Ampalanche

[moon]

There are a few DIY amp-builders here so I thought maybe someone might be interested in my new amp project: a modular design with a central hub and separate preamps.

Schematics here (v2)

the hub (main unit)
- schematic
- draft layout

preamp / power supply boxes
- Matchless Spitfire/Lightning
- Gibson Goldtone GA-15 (aka Trace Elliot Velocette)
- 5E3 Deluxe
- Divided by 13 CJ11

There are lots of little 15-wattish amps I'd love to build - 5E3 Deluxe, Matchless Spitfire and others - but funds are tight. However, if you examine the circuits, lots of these amps have very similar transformers and power amp designs. It should be possible to cut costs by putting all the common parts in one, shared box - see the linked "hub" schematic and layout.

Power supplies are an important part of an amp's DNA. The boxes which plug into the hub will contain (most of) the amp's power supply circuitry as well as the preamp. I say "most of" because the initial part of the power supply - rectifiers and choke/resistor options - are sharable and hence placed in the hub

The schematics shown - CJ11, 5E3, Spitfire/Lightning, GA15 - pretty much covers most of my dream list of tube amps for home/recording use. A Mesa Boogie Lonestar Special would be nice too, if I can adapt it to be compatible with the hub design.

The beauty of this idea (assuming it all works out... ) is that adding a new amp costs peanuts if all you have to do is put together a preamp module & a handful of filter caps. Why build just one when you can have a whole avalanche of choice, boutique tube amps?

Will post some clips in due course.

[muscmp]

moon: the link is no good as it just goes to dropbox. sounds interesting tho!

here is one i've been thinking about. it has been around for a while and is fully tweak-able, the ax84.

http://www.ax84.com/p1.html

play music!

[moon]

I'd linked to a folder but dropbox doesn't allow that. Fixed now.

The P1 sounds like a kind of EL84 Champ? I'll need to look for some clips to check it out.

[el_kabong]

Moon - Very cool idea, I think, and one that's passed through my own mind a time or two. After a fashion, this might be considered as a modern take on amp-slaving and/or cascading, as the case might be, which is as far as I've taken it myself.

I am presently collecting schematics (and trying my best to understand them ). Glad to see the CJ on your list, btw.

I'll definitely check out your links and hope you'll update on the subject now and again.

[Bob Womack]

I'm unable to tell from the schematic (my technical limitations): What are your bias options? Both fixed and cathode? Without cathode, you won't get the 5e3 sound at all.

Bob

[moon]

All the amps are cathode biased. The Hammond 372BX PT I'll be using does have a 50V bias tap though which could come in handy for a future build.

I could have a problem with 300-0-300 for the 5E3. Might be a bit on the low side. I think I can adjust the bias resistor to compensate, leaving me with no significant change apart from a little less headroom. If I really had to, I've got room in the hub chassis to add a second PT. Would love to have a good 5E3 .

At least the CJ11 will be OK. Cathodyne deluxe power amp with a blackface pre sounds interesting.

I've begun ordering parts but I probably won't start building for a couple of weeks. The project is a bit beyond my capabilities to be honest so I'm going to get some feedback from a couple of technical forums first. I'm pretty sure it will work but I ought to check I haven't done anything stupid. Amp building is a lot of fun but you've got to be very careful and precise working with electrical circuits.

[moon]

Originally Posted by el_kabong

I am presently collecting schematics (and trying my best to understand them ). Glad to see the CJ on your list, btw

Aiken amps has some great technical articles.

Also check out The Valve Wizard.

And here's an interesting little article on carbon comp resistors. It seems there is a real argument for carbon comps - but only at specific locations.

About this time last year I got a DIY Champ kit and at first I felt like a chimpanzee who had been given the plans for a nuclear reactor.

"Oook?"

Gradually it all starts to come together though. Lots of good information and advice out there on the net, as always.

[clintj]

Very ambitious! Can't wait to see some build pics and the finished amp.

[Dru Edwards]

Sounds like a great idea, Moon! I'm not skilled in the electronics so I can't comment on the feasibility.

Are you a member of an amp building/modding Forum? I imagine there are lots of little 'tricks' that can assist you.

Can't wait to see/hear the finished product!

[moon]

The box and transformers arrived really quickly - great service from Bluebell Audio in the UK.

It'll probably be a few weeks before I get this finished. Still trying to source parts. I'll need lots of 450V+ rated switches and connectors which are proving hard to track down, even at Mouser.

I was reading up on the 5E3: I can actually get normal plate voltages with a 300-0-300 PT - but not with the standard Tweed Deluxe 5Y3 rectifier. If I swap in a 5AR4 (as used in the CJ11) there's a much smaller voltage drop - but theory says that will create less power chord compression and a different kind of "bloom" / "kerrang" or whatever you want to call it. The difference should only be noticeable when you smash a big signal into the power tubes.

The right speaker/cab will be important too for an authentic 5E3 sound. After I've finished the amps that will probably be the next thing to experiment with.

Incidentally, although I did a shameless hack-job in the cab-build topic I've got a very different attitude to high-voltage circuits. Everything will be precisely planned, triple-checked, and carefully assembled as best I can. This kind of thing has to be done to a high standard.

[MuddyDitch]

Now that looks like a really cool project. Be sure to post updates as you progress. Best regards.

Erik

[moon]

Will do

These are all tried and tested circuits so that just leaves the problem of creating a sane layout where things like transformers & heater wires aren't inducing noise in other parts of the circuit. I took a Ceriatone Spitfire as a starting point. This has the transformers arranged pretty much as in the photo and the heater wires running across the middle of the chassis.

The 17x10 layout could maybe be squeezed down smaller but there's less risk of noise in a bigger box where everything can be spaced out a bit more.

I've just remembered there's no proper grounding scheme shown in the layout. I'd better go and read up about star grounds... That must be one of the first rules of amp-building: don't be the ground, design the ground.

PS: Dru I also stop by the music electronics forum from time to time. Lots of technical discussions there and they've even got a good pickup-winding sub forum. Also TDPRI.

[muscmp]

Originally Posted by moon

Will do

These are all tried and tested circuits so that just leaves the problem of creating a sane layout where things like transformers & heater wires aren't inducing noise in other parts of the circuit. I took a Ceriatone Spitfire as a starting point. This has the transformers arranged pretty much as in the photo and the heater wires running across the middle of the chassis.

The 17x10 layout could maybe be squeezed down smaller but there's less risk of noise in a bigger box where everything can be spaced out a bit more.

I've just remembered there's no proper grounding scheme shown in the layout. I'd better go and read up about star grounds... That must be one of the first rules of amp-building: don't be the ground, design the ground.

PS: Dru I also stop by the music electronics forum from time to time. Lots of technical discussions there and they've even got a good pickup-winding sub forum. Also TDPRI.

moon: you may want to check out the diyaudio forum too. here is a link.

http://www.diyaudio.com/forums/instruments-amps/

play music!

[moon]

Thanks - I'll check that out.