[wolfy]

Can you check the voltages out of the tranny?

 

[Samgotit]

Quote:

Originally Posted by wolfy Can you check the voltages out of the tranny?

Transformer 13.5V AC
Bridge rectifier 16.5V DC
Regulators 6.0V DC out

 

[shlomomofo]

here's a picture of the bypass i did, using 3uf 200vac aerovox caps. there is a bit less bass now than with the 1uf mylar caps i was using before. bass is also muddier. there is a bit more detail in the mids and highs, however. hopefully the bass gets better as the caps break in, as has been suggested.

i've got replacement caps for c37 and c28 (1000uf) on the way from digikey. i'll post a pic and thoughts after i get those puppies in...

sam- you used the higher voltage aerovox caps? i noticed that yours have both leads on one side. is there any reason to think they would sound different? just curious...

 

[Samgotit]

Quote:

Originally Posted by shlomomofo sam- you used the higher voltage aerovox caps? i noticed that yours have both leads on one side. is there any reason to think they would sound different? just curious...

I suspect that our caps are basically the same thing. Please, someone let me know if I'm wrong. Here is part of a PM sent by dsavitsk:

Quote:

Any non-polar cap will have both a DC and an AC rating, though they usually only state one, and which they state is usually determined by where the cap will generally be used. To figure out the other rating, multiple an AC rating by 1.414, or divide a DC rating by 1.414. my guess is that the DAC-AH doesn't have any voltages higher than 30V or so, so I am sure your Aerovox caps are fine.

My 400VDC/1.414 = 282.8VAC
Your 200VAC * 1.414 = 282.8VDC

The leads on my caps are actually axial. One lead is just bent upward and runs up the side of the cap. It is then covered by the label.

I hate to make statments like this without reference, but either time or placebo has restored some of the bass. I like it over active.

Sam

 

[shlomomofo]

Quote:

...either time or placebo has restored some of the bass.

you are not imagining the increased bass... i've noticed a definite increase in punchiness and tightness over just a few hours. even now, it sounds better than the mylar caps i replaced. i was a bit worried when i first turned it on earlier, but now i'm happy.

 

[shlomomofo]

i also have 6 vdc between pins 4 and 5 on the dac chips...

 

[Samgotit]

I posted this question in another thread :

Could we repace the whole 10.5V supply section with a TREAD by hooking it up to the transformer leads and remove the two LM7808s and the Monolithic bridge (TREAD uses the LM317T and it's own bridge) that supply the DACs. We could control voltage (up to 8V max) to the DACs that way? Would this be worth the trouble.

Power supply section to 8 TDA1543s:

If so what would need to be done to the capacitance in that section.

I'm learning, so if this is ridiculous or I'm missing something please don't hold back.

Full Schematic
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

Thanks for any help,
Sam

 

[shlomomofo]

just got the panasonic 1000uf caps in the mail, to replace c37 and c28. can someone give me a hint as to whether it matters which direction i put the caps in? my best guess is that the positive (long) lead should go toward the 1543's.

also, i've been curious but have yet to ask... do i need to physically cut the link to the opamps somehow to complete the bypass?

thanks.

edit: i think i figured it out... it seems like the stripe on the side of the cap lines up with the negative lead. is this universally true? if so, i'll just put the new caps in the same way as the old ones.

 

[dsavitsk]

The longer lead is positive. On the stripe, you will see a bunch of minus signs. This indicates that the stripe is in line with the negative lead. If you put the cap in backwards it will explode and make a big mess.

 

[shlomomofo]

note to self: do not, for absolutely any reason whatsoever, put the caps in backwards!

thanks for the info, dsavitsk.

 

[Samgotit]

That was fast. I didn't have a chance to order yet.
Borrow an old welding helment, power up the DAC, and let us know what you think!


BTW, I believe it is the dropout voltage from the regulator that's giving us 6v at the DACs. Maybe its time for a LM7809 or LM7810?

Take Care,
Sam

 

[dsavitsk]

Quote:

Originally Posted by Samgotit That was fast. I didn't have a chance to order yet. Borrow an old welding helment, power up the DAC, and let us know what you think! BTW, I believe it is the dropout voltage from the regulator that's giving us 6v at the DACs. Maybe its time for a LM7809 or LM7810? Take Care, Sam

The 7808 shoud put out 8V. The dropout V is 2V meaning that so long as the input V is 10V or higher, everything should be fine. I have no idea why you only have 6V ... have you tried using a different meter or changing the meter's batteries?

http://www.national.com/ds/LM/LM340.pdf

 

[Samgotit]

Or...Maybe we should just make our own power supply for this section using the transformer leads.

See bellow:
http://ourworld.compuserve.com/homep...den/page12.htm

Cheers,
Dr. Frankenstien

 

[Samgotit]

Quote:

Originally Posted by dsavitsk The 7808 shoud put out 8V. The dropout V is 2V meaning that so long as the input V is 10V or higher, everything should be fine. I have no idea why you only have 6V ... have you tried using a different meter or changing the meter's batteries?

I see. Thanks.

Shlomomofo and I are getting 6V. My meter is less than stellar, but when I check it against a 9V battery I get 9V.

I'm getting 16v out the transformer. I don't get it.

Thanks,
Sam

 

[shlomomofo]

ami doing this correctly to get the right voltage after the regulators? (see picture attached)

meter is set to "200 DCV"...