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Funky X88R / SLO problem

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8/29/2000 2:57 AM

Funky X88R / SLO problem

I guess this question is really aimed at Joe L or Mitch who seem to have a pretty good grip on Soldano stuff, but anyone else who can lend a suggestion is very welcome to do so! Well, I just fired up my latest soldano type "clone" and I'm having trouble with the circut occilating when the Warren H. mod is OFF (when the .001 cap across the gain pot is in the circut). The preamp is basically an X88R with only the clean and lead chanels, although when I first built it I kept the SLO style "effects loop" as I think it adds to the tone. When the amp was set up like this (with the FX loop tube) there were NO problem with the amp occilating when the cap was in the circut. I decided to remove the loop stage and have plans to make a "real" post-mater loop with that tube socket, so now the lead chan is wired up identically to the X88R, and now the the thing goes crazy when the gain is past 2 and the cap is in the circut. What can I do!?!?!? I've got all the grid leads shielded now to try and stop this, but nothing seems to be working! Please help me, I'm starting to get really ticked at this thing!

Peace!
-Ryan

8/29/2000 11:14 PM

Ryan,
I also did the same with removing the second cathode follower and wound up getting the sqealing. Since you changed the circuit to the X88 style that can change the gain in the circuit alot. Joe L. could probably inject a Idea on what you could to to pad the gain down to stop the sqealing. After I removed the 2nd cathode follower and had my SLO sqeal I tried padding the the circuit in different areas but that caused tone chages I didnt care for. You might want to consider putting it back as a stock SLO clone, then add another 12AX7 to the chassis and try the Dumblator fx loop to have the more ideal loop after the master volumes. If you want to keep the X88 type of circuit then you will need to probably build the circuit identical to the schem and still add anther preamp tube for the loop. Sorry I couldnt help ya more but what your doing ventures into the experimental stages which in time could produce good results but also can be very time consuming and frusterating too. Good luck

8/30/2000 1:24 AM

It's very hard to troubleshoot gain problems like this without an accurate schematic of the amp Ryan. I would check real closely to see what is happening as far as clipping after the first CF stage. The signal level should be low enough to not cause the second CF stage to go into clipping until really pushed and may be the cause of the excess gain and instability you are hearing. I bet you are not loosing enough signal after the first CF and things are going nuclear on you!

Good luck with it Ryan.

..Joe L

8/30/2000 2:41 AM
Ryan	Thanks for the suggestions guys. I ending up wiring the second CF stage back into the circuit. It doesn't squeal when the cap is in the signal path but rather it hums now, silent when the cap is removed. Kinda fishy as I've built an SLO preamp before and didn't have this problem. Until I pick up a new scope I suppose this is as good as it'll get. Thanks again! -Ryan

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