severthee]

Thanks for the tips!
Makes sense. I did have some problem after the re-cap where I did not get any sound from the preamp section. I can hear the channel switch popping, and I can plug the guitar direct to the fx return power section and sound came out fine. Turns out the pin 4 heater of V1 has a bad connection to the jumper wire connected to + of the big 2200uf 50v cap(c45). I fixed that jumper (jp504) but did not check the others.

I'll check the grounding around the reverb as well as swap out the j202. Hoping to fix this finally. Will report soon

[Enzo]

I too suggest looking for one of the many short bare wire jumpers being broken.

[severthee]

Did all the suggestions above, this time I traced almost everything from the input until the power section. All the earth ground, chassis ground and that other ground symbol with a circle.
then I checked the whole reverb circuit from the relay back to the pin 7 grid of v1b. checked all the grounds in the reverb circuit. all the -30v and -15v connections. they were good.
i reinforced all the jumpers. this took two days lol. took my time reinforcing the jumpers on the pot side then had a break because I wanted fresh eyes and hands for jumpers on tube side. In short, i was patient because I don't want to open this amp ever again lol.
Lastly, I changed the j231 jfet. actually mine had J202 stock, so I replaced it with a J202.

Results, I got the reverb back. but it is so subtle. i don't remember it being this way when stock. I slap on the guitar string and I can hear the reverb when I'm close to the speaker. and this is with the reverb knob on max 12.

Before the reverb went kaput on me, the reverb will be really loud at around 3 -6 (halfway) of the knob, then it will pick up a really low hz humming feedback, then I would turn down the reverb maybe around 2-3 marker of the knob. still those settings were louder than the max I got now. old humming reverb's 2 is equal to Now at max 12
Now i'm thinking, was this the stock reverb of the classic 30 very subtle. and the super loud low hz feedback reverb I had before was the "broken" version?

I can try putting a cmoy headphone amp between the tank and the output jack, but is there any resistor or cap in the rebound circuit I can tweak to make the effect louder?

thanks!!!

[Enzo]

The circuit does not need to be modified to work.

Pull the return cable from the pan OUTPUT jack, and touch the tip of it with a finger. Is that hum loud and strong?

Do we now have the correct EB type pan in the circuit? And inside it all the innards are moving freely, no foam block on the springs etc?

Just to check, play into the amp as normal with the reverb drive connected, but instead of connecting the return cable. connect the pan OUTPUT to some other amp. IS the signal strong over there?

The low sound is acoustic feedback through the pan. Worry about that later. We get the basic reverb function back to strong first.

You changed Q1, but is it now turning off and on fully? Short across it source to drain, does that restore full reverb? Is there any gate voltage there?

Your reverb defaults to ON by way of teh grounded shunts in the footswitch jack. Are those contacts clean and solid?

[severthee]

The circuit does not need to be modified to work.

Pull the return cable from the pan OUTPUT jack, and touch the tip of it with a finger. Is that hum loud and strong?

I did this test when I lost the reverb and i remember the hum was not loud. Sounds like a fizz. Will try it when I get back to the amp

Do we now have the correct EB type pan in the circuit? And inside it all the innards are moving freely, no foam block on the springs etc?

Yes Its the stock 4eb2c1b. Has 200ohm for output and about 60ohms for the input. I know I didnt mix it up with the fender blues deluxe's.
Yes springs moving free as far as I can tell. Although I read this tank should be mounted vertically, I had it lying down since I got it ages ago

Just to check, play into the amp as normal with the reverb drive connected, but instead of connecting the return cable. connect the pan OUTPUT to some other amp. IS the signal strong over there?

Will do this too

You changed Q1, but is it now turning off and on fully? Short across it source to drain, does that restore full reverb? Is there any gate voltage there?

Your reverb defaults to ON by way of teh grounded shunts in the footswitch jack. Are those contacts clean and solid?

Thanks for this suggestion, I feel stupid. Was that jfet just an on and off switch controlled by the footswitch? Because if it was I shouldn't have replaced it and shouldve bypassed it instead. Connecting c23 direct to the reverb pot. I did'nt care about the footswitch anyway.
I havent checked that footswitch jack, but if it's dirty I can just connect a plug with the tip shorted to the sleeve right?

[severthee]

Now that I'm looking at a Delta Blues schematic, It doesnt have that jfet and all that other components found in the classic 30!. from c30 22uf cap to the big r33 1.5k 1watt resistor. What's prone to failing here? Can that 1n4148 diode short out by a surge from a bad resistor?

[Enzo]

Nothing is "prone to failing" here.

The Delta Blues is the same amp as the C30, but it doesn't have foot switchable reverb, the reverb there is always on. So they didn't include the footswitching circuits.

If you don't care about FS turning off reverb, then pull the JFET and put a jumper wire in its place.

Surge from bad resistor??

Just do straight troubleshooting - isolate the problem. The JFET either is or is not killing the signal. Just find out. We need not waste time trying to decide what is prone. WHEN the electronics fails in this reverb circuit, by far the most likely thing is the IC. Any other part CAN fail but not very often.

[g1]

I know you would prefer to not flex the jumpers again. If Q1 is accessible and you want to bypass the reverb switching, just jumper the drain leg to the source leg with a wire, and clip the gate leg.

[severthee]

Haven't had time to open the amp again, but I did several tests from the outside.

1. Touched the rca of the return > hum is loud. was not able to record this though

2. Connected the reverb tank's Input from c30's driver, then the tank's output to a different amp (Fender BD) > reverb signal came out fine out of the Fender BD while dry signal from the c30

3. checked the footswitch jack, they're good. Also inserted a plug with tip shorted to sleeve, same subtle reverb on max.

4. Plugged the Guitar jack to the reverb's RECOVERY circuit via the Return RCA. same sputtery distorted sound
> https://youtu.be/nG0kD-3WPfs

5. Reverb tank's output plugged normally to the recovery circuit. This was the sputtery sound I had before, but better than the last time. On my first post when I move the springs like this they sounded like pulling a Guitar plug from the jack > https://youtu.be/w2A9JQHjBcs

6. here the Reverb Tank's output is plugged direct to the amp's guitar INPUT. This is the boing sound I'm used to. >
https://youtu.be/WWOWjtmqDZk

7. Here's the subtle reverb, you can't even hear it on your speakers but probably with headphones on. but It's there I'm not imagining it haha > https://youtu.be/5JF1dU2sA2g

nothing valuable since I haven't opened the amp, I'll deal with the Q1 soon. reluctant to succumb to Murphy's law everytime I take out that 3pc board to be honest lol.
Just enjoying the tone for now after the re-cap, and the bright cap on the pre-gain pot. everyone seem to be taking out those bright caps in their Fender's but it's adding the right amount of shimmer on this Peavey.

[Jazz P Bass]

It appears that you have proved that the circuit works through the pan.

Up next is the output from U1B/ pin 7.
After that is C23 & the JFet.
I would do as suggested & remove Q1 & jumper across pins 2 & 1.

peaveyclassic30 Rvb Circuit.pdf

Edit: Q1 Pins 2 & 1

[nevetslab]

5. Reverb tank's output plugged normally to the recovery circuit. This was the sputtery sound I had before, but better than the last time. On my first post when I move the springs like this they sounded like pulling a Guitar plug from the jack > https://youtu.be/w2A9JQHjBcs

So you still have the same sputtery sound thru the Return circuit for the Reverb. When you rotate the Reverb pot, in this condition, does the pot sound gritty? If so, rack the pot back and forth a whole lot....might just be a dirty pot. If that isn't the case, then we're homing in on the circuit causing the issues, as the Send to the Reverb Tank is good, and sounds normal coming back thru a different amp. Could be the IC U1, could be any of the components. Input cap C22, output cap C23, Gain network cap C29, output load network C30. I agree with removing Q1, replacing with a jumper across pins 2 & 1 (pin 3 is gate).

[severthee]

So you still have the same sputtery sound thru the Return circuit for the Reverb. When you rotate the Reverb pot, in this condition, does the pot sound gritty? If so, rack the pot back and forth a whole lot....might just be a dirty pot. If that isn't the case, then we're homing in on the circuit causing the issues, as the Send to the Reverb Tank is good, and sounds normal coming back thru a different amp. Could be the IC U1, could be any of the components. Input cap C22, output cap C23, Gain network cap C29, output load network C30. I agree with removing Q1, replacing with a jumper across pins 2 & 1 (pin 3 is gate).

Yes correct! the reverb pot sounds gritty when turning from 0 to 12. gritty parts are somewhere halfway.
If I'm taking out Q1 , I can just disconnect the output load c30 22uf 25v capacitor right? I don't see this capacitor in the delta blues schematic.

I'm opening up the amp tomorrow, and will update.
Thanks for everyone's suggestion, really appreciate it. I only know how to read schematics but not the theory and implementation on how most of the components work
dumb i thought that jfet was used as a boost because that's how I was using them for some pedals