Audio Asylum Thread Printer

Get a view of an entire thread on one page

FAQ / News / Events

Tech Square

Are there any "issues" with the use of a transformer in place of an output coupling cap (to stop DC)?

203.12.195.65

I am considering using coupling transformers, in place of coupling caps, on the output of a phono stage. But I have a few Qs: :-))

The spec sheet for the Lundahl LL1527 says it has a 0.4dB loss at the mid-band.
Q1: Does this imply the loss is different at different frequencies?

The spec sheet also specifies some particular input & output impedances for the loss & frequency extension figures it quotes - source 800ohms, load 4Kohms. This seems to me to not be compatible with the real-world situation which a phono stage finds itself in ... a phono stage feeds a line-stage preamp ... which is likely to have a Zin of 10-50Kohms?

Q2: Will this different load change the behaviour of the transformer? In particular, will it worsen its performance - in terms of loss & frequency extension?

Q3: The source impedance, also, is around 25ohms (not 800ohms) - so will this affect the performance of the transformer?

Thanks for any input,

Andy

Follow Ups:

RE: Are there any "issues" with the use of a transformer in place of an output coupling cap (to stop DC)? - tesla 08:32:10 01/15/13 (2)
Perhaps you should post your question to Lundahl. I would think they are the expert on their transformer.
"The Blues isn't about feeling better. It's about making other people feel worse and making a few bucks while you're at it" "Bleeding Gums" Murphy

Edits: 01/15/13
- RE: "issues" ...coupling cap (to stop DC)? - grhughes 05:05:01 02/17/13 (0)
  1. Some transformers can't tolerate any DC in their primary winding, so you would have to use a coupling cap to keep DC out of the transformer so you would not replace the coupling cap. Transformers in audio really are AC devices and DC in their winding requires special construction, ie gaps to prevent saturation. Even in AC, saturation is a problem on peaks. There are many different types of transformers each for a particular application so you need to direct this question to the manufacturer.
  
  2. In audio, you want a low output impedance feeding a high input impedance by a factor of 5 or more to insure good frequency response. It's not like an AC power delivery system where you are concerned about power efficiency at only one frequency. An audio signal is broad band. Ray
  
  "The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-�douard Jeanneret)
- Yes, I did ... - andyr 11:06:31 01/15/13 (0)
  And their answer suggested these loading issues make life difficult. So I will continue to use a coupling cap.
  
  Regards,
  
  Andy

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.

This post is made possible by the generous support of people like you and our sponsors: