Ok, rare strait forward question: what should the voltage be coming out of Q1? I did a quick comparison of the two boards, and was able to trace back a difference between the two to Q1, with the working board having just under 20v leaving, and the other zero. I replaced q1 on the non working board, and now get just under23v leaving it, which leads to a consistent 3v difference from then on between the two boards. Can someone tell me which is correct? Thanks as always.
About 20V there is correct.
There are 13 voltages on the schematic - are all thirteen of them 3 volts higher? Check the 0 volt points first, the top of R13 and the top of R17
Hi Folks,
It took a while to get the two boards stabilized, but now that seems to be the case, so I checked voltage. What follows is Wayne/pcb #1/ pcb#2
Input R9: 20.2/22.6/19.7 (two boards noticably different, can't see why)
Output R9: 10.1/7.2/7.6 (two boards similar, but noticeably different from Wayne)
Output Q3: 9.4/7.1/7.5 (ditto)
Input R24: .01-.04/.06/.06
Drop across R6: 1.5/1.5/1.5
Output R6: 21/20.4/20.3
Input R13: 0/0/0
Input Q10: -23/-22.5/-22.6
Input R27: -22.3/-21.9/-22
Output Q11: -23/-22.5/-22.6
Input R17: 0/0/0
I am getting +- 23.6 at the output of the resistors at the regulators.
So, the area that is most different is around Q1 and Q3, and inconsistently so. PCB #1 has voltage two high going into Q1, but they both have voltage too low leaving.
Any thoughts? Thanks again for your time. If there is anything I can do to clarify, let me know.
It took a while to get the two boards stabilized, but now that seems to be the case, so I checked voltage. What follows is Wayne/pcb #1/ pcb#2
Input R9: 20.2/22.6/19.7 (two boards noticably different, can't see why)
Output R9: 10.1/7.2/7.6 (two boards similar, but noticeably different from Wayne)
Output Q3: 9.4/7.1/7.5 (ditto)
Input R24: .01-.04/.06/.06
Drop across R6: 1.5/1.5/1.5
Output R6: 21/20.4/20.3
Input R13: 0/0/0
Input Q10: -23/-22.5/-22.6
Input R27: -22.3/-21.9/-22
Output Q11: -23/-22.5/-22.6
Input R17: 0/0/0
I am getting +- 23.6 at the output of the resistors at the regulators.
So, the area that is most different is around Q1 and Q3, and inconsistently so. PCB #1 has voltage two high going into Q1, but they both have voltage too low leaving.
Any thoughts? Thanks again for your time. If there is anything I can do to clarify, let me know.
Is R5 correct on the board with 22.6?
My readings were similar to yours until I bumped up R21-R24 to 20 ohms, on advice from Salas.
Ok, progress--tested around r7, something was obviously wrong (got same voltage both sides), replaced it, and that sorted the first voltage anomaly noted above--now I am getting around 19.6 v out of q1 on both boards. I will try 20 ohm resistors as suggested when I get them (hello, mouser).
One odd thing--I tested the r7 I pulled from the board after replacing it, and it tested out ok. The problem must have been the solder, I guess? I don't know.
One odd thing--I tested the r7 I pulled from the board after replacing it, and it tested out ok. The problem must have been the solder, I guess? I don't know.
Ok, replaced the 10 ohm resistors in r21-24 with 20 ohm, and now get 9.6 and 10.2 v out of r9. Is this difference significant? I haven't looked too hard, but so far can't trace it to anything.
Other than that I can't see anything to do beyond put it all back together and try again.
I fried two more 10ohm resistors and 1 more 7924 if there is anyone taking a tally...
Other than that I can't see anything to do beyond put it all back together and try again.
I fried two more 10ohm resistors and 1 more 7924 if there is anyone taking a tally...
When? Which PCB? After you measured the proper voltages when you changed the source resistors?
Re: the fried resistors, I believe that I still have issues around the connection of the psu to the pcb's. After I got the second pcb to work, I retested the first (which had already tested out fine), there was a crackle noise, and the resistors at the entrance of the negative input fried. I replaced them and the 7924. Then it worked. My guess is that there is still something going on with the connection between the psu and the pcbs.
I did plug everything in and gave it a spin before work. First off, sound--real sound, Janis Joplin sounded like Janis Joplin, major step forward. But, not yet fully functional. Remaining issues:
1) I need to check the power supply connection as mentioned above--it is not stable in the case, there was some crackling when I tried to set it firmly, as I wasn't hearing one channel. It may be just the need to tighten everything up, but I didn't have time to look.
2) The levels are very different--one channel is comparable to the unit I currently have in place, maybe a bit softer, but not too much. The other was very soft, much less amplification. For reference, I am using a 30W Pass integrated amp, which I normally turn up around half way to listen (not too high a volume). To get a comparable volume, I had the left channel up around 55%, and the right near 100%.
3) there was some crackling on the left channel.
I didn't have time to a/b it, or even really give it a good listen, so I can't comment much on the quality, except to say that (level issue aside) it works--I could use it to play records.
So, I will take a hard look at the connections of the power supply (at a minimum, tightening everything, which I realize I forgot to do). I am not sure what to do about the levels. I will start by testing the voltages again with everything hooked up, see what that tells me.
Thanks as always.
I did plug everything in and gave it a spin before work. First off, sound--real sound, Janis Joplin sounded like Janis Joplin, major step forward. But, not yet fully functional. Remaining issues:
1) I need to check the power supply connection as mentioned above--it is not stable in the case, there was some crackling when I tried to set it firmly, as I wasn't hearing one channel. It may be just the need to tighten everything up, but I didn't have time to look.
2) The levels are very different--one channel is comparable to the unit I currently have in place, maybe a bit softer, but not too much. The other was very soft, much less amplification. For reference, I am using a 30W Pass integrated amp, which I normally turn up around half way to listen (not too high a volume). To get a comparable volume, I had the left channel up around 55%, and the right near 100%.
3) there was some crackling on the left channel.
I didn't have time to a/b it, or even really give it a good listen, so I can't comment much on the quality, except to say that (level issue aside) it works--I could use it to play records.
So, I will take a hard look at the connections of the power supply (at a minimum, tightening everything, which I realize I forgot to do). I am not sure what to do about the levels. I will start by testing the voltages again with everything hooked up, see what that tells me.
Thanks as always.
OK, I will add more later on this, but...
I have a Pearl II.
Following the previous note, I took apart the riaa and realized that the problematic board had a serious problem--I had fried the voltage regulator so many times that the pcb itself had been damaged (I am guessing from the constant soldering/desoldering process). I was on the verge of punting, and getting a new pcb to start over with that channel, but sent a picture to 6L6 before I placed the order. He said he would give it a shot, so I sent the board to him. A week later it returned, with a nifty little bridge across the damaged part of the pcb (I forgot to photograph, but will the next time I take the riaa apart). There was a small amount of drama following this, but once I got the output/input wires connected to the rca's properly, it worked! The only immediate issue was hum, which was loud enough to be troublesome. It turned out that just moving the riaa away from my integrated amp, and putting the cover on, took care of most of that. If you crank the amp enough and put your head close to the speakers you can still hear it, but if I were to get another stand to get the riaa further away that would eliminate most of that.
The level of the Pearl II is lower than that I am replacing with it (an old musical surrounding phonomena), which makes a/b'ing it a bit tricky. I played with it a bit last night, but ended up just listening to records. Eventually I will do it right, but for now I have the Pearl II in the system.
So, quickly, thanks to all for the help throughout this process (and particularly to 6L6 for general guidance and stepping in at the last moment and saving a pcb). To answer a question I asked on a different thread, yes--a person with no particular background in any of this, and no experience with electronics, soldering, pretty much anything useful in this area, can do it. Try!
I will post a more detailed summary at a later date, with an updated BOM, and anything else that I can think of that I wish I had known. One last time--thanks to everyone for helping out with this, I never would have even tried, let alone finished, if you had not.
I have a Pearl II.
Following the previous note, I took apart the riaa and realized that the problematic board had a serious problem--I had fried the voltage regulator so many times that the pcb itself had been damaged (I am guessing from the constant soldering/desoldering process). I was on the verge of punting, and getting a new pcb to start over with that channel, but sent a picture to 6L6 before I placed the order. He said he would give it a shot, so I sent the board to him. A week later it returned, with a nifty little bridge across the damaged part of the pcb (I forgot to photograph, but will the next time I take the riaa apart). There was a small amount of drama following this, but once I got the output/input wires connected to the rca's properly, it worked! The only immediate issue was hum, which was loud enough to be troublesome. It turned out that just moving the riaa away from my integrated amp, and putting the cover on, took care of most of that. If you crank the amp enough and put your head close to the speakers you can still hear it, but if I were to get another stand to get the riaa further away that would eliminate most of that.
The level of the Pearl II is lower than that I am replacing with it (an old musical surrounding phonomena), which makes a/b'ing it a bit tricky. I played with it a bit last night, but ended up just listening to records. Eventually I will do it right, but for now I have the Pearl II in the system.
So, quickly, thanks to all for the help throughout this process (and particularly to 6L6 for general guidance and stepping in at the last moment and saving a pcb). To answer a question I asked on a different thread, yes--a person with no particular background in any of this, and no experience with electronics, soldering, pretty much anything useful in this area, can do it. Try!
I will post a more detailed summary at a later date, with an updated BOM, and anything else that I can think of that I wish I had known. One last time--thanks to everyone for helping out with this, I never would have even tried, let alone finished, if you had not.
First let me say thanks for this thread because it’s got a lot of valuable info in it, and it’s captured in 5 pages vs. 155 pages of the main build thread.
I built a Pearl II and it worked perfect right out of the gate. I needed a little more gain though so I changed a resistor to get another 10db and that’s where the trouble started. When I pulled the pcbs out of the case I accidentally touched the bottom of the PCB to the live power coming in and burned up R30 and R32, as posted earlier here.
Initially that was it- easy enough. The other channel still worked. I replaced R30 and R32 and now neither channels work, leds won’t light on either side. I checked U1 and U2 and seem to get close voltages indicating things are good there. Voltage seems to start to drift around R8 and R10 but still within 1-2 volts of target. I seem to get nothing though at Q4 or anything after that on the - side. Any ideas? I hate just replacing parts hoping it works…
I should add that I’m a very amateur, I can follow directions but I’m no electrical engineer. The solder connections all look good.
I didn’t build Wayne’s power supply either, just using a wall wart thing from a standing desk that puts out 27v.
The fact that the pre worked great until I swapped the gain resistor makes me think that the basics (soldering, power supply, connections, etc.) are all okay.
I built a Pearl II and it worked perfect right out of the gate. I needed a little more gain though so I changed a resistor to get another 10db and that’s where the trouble started. When I pulled the pcbs out of the case I accidentally touched the bottom of the PCB to the live power coming in and burned up R30 and R32, as posted earlier here.
Initially that was it- easy enough. The other channel still worked. I replaced R30 and R32 and now neither channels work, leds won’t light on either side. I checked U1 and U2 and seem to get close voltages indicating things are good there. Voltage seems to start to drift around R8 and R10 but still within 1-2 volts of target. I seem to get nothing though at Q4 or anything after that on the - side. Any ideas? I hate just replacing parts hoping it works…
I should add that I’m a very amateur, I can follow directions but I’m no electrical engineer. The solder connections all look good.
I didn’t build Wayne’s power supply either, just using a wall wart thing from a standing desk that puts out 27v.
The fact that the pre worked great until I swapped the gain resistor makes me think that the basics (soldering, power supply, connections, etc.) are all okay.
