Peavey Classic 30 - Praise and Questions...

[PlayItAll]

Just bought a new-in-the-box Peavey Classic 30. I'm really enjoying it! Apparently, the earlier models didn't have a tube guard, but this one has one that is almost _too_ protective! You have to remove six screws to get it off and it has to be removed to get to the tubes. Since I love to swap preamp tubes around, I may fashion a different one that protects them but doesn't have to be taken out to change a tube. Anyway, I was glad to see Peavey made the change to these new models - it shows they listen to their customers. It also came with JJ tubes, which surprised me a little...

I searched these forums and found the link to blueguitar.com which has a bunch of mods detailed for the Classic 30. The only one that I think I might like to make would be the Boost Switch Mod (copied here:

For the boost cap (C11), I recommend using a 750pf cap. With this value, the boost switch works similar
to a Shift switch on an older Mesa Boogie amp: it kicks the volume up a notch and boosts the midrange
response. For more boost and tonal shift, you can use a .001uf or .0015uf cap instead. Using smaller values
such as these, the 220k resistor (R12) to ground could be eliminated or replaced with a very high value (I
used a 2.2M resistor). With the stock boost cap, I found the gain boost and tonal shift to be too drastic to be
usable for vintage blues tones. With the values I recommend, the boost switch offers an alternative voicing
which retains much of the tone and character of the unboosted mode.
If you choose to replace the boost cap with a lower value as recommended here, you will sacrifice much
of the gain of the stock boost circuit. To recapture some of the gain lost I suggest that you replace the 100K
plate load resistor for V3A with a 120K or 150K resistor as outlined later in this article.

So my first question is, can I just perform this mod without doing the other tone stack mods or do they need to go hand-in-hand? I actually like the overall tone of the C30 as is, but would just like to make the boost less drastic.

My second question is concerning some hum when the reverb is turned up past three or four. As the reverb is turned up, a steady, low humming tone creeps in. It's not awful, and it's certainly below the noise floor for performing, but if there is an easy way to decrease it, I'd like to do it.

Thanks so much to everyone for any help or advice you can offer.

A new Classic 30 Convert,
Ed

[Mark Black]

I'm no help on the mod question (having not done that one), but I might be able to help on the reverb hum. A couple questions first -

Is it a true hum/buzz (as in AC line noise)? Or is it a low-frequency feedback oscillation (I have experienced this on one of these before). One way to tell would be to get it going and then firmly grab the reverb tank top or press on it. If the noise goes away or changes it's probably the oscillation. If it stays the same it may be a shielding or grounding problem.

The one I had problems with was oscillating at a very low frequency, and the cure turned out to be a couple pieces of heavy rubber weatherstrip stuck along the length of the top of the tank.

Good luck!

[Amp Kat]

That reverb hum Mark is a low hz hum and I've tried shielding with heavy duty cables and it cut it back some but not much at all and they all have it so it is a consistent problem that may be fixed but I havent' seen it yet. It is op-amp driven and it is possible the driver circuit is a little hummy so the cause may not be a shielding issue. I've modded several of these including one I'm doing right now and yes you can just do the boost mod as that's really the only one I personally like but the others certainly don't hurt and are a step in the right direction. Do the 2.2M resistor mod too as it will mute some switching noise to almost nill. Enzo makes a tube retainer for the 84's as they rattle a bit so he may have just what your looking for. The Blue Marvel is an ok speaker but a better one will make all the difference in it's tone.

[tubeswell]

You can also try a different Op Amp chip in the 'verb circuit. The stock C30 uses a 4558, but I put in a TL072 (which is a straight substitute in the same chip socket) and it seems to be a bit quieter on the noise front. There are also other 4558 substitutes which are probably higher performing. Why doesn't Peavey use better parts? (well who knows?, depends on who their supplier-of-the-day is I guess)

I agree with Amp Kat that you should do the 2M2 resistor for R12 - this does a better job of dumping the switching noise to ground when you use the boost. I think you should also do the treble cap if you're doing the Boost cap, because the two caps are in parallel when the boost is engaged, and the one affects the other. A 330pF Treb cap works well with the 390pF Boost cap and gives a less-bright treble control when the boost is disengaged. This gives the amp a more boutique sound IMHO.

But it is definitely worth doing all the blue guitar Tone Stack mods to the C30. I did the 330pF treb cap C14 (Mica), the 390pF Boost cap (Mica), a .022uF (polyester Film) mid cap, a .047uF bass cap (Polyester Film) and the 56k slope resistor (R19) mod, as well as changing R41 (Plate Resistor on V3A) to 120k. These mods work wonders for the amp. I also have GEJAN5751s in V1 and V3, for a more-creamy fuller sound without compromising the volume.

If you are going to do the .047uF Bass cap mod, then you should also put in more robust screw-retainer clamps on the chassis mounts, so you can tighten the chassis mounting screws more without stripping the retainer clips. This helps eliminate chassis rattle and is so simple to do with better clamps (- Why don't Peavey use better clamps in their amps? Hey that rhymes! Same story as the op-amps, caps & resistors.)

Also when working on the amp, be careful with the little jumper wires between the boards and esp the 7 strand jumper cable from the middle board to the extn spkr/footsw socket board. If you break any of these you are likely to encounter problems ranging from weird oscillations to no sound. Due to the design of the switchable extn speaker socket, the C30 circuit routes the OT output through the little sub-board back to the main board and thence to the internal speaker, so if those wires get broken the amp won't work.

I've also done a whole lot of other mods to mine which I won't bore you with now.

[Don Moose]

So my first question is, can I just perform this mod without doing the other tone stack mods or do they need to go hand-in-hand? I actually like the overall tone of the C30 as is, but would just like to make the boost less drastic.

My second question is concerning some hum when the reverb is turned up past three or four. As the reverb is turned up, a steady, low humming tone creeps in. It's not awful, and it's certainly below the noise floor for performing, but if there is an easy way to decrease it, I'd like to do it.

If SteveA doesn't wander into this thread in a few days, try emailing him via blueguitar - some of us ... more senior folks don't find time get here every day.

Hope this helps!

[PlayItAll]

Thanks - and a question about "pseudo MV"

Thanks to all for the advice... I'll tell ya what, the more I play with this thing, the more I like it as is. I'm finding I don't find myself longing for the boost function anyway because the sound of both channels without the boost engaged is plenty fat.

Maybe my perception will change once the "honeymoon" is over, but I'm not sure if I want anything different from the stock model right now. Time will tell...

I do have another question:

I saw a homemade product on eBay called an Omnisonic volume box. Just a simple volume pot on a box with an in and an out jack. It was for use in an effects loop and would act as a master volume of sorts.

I have a Boss CS3 compressor that has a few mods in it to make it a little more hi-fi. I don't use it much, so I decided to put it in the effects loop of the C30. Then, I set the compression to off and use the level and tone controls as master volume and tone controls for the C30. It seems to work very well. I am able to crank the normal and lead channels to where I want them and then fine tune the overall volume and tone with the compressor.

Is there anything wrong with running the amp/ compressor this way?

Gosh, I sure hope not cause I'm doing a lot of it!

Thanks,
Ed

[tubeswell]

I have a Boss CS3 compressor that has a few mods in it to make it a little more hi-fi. I don't use it much, so I decided to put it in the effects loop of the C30. Then, I set the compression to off and use the level and tone controls as master volume and tone controls for the C30. It seems to work very well. I am able to crank the normal and lead channels to where I want them and then fine tune the overall volume and tone with the compressor.

Is there anything wrong with running the amp/ compressor this way?

Ed

No problem. IN saying this, the C30 FX send is a line level output, so if you are running a pedal or FX unit (with a high gain) from the FX send, it would pay to back this off considerably if its adjustable (otherwise run it in front of the amp input), otherwise the signal going into the FX unit will be too powerful and is likely to result in unpleasant noise.

[Mars Amp Repair]

Thanx for the questions Ed. Lots of good experience to learn from here for all.
As far as the reverb hum I'm not certain of the Classic 30, but I have actually found a few amps where the orientation of the tank can affect hum induction pick up from the power xformer.

Of course removing the tank from the case & moving it around would prove this idea out in a hurry...glen