My 36W Project

Double-Bubble! Place for discussing the 36W version...

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Bieworm
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Re: My 36W Project

Post by Bieworm »

Jack, that's what you get with adding a gain stage. Did you attenuate the signal before cascading? You might wanna play with some values there with a/the voltage divider ...
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"THIS should be played at high volume..preferably in a residential area"

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TriodeLuvr
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Re: My 36W Project

Post by TriodeLuvr »

Bieworm wrote:
Mon 02/22/21 3:12 pm
Jack, that's what you get with adding a gain stage. Did you attenuate the signal before cascading? You might wanna play with some values there with a/the voltage divider ...
I built the entire preamp section identical to the Marshall 2104. I did add a voltage divider just ahead of the PI, but it's only marginally helpful. The problem is that there's a huge difference in signal amplitude between the Low and High inputs (approximately 60X). If the PI is attenuated enough to make the High input work well at the MV pot, then the Low input doesn't have enough gain. On the other hand, High gain can't be reduced at the cascade stage without changing the tone of the amp. The additional gain is responsible for allowing the player to crunch the preamp.

I should add that I do have a solution for this, because there's an effects loop between the preamp and the PI that wasn't present in the original design. I can install a send-return patch cable, then use the Send Level pot to reduce MV sensitivity (that won't change the preamp tone). I just want to be sure this sensitive behavior of the MV pot doesn't point to a wiring error or bad component somewhere. That's why I asked whether it's normal for the MV series.

Thanks!
Jack
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TriodeLuvr
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Re: My 36W Project

Post by TriodeLuvr »

No new pics yet, but there's progress. It's funny what you learn about amplifier construction when you do something like this for the first time. The amplifier chassis wouldn't fit into the Peavey combo cabinet all the way because the HV cage that I made hit the speaker. The chassis stopped about 1/4" back from where it needs to be. So, I scrapped the cage and made a new one that adds about 1/2" of clearance. Probably can't remove the speaker once the chassis is bolted in, but that might have been true of the original design, too.

Also, I found out yesterday that amplifier mounting straps are readily available in various lengths from Antique Electronic Supply and probably others. I had assumed this would be an OEM-only item, so I never looked. And of course, none of them will fit the 6-1/2" spacing I used for the cage nuts. Doh! So, I spent a few hours today milling two aluminum straps. Now I have to finish the metal and anodize them, much more work that I would have undertaken had I known.

I might have to build a few more amps and sell them just to get my educational investment back... :)

Jack
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Re: My 36W Project

Post by TriodeLuvr »

Here are the final pics of the amplifier chassis. The chassis and Hammond speaker have both been mounted in the donated combo cabinet now. I'll post pics of that as soon as I finish the new nameplate. (It's not a Peavey anymore!) :)

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