Soldano x88r clone build.

[Captain chunkulus]

So I've been working on a soldano x88r ish circuit. 3 channels  high gain, low gain, clean. I have it  working but have some grounding issues. I have the first 2 filter caps grounded near the power transformer. Everything else is grounded near the input jack. What I'm curious about is that the more I read on grounding schemes, the more confused I get. Do I take each individual tube circuit and ground the grid leak resister, cathode resister etc to a single point then, bring all the individual nodes to a single star ground on the chassis near the input jack? Also, all three channels share a single input stage. So, the low gain distortion channel uses the 2nd half of the 1st tube so should I ground the first tubes grid leak and cathode registers as well as the input jack to a single point then run 1 wire to the common preamp Star? I'm just trying to learn more about the best ways to eliminate hum and such. Thanks in advance for any info, advice.

[DummyLoad]

second filter feeds pre-amp circuits. tie second filter to preamp ground.


--pete

[Captain chunkulus]

Okay, tried that. Made some difference. So, here's what I've done. There are 6 tubes. Each has its grid leak resister,  cathode resister and corresponding gain pot or tone stack depending on the stage tide together at one point for each tube. Then there is a single wire run from each tube common point to 1 single ground point near the input jack. The 22uf filter caps grounds are all in a line and tide to the last tubes ground point. Not to each individual  tube stage. The reservoir cap is grounded near the transformer.  The heaters are elevated to about 70v dc. Gain pots add 120hz buzz and when turned down I get 60hz hum from the master volumes. Do I need to tie each preamp filter caps to the stage it belongs in instead of just in line? Also, How do I determine which filter caps goes to which cathode ground? Thanks for any help. Just trying to learn stuff. Thanks, j.

[shooter]

I'm a brute force troubleshooter so take it with a lb of salt 

I would;
1. disable the power to all the relays n switching logic.
2. I would temp wire like the schematic and evaluate hum/hiss/noise
A) If I'm happy;
b) hardwire ch1 - still happy
C) hardwire ch2 - unwire ch1 - still happy
........
Then I would gather notes and spend quality time pondering what next

oops
schematic

[DummyLoad]

class A is susceptible to PS noise -as there's no cancelling effect of push-pull stage. possible causes? poor layout, unshielded tubes or shielded tubes with the shield ungrounded (60Hz), poor PS filtering/grounding (120Hz buzz + i would have used a 10-15H 20mA choke with the RC networks) try lifting the switching PS ground and leave it floating or it could be lifted off ground with series of 47-51R and .01iuF cap.

grouped the grounding - the coupling caps isolate the power rails ( see attached). use shielded wire and that itself will help immensely. the filaments are DC - try using a 12VDC battery to power the filament string to confirm DC PS isn't source for buzz. a 12V motorcycle/UPS battery is adequate for testing purposes. 


--pete

[Captain chunkulus]

The schematic that I used is laid out a little different as far as the tubes go I think anyway. Also, you refer the heaters being  dc. Is that the same as dc elevated? Because I'm using a separate filament tap and elevating the heaters with dc. I also have the first tube running on pure dc with 16,000uf of filtering. Also, I did use a chokearlier instead of the resister between the reservoir cap and the filter caps that feeds the preamp .

[Captain chunkulus]

Also, this is the relay circuit I used.

[sluckey]

This is strictly a preamp, right? Should not be plagued with the same kind of grounding issues that an amp that has a preamp and power amp powered by the same power supply and located in the same enclosure. That's not to say there wont be other grounding issues. IE, you may need to float the grounds in the preamp to prevent a ground loop between the preamp and power amp (or whatever the output connects to. Can we see some hi rez pics of this project.

[Captain chunkulus]

Heres a video

[Captain chunkulus]

The pictures I took won't upload fir some reason.

[Captain chunkulus]

Okay, so I rewired the preamp filter caps. They are now grounded to the cathode node for the stage they decouple. No difference in hum. So essentially I have each individual stage star grounded. To one point on the chassis near the input. I have the reservoir cap grounded near the power transformer. I tried tying the preamp Star to that point, no difference.  Next I'm going to try to power the filaments with a 12v lawn mower battery. At this point I'm at a loss. On a side note,  the power transformer is not center tapped. I'm using a bridge rectifier.

[sluckey]

Your schematic shows several VTL5C1 optocouplers. I didn't see any in your video???

[Captain chunkulus]

I'm using relays instead to ground out the signal so there isnt any cross talk when changing channels.

[Captain chunkulus]

Okay, so it appears that the buzz sound comes from the gain pots and is eliminated by turning them to zero. The hum is affected by the master volume and completly goes away when zeroed.  I disconnected the relay power and it did not affect the buzz or hum in any way. I pulled tubes 2,3 and four which go to the high gain channels and the buzz nearly disappeared from the clean channel. Replaced tube 2 and 3 and it dud not affect the clean channels hum or buzz at all. Replaced tube 4 and the buzz returned on the clean channel. I'm planning on trying to hook the heaters to a battery today but thought I would share this first. Also, chop sticking wires produces zero change in hum/buzz levels.

[Captain chunkulus]

Okay, tried a battery for the filaments. Same hum. No change at all.

[DummyLoad]

buzz is coming from a full wave rectifier. what do you hear when you disconnect relay PS?


--pete

[Captain chunkulus]

Same buzz with the relay tranny unhooked.

[Captain chunkulus]

Could physical location of relay power supply to bridge rectifier cause this? See pics. The relay power supply is near the bridge.

[Captain chunkulus]

So after spending a bunch of time trying to track down the hum/buzz, I've come down to just a 120hz buzz/hum. Running the heaters on a dc battery did not reduce anything. I've tried every kind of grounding scheme including star grounding each individual stage, no change at all. I now have more or less a hoffman grounding schem. All cathodes and  related circuits in a straight line as they are in the circuit. So, could it be a power supply issue? I'm at a loss. It doesn't appear to be ground hum. However. If I turn the gain pots down the 120hz volume gets a lot lower. If I turn down the master volumes there is zero hum/buzz. If I remove rubes 2,3 and 4 leaving just the input tube the clean channel and the recovery tube the clean channel has zero buzz/hum but nothing I do affects the two distortion channels in any way as far as noise goes. Hmm. 

[shooter]

I've had 1 hummer PS but it's missing a couple isolation washers, probably the reason, but it's my BB PT so nbd.
yours still sounds like it's being coupled/induced into the signal path so it's time for a scope, or a listening amp, or more brute force cut/jumper till it's isolated

[sluckey]

Maybe it's your layout.

[Captain chunkulus]

At this point in sure. Lol oh well, going to try to narrow it down and see if it's some sort of coupling. Maybe use more  shielded runs of wires. 

[shooter]

I did a lot of chip builds on boards like yours but when I started doing tubes they ALWAYS hummed, experimented some and found the whole spacing was way to close for wire separation.  did a couple more "skipping" 5-6 holes was better, but I just gave up and started doing turrets - last 5 builds hum free.  I also reduced my part count by a factor of 2 or more 

[Captain chunkulus]

That's kinda what I've been thinking. Maybe mount the tubes separate and spaced farther apart. Then just use turret board for the circuit. That's a lot easier to deal with tracking down issues  for sure. Lesson learned me thinks. Lol

[Captain chunkulus]

It's funny, the last build I did was a rats nest for sure but it's completely  hum free.  But the tube spacing was much farther apart.

[sluckey]

My concerns were not about the overall layout. Haven't seen that. I was concerned about the high gain preamps laid out on a vector board. Lot's of little antennas on that board.

[Captain chunkulus]

Ah... that makes sense. Totally. Thanks for all the help guys. Think I'm going to start over. Wouldn't be the first time. Lol

[Captain chunkulus]

Okay, before I decide to scrap this project all together and start over. I would like to post a couple of other findings to see if you guys have any ideas. First of all I want to post the plate voltages of the tubes.
I still have the hum/ buzz but I have tracked it down to tube B and E according to the schematice.  When I ground out the input signal to either of those tubes the hum goes away on the clean Channel and the low gain Distortion Channel. If I remove the tubes that does the same thing. Can't find anything wrong with the circuitry as far as grounding goes. And it's reading exactly 120 hertz hum / Buzz. The hum / Buzz is affected by the gain pot and the volume pot of that channel. If I turn either down the hump goes completely away but still persists when I switch to either of the other two channels. Unless, I ground the signal out Hans the High game channel. I have unhooked all relay stuff including the power supply to the relay no difference and hum or Buzz. I physically relocated Parts on the board to get them away further from the tubes no difference in hum. I am also running the haters elevated at 77 volts. I am providing voltages just to see if there's something I'm missing. Thanks for any help guys. J

[sluckey]

Your voltage readings don't make sense. You show node A as 193v on one tube then 317v on the next tube. And node B is 199 and then 321. I know this is probably an error in measurement or transcribing to the schematic. But our suggestions can be no more accurate than the info you provide. Please recheck these voltages.

[Captain chunkulus]

Sorry, the schematic I posted  has the voltages with what I measured  at the plates and cathode.

[Captain chunkulus]

Okay, rechecked my voltages. Gonna list them in order.
V1a's signal is used on all channels it's 201v and has 150k plate resister.
V1b signal is used on the low gain pre it's 334v and has a 220k plate resister.
V2a and b is a cathode follower for the low gain pre  it reads170v, 313v, and the cathode is 169v it has a 100k plate resister.
V3 a and b go to the high gain channel.  V3a is 209v v3b is 340v.it has 2 220k plate resisters.
V4 is a cathode follower for the high gain channel. It reads v4a 198v v4b 311v and the cathode is 197v it has a 100k plate resister.
V5 is for the clean channel v5a reads 299v v5b reads 291v. It has 2 100k plate resisters.
V6 is a recovery stage that is a cathode follower. It reads v6a 242v  v6b 462v cathode reads 247v.it has a 100k plate resister.

After the rectifier at the resavoir cap it reads 463v.
At the first filter cap it reads 460v that point feeds v6 and is a 100uf 500v cap.
The 3rd filter cap is a 22uf 450v. It feeds v2 an v4 cathode followers and it reads 312v.
The 4th filter  cap is a 22uf 450v and feeds v5 it reads 422v
the 5th filter cap is a 22uf450v and ot feeds v3 itreads 438v
the 6th filter cap is a 22uf 450v and it feeds v1 it reads 421v.

Don't know if any of this is useful. J

[PRR]

The DC voltages "probably" have nothing to do with hum/buzz.

> Don't know if any of this is useful.

I'm not sure what it says. "V1a feeds all channels it's 201v"--- it isn't sending 201V to all channels, but that's what it seems to say.

A FULL set of voltages on a standard tube stage will include B+, P, G, K.

B+ is often omitted, but can be key data.

Grids are often at "zero". If I put a 1.5V needle-meter on a grid and it hardly moves, I don't make a note. Some tube-amp grids are biased way high. And some of these won't read right due to meter loading. But if it isn't zero (or same-as the previous plate, a common plan), make a note and we can sort any discrepancy later.

If we know B+ and P, and the resistor values, we can know the voltage at K. *Except* when the amplifier is unhappy and we suspect wrong parts or mis-wiring. Then a K value may be the key clue.

[nandrewjackson]

What "brand" are the green boards? I bought some discount ebay through hole boards, they were brown, they conducted randomly through the board. Took a while to find that little gremlin, only buy jameco boards now.

[Captain chunkulus]

Well, I think my layout was more the issue. After doing a ton of research I realized that soldano had all 3 of the cathode followers at the end of the chain. I had them in order of preamp usage. Don't know if that made it hum or not. Not really sure. It worked and sounded good but I decided to scrap it and start over. Built a new power supply using f&t capicitors. Also changed the tube layout.  The plan this time is to work on 1 channel at a time and get that working. I've also scrapped the soldano circuit  all together. I'm doing my own tweaked marshally thing. We'll  see how it turns out those time.

[Captain chunkulus]

Pic