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Dr Tony Balls wrote: Sun Aug 21, 2022 7:26 am

Talk to me about the black dome covering the photo cells. I have a Musitronics Phasor II clone that I suspect would go deeper if it had a cover with a reflective (or is it unreflective?) inside. Where’d you get that part?

tommy wrote: Sun Aug 21, 2022 9:37 am Talk to me about the black dome covering the photo cells. I have a Musitronics Phasor II clone that I suspect would go deeper if it had a cover with a reflective (or is it unreflective?) inside. Where’d you get that part?

Historically a Univibe would have a shield like that which did two things: 1) block any outside light from influencing the photo cells, and 2) provide a reflective surface for the light to bounce off of. In those units the photo cells werent aimed directly at the bulb so they needed a reflective roof to capture the light. In a modern build you can get around the need for a reflector by aiming the photo cells directly at the bulb, but its still helpful to have a shield to block any outside light. Its not super necessary once the back is on the enclosure but its helpful while calibrating it and it cant hurt.

I made the parts with a copper pipe cap and wire leads soldered through the outside to anchor it to the board, then painted it black. I probably could have looked cooler in raw copper, but I would have wanted to seal it in some way and only had black paint on hand.

Dr Tony Balls wrote: Sun Aug 21, 2022 7:17 am

Ace K wrote: Sat Aug 20, 2022 8:25 pm

Dr Tony Balls wrote: Mon Aug 15, 2022 10:58 am Slow couple of months there...

AB165 Bassman-style preamp. Customer is in love with the sound of his AB165 Bassman but needs something mass-transit friendly. He'll be pairing it with a pedalboard power amp (Quilter or the like) and have an all-in-one pedalboard rig that can connect direct to a cab. It reproduce the Bassman preamp with FETs in place of 12AX7 triodes, running at 18V off a standard 9V supply, with an added master volume. I tested it by plugging it in to the power-amp in on a Sunn Beta and it rips!

would love to hear samples!

I sadly didnt have time to make any but the customer reported this on the OSG forum, for what its worth:

Well, it arrived today and Tony really knocked it out the park! I jury-rigged together a way to test it as best I could from what I have in the house....

Guitar > pedalboard > BALLSMOM > Cube 40 Poweramp in > ext cab out > Marshall 1x12

I'd say it has slightly less overdrive than the real thing but that's no doubt down to the fact it's just preamp drive and no power tube saturation. EQ is nailing it too. I think, certainly in a live situation, I don't think anyone in an audience would even notice. It sounds really, really good.

10/10 would recommend

This is impressive, because all the Catalinbread FET clones of tube circuits just sound like a harsh fuzz to me. Seems to be a tough design to get right.

biscuitdough wrote: Sun Aug 21, 2022 1:54 pm This is impressive, because all the Catalinbread FET clones of tube circuits just sound like a harsh fuzz to me. Seems to be a tough design to get right.

I think people fuss with stuff too much, trying to make it a distortion pedal instead of a preamp/boost kinda thing. Its really not hard...replace the tube triodes with JFETs, pick appropriate anode resistors to get the bias right, and change nothing else. On the one I built I added a charge pump for 18V supply and a little more headroom, but thats about it.

Dr Tony Balls wrote: Sun Aug 21, 2022 3:55 pm

biscuitdough wrote: Sun Aug 21, 2022 1:54 pm This is impressive, because all the Catalinbread FET clones of tube circuits just sound like a harsh fuzz to me. Seems to be a tough design to get right.

I think people fuss with stuff too much, trying to make it a distortion pedal instead of a preamp/boost kinda thing. Its really not hard...replace the tube triodes with JFETs, pick appropriate anode resistors to get the bias right, and change nothing else. On the one I built I added a charge pump for 18V supply and a little more headroom, but thats about it.

I just did essentially this for an acoustic preamp - took a basic audio amplifier stage circuit example, chose transistors with a very wide range and then built an ac coupled preamp. Anytime I went to anything more complicated than that it sounded worse

I built a very similar Bassman pre once and I loved it aside fro it being pretty noisy. I used J201 JFETS. What did you use? I also only ran it off of 9vdc so maybe that was the issue. I had trim pots for bias which was cool because you could do either a Fuzz or a light OD thing with it. The fuzz was a great sounding bass fuzz, but it would fall out of bias all the time. I should revisit it.

Kniferide wrote: Mon Aug 22, 2022 10:46 am I built a very similar Bassman pre once and I loved it aside fro it being pretty noisy. I used J201 JFETS. What did you use? I also only ran it off of 9vdc so maybe that was the issue. I had trim pots for bias which was cool because you could do either a Fuzz or a light OD thing with it. The fuzz was a great sounding bass fuzz, but it would fall out of bias all the time. I should revisit it.

I just used J201s but didnt have any noise issues. Generally you want to see about half of the source voltage on the transistor drain.

Dr Tony Balls wrote: Mon Aug 22, 2022 12:08 pm

Kniferide wrote: Mon Aug 22, 2022 10:46 am I built a very similar Bassman pre once and I loved it aside fro it being pretty noisy. I used J201 JFETS. What did you use? I also only ran it off of 9vdc so maybe that was the issue. I had trim pots for bias which was cool because you could do either a Fuzz or a light OD thing with it. The fuzz was a great sounding bass fuzz, but it would fall out of bias all the time. I should revisit it.

I just used J201s but didnt have any noise issues. Generally you want to see about half of the source voltage on the transistor drain.

Now I want to build another one. I found the graphics mock up from the first one I built. Might build a 18vdc version and try fixed bias. It's a fun pedal.
Some reason I never took a pic with the waterslide decal attached. This was the box

Kniferide wrote: Mon Aug 22, 2022 4:14 pm Now I want to build another one. I found the graphics mock up from the first one I built. Might build a 18vdc version and try fixed bias. It's a fun pedal.

How do you mean fixed bias? Also if you want any input about how I did mine just let me know.

Dr Tony Balls wrote: Wed Aug 24, 2022 9:28 am

Kniferide wrote: Mon Aug 22, 2022 4:14 pm Now I want to build another one. I found the graphics mock up from the first one I built. Might build a 18vdc version and try fixed bias. It's a fun pedal.

How do you mean fixed bias? Also if you want any input about how I did mine just let me know.

I just mean a fixed resister value for the voltage to the Transistors. Mine had trim pots and was hard to dial in, gave an inconsistent result. Also, would a OpAmp like a TL072 be a viable replacement for the j201? Seems like you could get it on pretty small board. I'm going to dig mine up if I can find it and F around.