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RE: Input transformer

104.28.103.19

In Reply to: RE: This circuit is balanced but not differential. posted by Ralph on February 07, 2024 at 09:56:31

Example schematic is from the Jensen website; is it as simple as replacing the 12SN7 100k grid resistors with 5k for each tube, to properly load the transformer's 10k secondary? (Plus the r and c off the xlr pin 1)

On the source side, the output impedance of my DAC is 188 ohms. Low enough?

I am using the Jensen as an example, but might use the Cinemag CMLI-15/15B2, which is 15k:15k vs the Jensen's 10k:10k. So I presume it would be 7.5k load resistors.

Plate resistors - I'll end up 30-40k, will have to see what's in the junk box. I'll keep the rectifier, that ugly potato masher fits the TV tube vibe.

Thank you VERY much for the help.

Back for a bit again. Ignore me if you like.

Follow Ups:

take a look at this application document - Ralph 08:23:16 02/08/24 (4)
The values in it suggest that the values you are asking about are incorrect.
- JT-11P-1 (Open in New Window)
- RE: take a look at this application document - Oldbean2 09:28:55 02/08/24 (3)
  I'm not sure that the application document you linked is the application I'm using; it appears to take a balanced line feed and convert it to a single unbalanced signal.
  
  The example I copied in my post (linked below from Jensen's site) keeps the balanced signal, with the + side going to one triode and the - to the other - as in my proposed amp. It shows the grid resistor for each triode at 4.99k to ground, for a total of (almost) 10k load on the transformer, matching the 10k secondary of the transformer.
  
  It seems intuitive to me. Or am I completely missing something?
  
  Back for a bit again. Ignore me if you like.
  - JT-11P-1 Balanced Tube Line Input Stage (Open in New Window)
  - My mistake - Ralph 10:18:41 02/08/24 (2)
    You got it right.
    
    The transformer presents about 13K load to your DAC with the dual 4.99K resistors. I don't know what I was thinking!
    - RE: Whew! Thought I had lost it for a minute - Oldbean2 12:02:19 02/08/24 (1)
      Thank you so much for helping out, I wouldn't have a successful build without it. I'll order a pair of input transformers.
      
      Kinda takes away from the junk box character of the amp, but that's ok, it's something new for me.
      
      Back for a bit again. Ignore me if you like.
      - Yeah, sorry about that. - Ralph 12:09:04 02/08/24 (0)
        
        In Reply to: RE: Whew! Thought I had lost it for a minute posted by Oldbean2 on February 08, 2024 at 12:02:19
        
        Your circuit is similar to the one at the link. You might want to take a look. There is a kit for it IIRC
        http://www.recproaudio.com/diy_pro_audio/diy_files/eqp_1a/eq (Open in New Window)

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