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Old 7th February 2009, 08:26 PM   #1
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Default Modular Gain Stages for Tube Guitar Amp

I enjoy tinkering with and building tube guitar amps, and an idea recently came to my mind to develop an approach to a modular type of amp, along the lines of what Egnator does, on a homebrew scale.

http://www.egnater.com/modules.html

My thought is that I could build several preamp gain stages with certain values for the few caps and resistors involved on small turret boards, so that I could pull the existing one, and drop in a new one rather quickly. If I standardized where the connections to the tube pins, pots, and input and output to the next stage are located on the turret boards, it should be relatively easy to do this. I could also modularize the eq stacks to allow easy insertion and switching in the same way.

As I thought about it more, I wondered if I could create a solderless way of doing this using some sort of connector that would make the connections easy to change. Also, if there was a type of switch I could mount on the board itself, I could easily change component values, remove cathode bypass caps, etc, without having to hardwire that stuff to a bunch of external switches.

Ultimately, I would think I could create an amp using very high quality hardware, transformers, tubes, etc, that would be extremely flexible and easily convertible as the mood strikes me by simply switching the arrangement of the cheaper passive components.

Has anyone taken this approach, and can you give me any advice about implementing it, what connectors and switches to use, etc.? I'm not necessarily going for something that just "plugs in", but something that, if possible, doesn't require me to heat up the soldering iron.
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Old 7th February 2009, 09:30 PM   #2
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This was first done commercially many many years ago. Search on "Seymour Duncan Convertible". It used a card edge type connector, like computer cards, and the tube modules consisted of PCBs with the the connector traces etched on.

Your biggest challenge will be to find connectors with high voltage ratings when you try to DIY it. Your best bet is to go through the Amphenol catalogue.
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Old 8th February 2009, 01:51 AM   #3
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I vaguely remember that amp. I think I was in my early teens when that came out. I just googled it and checked it out. That's kind of what I'm thinking of, except that I wouldn't include the tube socket in the module. They are already in sockets and easy to swap! It seems like it would have made their modules a lot cheaper and less fragile too. It would seem that they might have even been able to allow them to be swapped without opening the chassis at all.

I would also question the durability of the card edge connector if you did a lot of swapping. Does anyone here have one? Any problems?

I saw a picture of the sockets for the modules and noticed that they are located pretty close to the filter caps. (The ones rated for 500v!) Seems like a strange design choice for an amp where the user is directed to stick his hand in there on a fairly regular basis. Maybe they're not as close as they look in the picture. Either that or S.D. didn't have many lawyers on staff.

I checked out Amphenol, and it looks like I'll need to spend some time going through all of their options.
Thanks for the tip!
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Old 8th February 2009, 02:01 AM   #4
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Quote:
Originally posted by GravyBoat
I saw a picture of the sockets for the modules and noticed that they are located pretty close to the filter caps. (The ones rated for 500v!) Seems like a strange design choice for an amp where the user is directed to stick his hand in there on a fairly regular basis.
? It's a fairly easy task to put a resistive bleeder in an amp.
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Old 8th February 2009, 06:27 AM   #5
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I'd be afraid some guitarist would be stoned, or just dumb, and forget to turn the amp off. I guess this was before people started suing each other for making coffee too hot!

What do you think of these? They're rated for 600v and they come in different multiple pin configurations. I could connect the pins of each triode to a 3 pin socket, and then hang the opposite connector off of the component module.

link

I'm starting to wonder if this is a dumb idea. I'm afraid I'll end up with an amp I can configure 764 different ways, all of which sound like garbage.
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Old 8th February 2009, 03:00 PM   #6
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Quote:
Originally posted by GravyBoat
What do you think of these? They're rated for 600v and they come in different multiple pin configurations. I could connect the pins of each triode to a 3 pin socket, and then hang the opposite connector off of the component module.

I'm starting to wonder if this is a dumb idea. I'm afraid I'll end up with an amp I can configure 764 different ways, all of which sound like garbage.
Those look good, but expensive.

Well, IMHO, I actually don't think it's a great idea. The SD Convertible didn't take the market by storm. It's true that a guitar amp takes a lot of tweaking, but the clean way is to pick the best sounding tweak and build it that way. I'd be more tempted to build it the way Billy Zoom built his. He built it with various component values that are just selected via one of those ubiquitous blue DIP switches, played with it to pick his favourites, and then sealed it up and left it like that for 20 years, extra components and all.
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Old 9th February 2009, 02:10 PM   #7
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He built it with various component values that are just selected via one of those ubiquitous blue DIP switches, played with it to pick his favourites, and then sealed it up and left it like that for 20 years, extra components and all.
It would be absolutely impossible for me to have an amp for 20 years and not open that baby up and mess with something ! It's a sickness.

The more I think about it though, unless it's extremely easy to switch modules on the fly, I probably wouldn't do it very often, and would probably have at most 2 or 3 favorites that I ended up liking, which I could then implement with some king of switching scheme. Thanks for talking me out of such silliness! I'd miss the solder smell anyway.

I'm still going to give this some more thought, as it might make a nice set of tools for prototyping a design, making it easier to a/b changes. My main problem is that a lot of these types of changes are subtle and interactive and I have a hard time deciding which I like better while I have the amp up on the bench, especially if there's a fair amount of time involved in making the switch. Gotta check out those little blue DIP switches!

Thanks for the comments!
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Old 9th February 2009, 02:24 PM   #8
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FWIW,

Here is an website with extensive Seymour Duncan info including complete schematics and module construction.

Seymour Duncan
I own both a 100W convertible Combo, and a less common 100W head version.
The features on these amps were incredible, given the era, they offered more features than most amps today.

The problem was very poor implementation. Not just limited to the modules, internal wiring and connectors were horrid. You can commonly buy these amps for under $400.00 on ebay. If you are handy with a solder iron, these can be fixed up to be very reliable and for the low investment involved, they are actually pretty cool.

I built 6 modules for mine based on the website above.

The module idea is nothing new, and actually there are still a couple companies that offer modular amps. Randall makes a card style amp with the largest number of different pre-amp modules.
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