See BoM and schematic. Both Q1a and Q1b are P-channel parts. LSJ74 for the Linear systems parts.
Aleph J – diyAudio Store
Anand... 😀
Edited to store link vs. my download link. 🙂
Aleph J – diyAudio Store
Anand... 😀
Edited to store link vs. my download link. 🙂
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Yes. It may not be the only thing, but you will definitely need to replace Q1b with the proper part for the circuit to function.
Others will certainly chime in, but I don't think it's likely that you will have damaged anything with your substitution. So, if it were me, I'd:
1) Re-center my bias pot
2) Replace Q1b with the proper part
3) Start anew with bias and offset
As you've seen, this is a group effort. I'm a total novice, so please wait for at least one more person to chime in. Sorry for the delay after my first reply. Crazy day.
Others will certainly chime in, but I don't think it's likely that you will have damaged anything with your substitution. So, if it were me, I'd:
1) Re-center my bias pot
2) Replace Q1b with the proper part
3) Start anew with bias and offset
As you've seen, this is a group effort. I'm a total novice, so please wait for at least one more person to chime in. Sorry for the delay after my first reply. Crazy day.
Thank you for your insight.
Will i need to desolder to re-enter the bias pot?
I have to sign off in a bit, but I don't want to leave you hanging. Plus, my tired thoughts are not my best thoughts 😀
I'm also not sure I understand your question.
You will need to desolder the 3 legs of the JFET Q1b and replace it. I'll do my best to be clear, but a YouTube video is perhaps a better resource.
What I'd do is:
1) Clip all three legs close to the board and remove the part. Save the part for potential future use.
2) Heat each pad and remove the remaining piece of the leg in the through-hole.
3) Clean the pad / hole and remove all remaining solder.
4) Install the new part.
For your bias pot. It's likely a 25-turn pot. Turn it in either direction until it clicks. Turn it 12.5 turns (or about that) in the opposite direction. to "recenter" it. It does not need to be exact.
I'm also not sure I understand your question.
You will need to desolder the 3 legs of the JFET Q1b and replace it. I'll do my best to be clear, but a YouTube video is perhaps a better resource.
What I'd do is:
1) Clip all three legs close to the board and remove the part. Save the part for potential future use.
2) Heat each pad and remove the remaining piece of the leg in the through-hole.
3) Clean the pad / hole and remove all remaining solder.
4) Install the new part.
For your bias pot. It's likely a 25-turn pot. Turn it in either direction until it clicks. Turn it 12.5 turns (or about that) in the opposite direction. to "recenter" it. It does not need to be exact.
Thank you so much for your help!
I will do these things and see if I can find the jfets online.
I really appreciate your input.
My pleasure. In all seriousness, this is an incredible community, and while I might seem like I know what I'm doing... and I'd never provide advice I wouldn't do myself, I'd wait for at least one more person to chime in with any additional thoughts.
Here's where I'd get them...
Linear Systems Matched JFETs – diyAudio Store
They sell matched quads. Someone else will need to tell you if the best advice is to simply replace all 4 (2 on one board and 2 on the other). In hindsight... that's what I'd do b/c the chances of getting a match to your existing Q1a is slim. but rather than spend your money.... maybe someone can chime in.
Best of luck. Hope to hear of success and good tunes.
Here's where I'd get them...
Linear Systems Matched JFETs – diyAudio Store
They sell matched quads. Someone else will need to tell you if the best advice is to simply replace all 4 (2 on one board and 2 on the other). In hindsight... that's what I'd do b/c the chances of getting a match to your existing Q1a is slim. but rather than spend your money.... maybe someone can chime in.
Best of luck. Hope to hear of success and good tunes.
The matched quad is currently out of stock.
They still have the same thing I previously purchased with a pair of lsk170 and a pair of lsj74. I guess I could pair up the LSJ 74 and remove the LSK 170. They should be 2 matched pairs this way, probably not as good as a matched quad but might get the job done.
Great thought, but not one I can be sure about. My WAG is that if you took the LSJ74 out of Board A and installed it with the Board B, you'd be good with that match.
Then, you could put the other pair from your future order into the other board.
That you should DEFINITELY confirm with someone.
Then, you could put the other pair from your future order into the other board.
That you should DEFINITELY confirm with someone.
kingsportal,
Sorry I was away for a while, but I just want to write that I would proceed as ItsAllInMyHead suggested.
If you don't want to wait for the LSJ74 matched quad to be back in stock at the
diyaudio store, you can order matched 2sj74 from seller punkydawgs on ebay:
Toshiba 2SJ74 LAB MATCHED QUAD to 0.03mA / 4mV ("B" "BL" 7-9mA Range) | eBay
Sorry I was away for a while, but I just want to write that I would proceed as ItsAllInMyHead suggested.
If you don't want to wait for the LSJ74 matched quad to be back in stock at the
diyaudio store, you can order matched 2sj74 from seller punkydawgs on ebay:
Toshiba 2SJ74 LAB MATCHED QUAD to 0.03mA / 4mV ("B" "BL" 7-9mA Range) | eBay
Thank you so much!
I already place the order for these. I'm not very patient so I'm glad you chimed back in.
Excellent choice. Note - With this plan, be sure to replace all 4 parts. Q1a and Q1b in both channels with the new Toshibas.
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Yes, and please desolder the original jfets carefully so that you still have 2 pairs of LSK74/LSJ170 for another amp project. 😀
^ +1 
Slightly rephrased perhaps, just save your parts. 😀
See my previous recommendation if you're in any way reluctant to de-solder. I don't mind losing a bit of the leg/leads when saving the parts for future use. I like to clip the legs to remove the parts. From your previous pics, it looks like you installed them nicely above the board leaving plenty of the leg.
That allows me to not heat the part to de-solder it, reducing the risk of damage. It makes it (for me) much easier. It's not too hard to desolder the 3 legs and remove the part, but I'm a fraidy-cat and clip the leads. My $0.02
Slightly rephrased perhaps, just save your parts. 😀
See my previous recommendation if you're in any way reluctant to de-solder. I don't mind losing a bit of the leg/leads when saving the parts for future use. I like to clip the legs to remove the parts. From your previous pics, it looks like you installed them nicely above the board leaving plenty of the leg.
That allows me to not heat the part to de-solder it, reducing the risk of damage. It makes it (for me) much easier. It's not too hard to desolder the 3 legs and remove the part, but I'm a fraidy-cat and clip the leads. My $0.02
Thank you guys very much for your knowledge. I will certainly follow your advise to clip the distal legs. It was a little confusing when I purchased from diy store, especially because the matched quad was sold out. I'm glad to have gotten the toshiba anyway, considering that they are genuine. It will definitely sound better than it does now. Lol.
I will check the pin out of the toshiba.
I assume they will mount flat side to flat side like I did previously.
With much appreciation , thank you guys for helping with my project. I actually thought it was going to work because I took my time. I was one component off, way off apparently.
I will check the pin out of the toshiba.
I assume they will mount flat side to flat side like I did previously.
With much appreciation , thank you guys for helping with my project. I actually thought it was going to work because I took my time. I was one component off, way off apparently.
Good job Kings...try using a toothpick to push through the holes after heating to make way for new legs.
Glad to see things worked out. I suspected as much (post 6556) given that you couldn't adjust the offset or bias. You had 50% of the JFETs right though!
Best of luck,
Anand.
Best of luck,
Anand.
