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Old 8th August 2012, 05:37 PM   #1
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Default DAC transformer hot

I recently replaced the two 15k resistors on my Minimax DAC's tube output with KandK compact cascode kits (trim voltage was properly ajusted)
I noticed when running tube output the EI power transformer gets really hot compared to when I'M running SS output. This is with the lid off so the tube's heat is not a factor.
The other day I started hearing static from my right speaker with the tube output switched on. With SS output it sounds fine.
I recently changed some 3.3uF film caps on the output because of a similar problem and everything sounded fine until now. I'm going to try resoldering both caps in case a cold joint or bad contact(the cap leads are a bit big for the pad holes) is the culprit but I'm still puzzled with the hot power trafo.
Any clues?
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Old 10th August 2012, 07:49 PM   #2
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Location: Prior Lake, MN
Hi McCrackers, I'm wondering if you are overtaxing the power supply? Transformers can get hot if you draw excessive current. Unfortunately I don't have that dac. You might try powering just one channel (tube circuit) and see if it runs cooler and without static. A larger VA transformer might be a solution. Static could be an indication that a failure is immenent. Since the SS solution works OK, the dac is healthy and your problem is in the tube circuit or power supply. With luck someone may have some more direct experience and chime in. Dave
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Old 10th August 2012, 08:25 PM   #3
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Thanks for your reply. I'm going to try to resolder the output caps and see if the static stops.

The problem is that the pads where the caps are connected are starting look pretty bad from all the soldering/desoldering. In addition the cap leads are too big for the holes so they're soldered TO the pads as opposed to IN them.

If that doesn't work I'll try pulling the cascode kits and replace with original 15K resistors or continue running SS only.

I have no room to fit a larger trafo in the case and I'm reluctant to having an extra box.
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Old 10th August 2012, 10:36 PM   #4
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Location: Prior Lake, MN
Hi McCrackers, Understood. I try to limit how much soldering and unsoldering I do in my projects. It can get ugly in a hurry. Sometimes it's unavoidable. It's possible that you have a cold joint causing that static. The cascode circuit I'm guessing draws a good amount of filament current. That maybe what is causing the heating in your transformer. Wish I had more knowledge on that specific dac. Hope you find a solution.
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Old 29th December 2012, 02:37 AM   #5
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Join Date: Feb 2009
Quote:
Originally Posted by McCrackers View Post
I recently replaced the two 15k resistors on my Minimax DAC's tube output with KandK compact cascode kits (trim voltage was properly ajusted)
I noticed when running tube output the EI power transformer gets really hot compared to when I'M running SS output. This is with the lid off so the tube's heat is not a factor.
The other day I started hearing static from my right speaker with the tube output switched on. With SS output it sounds fine.
I recently changed some 3.3uF film caps on the output because of a similar problem and everything sounded fine until now. I'm going to try resoldering both caps in case a cold joint or bad contact(the cap leads are a bit big for the pad holes) is the culprit but I'm still puzzled with the hot power trafo.
Any clues?
Excuse me for being so direct to you.
I don't use this forum normally but a professional is going to install compact cascode CCS kits for the tube output of my EE Minimax DAC and I would like to know the correct current settings. bias point or trim settings.
Could you please tell me what they are and if it was ultimately successful?
Greetings Russell Gray from Holland. my e-mail is russ42midlife@hotmail.com
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