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Old 13th September 2011, 07:47 PM   #11
josha is offline josha  United Kingdom
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So I got the soldering iron out tonight! First I popped the op-amps out and replaced with sockets, then i rummaged around for some replacements, I thought I had some ne5532 but one's a P and ones an N so no joy there (the first and second stages are handled by the same op-amp, so I have to replace both, even with the second stage out of the equation). Then I remembered I had two OPA134's, slightly different pin-outs so I modified another set of sockets, joining pins 5+6 and re-routing pin 7 to 2, lifted pins 1 and 5 and popped these in.

While I was there I swapped the two decoupling caps on the DAC for slightly larger Elna's. Funny how scientific method goes out of the window when a soldering irons involved! One mod at a time.......yeah right.

I couldn't remember which caps you mentioned, abraxalito, so I left those alone (I know which they are now so I'll try that next time).

Well, the opa's to my ears, in this config, sound pretty awful - metallic and closed in with none of the 'musicality' I thought I had before, a bit disappointing. So the LM833's are back in for the time being, better but somethings not quite the same.....maybe the decoupling caps on the DAC? They were 47uF (with 47n SMD's underneath), now the top's are 100uF, bigger not always better I wonder.

Anyway, I need an I/V, I've got my eye on the D1 and a couple of other fairly simple ones (I really want tubes but I haven't figured out why ;o)......ah well, back to the reading!

Thanks for all your input!
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Old 13th September 2011, 09:25 PM   #12
simonov is offline simonov  Bulgaria
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Quote:
Originally Posted by AndrewGM View Post
What a refreshing thread

I remember being at the beginning too and wondering what to do first.
I was unable to help myself and did loads all at once so I never really knew which tweak did the most.
The first mods ( like the ones your doing now ) seemed to have the biggest jumps in SQ.....so don't stop !!

I'm sort of willing you on here.....

Sorry but I've nothing to offer with regards to your machine but I have modded and use daily a phillips based player with 7220 and 1541A.
Your doing all the right things and if you keep going you'll end up with something pretty special.

Just one thing - there is a fantastic value clock from vintage audio lab on e bay ( which is red in colour if you look for it ) it's about 25 and works very well. It'll also give you multiple clock feeds of various useable freqencies ( 2.8,5.6 and 11.289 ) if you want to go mad. If you have a 1541A you can feed pin 2 and 4 with 5.6 and 11.289 for a very noticeable gain. Give it it's own small encapsulated transformer and it's quite excellent.

Good luck
Yes. Clock upgrade brings a significant improvement over the standard circuit. Using TDA1541A requires 5.6448MHz applied to both pin 2 and 4. I'd recommend feeding 11.2896MHz to a separate flip-flop and applying it to pin 2 and 4. The flip-flop should be powered by the same PSU powering the SAA7220 chip.

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Old 13th September 2011, 10:00 PM   #13
josha is offline josha  United Kingdom
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A clock is on the to-do list and the one from vintage audio labs looks great value! I'm going to sort this output stage first though, I think I took a step back earlier, I need to check my work - on further listening I think I've got some distortion now, it's funny, I seem to have lost some of the clarity somehow/somewhere - I'll have a look over it tomorrow but I'm thinking the 134's were just highlighting whatever it is that's amiss.
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Old 14th September 2011, 02:12 AM   #14
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Quote:
Originally Posted by josha View Post
Well, the opa's to my ears, in this config, sound pretty awful - metallic and closed in with none of the 'musicality' I thought I had before, a bit disappointing. So the LM833's are back in for the time being, better but somethings not quite the same.....maybe the decoupling caps on the DAC? They were 47uF (with 47n SMD's underneath), now the top's are 100uF, bigger not always better I wonder.
I find metallic sound is not the opamps themselves, rather its caused by digital (HF) currents flowing in the grounds. So the trick for sweet sound is to get clean grounds - which means not having groundplanes by and large. Or if groundplanes already exist then cutting them in appropriate places to get back to some semblance of star (single point) grounding.

One improvement I've found is to decouple opamps rail to rail, rather than rail to ground. This way HF currents on supply rails don't get to contaminate the ground. Ideally the ground is a signal reference only, not trying to do double duty as a power supply connection as well.
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Old 14th September 2011, 06:30 PM   #15
josha is offline josha  United Kingdom
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I took the board out earlier, touched up my soldering (I must have been rushing last night) and gave it a good clean - I use a solder pump for de-soldering and it drops solder everywhere, it's easy to forget the basics when your heads full of 'discreet this and j-fet that!) I also re-positioned some of the caps/resistors - they're vertical on this board and my sausage fingers keep bending them over. Anyway, I'm back to where I was - nice sound, no noticeable distortion. So, waiting for a few parts and it's onto the next mod!
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Old 14th September 2011, 09:29 PM   #16
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Quote:
Originally Posted by simonov View Post
Yes. Clock upgrade brings a significant improvement over the standard circuit. Using TDA1541A requires 5.6448MHz applied to both pin 2 and 4. I'd recommend feeding 11.2896MHz to a separate flip-flop and applying it to pin 2 and 4. The flip-flop should be powered by the same PSU powering the SAA7220 chip.

Click the image to open in full size.
I can't remember now which pins on the TDA I fed 5.6 and 11.2 but it works fine and they both go directly to chip instead of via flip flop.
I also do not want any connection to the DAC chip that involves the 7220 power supply - I have a separate transformer and ps for 7220 - it's best kept completely away from TDA whenever possible.
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Old 14th September 2011, 09:59 PM   #17
simonov is offline simonov  Bulgaria
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Quote:
Originally Posted by AndrewGM View Post
I can't remember now which pins on the TDA I fed 5.6 and 11.2 but it works fine and they both go directly to chip instead of via flip flop.
TDA1541(non A) accepts 11.2896MHz on pin 4 and 5.6448MHz on pin 2. That's what the datasheet says. TDA1541A does not support such an operation. At least the datasheet doesn't point it. Maybe this mode is supported unofficially. Anyways you CAN'T feed 11.2896MHz to the BCK rail (pin2) so you still need to divide by two.

Quote:
Originally Posted by AndrewGM View Post
I also do not want any connection to the DAC chip that involves the 7220 power supply...
You actually don't want ANY frequency conditioning IC connected to the analog PSU(DAC PSU). The best option is of course the frequency division device to be powered from the same PSU that powers the separate clock module.
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Old 14th September 2011, 10:13 PM   #18
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' The flip-flop should be powered by the same PSU powering the SAA7220 chip '.

I must have misunderstood the above then

1541A does support it and works very well in this configuration
11.289 on pin 4 and 5.6 on pin 2 is how I have it - thanks.
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Old 14th September 2011, 10:18 PM   #19
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DIR9001+TDA1541A Classic NOS DAC

btw - like your blog very much - particularly this NOS DAC of yours - Very nice

Andrew
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Old 14th September 2011, 10:26 PM   #20
simonov is offline simonov  Bulgaria
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Thanks Andrew. And I'll try the 1541A with separate clock on pin 4.

Regards,
Venci
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