Peavey Classic 30: Using EFX Send to Feed Multitrack

0degreesk

New member
I live in an apartment now and don't want to disturb my neighbors too much. I have an older PODxt but rather than use its cabinet modeling I thought to feed its input from my Peavey Classic 30 via its EFX Send output. I've disconnected the speaker from the amp, so the amp is essentially a head now.

Does anyone have any thoughts about this? It seems to work okay, but I'm not clear on the technical issues. For example, is the output of the EFX Send the proper strength? I'm thinking it has to be stronger than the signal my guitar would send to the PODxt input. Any suggestions on how I should handle the amp levels related to the PODxt levels would be appreciated.
 

TalismanRich

Well-known member
I don't know about using the EFX loop, but it should be ok. The signal level is -6dB or 0.5v nominal, so not drastically out of line with a standard line level signal.

I can't find where in the schematic the EFX loop is, so its difficult to know if it turns off the power amp section. I would either remove the EL84s from the power amp section or put some type of load on the amp. You don't want to run power through the output transformer with no load.
 

0degreesk

New member
I don't know about using the EFX loop, but it should be ok. The signal level is -6dB or 0.5v nominal, so not drastically out of line with a standard line level signal.

I can't find where in the schematic the EFX loop is, so its difficult to know if it turns off the power amp section. I would either remove the EL84s from the power amp section or put some type of load on the amp. You don't want to run power through the output transformer with no load.
Thanks for the response. You're saying I should basically remove some of the tubes? There's a schematic on Page 6 of a PDF manual at https://peavey.com/manuals/80301964.pdf

In the back of the amp, I see four bigger tubes labeled "6BQ5/EL84" and three smaller ones "12AX7". From the specs in the PDF and your comment, I assume that means you recommend I remove all four of the bigger tubes, but I wouldn't know which of the three smaller ones is connected to the power amplifier part of the equation. Would it be safe to just remove one until the preamp still works but the power amp doesn't?

Edit: Sorry, that's not a schematic, but more of a signal flow chart or something.
 
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TalismanRich

Well-known member
Unfortunately, the flow chart doesn't have the EFX loop on it, so I don't know where it cuts the signal off (before or after the preamp/tone controls).

The power tubes are the EL84s. The 12AX7s are the preamp tubes. Running a tube amp without a speaker load can burn up the power transformer. There are several dummy loads available. The Classic 30 is set up for 16 ohm loads. You can build a dummy load for not too much money. A couple of 8 ohm 50 watt power resistors mounted on a good heat sink would do the trick.
 

TalismanRich

Well-known member
I found a schematic for the Classic 30. Perhaps ECC83 can look over the schematic and confirm that you can just run out of the EFX loop. It looks to me like the loop is post tone control, and breaks the signal going to the power section.

peavey_classic_30.jpg
 

0degreesk

New member
I found a schematic for the Classic 30. Perhaps ECC83 can look over the schematic and confirm that you can just run out of the EFX loop. It looks to me like the loop is post tone control, and breaks the signal going to the power section.

View attachment 109191
Is ECC83 another user? I can say for certain that my running a cord from the EFX Send didn't stop the speaker in the amp from working, which is why I had to disconnect it. It doesn't sound like the treble/mid/bass are having an influence on the sound, but the reverb is definitely there.
 

TalismanRich

Well-known member
I've sent a message to Dave (ECC83) to look this post over. He's good with tube stuff.

Looking the schematic, try plugging a 1/4" plug into the Return jack. That might be where the breaker is. In any case, you DON'T want to run a tube amp with no speaker attached. Its a sure way to smoke the output transformer. The EFX loop is definitely after the tone controls based on the schematic.

OK, I dug out my Classic 30 and plugging a jack into the RETURN with nothing else cuts the majority of the signal. There was a small amount of bleed though, but it was probably 95% gone. No tubes pulled or anything. Unplug and it's back to normal. I didn't check running the SEND to an interface or anything.

I would think that would be safest way to go for now. Hopefully Dave will check in over the next day and look over this.

FWIW, I've used my PODxt for quite a few songs. Never thought about sending it to an amp.
 
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ecc83

Well-known member
Ok, took a while, latest Ms update forked my printer! Got it back now. So, bit of an odd FX loop setup but yes, plugging into the Return will stop a signal getting to the (also odd) PI and its driver so taking a signal from the FX out will not, of itself silence the amp. This is the usual configuration. So, yes, put a jack plug into the FX return or there will almost certainly be damage if no load is connected. It is also possibly, but unlikely, that even with the power section so defeated, a 'spike' or other interfering signal could get into the PI driver and cause trouble. If a fully rated load cannot be used just use a shorted jack plug. So long as there is no signal, no harm and IF a spike occurred the valves would handle such a momentary overload quite happily. NEVER of course put a short on a transistor PA!

There is I see an 'annoyance' in that circuit I think? The master volume is pre the FX loop, bit odd?

Dave.
 

TalismanRich

Well-known member
Yeah, The way the Peavey is set up, the normal channel only goes through one side of V1, then to the second side of V1. In the drive channel, V2 is between the two sides of V1, and the volume is controlled pre and post V2. If you want a lot of gain, crank up the Pre boost and drop the overall signal with the Post boost. Its not really a master volume for controlling drive of output tubes. Its a bit wacky, but once you get it set, you just flip channels.

Thanks for confirming my suspicions.

Just for the record (and for future reference), is there an issue with pulling all 4 EL84 tubes in the power section? Would it hurt the PI if the power tubes aren't there?
 

ecc83

Well-known member
"Just for the record (and for future reference), is there an issue with pulling all 4 EL84 tubes in the power section? Would it hurt the PI if the power tubes aren't there?"

There could be Rich, removing the main load on the HT supply will cause the voltage to rise, that might put the filter caps under greater stress and they might pop. Should not happen with a well designed amplifier but often that is not the case with gitamps!
I also never cease to be amazed at how tight arsed mnfcts can be! The FX send is driven by a cheapo emitter follower when a few pennies more could have seen an op amp section there with greater headroom and vastly lower distortion.

A good solution is a load. A 50W allyclad resistor in a tin and a jack cable and the amp is safe as houses. You could get more sophisticated and have a DI feed from the load, even a headphone output. All pretty easy 'tronics.

Dave.
 

0degreesk

New member
Thanks for the in-depth research and replies. There was so much more going-on than I'd even imagined. I'm glad I asked and avoided screwing-up the amp.
 
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