Help!! problem with Non HRM with FX loop

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heisthl
Posts: 1800
Joined: Fri Sep 29, 2006 5:35 am
Location: Phoenix

Re: Help!! problem with Non HRM with FX loop

Post by heisthl »

JimiB wrote:
I've also gotten into the habit of putting a resistor before the loop input (10k to 100k) and one on the output (10k-100k) But you've probably done that if you were loosely following a schematic I posted
what purpose does this serve?
It makes it look "cool" on the eyelet board. 8)
Others (not me) have had strange ground hum issues on the MV that were corrected with this change (MV0 no hum, mv5 lots of hum, mv10 no hum). I just put them in for insurance - they don't seem to affect tone. Many schematics (without D'laters) show a 100k between the MV and the PI.
http://ampgarage.com/forum/download/file.php?id=1178
Former owner of Music Mechanix
www.RedPlateAmps.com
shane
Posts: 132
Joined: Fri Jan 14, 2005 2:18 pm
Location: birmingham UK

Re: Help!! problem with Non HRM with FX loop

Post by shane »

Hi Guys
I've been trying in vain with this amp (sorry no pics yet will get round to it!). I've redone the ground system to be more like the typical layouts shown and corrected some tone stack wiring issues I found (I had done the PAB wiring wrong :( )
Now one issue I have is that the signal level going into the loop is so high its causing severe clipping in both the send and return sections!

This occurs even on the clean setting, I have tried replacing the 27K cathode resistor on the send section with a 100K to allow more swing but it still clips the bottom of the followers output. The return amp just clips top and bottom unmercifully! I have to keep the pot that controls the output from the preamp into the follower almost at zero to get a clean sound.
Could this be part of my oscillation problem?

What kind of signal levels should be going into the loop normally?
and what voltage (dc) will the followers cathode normally sit at?

I am quite suprised at the voltage level coming out of CL2 (its up around couple hundred volts!!!)I'd have thought the tone stack would have reduced the signal from CL1 more.

So I have I made yet another monumental cock up or is this normal?

Getting balder by the minute :D

Cheers
Shane
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