A solid-state, FET ReVibe project

midwayfair · January 22, 2014, 12:40:14 AM

Or you can use this thing I've described here:
http://www.diystompboxes.com/smfforum/index.php?topic=105261.0

9V --_-------_
| |C (Q1)
R1--->]B
| |E >--C1
R2
|D (Q2)
in--> ]G
|S
R3>Ground

Q1: NPN BJT. Q2: N-channel FET

The gain on that stage is not quite as high as the SSRP, but it's a ton of DC gain, it's not overly distorted, and it has very low current draw.

EDIT: The omega can be adjusted to have clean output as well. http://www.runoffgroove.com/omega.html

ANOTHER EDIT: I realized, though, that you were hoping not to redesign. Sorry. There's not a whole lot you can do within the topology, assuming the FET's bias is settling properly.

jubal81 · January 22, 2014, 01:02:32 AM

Thanks for the input. I suppose I could do some desoldering and dead bug an extra resistor in there for the SRPP. What sticks out to me is that 100K drain resistor. I've never seen that there like that before.

It doesn't need very much more gain at all - just a smidge to get it to unity. Maybe I could attenuate the dry line a hair so they match and then do the boostification in the mixer ...

jubal81 · January 22, 2014, 09:23:09 PM

Alright all fixed. The driver transistors needed some rebiasing. Changed R13 from 2.2K to 390R and R12 from 10K to 20K.
No hint of distortion on any dwell setting and unity volume. Just tons of warm, luscious reverb.

jubal81 · January 23, 2014, 02:58:50 AM

Mixing board laid out and ordered. It's going to be a long couple weeks.

jubal81 · January 24, 2014, 05:19:55 AM

I've decided I'm going to go with a floor unit - Solemate style. Hammond makes a 10"x6"x2" that I think I can make work - if I take the spring unit out of the housing and remount it in the hammond box. After doing some reading, the housing is meant to shield the springs from magnetic fields (transformers). No transformers in my build, so I don't see why it would be a problem.

I'm also abandoning the illuminated panel idea. I found out the El Panels I can afford:
1) aren't that bright
2) Dim significantly over time
3) only last about 100 hours

Now I'm thinking of using a clear acrylic panel with transparencies/paper underneath and I have plenty of Tweed on hand. Having trouble finding dial graphics I like. though.

jubal81 · February 02, 2014, 04:57:55 AM

Now that was seriously speedy - nine days from order to my door.

jubal81 · February 04, 2014, 08:20:51 PM

Box and a few other parts finally got here - damn ye, snowstorm.

I'm leaning toward the white knobs.

lincolnic · February 05, 2014, 06:22:11 AM

I vote for the white knobs too.

drrico · February 05, 2014, 10:14:46 PM

White! Very snazzy.

jubal81 · February 06, 2014, 06:45:41 PM

Officially getting very awkward to work with (up to 4 boards wired together, now). Trying to get creative with 1776 relay board - using a TLP222G opto FET to use the relay board to use the rate LED as on-off indicator.

Spent yesterday dialing in the Cardinal. Swapped in 2N5457s for Q1&2, biased (looking for max headroom) and wired up a rotary switch for the modes - the two standard and a 39n C6 for vibe mode. I already updated the graphic, just need to print out a new one.

jubal81 · February 06, 2014, 07:30:45 PM

Good news: The switching works as intended - rate & indication with one LED.

Bad News: Back to the bias drawing board with the Cardinal - getting a bit of clipping again today. Ugh.

I've also decided that instead of grounding the input mixer to drop out the tremolo, I'm going to wire it to provide the bypass signal. The problem is that just cutting out the tremolo is like cranking up the dwell knob, but when I want to turn on and off the modulation, I just want the modulation on or off. Simple fix.

jubal81 · February 06, 2014, 11:42:41 PM

Hours later:
If the Cardinal didn't sound so amazing, Id've given up on it. Top prize for most difficult circuit I've ever tried to dial in and get working consistently.
Changing Q3 to 5457 did add more headroom, but now the effect is voiced very differently. Whew. A few more lifted pads and I'm going to have to order another and start from scratch. Just hope I don't futz anything up get those opto out.

jubal81 · February 07, 2014, 01:50:29 AM

Whew! just barely.

R9 pad lifted but I got in there and patched it up. The magic number for R9 with the 5457 was 1K. I brought the vibe cap back down to 33n.
I finally think I'm golden on this sucker - out of this world sound on all three settings and I can't get it to clip with single coils - hum buckers will still rattle it, though. I was hoping to have it boxed up by now, but I'm feeling great about how it's working and sounding - just wish I hadn't fallen victim to my own hubris and socketed the transistors and drain resistors.

jubal81 · February 11, 2014, 10:37:02 PM

Looking positive ...

jubal81 · February 13, 2014, 06:05:01 AM

A couple hours yesterday and 10 hours today and I've got a preview. Still waiting for knobs. Everything worked right off the bat, which was a relief because I depleted what I thought was a hefty strategic wire reserve.

I used little velcro squares from Walmart to secure the boards and I really like it.
The 1776 relay boards work great and are very quiet.

Oh yeah, what you see in the corner is a Bloviator II. I put it on top with a DPDT to use as a switchable output buffer.

I need a better solution for the faceplate. What you see is just a printed presentation paper under a piece of lexan. I got it on and together, but it's just rickety. Maybe you guys can give me some ideas on how to get something pro on there.

I also have got to find a way to make a good demo. This sounds so great you just can't believe it. It's utterly sublime.