2. amps-preamps
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TRL Dude or Joule 150 MKII for Major Pre Upgrade

Thinking of either of these for what I view as a huge pre upgrade in my system. Current system is:

-Celestion A3
-Krell KAV250a (500 wpc/4 ohms).
-Nohr CD-1
-Rotel 995 preamp

I am looking to pickup warmth, depth and much more soundstage. Quality bass is also important to me. I want to keep the Celestions and feel that my current pre is the weakest link. Will also will update my digital source and ss amp down the road.

My thinking is that it will be worth paying up a bit for a higher quality pre that I can grow into.

Also I have a small naive question...with either of these pre amps will the sound difference be that great compared to the Rotel.

Thanks...any comments are appreciated.

-Iggy
iggy7
almarg's avatar
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almarg
9,670 posts
 
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
grannyring's avatar
grannyring
6,525 posts
 
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?
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grannyring
6,525 posts
 
Correction the grid stop resistor should measure over 1000 ohms and often is a very high value.
almarg's avatar
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almarg
9,670 posts
 
No, don't solder a resistor between the RCA and pin 1 of the tube socket. That would put the 1K in parallel with the 100 ohms, resulting in an overall resistance of about 91 ohms.

Hopefully you can unsolder the wire that is presently connected to the RCA jack, and put the resistor in series (i.e., connected between that wire and the RCA jack). That would result in an overall resistance of 1100 ohms.

It might be a surer bet, though, to use a resistor having a higher value, such as the 3K or 4K values I mentioned. The main constraint on how high a value should be used is, I believe, that if it gets too high the bandwidth of the low pass filter formed by that resistance and the input capacitance seen looking into the grid of the tube, based on the Miller Effect, will reduce the overall bandwidth of the amplifier (which is spec'd at 150 kHz). Calculating from the 6SN7 data in my tube manual, I believe that 4K would still be low enough to not have a significant effect on that bandwidth.

Best regards,
-- Al
johnsonwu
469 posts
 
All depends on how long that curcuit trace is from the RCA hot pin to pin1.
If its less than 3 inches then a 1k grid stop in series ie
UNSOLDER RCA hot and put 1k inline.
SOLDER Socket-hot-->1k-->wire to grid@6sn7.
But if its any longer then you will need help from Aesthetix.
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