Output Cap v. Output Transformer

dsavitsk · 16th July 2005, 04:59 PM

Not sure which forum to put this is, but this seems as good as any.

Would there be any advantage to using an output transformer instead of an output cap for a NOS DAC? As I understand it, both block DC and allow AC through, but a transformer with a 1:1 winding should be able to do this while avoiding phase problems and a frequency rolloff. So, what is it I don't understand that would suggest that a cap is a better choice?

-d

Cobra2 · 16th July 2005, 06:19 PM

..don't like DC....so you still need that cap...

Arne K

kevinkr · 16th July 2005, 08:44 PM

Use a transformer, it can provide isolation for ground loops. You should however not allow dc to flow in the primary, so depending on the spdif driver topology you may need a cap. If you are using a reclocked FF to drive it I don't think the cap is necessary.

Kevin

edit typo

Extreme_Boky · 17th July 2005, 11:27 AM

Depending on your analog stage there may be no need for coupling capacitor before primary windings. However, if there's more than 10mV DC offset (with a temerature drift), it could affect high frequency transfer to secondary - so you'll have to use the capacitor. If you have to use capacitor, there's no point in using transformer. Very good, for the money, is Black Gate type C 4.7uF / 50V.

Regards,
Extreme_Boky

kevinkr · 17th July 2005, 04:00 PM

Hi Boky,
He was talking about spdif output, not analog output, and here I think the transformer is superior in terms of providing isolation between the transport/player electronics and the outside world - ground loops, etc.

Kevin

dsavitsk · 17th July 2005, 04:32 PM

Quote:

Originally posted by Extreme_Boky
Very good, for the money, is Black Gate type C 4.7uF / 50V.

It currently has BG type N 4.7uf/50V caps and I am trying to find soemthing to replace them. It is essentially between oil caps, Auricaps or RelCaps.

Quote:

Originally posted by kevinkr
Hi Boky,
He was talking about spdif output, not analog output

I meant on the analog end, sorry I wasn't clearer.

-d

gmarsh · 17th July 2005, 04:40 PM

ideally, a transformer should work great.

Practically, you're dealing with leakage inductance (hello, phase!), saturation at low frequency, core loss at high frequency, etc... And if you're driving the transformer with a voltage source (eg, an op-amp), you'll want to put a series C in there anyway.

kevinkr · 17th July 2005, 05:43 PM

Sorry, I misinterpreted your question, seemed natural to me that this would relate to the spdif end and not the analog output end. Transformers are occasionally used and can sound very good, however a good one is going to cost more than a very good capacitor, a bad one may be worse than any capacitor you could find.. LOL
IMHO they make a lot of sense in I/V applications, but not much sense in a voltage source driven application unless you need galvanic isolation (LOL), need impedance transformation and/or want to drive a balanced line without any additional active circuitry. BTW the BG N type capacitor is pretty good, I would be surprised if the was a lot to be gained by replacing it with another type - I could be wrong.

Kevin

Extreme_Boky · 18th July 2005, 01:01 AM

Quote:

It currently has BG type N 4.7uf/50V caps and I am trying to find something to replace them. It is essentially between oil caps, Auricaps or RelCaps.

I have tried N type and wasn't impressed. Give C type a try... It is very close to 4.7uF / 200V AURICap I use in certain applications. I personally prefer Black Gate 4.7uF / 50 V C Type.

Regarding SPDIF output, I agree that using transformers for isolation and impedance matching is the best way to go. SCHOTT's are good and I tried couple - the lower leakage inductance - the better!

Regards,
Extreme_Boky

dsavitsk · 18th July 2005, 02:43 AM

Quote:

Originally posted by Extreme_Boky
Give C type a try...

Where does one get "C Type"? I have looked at http://www.kyoto-electro.com/ and Percy and neither list these?

16th July 2005, 04:59 PM	#1
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	Output Cap v. Output Transformer Not sure which forum to put this is, but this seems as good as any. Would there be any advantage to using an output transformer instead of an output cap for a NOS DAC? As I understand it, both block DC and allow AC through, but a transformer with a 1:1 winding should be able to do this while avoiding phase problems and a frequency rolloff. So, what is it I don't understand that would suggest that a cap is a better choice? -d

16th July 2005, 06:19 PM	#2
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	Trafos... ..don't like DC....so you still need that cap... Arne K __________________ Ars longa, vita brevis

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16th July 2005, 08:44 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Use a transformer, it can provide isolation for ground loops. You should however not allow dc to flow in the primary, so depending on the spdif driver topology you may need a cap. If you are using a reclocked FF to drive it I don't think the cap is necessary. Kevin edit typo

17th July 2005, 11:27 AM	#4
Extreme_Boky diyAudio Member Join Date: Dec 2003 Location: Sydney	Depending on your analog stage there may be no need for coupling capacitor before primary windings. However, if there's more than 10mV DC offset (with a temerature drift), it could affect high frequency transfer to secondary - so you'll have to use the capacitor. If you have to use capacitor, there's no point in using transformer. Very good, for the money, is Black Gate type C 4.7uF / 50V. Regards, Extreme_Boky

17th July 2005, 04:00 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Hi Boky, He was talking about spdif output, not analog output, and here I think the transformer is superior in terms of providing isolation between the transport/player electronics and the outside world - ground loops, etc. Kevin

17th July 2005, 04:40 PM	#7
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	ideally, a transformer should work great. Practically, you're dealing with leakage inductance (hello, phase!), saturation at low frequency, core loss at high frequency, etc... And if you're driving the transformer with a voltage source (eg, an op-amp), you'll want to put a series C in there anyway.

17th July 2005, 05:43 PM	#8
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Sorry, I misinterpreted your question, seemed natural to me that this would relate to the spdif end and not the analog output end. Transformers are occasionally used and can sound very good, however a good one is going to cost more than a very good capacitor, a bad one may be worse than any capacitor you could find.. LOL IMHO they make a lot of sense in I/V applications, but not much sense in a voltage source driven application unless you need galvanic isolation (LOL), need impedance transformation and/or want to drive a balanced line without any additional active circuitry. BTW the BG N type capacitor is pretty good, I would be surprised if the was a lot to be gained by replacing it with another type - I could be wrong. Kevin

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