Reverb unit scratch build questions

[mort]

Sweet! I like the picnic table check design.

Is the tank sitting directly on the wood or do I see bubble wrap in there? I was thinking of raising mine with some stand-screws and springs, or possibly just getting a bag for it... haven't decided yet.

[tubeswell]

Yep that would be bubble wrap (as extra damping from cab vibration)

[mort]

here's a quick question; would I be likely to get unwanted noise by laying out the bridge rectifier so close to the signal path?

[tubeswell]

here's a quick question; would I be likely to get unwanted noise by laying out the bridge rectifier so close to the signal path?

I doubt it in that position. That is next to the 6V6 cathode resistor, which is not all that sensitive to EMI in any case, because of the relatively high amount of current going through it and the fact that it is bypassed. FWIW, I would use a 50-100V bypass cap in that position tho'. That cathode sits at about 25-27V. 2CW

[mort]

Ok great.

And it never hurts to over-spec a little. I will follow your advice about the bypass cap.

[mort]

Just finished with the chassis portion of the project. Sounds really sweet too.

I am having a tiny bit of trouble though. When I turn the amp('62 Princeton) up past 5 or so I get some fairly loud buzzing(even when I turn off the reverb unit) and the amp is usually pretty quiet. Also, if I drop the dwell down to it's lowest position it produces more buzz. I'll get some voltages up a little later but for now here's a photo to look at. I like photos.

[tubeswell]

Hiya mort

What layout did you use for the grounding? (What you describe sounds like a grounding issue, especially if the mix is turned to the dry side and still buzzes). In my (ever-so-humble) experience, that RG Keen grounding diagram I uploaded is fairly critical for these things, right down to isolating the input and output jacks and the reverb pan send and return sockets.

[mort]

I was just poking around in there and noticed that the cap that you suggested for me to up the value on is already cooked. I was planning on getting a replacement with my next parts order but it looks like I'll have to move a little quicker on it

As for grounding, I could probably use some improvement. I have the 4 grounds from the signal section individually grounded to the brass plate behind the control pots, most of the pots and jacks are just grounded through their mounting, the neg side of the filters is grounded to one of the bolts that holds down the eyelet board, and the heater CT and ground lead from the power cable are grounded to a bolt that fastens the PT to the chassis. The brass plate ground solder welds are pretty cold. I only have a fine tip on my gun at home and couldn't get it hot enough to flow well. I'll have to take it up to work to fix that.

[mort]

will a 33mfd @ 50v work just as well in that position?

[tubeswell]

will a 33mfd @ 50v work just as well in that position?

Try it and see - you'll get more bottom end, which the single-ended RT may not be able to handle that well. The goal in these units is to keep the signal clean. They sound crappy if you get anything much in the way of clipping or other distortion (except for harmonic distortion).

Re: the grounding, I would be tempted to re-do it completely. I am not kidding about how well that RG grounding scheme works for these things. You ideally only want one ground return point to the chassis in the entire signal chain. Anything else will most definitely increase the likelihood of more noise-to-signal ratio at the output. The goal of keeping the signal clean includes eliminating the noise floor as far as possible, because it all gets amplified in the following geetar amp.

[mort]

I've been looking over that grounding scheme and plan on giving it a try. Do I have it right that I'm to run *everything* to one spot and then jumper over to the chassis ground? As in, the spider 'hub' should not be attached to the chassis?

And with my first project it was suggested by someone to spilt the signal grounds from the power section grounds and it helped with the buzzing a noticeable amount. I just mention it because that idea conflicts with the spider idea.

[tubeswell]

I've been looking over that grounding scheme and plan on giving it a try. Do I have it right that I'm to run *everything* to one spot and then jumper over to the chassis ground? As in, the spider 'hub' should not be attached to the chassis?

Worked for me in that unit. But is is important for everything to have its separate wire to that point, and to keep that last jumper as short and fat as possible. The goal is to stop (micro) voltages forming across lengths of wire, which could otherwise interact and induce AC 'backwobble' into the signal path through the filter caps and supply rail.

And with my first project it was suggested by someone to spilt the signal grounds from the power section grounds and it helped with the buzzing a noticeable amount. I just mention it because that idea conflicts with the spider idea.

That works in simple geetar amps, and I too use that split grounding method is most all of my other amps. But in this case you are going to have two amps, each with their own grounds, both daisy-chained together. Therefore the number of creative ways you can come up with of reducing ground return contact points, whilst simultaneously eliminating possible source of ground-potential (micro)rises between different parts of the signal chain, would be advantageous.

[Kazooman]

WOW, you reverb build looks great. I think I will have to pull mine apart and rework the wiring to make it neater now that I know what I am doing. Part of my problem is that I had to make my chassis a bit narrower that the original to allow enough room for the relocated reverb pan. I don't have a lot of room and there is no lip on my chassis for me to tuck in the wires to the tubes. I may also try the different cap value since I think a bit more bottom end may be the difference between how my clone and my original sound.

Are you getting some buzz or hum from your PT through the reverb transformer? The original has the PT mounted inside the chassis and the choke and RT on the outside. Maybe turn the PT 90 degrees?

[mort]

Thanks Kazooman, my first project was wired all crazy and eventually I stripped it and reworked it all.

As for the buzz, I'm guessing it's a ground problem mostly, like tubeswell suggested. I do suspect a small bit of trouble from elsewhere, but first things first. I could easily enough try what you suggest though, when I get some time to work on it again.

Something else I might add is that I first had a 6v6 in it and it sounded good, jammed on it for a while and was happy. I tried a 6K6 and wow, what an improvement. So much smoother and natural sounding. silky even. The effect doesn't get quite as exaggerated with the 6k6 but I don't mind that at all.

[mort]

point of interest here... I plugged it in through a different amp today and it didn't make near as much noise. Still a little at pretty high volume but drastically less. What does that mean? Is it pretty common to have mystery 'mismatches' or is there something explainable going on?