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Cardinal: Only normal tremolo?!

Started by Tremster, October 23, 2013, 06:14:26 PM

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Tremster

Finished populating my Cardinal board. All the parts seem to be oriented correctly, both trimmers are wired not as trimmers but using regular pots. All these work, although the wave pot is rather subtle.
I get lush tremolo.
However, the 3-way switch doesn't seem to be doing anything, to my ears all positions sound the same, regular normal tremolo as in my other tremolos, I don't hear any phasing/vibe artefacts. Can this be?
I'm using a waterclear LED for D2, I didn't see that a diffused one is recommended. Is that it?
Using a TL072CP for the IC, but a TL062 doesn't make a difference.

Voltages:
Q1
D 7.95
S 0.59
G 0.00

Q2
D 4.91
S 0.91
G 0.00

Q3
D 1.21
S 0.00
G 0.00

IC TL072CP
4.23   8.59
4.40   4.47
4.35   4.47
0.00   4.47

Any help appreciated. Thank you!

midwayfair

Q3 drain voltage is way too low*, just needs a bias adjustment. try replacing R9 with a 3.3K or 2.2K (or use a socket there if you want to experiment a bit). If that doesn't fix it, use an audio probe to make sure you have signal getting to Q3.

*This is a danger in general with the way I biased that FET. I knocked down the drain voltage pretty low to squeeze enough output to match Q2, but in doing so I kind of put everyone at danger of having a non-functioning transistor if their J201's "gain" was too low. Then all the fake JFETs being sold made this an even more likely problem, because most of the fake J201s had lower gain than the part was speced for. Even before considering the normal issues with FETs being delicate little snowflakes.

Tremster

Thank you.
No difference though. I removed R9 and socketed it and tried several other values with no effect. Actually, pulling R9 completely doesn't make a difference.
Reflowed all solder joints etc. etc.
Board starts to look bad from all the soldering. I hate desoldering...

midwayfair

Quote from: Tremster on October 24, 2013, 05:30:45 PM
Thank you.
No difference though. I removed R9 and socketed it and tried several other values with no effect. Actually, pulling R9 completely doesn't make a difference.
Reflowed all solder joints etc. etc.
Board starts to look bad from all the soldering. I hate desoldering...

I hate desoldering too, but the important thing at this point is to take things slowly and only desolder what's necessary.

Can you post a picture of at least the top side of the board?

1) First, let's make sure that your guitar signal is making it to Q3 and getting amplified. Did you socket Q2? This might be easier if we can work on just the treble band. If you didn't socket Q2, then it's best to use your audio probe. Follow the signal from the output of Q1 to the input of Q3. Do you have signal at the gate of Q3 in either mode? If you do have signal at the gate, do you have signal at the drain?

2) Next, let's check that the LFO is doing what it's supposed to on Q3. Measure the resistance to ground from the gate of Q3 with the DEPTH at max and the RATE at minimum. It should change, going from about 1K to well over 1M. If it has continuity to ground (beep), flip the mode switch. If you have continuity to ground in BOTH modes, then there's something wrong for us to track down.

If you have signal getting into Q3 and not making it out even with proper bias on the drain, then it's possible it's a bad/fried transistor. If you have no signal on Q3, or the signal is grounded out, there aren't too many parts that could be the culprit.

Eventually you'll track down the problem. I had a recent build that drove me nuts until I figured out that some excess solder had formed a bridge on the TOP of the PCB under a socket. That one drove me nuts for two days. :)

Tremster

#4
I tried several J201s, so that's probably not it.
I soldered the joints from the topnow , too, and made some ugly stains that I cleaned off again.
I left the legs on the vactrols until I'm sure I don't have to remove them again.
Don't have an audio probe yet, I have to admit, that thing has always scared me. Will finally have to make one on the weekend.
Have to go for now, but here are the pictures. Thank you!
[images deleted]

Tremster

Made an audio probe and tried around with it, what an adventure.

Quote from: midwayfair on October 24, 2013, 06:09:40 PM
Did you socket Q2? This might be easier if we can work on just the treble band. If you didn't socket Q2, then it's best to use your audio probe. Follow the signal from the output of Q1 to the input of Q3. Do you have signal at the gate of Q3 in either mode? If you do have signal at the gate, do you have signal at the drain?
I did socket Q2 and followed the signal path, hopefully correct, I get signal at every part.
I do have signal at the gate of Q3 in either mode, loud in one outer (1) and the central position (2) of the switch, faint at the other outer position (3).
Signal also at the drain in position 1 and 2, none at 3.

Quote
2) Next, let's check that the LFO is doing what it's supposed to on Q3. Measure the resistance to ground from the gate of Q3 with the DEPTH at max and the RATE at minimum. It should change, going from about 1K to well over 1M. If it has continuity to ground (beep), flip the mode switch. If you have continuity to ground in BOTH modes, then there's something wrong for us to track down.
Erm. I think I might have done that one wrong, but there is no beep and no reading in any position at the gate, readings at the drain in positions 1 and 2, beep at source in all positions.

I'm lost. Thank you.

midwayfair

Hm. When you audio probe the gate of q3 with the depth maxed, the sound doesn't change, it's just always loud in certain switch positions? But you don't get continuity to ground at the gate when you flip the switch? (Also, it's a little weird that you get any signal at the gate in position 3, because all the signal should be dumped to ground.)

Time to track down whether the switch is connecting to ground in th e center. Do you get a beep on the continuity setting from the center lug to ground? And do the outside lugs connect to where the should connect? Does the center lug connect to anything that SHOULDN'T connect to ground? :/

Also, a clarification. You say "only normal tremolo". This led me to believe that the treble band was inaudible. You also said that the switch doesn't change the sound? But you just did some listening and you confirmed that you have loud signal on the treble band in two of the positions. So you still hear no difference in sound when you flip the switch when you're running through the whole effect? If that's the case, make sure the treble band is making it all the way to the output. (That is, just pull q2 and see if you have signal at the volume control.)

Tremster

OK, made another audio probe as the capacitor on the first one was falling off. Derp.

Quote
(Also, it's a little weird that you get any signal at the gate in position 3, because all the signal should be dumped to ground.)
You're right. With the new probe, no signal at drain and gate in position 3.

Quote from: midwayfair on October 28, 2013, 10:04:22 PM
Hm. When you audio probe the gate of q3 with the depth maxed, the sound doesn't change, it's just always loud in certain switch positions?
It is tremolo'ed in positions in 1 and 2, no signal at 3.

Quote
But you don't get continuity to ground at the gate when you flip the switch?
Correct. None. In all positions.

Quote
Do you get a beep on the continuity setting from the center lug to ground? And do the outside lugs connect to where the should connect? Does the center lug connect to anything that SHOULDN'T connect to ground? :/
Yes, it beeps at the center lug.
Checking and double checking, the switch seems to be wired ok, the right wires in the right positions, nothing touching anything. Etc.

Quote
If that's the case, make sure the treble band is making it all the way to the output. (That is, just pull q2 and see if you have signal at the volume control.)
Signal at Volume lug 2 and 3

midwayfair

Before I make a final suggestion ...

I'm mystified. One of the lugs of the switch is connected to the gate of Q3. Your switch is connected to ground. The signal goes dead when you put it into position 3. I don't understand how you can't be getting continuity to ground at the gate.

Anyway, I guess that's not really important, because it's doing what it's supposed to.

what does the signal at the gate of Q3 SOUND like (remove Q2 while you're doing this)? Is it really thin and trebly? Basically, I'm asking, do you have a treble band with tremolo when Q3 is in and a full-range band with tremolo when Q2 is in? Or is one of the bands NOT working? OR is it just that you're not hearing much "phasing"?

Anyway, if you have both bands working and you're just not hearing much in the way of complexity, remove C2.

Tremster

I can guess what your final sugestion will be, and I'm beginning to doubt my ears myself.
Probing the signal at the gate of Q3 sounds full and rich, lush tremolo.
No difference in sound with or without Q2 in.
Just no phasing, ever.
Haven't removed C2 yet.
If you're ever in Berlin, I'll buy you a drink.

midwayfair

Quote from: Tremster on November 01, 2013, 06:55:18 PM
I can guess what your final sugestion will be, and I'm beginning to doubt my ears myself.
Probing the signal at the gate of Q3 sounds full and rich, lush tremolo.
No difference in sound with or without Q2 in.
Just no phasing, ever.
Haven't removed C2 yet.
If you're ever in Berlin, I'll buy you a drink.

Let me put it another way: do you have output and tremolo on ALL the drains?

Tremster

Quote from: midwayfair on November 01, 2013, 08:03:16 PM
Let me put it another way: do you have output and tremolo on ALL the drains?
Output yes, but tremolo only at Q3.