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Best DIY tube amp to pair with Metasonix modules
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Author Best DIY tube amp to pair with Metasonix modules
equalpyramid
I've been looking at some tube amp projects to power speakers. Now I'm not after anything "audiophile", but some of the cheaper kits at Tube Depot looked interesting.

Tube Depot Kits

So Eric, or anyone else that knows about tubes, are those money well spent? Any suggestions?
metasonix
The "cheaper" kits are literally built on slabs of wood. Safety hazards. If you build one, put it in a proper enclosure.

Any of them would be fine. Just realize, they are "hi fi" amplifiers, and not intended for music amplification. So they will have low voltage gain. You cannot use them as guitar amps, without adding an instrument preamp.
equalpyramid
I see. My intention was to simply use them between line out and speakers for studio use only. If I can find schematics for the IMP amp (2 X 6021 subminis), then I'll build that one.
tablebeast
http://xfmr.blogspot.com/2012/06/brute-force-of-jekyll-hyde.html
tablebeast
I make tube amps that go great with the Metasonix stuff out of old Akai / Roberts tube reel to reel monoblock amps and have some DIY schematics available.
My Pre+Amp has a line input as well as a hi-z input so it can handle passive or active instruments as well as line level devices. It also has a dummy load on the speaker output with a padded headphone/line out jack so you don't even have to use a speaker and can listen or record directly. The two modes consist of a cleaner mode with negative feedback employed and a more driven mode with the feedback removed and gain boosted. When I build them into the Akai donor modules I always include the Brute Force preamp circuit in the same box since there is plenty of room and resources for it. This preamp can be used separately or in conjunction with the amp. Think of it as a modular tube amp: perfect for your modular tube synth!
equalpyramid
eek! Wow, tablebeast, that's quite the DIY gear collection. Care to share some tips with us?
tablebeast
Quote:
Wow, tablebeast, that's quite the DIY gear collection. Care to share some tips with us?


Sure, the site will eventually have full tutorials for my most popular designs and then I was thinking maybe a generic tutorial where I mod 2 or 3 PA amps all at once so that I can cover the gamut of different designs somewhat. I am just building up the blog right now to stretch my legs and get used to writing copy. Once my full site is up at xfmr.org you'll see much deeper posts with more detail including videos.

So, as far as tips? Find some old tube gear with a proper power transformer power supply, as in DON'T mess with those readios and amps that have all the tubes strung together in series using 120v AC from the wall for heaters. These kinds of units have tubes that have numbers like 50 or 35 in them. The most famous American radio design with these tubes is called, "The All American 5" or AA5. They don't use a power transformer and rely on mains AC to run the heaters and B+ voltage. They ground one side fo the AC signal, essentially giving you a hot chassis. DANGEROUS to experiment on, so save yourself the headache. You will also need plenty of room to work, proper tools, and know how to experiment safely. Plate voltage is only dangerous if you don't take simple precautions. With my designs I like to find a donor that I like the looks of. I will check out the guts and maybe find a schematic online. Then I think about the resources it has available and think of what kind of design will be appropriate. Making guitar amps out of old PA amps is probably the easiest thing you can do. Usually the hardest part of that conversion is getting the 1/4" jacks installed in place of the other types of jacks while still looking good. Also, keep in mind you're first couple of projects are going to be ugly and likely not work quite right. Just read up on what you did wrong and improve with each project.
Moog$FooL$
tablebeast wrote:
Quote:
Wow, tablebeast, that's quite the DIY gear collection. Care to share some tips with us?


Sure, the site will eventually have full tutorials for my most popular designs and then I was thinking maybe a generic tutorial where I mod 2 or 3 PA amps all at once so that I can cover the gamut of different designs somewhat. I am just building up the blog right now to stretch my legs and get used to writing copy. Once my full site is up at xfmr.org you'll see much deeper posts with more detail including videos.

So, as far as tips? Find some old tube gear with a proper power transformer power supply, plenty of room to work, and experiment safely. Plate voltage is only dangerous if you don't take simple precautions. With my designs I like to find a donor that I like the looks of. I will check out the guts and maybe find a schematic online. Then I think about the resources it has available and think of what kind of design will be appropriate. Making guitar amps out of old PA amps is probably the easiest thing you can do. Usually the hardest part of that conversion is getting the 1/4" jacks installed in place of the other types of jacks while still looking good. Also, keep in mind you're first couple of projects are going to be ugly and likely not work quite right. Just read up on what you did wrong and improve with each project.


woot woot!!

looking fwd to more posts like this.

equalpyramid...... hello! thumbs up

come by a Vansynth meet some time if that interests you. it's always fun to chat with other diy's from Vancouver.
equalpyramid
Moog$FooL$ wrote:
equalpyramid...... hello! thumbs up

come by a Vansynth meet some time if that interests you. it's always fun to chat with other diy's from Vancouver.


Sounds like fun. When are they happening?
Moog$FooL$
equalpyramid wrote:
Moog$FooL$ wrote:
equalpyramid...... hello! thumbs up

come by a Vansynth meet some time if that interests you. it's always fun to chat with other diy's from Vancouver.


Sounds like fun. When are they happening?



check out this thread for future updates.....

https://www.muffwiggler.com/forum/viewtopic.php?t=61875&highlight=vanc ouver

maybe post to it just to say hi & get notifications. the other fella of this loose-group that i know to be interested in tube stuff is Davemoog.
Chrome Dinette
Eric Barbour wrote a project article in VTV, #10 I think, for an amp that was said to be suitable for hi-fi or musical instrument use. It was pretty complicated, though, and used tubes that may be hard to find now.
equalpyramid
Okay, so following the great advice on this board/thread, I found an old PA amp that fits the bill.

It's a Soundmaster, made in Canada, and uses three 6sc7 instead of 12ax7 and 807 for power. I will change the elec caps before trying anything, but I'm stoked. I will keep it as a PA config for now, since it's for studio use only.
Moog$FooL$
wow! good find eqp. thumbs up
i'd love to see some pics.
please keep us updated.
metasonix
equalpyramid wrote:
It's a Soundmaster, made in Canada, and uses three 6sc7 instead of 12ax7 and 807 for power. I will change the elec caps before trying anything, but I'm stoked. I will keep it as a PA config for now, since it's for studio use only.

Good choice. 807s are great for PA amps, since they were originally meant for radio transmitters, where they would be run too hard intentionally......NOS 807s and 5933s (premium version) are still fairly easy to find for reasonable prices. New ones are still being made in China.

Change all the filter caps and other electrolytics, check the output and power transformers for shorted or open windings, and you should be okay.
equalpyramid
metasonix wrote:
equalpyramid wrote:
It's a Soundmaster, made in Canada, and uses three 6sc7 instead of 12ax7 and 807 for power. I will change the elec caps before trying anything, but I'm stoked. I will keep it as a PA config for now, since it's for studio use only.

Good choice. 807s are great for PA amps, since they were originally meant for radio transmitters, where they would be run too hard intentionally......NOS 807s and 5933s (premium version) are still fairly easy to find for reasonable prices. New ones are still being made in China.

Change all the filter caps and other electrolytics, check the output and power transformers for shorted or open windings, and you should be okay.


Thanks for the info. I'll get on that asap. Excitement got the better of me and I tested it before finding replacement caps. It sounds AMAZING. I love the distortion on that thing. Pots need a change and I want to add an output volume to allow for distortion without cranking the volume up as well.

The output is wired using 5 pin connectors, labeled 0W, 4W, 8W, 15W and 500W. After a bit of testing, I get the best sound out of 7ohm speaker cones from the 500 and 4 connections, but I'm not sure that's normal. Any tips?

And as far as caps are concerned, should I aim for Sprague Atoms? Anyone care to elaborate on the topic of audio capacitors? Where's the best place to get them from? I checked Tube Depot, but they had only one of the values I needed. This unit also has mustard caps, domino caps, air elec cap, and a tall, cylinder cap. Which can I keep?

Pics coming soon, as internet is coming from the neighborhood coffee shop for another week.
Moog$FooL$
eqp........ as far as "caps" how old is this thing?

eric's advice was solid...... change all the electro's. BUT!! what does it sound like & how's it acting? maybe you don't need to change them yet. seriously, i just don't get it

i've changed out numerous filter & bypass caps (electros of course) in many guitar amps & i like to buy from some nice folks at http://justradios.com/.

they're Canadian too. love

as for spragues..... i wouldn't waste the cash. i just don't buy into that "tube amp guru" bullshit.

ummm...... i don't know what else to say. hmmm..... maybe tablebeast or eric have some more help.

anyways, i'm in your town so if you need to chat, i'm a friendly swell fella & i don't mind lending a hand. Darren. thumbs up
Chrome Dinette
Yeah, Sprague Atoms are nothing special for too much money. Also, they are huge compared to other caps of the same value and voltage rating.
equalpyramid
Moog$FooL$ wrote:
eqp........ as far as "caps" how old is this thing?

eric's advice was solid...... change all the electro's. BUT!! what does it sound like & how's it acting? maybe you don't need to change them yet. seriously, i just don't get it

i've changed out numerous filter & bypass caps (electros of course) in many guitar amps & i like to buy from some nice folks at http://justradios.com/.


Thanks a bunch. Afaik, the amp is from the late 50's. It sounds really good, but the pots are garbage. I'll be able to properly evaluate after I change them. It won't be much work, it seems extremely well built.

Thanks for the link... I'll keep you folks updated.
metasonix
equalpyramid wrote:
The output is wired using 5 pin connectors, labeled 0W, 4W, 8W, 15W and 500W. After a bit of testing, I get the best sound out of 7ohm speaker cones from the 500 and 4 connections, but I'm not sure that's normal. Any tips?

Those are speaker impedances. 4 ohms, 8 ohms, etc. The 500 ohms is used in 70-volt commercial PA systems, for driving long strings of speakers all over a large building.
Quote:
And as far as caps are concerned, should I aim for Sprague Atoms?

Buy good quality high-voltage electrolytics, like Nichicon or Panasonic. Sprague is overpriced.

Quote:
Anyone care to elaborate on the topic of audio capacitors? Where's the best place to get them from? I checked Tube Depot, but they had only one of the values I needed. This unit also has mustard caps, domino caps, air elec cap, and a tall, cylinder cap. Which can I keep?

Don't change the film coupling caps unless they are bad. There's all kinds of overpriced crap you can use, don't waste your money. Panasonic or Illinois capacitors are okay.

If you want to see what kind of overpriced shit you can buy, start here.
http://www.partsconnexion.com/capacitor_film_all.html
Audio Note silver foil, for example......
http://www.partsconnexion.com/capacitor_film_audionote_silver.html
equalpyramid
Update!

The restoration was very successful. Works like a charm and overdrives as well as any 12AX7-based circuits. I fucking love this thing. Simple things become complex and buzzy. I strongly recommend them.


Moog$FooL$
ah yes..... one of those came in to NJAMS when i use to work there.
good for you. thumbs up

were the 6sc7 in their when u got it? or did u buy some new olds??
equalpyramid
I got a full set of NOS, but will hold onto the original ones until I can test them (won't mind having spares). Checked for a difference in sound between GE's metal and Tung-Sol's glass 6sc7's, so far they are pretty damn close, but will investigate more later. I'll do my best to get a demo up to.
zerosum
Octal tubes are so pretty! love Dead Banana
tablebeastly
[original post deleted]

I would like to apologise for drawing people into disputes which I now feel do not belong here based on forum feedback. My intention was purely objective and was to warn members of the music community - particularly those with a love for the esoteric and the creatively unpredictable of a certain risk in dealing commercially with certain members of the community.

I think now is the time to reflect less on the past and look to the future which after all is the only direction in which we are travelling.

Much respect to all of you who frequent this great site and perhaps without realising it provide much support and motivation to us all.

Peace.
metasonix
tablebeastly wrote:
So... anyone reading Jesse Mesa Savage of Raleigh North Carolina sage and helpful advice on DIY, beware, and keep it DIY - don't pay any money to Jesse.

I wish I wasn't writing this. I wish I'd given the 6500 USD to Eric not Jesse.

Thanks. Tablebeast is a "legend" in the guitar business. And he's far from the only one. It seems to be like the Harley-Davidson world, which is full of douchebags, liars, con men, and angry fat white guys.
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