Peavey classic 30 questions; mods, speaker impedances, etc.

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parsec
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Peavey classic 30 questions; mods, speaker impedances, etc.

Post by parsec » Wed Jul 26, 2017 8:06 pm

Hi guys,

I just picked up an old Classic 30 II. I was keen to try modding it but was surprised to find that it actually sounds pretty good. I pulled it apart anyway to find that it has already been quite thoroughly modified (blue mod, adjustable bias, 15/30W switch). I am pretty pleased with it, but wanted to make a couple of minor changes.

The stock 16 ohm speaker seems a bit subpar. I have a closed back 8ohm vintage 30 cabinet that I tried with it that sounded better. I'd like to leave it as an 8 ohm cabinet for use with other amps, but with the way the amp is internally wired, this means that the internal speaker doesn't draw much current when in parallel with the 8ohm external. Additionally, it's generally easier to find used 8 ohm speakers to replace the stock (16ohm) speaker. I'd like the option of being able to use the internal speaker alone or with an external (for playing with a drummer etc.)

I came up with a couple of wiring ideas to be able to use two 8 ohm speakers in series. I wanted to see if you guys had any better ideas, as they're both a bit suboptimal.

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Idea 1; Use the external speaker jack in this novel way such that the 8 ohm tap feeds the internal speaker when the external speaker is disconnected. When an external speaker is connected, the 8 ohm tap disconnects and the 16 ohm tap feeds the two speakers in series. This idea has the obvious disadvantage that the external speaker is effectively floating. This would require the external speaker jack to be modified such that the sleeve is electrically isolated from the chassis, and it would also require the use of a special cable with a plastic body that is well insulated. Not ideal, but I think it'll work.

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Idea 2 (Diagram attached); Add a DPDT switch to manually change impedance taps based on whether an external speaker is connected. Apologies for the shit diagram. The idea is that the two switches are ganged so that when set to internal mode (8 ohms), the 8 ohm tap is connected to the internal speaker which is then earthed through the switch. When set to 16 ohm mode, the internal speaker is in series with the external speaker. This means that to use the internal + external speaker, the switch must be toggled to 16 ohm mode. It's not ideal though, as I have to drill and add yet another switch.

What do you guys think? Does anyone have any better ideas for being able to use either a single 8 ohm internal speaker or an int + ext 8 ohm in series?

I have a couple of other quick questions that I considered starting another thread for, but didn't want to spam too much.

Has anyone added the presence control in this version of the blue mod? It's not in the writeup he's done, but can be found in the 1999 mod schematic. http://www.blueguitar.org/new/schem/pea ... 0schmd.pdf
My amp seems to have been modded with the 1998 changes, but I'd like having a presence knob as well. Is it worthwhile?

My amp seems to make this awful high pitched noise when cranked on the clean channel. It almost sounds like the reverb tank is being rattled by the chassis and coupling back into the circuit, even though it happens when the reverb is set to zero. Maybe it's the power tubes being microphonic. Has anyone else experienced this? I'll try to record it when I have my amp back together.

Thanks

parsec
New Member
Posts: 2
Joined: Wed Jul 26, 2017 6:01 pm

Re: Peavey classic 30 questions; mods, speaker impedances, etc.

Post by parsec » Thu Jul 27, 2017 3:38 am

It turns out you can buy stereo jacks with isolated DPDT switches built in, so that makes life much easier. I'll let you know how it goes.

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