Experience with this DIY DAC ?

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thebergerac

Member
Joined 2008
Could anyone help to decide if I could use UTC A21 for impedance and level matching between +4DBu (Pro) and -10DBu (Standard) output/input. I need to connect Pro gear to home electronics. I can see a lot of chatting about these issues. A10 looks ideal but it is very costly. I am lost with this whole matching math.

These are specs I could get:
--A20 mixing, matching
Z Pri 50, 125/150, 200/250, 333, 500/600
Z Sec 50, 125/150, 200/250, 333, 500/600
10-50kHz
+15
--A21 mixing, matching
Z Pri 50, 200/250, 600
Z Sec 50, 200/250, 600
30-30KHz
+15

Appreciate you help

Andrew
 
B

Bill Fuss

RIP
Joined 2005
Richie ma said:
I finally completed my DAC last night with 1:1 transformers, only had quick listen through head phones and found it very pleasing. I would say that for my intended application i would like a little more gain.

Would 1:1.41 or 1:1.5 give me that and if so would the RC filter values need changing?
Click to expand...

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.
 
Franz Gysi

Franz Gysi

Member
Joined 2007
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
 
johnm

johnm

Member
Joined 2003
Interesting point - I have a pair I received a few days ago but haven't gotten around to trying them out yet.

How would one go about demagnetising a pair of these line matching transformers? Is it fairly straight forward for the home user?

I have one of those 'wand' type tape head demagnetizers - would that be of use?


Thanks,

- John


EDIT: Some useful comments contained in this link:

http://www.tomshardware.co.uk/forum/page-42143_32_0.html

"Excesive second harmonic distortion may be caused by premagnetized cores." Could explain the nice warmth of the UTCs by some users?
 
Franz Gysi

Franz Gysi

Member
Joined 2007
John

I think, I mentionned already the procedure to degauss trannies in this thread...

Simply attach a load and a scope on the secondaries.

Insert a 50Hz Sinus in the primaries from a generator. Turn up the level, till the core is saturizing (sinus has flat tops).

Then slowly reduce the input level to zero within 5 to 10 seconds.

Repeat it several times.

Then, do the same procedures "backwards", connecting the generator to the secondaries, the load and the scope to the primaries.

Thats it

Franz
 
B

Bill Fuss

RIP
Joined 2005
Good advice Franz. You can do it without a scope but you have to have a signal generator and also know the voltage rating of the trafo and the load that rating was taken at. For instance, a trafo rated at 5v with a 600 ohm load @ 20hz. Crank the signal up until you get 5v across the load, let it soak for a minute or two, then back the signal down slowly to zero, just as you would with a tape head demagnetizer.
 
piero7

piero7

Member
Joined 2009
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
Click to expand...

Hi franz! Welcome back! Thanks for your very interesting post ;)
 
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