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Old 1st June 2009, 06:55 AM   #621
adamus is offline adamus  United Kingdom
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are you not getting high dc offset?
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Old 1st June 2009, 01:49 PM   #622
brianco is offline brianco  Ireland
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Location: Scottish Borders - Kelso; on the famous Tweed River!
Quote:
Originally posted by adamus
are you not getting high dc offset?

Yes - at the DAC outputs, but at the speaker terminals with normal range volume set it is 6 to 8 Mv. The Pre-amp is probably blocking the somewhat higher offset at the end of the DAC.
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Old 1st June 2009, 03:18 PM   #623
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Be aware that Zout will be a tad on the high side when using only a 1:1 transformer out.

If we take Legarems circuit as example Zout will be 118(dacout)+1k(ser.res)+1k(ser.res)+150+150(primdc r)+150+150(secdcr)//40k(resload)=2.7kohm

Without series resistors(we can probably do that as the LL1690 should be ca 1k at 2Hz and the datasheet says min 1k AC-load), Zout is just above 700ohms.

To get a lower Zout with seriesresistors one could go for 2:1 and this gives us just above .9kohms with 1k and .5kohms with 220ohm series-resistors. If we skip the resistors we are down to ca 400ohms. The output will still be above 1Vrms.

Another, but far more complicated, way to do it, is to feed the DAC signal without caps to a differential tube(ex. 6H30) stage loaded with a 1689/PP Lundahl connected 9 or 18:1. This way Zout will be extremely low. It will probably also sound much better than using a cathode-follower. And it is completely capacitor-free.............
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Old 1st June 2009, 03:54 PM   #624
JC951t is offline JC951t  Taiwan
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Hi Guys,
May I ask, which vendor are you buying from ?
Theres 3 listed on ebay with CS4397 & 4398
dac & theres 1 listed at US35.00 plus

Thks
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Old 1st June 2009, 07:41 PM   #625
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Quote:
Another, but far more complicated, way to do it, is to feed the DAC signal without caps to a differential tube(ex. 6H30) stage loaded with a 1689/PP Lundahl connected 9 or 18:1. This way Zout will be extremely low. It will probably also sound much better than using a cathode-follower. And it is completely capacitor-free.............
Something like this. Output will be in the ballpark of 0dBU. By connecting the LL1689 9:1, output will be 6dB higher. R4 to be choosen for optimal loading of the chip. R2 shows Zout and should be of a lot higher value or omitted.

Click the image to open in full size.
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Old 1st June 2009, 08:39 PM   #626
brianco is offline brianco  Ireland
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Thank you for that Lars.
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Old 1st June 2009, 10:29 PM   #627
vaughn is offline vaughn  United States
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Quote:
Originally posted by JC951t
Hi Guys,
May I ask, which vendor are you buying from ?
Theres 3 listed on ebay with CS4397 & 4398
dac & theres 1 listed at US35.00 plus

Thks

Yes, I am curious also as I would like to give one these a try but would like
to get the same unit of purposes of continuity when modifying.
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Old 2nd June 2009, 01:40 PM   #628
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These UTC A-43 transformers might be worth a try:

Ebay New UTC A-43 transformers (x16) $49!!!!!

The max level is +15dB which isn't ideal, but they are very cheap so probably worth a play.

I ordered a batch :-)
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Old 2nd June 2009, 01:56 PM   #629
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Ignore my last email.

The price is $49 for 1, not 16!!!!!!
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Old 3rd June 2009, 03:27 AM   #630
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Default suggestion?

Hi. I'm new in this group. Someone I know bought a pair of Digitec transfos and told me about this thread. Since I was looking a good DAC kit or something to improve the "digital side" of my audio stuff, I read with interest several posts here...

So I began to look for LOT and found some...Jensen are too expensive (so are the new Tamura) and others are very big to fit in a "regular" space like Tamura GA80080, UTC HA-108 or old Triad.
Lundhal is interesting and also Sowter:

http://www.sowter.co.uk/specs/5069.htm

and also:

http://www.sowter.co.uk/pdf/3603.pdf

with the OCC wire option:

http://www.sowter.co.uk/occ.php

But someone knows about that one?

http://www.altrancorp.com/audio_transformers.asp?id=45
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