JCM 800 – building a quieter version

[Willholmania]

I own an old vertical input Marshall JCM 800 50 watt combo (4010). It sounds great but it's ridiculously loud. Louder, in fact, than an Orange Overdrive 120 I recently sold. I mean absolutely deafening. I keep waiting for the call from Angus Young to do a stadium tour on rhythm guitar for AC/DC, but he's got his cousin in the band now so it looks like I've missed the boat again. So I don't need the level of volume it's capable of.

I don't want to start chopping a vintage Marshall up (I did, but I've been talked out of it) so I've decided I'd like to build another one, with a less deafening power amp. (I don't want an 18 watt job. I have an 18watt Ampmaker P1800 I built. It sounds great, but it's not quite loud enough.) Just a pair of EL34s or similar turned down to something more like 30 or 40 watts flat out. I know this is rated at 50 watts but an engineer I know says that's the undistorted rating, and that flat out he's seen the 50 watters churning out 80 or 90 watts when fully cranked. Which is how I use mine, albeit with an attenuator. But it's still too loud.

Does anyone know of a circuit I could use to build a Power amp that wouldn't be so powerful? I love output stage distortion so want to be able to run it cranked. Why is the original circuit so powerful? The transformers in it are bigger than some I've seen in 100 watt amps.

[pdf64]

How about a power scaling circuit http://music-electronics-forum.com/t39928/#post390793

[tedmich]

SV1 - Super-Versatile Super-Value Power Scaling Kit for Fixed Bias

[Willholmania]

How about a power scaling circuit http://music-electronics-forum.com/t39928/#post390793

Yes - I already have a power scaling circuit built for it which I plan to install. But it seems a bit daft to build an amp with a power stage that's way too loud. I'm never going to need 90watts, so I'd like to build it with a power stage of around 30 to 40 watts.

[pdf64]

But an overdriven 40 watt amp will likely put out over 70 watts; that's barely 1dB less than 90 watts.
How about trying JJ 6V6 into the Marshall (with bias suitably adjusted)? Maybe also try them with the load impedance selector set a step down, eg set amp to 8 ohms with a 16 ohm cab.

[tedmich]

Build an "amp crypt" ?


LOL

You could attach dowels to the knobs and put them through the wall so you can tweak settings, or pay a midget with a walkie talkie and a headlamp...

[R.G.]

It's not widely appreciated, but speakers vary **a lot** in how loud they are for the same signal level fed to them.

You might want to at least think about changing speakers. Are there any impedance selectors on this thing? Sorry - I'm bored silly by Marshalls and have no clue what's on what model.

[pdf64]

When a man is bored with Marshalls, he is bored with life?

[Enzo]

I'm not so bored with them, but I don't like how they are made, I don't like how they are designed, I don't like how they are documented, and I don't like how they sound.

[dai h.]

maybe try a post phase inverter master volume (the kind that replaces the (typically 220k) grid load/bias return Rs), or change the PT to a lower B+ type (about 385V) if the one now is the higher B+ (450V or so) type, or do both.

[big_teee]

If they are Tweaked right I dig the 2204 circuit with a few changes.
One change I wouldn't want to do without is the dual Master Volumes.
One before and one after the PI.
I've built two that way, one with EL34s, and One with 6L6 TAD short bottles.
Everyone seems to like them, and you can turn them down to Bedroom levels, if you go to smaller speakers.
T

[olddawg]

Honestly... I would just get a smaller amp and run it through one 12" speaker. You could butcher this amp all you want and still not get what you want. IMHO it will never sound like it does cranked now at a lower volume. It isn't 1985 anymore. Most local venues will not tolerate that kind of volume, it drives the crowd away and pisses off the proprietors unless you are outdoors or playing top tier gigs. (Where I am there are city noise ordinances and there's even a cop on Friday night at the door with a db meter) If you are a clubbing musician, a small 15-20 watt dual channel amp with a Marshalish and a Fenderish channel and a half watt switch will get you there. I have a lot of vintage amps. Want to know what I'm using for club gigs nowadays? A Bugera V22 combo stock, original Chinese tubes, original speaker, no mods. $249 on sale, free shipping. The reverb isn't that great but it gets the job done. A couple of pedals and it's fine. I mean there is a difference but it's like the difference between a $20 and a $200 bottle of wine. And.. The audience doesn't care. I've thought of putting a Marshall logo on it to satisfy the gear snobs, lol.

[tedmich]

Guys still buy this

when what they really NEED is this

go figure

[olddawg]

And if you still want to look cool and get a Marshall sound at a low volume.... Buy a stock late version 5 watt Epiphone Valve Jr head off of CL for $89 and set it behind that beast plugged into its speaker. Hit the VJ with a Rocktron Big Crush and the OD of your choice. But you still may need an attenuator... Seriously, lol.

[tedmich]

Immortals/cardboard stacks/Hellfest/Photoshop