[Samgotit]

Quote:

Originally Posted by shlomomofo ami doing this correctly to get the right voltage after the regulators? (see picture attached) meter is set to "200 DCV"...

That's right.

Sam

 

[shlomomofo]

Quote:

First thing to go were the three rectifier modules, these I replaced with BYV26E ultra fast diodes. The next items were the two small digital input caps, these I replaced with RTX MIT film caps and this was followed by removing the two 390R feedback resistors and replacing them with HOLCO\'s. last but not least, resistors R35 and R36 were replaced with 274R CADDOCKS.

some more ideas, from a user review at the diyclub website.

what are those diodes he's talking about? is that a good idea? might it fix the mysterious problem of the missing 2V? what kind of impact would those 2V have on the sound, anyway...

 

[Samgotit]

I remember reading about fast diode replacemet at one time. That quote might even have been it. From limited reading I think the jury is out on fast diodes as far as an audible difference is concerned.

The diodes (monolithic bridges) are at BR1 2 and 3. They convert AC to DC which is then passed on to the requlators. I think.

R36, 37 "need" to change after we get the power issuse resolved. I think.

I'd also like to know what 2V would do?


Sam

 

[Samgotit]

I forgot to mention.

This is how I understand we calculate the values of those I/V resistors. Here is link originally provided by Dsavitsk:
http://www.diyaudio.com/forums/showt...ht=#post173483

I'll use 8V as an example:

8V-1.2V-1.8V=5V (The other values are from Voc on the data sheet)

We have 8 DACs connected with each resistor for L and R channels, so for each resistor:
5V/(2.3e-3*8) = 272 ohms

I think.





Sam

Revised!

Revised again!

 

[tilt]

Quote:

Originally Posted by shlomomofo just got the panasonic 1000uf caps in the mail, to replace c37 and c28.

And the verdict is.......?

 

[Samgotit]

Quote:

Originally Posted by Samgotit I forgot to mention. This is how I understand we calculate the values of those I/V resistors. Here is link originally provided by Dsavitsk: http://www.diyaudio.com/forums/showt...ht=#post173483 I'll use 8V as an example: 8V-1.2V-1.8V=5V (The other values are from Voc on the data sheet) We have 8 DACs connected in series with each resistor for L and R channels, so for each resistor: 5V/(2.3e-3*8) = 272 ohms I think.

Looking at the schematic I can't tell if these resistors are in the path anymore. Can someone verify if R36 and R35 are still in the signal path in the bypass configuration?

Thanks,
Sam

 

[shlomomofo]

sam- those resistors are still in the signal path, immediately before the bypass coupling caps. and thanks for the info on the rectifiers. when i read it the first time, i thought he said he replaced the "regulators"... but of course i was wrong.

Quote:

And the verdict is.......?

i won't be putting in those caps until tomorrow. i'll give my impressions after my amplifier comes back from the shop early next week (warranty issue - dealer is trying to isolate the source of some parasitic oscilation. actually he's just sending a new one, but that's a topic for another thread

).

 

[Samgotit]

Ok, Great!

It looks like the stock I/V resisotors at 270 ohms are the optimal value for 8V. I guess we need to work on our skimpy 6V supply voltage.

Thanks,
Sam

 

[shlomomofo]

can someone point me to the place in the schematic where it says specifically that the supply voltage should be 8v?

 

[Samgotit]

It does not say specifically. The power supply in the schematic to the DACs is 10.5V from the transformer, but the LM7808 regulators are rated at 8V supply out (7.7V min). Why we are not getting that is the $64,000 question. There is nothing in the path between the regulators and the DACs?

Cheers,
Sam

 

[dsavitsk]

What does the regulator chip on the board actually say? Maybe they changed things from the schematic?

 

[Samgotit]

Quote:

Originally Posted by dsavitsk What does the regulator chip on the board actually say? Maybe they changed things from the schematic?

They are completly blocked and I can't read them from any angle. The regulator for the CS8414 is the NEC LM7805A. I think I'll just order regualtors and replace them?

Thanks,
Sam

 

[shlomomofo]

Quote:

Originally Posted by Samgotit They are completly blocked and I can't read them from any angle.

i should be able to read the writing on the regulators when i take out c28 and c37 later tonight. i'll let you know what i find...

 

[shlomomofo]

mystery solved! i wonder why diyclub used 7806's instead of the 7808's in the schematic... cost cutting or "better" sound? in any case, 6 volts is certainly within the specs for supply voltage to the 1543's (5v typical and 8v max). does anyone think it would be worthwhile to swap out the regulators for 7808's?

 

[shlomomofo]

... and here's a picture of the new caps in the c28 and c37 positions. like i said, it's tough for me to judge this one. i'm using my old yamaha amp (decent solid state) while my tad-60 (awesome tube amp

) is out of commission.

listening to some thievery corporation -- bass seems tighter, and it seems like there's more of it... but take that with a grain of salt, for sure. you will just have to swap those caps out to find out for yourselves! it's a cheap and easy mod, anyway.