TRL Dude or Joule 150 MKII for Major Pre Upgrade

Grannyring,

I have no experience with the Bel Canto but when your passive lightspeed is set to vol = 0 can you measure zero ohms at the output RCA relative to ground, much like the shorting RCA jack you tested? If it's zero ohms then I see no reason why connecting to the lightspeed would be different than shorting the inputs with a shorting RCA.

Recently I spent many hours tackling an interesting project on a previously modified Jolida which gives a buzz similar to what you are hearing. Turns out that power amp uses an AC filament for the gain stage and the center tap of the power transformer is faulty and I had to create an artificial center tap w balancing resistors.

Highly unlikely with your hybrid power amp cos judging from the build ($$$) it would likely use DC filament for the 6SN7s.

Check the input grid stop resistors again, it might be as simple as adding a 1k resistor inline with the signal input to the 6SN7s grid.

Grannyring, that info weakens my theory about the specific malfunction, but strengthens the idea that the amp is at fault. If the amp is in warranty I would return it for repair.

Ok, did one additional measurement per the instruction Jognsonwu above.
I measured the ohms reading from the RCA center to each of the eight 6sn7 socket pin numbers.

I did this to check the input grid stop resistor.This grid dropper resistor is used to form a low-pass filter to get rid of RFI/EMI. For more reference, please see the following link:
 
http://www.aikenamps.com/InputRes.htm

Pin one should measure 1000 ohms, not 100 according to two individuals that are helping me. Love input from Atmasphere or Al or others who may know something on the this subject.
 
Here are the measurements,
 
Pin 
 
1.   100 ohm
2.    3.9 mohm
3.    1.45 mohm
4.   .527 mohm
5.    3.9 mohm
6.    1.45 mohm
7.   .527 mohm
8.   .527 mohm
 
Checked and recheck.......before I call Aesthetix I could use some confirmation. I am not the most tech savy and must say I have a hard time thinking they would miss such an "obvious" thing? My amp is not under warranty and wonder if this is something that should be made right, or simply just one way to build an amp?

I greatly appreciate the help I have received from all and this is the last request I will make for help before calling Aesthetix again.

I agree completely. 100 ohms sounds way too low. And as the link you provided indicates, too low a value for the grid stopper resistor of the input stage could very conceivably result in rfi problems.

According to some quick calculations, 1K strikes me as a reasonable value. I believe that a value up to around 4K or 5K would not adversely affect anything, the overall bandwidth of the amp in particular.

Kudos to Johnsonwu.

Best regards,
-- Al

Jognsonwu, thanks for your insight. I am not sure how to wire such a resistor as my amp has a circuit board for each input tube/channel. Hard, if not impossible , for me to wire in a 1k resistor. Wish the amp was point to point wired!

It may be possible for me to simply solder an additional 1k resistor from the RCA to pin one and not undo anything else. Is this what you are suggesting?