| Author | Message | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
Hi Guys. I have retubed and recaped and replaced the speakers in my MM 210 HD130. I have my guitar (dual humbucker) set on 10. I start getting preamp distortion at anything above 1 on either channel when plugged into the A port, or above 2 when plugged into the B port. It will clean up if I roll the guitar's volume back to 7. I reallt think I should have more head room than this. Is this normal ?? If not, what else can I replace ?? | ||
| Chris Metcalfe (chris_m) Username: chris_m Registered: 10-2006 |
I found that having the bias set too low on my RD50 produced preamp distortion, which cleaned up when increased to 10ma or so per tube. Should be easy to adjust on your amp. hope this helps - you might try to measure the idle current flow ( subject to all the caveats on this site ) if you feel you can do it safely , or take it to a tech if you can't. | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
Thanks, I rebiased to factory specs (.5 v at the test point) didnt really make much diff. I swapped the final op amp with one of the ones in the reverb section and it increased head room a little. Any other Ideas ??? What about replacing the op amps ?? | ||
| Chris Metcalfe (chris_m) Username: chris_m Registered: 10-2006 |
Andrew I tried replacing all the ops-amps, but it made no difference in my case, although mine were more modern TL072s - yours will be older. However, reading some of the other stuff on this site, it seems true that various op amps do have different headroom, and they can go bad over time so you may be on the right track. There's a lot of info about various op-amps, particularly from Ed Goforth, who has tried a lot of substitutions. You could also try padding the input with a higher value resistor, as a last resort. I'll try and email you something on this, if i can find it Chris | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
great Thanks for the help | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
I would also look at the power supplies. If you have a problem with one of the power supplies feeding the preamp it will distort prematurely. Steve | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
Thanks, I think the final opamp was bad. I swapped opamps around and it was better. The power supply voltages were OK, the 16 vdc was 15 v but I think thats close enough. I ordered some browndog adapters , sockets and new opamps. It will be interesting to see if it makes a diff. | ||
| Edward Solberg (edward_solberg) Username: edward_solberg Registered: 05-2006 |
andrew, please keep us posted with your progress and findings: these things are of great interest and import to us all at the site. I am also wanting to experiment with various op-amps with a view to "voicing" my amp, much as we do with our fender's preamp tube selection. good luck with your amp... ed s | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
I sure will I should have the browndog adapters today and will mess with it this week. When buying the parts, I ended up buying a lot of 100, 8 pin op amp sockets. These have to be soldered to the BrownDog adapters. Would there be any interest in me building up a mess of the adapters and selling for a small fee ?? I'm going to have a ton of the opamp sockets left. | ||
| Andrew Wilson (awilson40) Username: awilson40 Registered: 05-2006 |
I just finished playing around with LF356N opamps. They do have brighter sound. I think the LM-307's have smoother, rounder tone and breakup a little better. The 307's also have a bit more head room. I did have a couple bad 307's as while I was swapping them around 2 of them would distort earlier than the others, and 2 of them would pick up radio station if I placed my hand anywhere near them. I ended up putting 356's in Channel 1, and in the reverb section and put the "known good" 307's in channel 2 and the final opamp (IC7). This seems to give me the best results. |
Tue, 03/25/2014 - 09:29
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