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Pulse transformer on CS8416/CS4398 DAC

post #1 of 12
12/10/09 at 11:46pm
Thread Starter 
I'm looking for info regarding the installation of a pulse trafo on the coax input of a CS8416 DAC. In this case the trafo is a Lundahl LL1572. Manufacturer suggested a 0.1uF cap on ground leg to protect the trafo from DC. I tried a poly cap and find the bass increased substantially but I'm still evaluating whether this is desirable or if it has upset the DAC's overall balance. Then somebody suggested that I should have used a ceramic cap instead. I later stumbled on a thread where some people had used 75R and 110R resistors with an LL1572 instead. Now I'm really confused.
Basically what I need would be if someone who has experience with this mod could give their opinion of the results(what to expect) and possibly provide some detailed installation tips.
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post #2 of 12
12/11/09 at 3:14am
Try this thread

Experience with this DIY DAC ? - diyAudio
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post #3 of 12
12/11/09 at 11:45am
Thread Starter 
Quote:
Originally Posted by fordgtlover View Post
Thanks for the link but I've been active on that thread for sometime now. I've gotten a few well intentioned replies but no clear pics and no detailed answers for my "newbious" questions. When it comes to DIY involving digital connections I basically need to be spoon fed.
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post #4 of 12
12/11/09 at 12:32pm
the standard, that I've seen, is a .01 (not .1) cap in series with the input (either leg) of the trafo. yes, that breaks DC (good).

one end (the input end) should have the cap on one wire and the trafo lead on the other. those go to the bnc or rca.

the other end of the trafo would have a 75ohm R in parallel with the 2 secondary windings of the trafo. this would be the circuit side of things (spdif receiver).

I cannot believe the value of the cap changes sound IN ANY WAY SHAPE OR FORM.

if you hear sound diffs, something else is wrong. adding a blocker cap (whose value is very non-critical and whose composition is totally TOTALLY irrelevant) should never change sound. if you even heard any sound diff, I'd be surprised (with and without cap). its better eng. practices but it should not (ever) affect sound.
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post #5 of 12
12/11/09 at 12:50pm
Thread Starter 
Quote:
Originally Posted by linuxworks View Post
the standard, that I've seen, is a .01 (not .1) cap in series with the input (either leg) of the trafo. yes, that breaks DC (good).

one end (the input end) should have the cap on one wire and the trafo lead on the other. those go to the bnc or rca.

the other end of the trafo would have a 75ohm R in parallel with the 2 secondary windings of the trafo. this would be the circuit side of things (spdif receiver).

I cannot believe the value of the cap changes sound IN ANY WAY SHAPE OR FORM.

if you hear sound diffs, something else is wrong. adding a blocker cap (whose value is very non-critical and whose composition is totally TOTALLY irrelevant) should never change sound. if you even heard any sound diff, I'd be surprised (with and without cap). its better eng. practices but it should not (ever) affect sound.
Thanks for your reply.
I got the 0.1uF value from K&K audio(Lundahl dist)
For all I know the trafo itself might be what's changing the sound. I added trafo and cap at the same time so I really don't know but there definitely is more bass. So if I understand correctly I should leave the cap(0.01 or 0.1uF) in place and add a 75R in parallel with each of the trafos secondary legs or only on the ground leg?
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post #6 of 12
12/11/09 at 1:09pm
the 75ohm R would go ACROSS the 2 output leads of the trafo. ie, in parallel.

like this:



I still have no explanation for 'more bass'. that is simply not a 'goal' of ground lifting the spdif input port. the only thing POSSIBLY to improve is lower jitter. maybe. and I'm not sure that 'better bass' is a jitter kind of thing.

at any rate, its usually a .01 uf cap but a .1 will work. the fact that spdif is a 'high freq' should indicate that .01 is the better value (passes HF and blocks LF, including DC).
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post #7 of 12
12/11/09 at 3:17pm
Thread Starter 
Quote:
Originally Posted by linuxworks View Post
the 75ohm R would go ACROSS the 2 output leads of the trafo. ie, in parallel.

like this:



I still have no explanation for 'more bass'. that is simply not a 'goal' of ground lifting the spdif input port. the only thing POSSIBLY to improve is lower jitter. maybe. and I'm not sure that 'better bass' is a jitter kind of thing.

at any rate, its usually a .01 uf cap but a .1 will work. the fact that spdif is a 'high freq' should indicate that .01 is the better value (passes HF and blocks LF, including DC).
Thanks for the schematic. When i say more bass I don't necessarily mean better bass. I only had a chance to test for a few minutes in less than perfect conditions. The "more bass" just might turn out to be "muddier bass". Since I only have my ears to do the testing mood, ambient noise and other factors may have impaired my judgment. I should have time over the weekend for further tweaking and listening in a more relaxed state of mind. To be continued...
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post #8 of 12
12/12/09 at 3:15am
Anyone have a diagram like this for the recieving end on a DAC ?
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post #9 of 12
12/12/09 at 1:12pm
Thread Starter 
Swapped the poly cap for a ceramic one and temporarily put in a 100R(didn't have any 75Rs on hand)
It's sounding great. Is it better than without the trafo? I honestly don't know. One thing though - no more heavy bass - in other words balance seems to have returned to normal.
Has the trafo settled? (I know that Lundahl output trafos are notorious for having a long break in period.)
Is it the ceramic cap?
Is it the resistor?
Where my ears playing tricks on me the other day?
Was it the bass from the kids in the basement listening to hip hop that was resonating through the floor and muddying up the sound?

I think I might try and install one of these on my Squeezebox's digital output. Apparently it's a worthwhile(inexpensive) mod.
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post #10 of 12
12/12/09 at 3:32pm
Quote:
Originally Posted by Turn&cough View Post
Has the trafo settled? (I know that Lundahl output trafos are notorious for having a long break in period.)
uhm. no.

no. small signal trafos has NO break-in period. forget THAT idea quick.


Quote:
Where my ears playing tricks on me the other day?
most likely.
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post #11 of 12
12/12/09 at 8:23pm
Thread Starter 
Quote:
Originally Posted by linuxworks View Post
uhm. no.

no. small signal trafos has NO break-in period. forget THAT idea quick.

most likely.
It appears there's already a 75R on the board so I removed the 100R .

What do I hear now? You don't want to know.
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post #12 of 12
12/12/09 at 9:09pm
its almost funny; some people seem to notice 'differences in sound' when they mess with spdif.

me, otoh, I NEVER hear sound diffs. I run spdif thru wet spaghetti (odd days of the week; even days I use toslink, proper, lol) and things still work fine for me.

I've sent spdif thru 'wrong' cables, long cables and just never seem to have problems with it. its quite a robust protocol, at least in my experience.

I can hear drop-outs if the signal is WAY out of spec. but usually once it locks-on, I can't tell 'good spdif' from 'bad spdif'. maybe my dacs all just do the right thing - don't know. but I never worry about spdif anymore since it never seems to really matter much.

I guess its a huge YMMV, then.
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