another sunking problem

[rhinson]

i thought maybe i should start another thread since my problem is close to the other guys (in that it seems to revolve around ic2 pins 1 and 7), but not exactly the same manifestation.  but it could be a board problem since it seems to be in the same area.

i just built 2 sunkings and am experiencing almost the same problem as the other sunking poster on both builds.   both builds  use the same parts.  the problem sounds very close to that one, with the problem around the voltages on ic2-- pins 1 and 7 are off and they will vary as you rotate the gain pot with the sum of both always being in the 9v range  (at the extreme pin1 will be 11v and pin7 - 2v or so, at the other extreme pin 1 will be maybe 7v and pin7 around 2)  the differential makes the pot have a lot of crackling noise.    the other voltages on the ic are as they should be.  i swapped ic's, pumps, etc. but no dice.  i also built one of these on a board i etched from the bajaman layout and did not have this problem---both voltages were around 4.5v and stayed steady with no change/crackle with rotation of the gain pot (same parts used).   i'm thinking perhaps this might be a bad batch of boards with some trace short somewhere.    any ideas would be very helpful----i hate to toss 2 boards full of parts.   perhaps brian could look at a sample board from his last batch and see if there's anything obvious to him pad wise, etc.     thanks very much.     rh

[madbean]

Nothing obvious from looking at a few of the boards I have on hand. Since my build is out on loan to someone, I may have to build a new one up and check it out.

From what you are describing there are a couple of clues. 1) you've got DC across your gain pot 2) something is wrong in the vb supply.

Can you tell me how you are testing these boards? Are they loaded into an enclosure, or are you testing on a breadboard?

Have you used the correct voltage tolerances on your caps? Ideally, 25v or above on all, but at least on C20 - C22.

Any subs part-wise I should know about?

Of course, it is always possible that there can be a manufacturing error. These boards were electrically tested as part of the manufacturing process, so I guess there should not be any discontinuity in the traces. But, when debugging it's best not to rule anything out.

I do happen to have another person's built board on hand, so I can check that one out (most likely it will be tomorrow before I get to it). That may help provide us a baseline to work off.

Having built these layouts several times, I can vouch for their correctness. So, that's at least one possibility eliminated

[mjcyates]

For what its worth, I have built 3 of these with no issues.

[rhinson]

Nothing obvious from looking at a few of the boards I have on hand. Since my build is out on loan to someone, I may have to build a new one up and check it out.

From what you are describing there are a couple of clues. 1) you've got DC across your gain pot 2) something is wrong in the vb supply.

Can you tell me how you are testing these boards? Are they loaded into an enclosure, or are you testing on a breadboard?

Have you used the correct voltage tolerances on your caps? Ideally, 25v or above on all, but at least on C20 - C22.

Any subs part-wise I should know about?

Of course, it is always possible that there can be a manufacturing error. These boards were electrically tested as part of the manufacturing process, so I guess there should not be any discontinuity in the traces. But, when debugging it's best not to rule anything out.

I do happen to have another person's built board on hand, so I can check that one out (most likely it will be tomorrow before I get to it). That may help provide us a baseline to work off.

Having built these layouts several times, I can vouch for their correctness. So, that's at least one possibility eliminated

hey brian,  i've used all 50v caps except a couple of the electrolytics (4.7uf and 47uf) are 35v, all the film caps are the panasonic, and 50v 1uf tant.    there is dc on both the gain and treb. pots in the real klon (i have a real one here to compare it to). it's the differential from ref. that will cause the crackle.   oddly, on my gain pot there is the correct voltage and no differential across the lugs which is correct BUT there is a differential across the treb pot lugs that seems to be controlled by movement of the gain pot (which crackles! until at full rotation--then i get a lot less gain and a muted tone, probably because pins1&7 are now at about 11v and -2v respectively)---just like the voltage differential at ic2 pins 1&7 (pin 1 being way higher than pin 7).   

my builds are boxed up, but i can undo the pots and flip them back to test.    any ideas would be appreciated.   i build a LOT of tube amps so i'm more familiar with that stuff with regard to troubleshooting.   but, some part/path short/something, etc. has caused the ic2 pins 1&7 to be severely offset from each being approx. 4.5v., though their sum is still about 9v.   the ONLY thing that gives me suspicion about the board is that i have 2 builds doing exactly the same thing.       rh

[madbean]

Okay, got it. I'll report back tomorrow once I've had a chance to get some of these orders back. We'll get it solved.

[rhinson]

ok,  looking at the schematic conceptually (from the pov of assuming no bad boards here, the ic's are good, etc.) what we have is the gain dual pot affecting with it's rotation the already messed up voltages on ic2 pins 1(too high) and 7 (too low)--and since the tone pot is between pins 1 and 7, that explains why it's floating voltages are off the same.  since the sum of the two is around 9v and stays that way as they are altered by the gain pot,  what part(s) causes these two pins to be in balance?  what kind of fault could cause them to be out of balance?    how are they balanced and how do they stay balanced in normal conditions?    what imperfection pre ic 2 would drive pin1's voltage high, and would this drive pin7's voltage low?     rh

[madbean]

Okay, this is a bit murkier than I thought. Are your readings on pins 3 and 5 on IC2 invariant under changes with the gain pot/tone pot? Are they the same, change inversely, etc? And, are they the same readings as pin2 of GAIN1 and pin3 of GAIN2?

[rhinson]

Okay, this is a bit murkier than I thought. Are your readings on pins 3 and 5 on IC2 invariant under changes with the gain pot/tone pot? Are they the same, change inversely, etc? And, are they the same readings as pin2 of GAIN1 and pin3 of GAIN2?

pins 3 and 5 on ic2 are unaffected by the gain pot rotation (they are 4.5v as they should be---and all lugs of the gain pot are invariant at 4.5v as well).    btw,  having just checked, pin7 on ic1 is also affected by all this---it drops from norm of 4.5v down to 1.4v as the pot is rotated.   all the other voltages on other pins are as they should be.     thanks for your help and suggestions man.   rh

[madbean]

Okay, this is a bit murkier than I thought. Are your readings on pins 3 and 5 on IC2 invariant under changes with the gain pot/tone pot? Are they the same, change inversely, etc? And, are they the same readings as pin2 of GAIN1 and pin3 of GAIN2?

pins 3 and 5 on ic2 are unaffected by the gain pot rotation (they are 4.5v as they should be---and all lugs of the gain pot are invariant at 4.5v as well).    btw,  having just checked, pin7 on ic1 is also affected by all this---it drops from norm of 4.5v down to 1.4v as the pot is rotated.   all the other voltages on other pins are as they should be.     thanks for your help and suggestions man.   rh

Okay, this is good info. I've got a build out and I'm going to take some voltages on it. I'll have more soon.

[rhinson]

Okay, this is a bit murkier than I thought. Are your readings on pins 3 and 5 on IC2 invariant under changes with the gain pot/tone pot? Are they the same, change inversely, etc? And, are they the same readings as pin2 of GAIN1 and pin3 of GAIN2?

pins 3 and 5 on ic2 are unaffected by the gain pot rotation (they are 4.5v as they should be---and all lugs of the gain pot are invariant at 4.5v as well).    btw,  having just checked, pin7 on ic1 is also affected by all this---it drops from norm of 4.5v down to 1.4v as the pot is rotated.   all the other voltages on other pins are as they should be.     thanks for your help and suggestions man.   rh

Okay, this is good info. I've got a build out and I'm going to take some voltages on it. I'll have more soon.

hey brian,  had a chance to look at anything regarding my problem here?    thanks man,     rh

[madbean]

Robert,

I will do my best to make that happen today. Sorry for the delay. Orders have stacked up due to my having to leave town unexpectedly for several days. But, I have a few debugging priorities to get to, including this so I will make an extra effort to give it some attention ASAP.

[rhinson]

Robert,

I will do my best to make that happen today. Sorry for the delay. Orders have stacked up due to my having to leave town unexpectedly for several days. But, I have a few debugging priorities to get to, including this so I will make an extra effort to give it some attention ASAP.

very cool--thanks very much.   i'll try to succinctly summarize the problem by listing the problem voltages here:

gain pot at min:     ic 1, pin 7--4.6
                          ic 2, pin 7--0.6
                          ic 2, pin 1--8.8

gain pot at max:    ic 1, pin 7--1.4
                          ic 2, pin 7--  (-2.9)
                          ic 2, pin 1--12.6

in essence, turning the gain pot is rebiasing the ic's (with ic 2 starting from an already misbiased balance between pins1 and 7)---so i guess that's where the "crackle" comes from---kinda like the zvex sho pot.  so there must be some part or bad connection condition that could cause this to occur---in the normal good build the turning of the gain pot doesn't affect voltage on these pins.   thanks man    rh

[madbean]

I've taken readings off two builds now. Here's what I have for the pins you mentioned.

IC1 pin7 - 4.46
IC2 pin7 - 4.46
IC2 pin1 - 4.46

Which is what I expected.

The first build I checked originally had readings that were way off on those pins. They were
IC1 pin7 - 8.29
IC2 pin7 - 7.74
IC2 pin1 - 1.26

The IC's used in that build were TL072CP and MAX1044. I replaced them with TL072CN and TC1044, resp., and got readings much more in line with my build. So, I'll need to do some checking into the CP vs. CN versions.

Also, I did not notice any voltage changes on those pins with either build, so this is all getting very interesting.

I'll have more soon.

[oldhousescott]

From what I can tell perusing datasheets, the CP vs CN has to do with thermal dissipation factors. That shouldn't be a problem, and either chip should work fine in this circuit.

[madbean]

Indeed, that's what I thought. But, the proof is in the pudding.

I have a few CP's on hand so I'll compare. Could be the first two are just crap.