New Year Modularity - New Preamp Build

[Crestone]

Happy New Year Everyone!

One of my New Year goals is to go modular!  One thing modelers have taught me is that it is tough to beat having modular capabilities in the studio - both for efficiency in trying new configurations and space.  As such, I’m taking a fresh look at everything from mixers to stomp boxes.  So, the cabs, pedals, FM3 and Katana stays.  Everything else is being sold as we speak.

That means I need to get busy on some new tube equipment which will be separate, rack-mounted preamp and power-amp modules.

My first pre-amp design is attached.  I call it the B-16F.  For this one, I wanted some Fender-ish tones, tube rectification and an Fx loop.  This will, be primarily coupled with a long-tail PI, PP 6V6 power amp.
But, other power amp projects are going to be an SS-rectified, LTPI EL84 as well as an LTPI EL34.
The only other pre-amp planned so far will be Plexi 1987 inspired, but also looking at a couple of Dumbles.  I’ll post these as they get designed.

Sorry to digress, just wanted to post the B-16F here for critique as it has not been built, yet.

[acheld]

Modular is the "new" old word these days.   

Which PCBs are you going to use? 

I've got a project in the works with similar ideas using Merlin's PCBs (search for VW BJ Hybrid if interested, posted just a few days ago).

I'll be interested to see what you do.   Great idea!

Cheers.

Chris

[Crestone]

I do my own PCBs.  Nothing wrong with Merlin's.  I just like to size the the holes such that I can use turrets, use 2 oz Cu and 3mm board.  Can't beat the PCB/turret combo, IMO.

[sluckey]

Can't beat the PCB/turret combo, IMO.

Good system until you want to modify something.

[acheld]

Merlin's boards are fairly flexible in terms of design options, but it is clear that a big departure from those options is not so easy.  I can live with that. 

For me, the pain is ordering the parts to fit -- I'm so used to point to point, or turrets, that these radial parts have not been a part of my lexicon.  You have to pay attention to the size of the part, lead spacing, and even the diameter of the leads themselves. 

That said, there are an amazing number of available components in radial format.   Reminds me of Baskin Robbins many years ago . . .

[Crestone]

Can't beat the PCB/turret combo, IMO.

Good system until you want to modify something.

Precisely why I add the turrets.  I also tend to oversize my component spacing just a tad and sprinkle in additional solder points ala the LC filter provisions on the power board.  I find that 98% of my mods are component swaps and jumpers anyway. 

It does extend the design phase a bit painfully, makes you think thru your design in terms of "what-ifs" and adds cost. It is, therefore, not for everyone.  In fact, probably not for most.  But for me, the benefits of a faster build, less lead fuss and neatness makes it worth the headache.

BTW, I borrowed your mod for the hi/low input switch.  Thought you would have caught that, lol!

[sluckey]

The problem shows itself when you need to remove or re-route a pcb trace to perform a mod. Then the pcb will become a pain in the ass.

BTW, I borrowed your mod for the hi/low input switch.  Thought you would have caught that, lol!

Not my mod. And it's not gonna do what you want. You wont hear any difference when you flip that switch.

[Crestone]

The problem shows itself when you need to remove or re-route a pcb trace to perform a mod. Then the pcb will become a pain in the ass.

BTW, I borrowed your mod for the hi/low input switch.  Thought you would have caught that, lol!

Not my mod. And it's not gonna do what you want. You wont hear any difference when you flip that switch.

I was like what the heck!  I hate visio somedays.  Aparently some connectors got discombobulated during a move.   Anyway, re-orienting the connectors properly should put those resistors in parallel.

[Crestone]

I've got a project in the works with similar ideas using Merlin's PCBs (search for VW BJ Hybrid if interested, posted just a few days ago).

I'll be interested to see what you do.   Great idea!

Cheers.

Chris

Chris, can't seem to find your project.  Certainly interested.  Would you mind providng a link?  Thanks!

[sluckey]

Click on his name and select show posts.

[Crestone]

One question that I do have is should I be employing some sort of ground lift scheme since I will have a chain of components?  I have made a half-assed attempt at this by isolating my input and output jacks.  Something tells me that this is not going to be enough.

[shooter]

as long it's a rack system, why not the top of the rack have ONE PS? 

[Crestone]

I did think about that and got nervous about when I may mix and match preamps and power amps.   I guess I could have one big power supply to run everything.  That would be very cool.  I know anything is possible, but do you think it reasonable to design a power supply that could run two or three preamps and two or three power amps?  They would all need to be powered up simultaneously in the studio, though not likely more than one combination would be played at a time.

Edit:  I hope I'm not misunderstanding.  I am referring to everything PT and beyond.  If you are referring to AC power, then yes everything will be run from one supply.  If that is the case, then everything shares same ground and means no need for ground lift, I suppose? 

[tubenit]

I think Seymour Duncan made tube amps with modular designs in late 70's or in the 80's, IIRC.   I think the "convertible" was one of them?

https://reverb.com/item/13588405-seymour-duncan-convertible-100-modules

With respect, Tubenit

[dunner84]

Sounds like a great project. I am currently doing something similar. I have a dumble ods, and slo overdrive pcb from Kevin O'Connor at London power. Dumble clean, dumble drive, and slo drive All accessible from a panel switch and footswitch. I'm adding a single switchable tube effects loop, 2 tube reverb, and a few on-board effects (compressor, and chorus)
The reverb and effects won't be part of the preamp signal chain. Instead they will all have dedicated in/out into a patchbay in the rack.

All crammed into a 1u enclosure.

The idea is for quick, direct recording, but all my amps have effect returns, or pre amp inputs.
I am limited in rack space, so any dedicated power amp I build for this will sit with my cabs anyways.

With regard to your ground isolation question, Kevin O'Connor has a ground link isolation circuit for this purpose. Might be worthwhile reading up on..

If you haven't already seen his site, it's londonpower.com

[Crestone]

Thanks tubenit and dunner84 for the links!  I am very interested in getting a Dumble preamp going soon and will check out Kevin's site.

For the one I am working on currently, I got rid of the 3rd stage, and instead used it as a part of  a mixer in the Fx loop.  This loop is an adaptation of one that Merlin presents in "Designing Tube Preamps".  I  merely added a bypass switch and a trimming pot.  Still thinking about that as it is somewhat redundant with the Sends Level pot.

Folks looking for an effects loop may want to check this one out as it always presents a constant impedance to the input signal and has active wet/dry mixing with the turn of a dual gang pot.