Experience with this DIY DAC ?

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legarem

legarem

Member
Joined 2005
Franz Gysi said:
Hello

I received a pair of UTC A-20 :rolleyes:

And I am asking myself: do you guys degauss your trannies, when you buy used ones?

I for myself, I will do it, before I use them. The chance is very big, they had some DC flowing through the coils (for example by testing it with an DVM), before I received them.

Every DC will magnetize the core.

And with a magnetized core, they will disturb (@Legarem: cozy jazz style sound of the UTC's?).

Franz
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Hi Franz

Something else to try again.

I will try it and post the results later.

About UTC transformers. The square waves at 20khz shows that they are bandwith limited. Digitecs, Studer,Tamuras square waves are showing that these transformers have greater bandwith. They are really square at 20khz and some have peaks beyond 20 khz which can be shown by ringing.

I think that this can explain the UTC sound which is mellower than the others.
 
Franz Gysi

Franz Gysi

Member
Joined 2007
About UTC transformers. The square waves at 20khz shows that they are bandwith limited. Digitecs, Studer,Tamuras square waves are showing that these transformers have greater bandwith. They are really square at 20khz and some have peaks beyond 20 khz which can be shown by ringing.
Click to expand...

Interesting! And the Lundahl's?

This parameters will (imho) not be changed by degaussing.

Maybe, I will not find the time to check my UTC's within the next weeks, as I have some private changes upcoming...

But I will follow the thread, interested if you remark some changes after degaussing.

Franz
 
Franz Gysi

Franz Gysi

Member
Joined 2007
Something else to try again.
Click to expand...

Yes, but I remember some older discussion, we had in this thread:

Burning in.

Maybe, the 50Hz method to degauss is very rough?

One idea: we could produce a wave file (for example with the freeware audacity), including for example 50Hz sinus decreasing to zero, followed by white noise up to saturation point, decreasing to zero.

This could be a way, to get rid of the long burning in phase?

Franz
 
preiter

preiter

Member
Joined 2006
legarem said:

About UTC transformers. The square waves at 20khz shows that they are bandwith limited. Digitecs, Studer,Tamuras square waves are showing that these transformers have greater bandwith. They are really square at 20khz and some have peaks beyond 20 khz which can be shown by ringing.

I think that this can explain the UTC sound which is mellower than the others.
Click to expand...
Isn't the limited bandwidth part of the reason for using these transformers? Since they are taking the place of the circuit which filters out the >20kHz digital artifacts, having limited bandwidth over 20kHz is a useful thing.
 
brianco

brianco

Member
Joined 2005
Years ago a friend designed a 37.4 Khz notch-filter. this was used with normal commercial DACs here in the UK. This device certainly improved the sound when placed in line immediately after the DAC (NO trannies involved then!) I have one of these boards somewhere in the meyhem called a garage. I'll attempt to find it and try it again.

With normal analogue we found that any form of bandwidth limiting certainly reduced the t hall-effect on replay.
 
R

Richie ma

Member
Joined 2009
Bill Fuss said:


If you are driving the phones directly it would depend on the impedance of the phones, the higher the better, but the rc filters wouldn't change.
Click to expand...

Only late night listening through the phones. The DAC will be used from my PC, into external mixer along with other sources in the mixer. The level is a little low using the transformer when mixing with the other sources, which is a bit of an issue. I do like the sound though.
 
B

Bill Fuss

RIP
Joined 2005
Richie ma said:


Only late night listening through the phones. The DAC will be used from my PC, into external mixer along with other sources in the mixer. The level is a little low using the transformer when mixing with the other sources, which is a bit of an issue. I do like the sound though.
Click to expand...

You should have plenty of signal unless you have placed a load on the secondaries that is pulling it down.
 
R

Richie ma

Member
Joined 2009
I only have the RC filter, 220r and 6.8nf on the primary, i have not put anything on the secondary. Compared to other sources, vinyl, cd player, synth's there's a marked difference. The DAC sounds fine if that was all that was being used.

Maybe, i'll have to find a way to give a little more gain by modding the mixer.
 
V

vaughn

Member
Joined 2008
I'm jumping on board this bandwagon and have a couple of questions...

1. I have searched and have seen the question asked a couple of times but
I haven't seen it answered; Is there a simple and effective way of switching
inputs? I have a Squeezebox and Oppo DVD player that I would like to be
able to plug directly into the DAC.
2. Can anyone provide me with a simple schematic for connecting the
UTC-A20? I have a pair on the way but haven't seen exactly which resistor
compliment and a connecting diagram for it.

Thanks and I'm glad this site is back up!:)
 
brianco

brianco

Member
Joined 2005
Tripmaster said:
Hi

Sorry to cover old ground but I would like to order one of these DACs and wondered if you wouldn't mind checking if I have the right one?

http://cgi.ebay.co.uk/NEW-Version-24bit-192Hz-DAC-DA-CONVERTER-W-USB-Kit_W0QQitemZ130325985765QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1e5808b9e5&_trksid=p3911.c0.m14#ht_7712wt_1165

Thanks
Richard
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This is the one which I have, but mine has not got the USB sector populated. It is unmodified other than removing the opamps and wiring in a pair of UTC a-20 transformers to the chip outputs (a la Jensen). Another Scottish member sent me some Russian Teflon caps - for which I am very thankful - and they have made the sound more seriously good - and seem to be improving daily!

It is a good board.:cool:
 
Last edited:
piero7

piero7

Member
Joined 2009
vaughn said:
I'm jumping on board this bandwagon and have a couple of questions...

1. I have searched and have seen the question asked a couple of times but
I haven't seen it answered; Is there a simple and effective way of switching
inputs? I have a Squeezebox and Oppo DVD player that I would like to be
able to plug directly into the DAC.
2. Can anyone provide me with a simple schematic for connecting the
UTC-A20? I have a pair on the way but haven't seen exactly which resistor
compliment and a connecting diagram for it.

Thanks and I'm glad this site is back up!:)
Click to expand...

Here:

An externally hosted image should be here but it was not working when we last tested it.


About your first question, remove switches and mount some relays
 
johnm

johnm

Member
Joined 2003
There are several different resistor and/or capacitor options with the A20 which people have used. It comes down to what sounds great to you.

A good starting point is the Jensen PDF (attached). Just leave out the capacitors to ground.

I have a pair of A20s and am using the 249R resistors for + and - primaries with 2n2 as per the Jensen diagram, with just a 680R resistor across the secondaries.

Has only had a few hours use and is sounding a little 'closed in' at the moment, but I expect that to change after a few more days music playing (fingers crossed!).

- John
 

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