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In Reply to: RE: w, we're sort of all tweakists; that's why we're in this particular Asylum. posted by jeffreybehr on November 20, 2007 at 10:09:13
hi Jeff,
What caps do you use usually? I use the Russian PIO and it is great. Also did you try the FR diode? Definitely a must! I know why you quite moding the SS amp, the parts are shrinking smaller fast, but I think at the very minimum the tweak you need to do is to bias the op amp closer to class A, by adding a 5K between the op amp output to the -ve of the power supply!
Best rgds
Wlee
Follow Ups:
I would be very careful about adding a 5k resistor unless I don't fully understand the design. Even then I would ask, why didn't the designer add one in the first place?
Adding a buffer like the BUF634 on an existing PCB might not be possible. But an OPA627/637-BUF634 combo makes for a great, very dynamic preamp. The OPA627/637 usually isn't suitable for low-impedance applications like phono stages and mic preamps, though.
hi Peter,
Tks for the biasing article! I have always wanted to try the SS current feedback in the biasing and CCS, but too lazy with the extra transistor!
You are right that if an amp is using IC OP amp now a day we must understand how it is being used, esp for season manufacturer such as Mcintosh. If in th eolder model, usually the op amps are over used and added cold and grainy sound...
Do you think 627/637 are still among the top op amp? I wonder why Mac still uses 5532/5534/4558 though I saw Philips 5534 at the phono and TI 4558 next to brandless 5532. However the sound is really greta, wonder why??!!
very best rgds
WLee
I haven't looked into the latest generation of opamps. But I guess the new super opamps are low-impedance types, like the AD797.
If I was to design a phono stage I would probably use some of the new opamps, or the AD797. For a preamp I would use the OPA627, or the better 637 if I need more gain. Since I don't know if there is a new better alternative to the OPA627/637, it is the best I know of.
I cannot speak for the opamps you mentioned. But aren't the 5532/5534 NEC chips? From everything I have read, they are pretty bad.
...Cardas Golden Ratios when I want to spend less money, and SoniCap Gen. 1s and 2s in less-critical applications. I've also had good luck with Mundorf Supreme Silver/Oils, but only where they'll face at least 25% less then their 1200VDC rating. I used one pair of 1500VDC AuriCaps in an ASL 805 SET in the parafeed coupling position that shorted or opened a pair of 1200V. Mundorfs.
I try to replace 'lytics in powersupplies with film caps. I've used both Solen metallized 'propylenes (MPs) and motor-run oil-impregnated MPs in PSs with very good results. Here's an ASL Hurricane with one each in parallel in the 2nd pole.
I used SoniCap Platinums in the 1st coupling position and Cardas GRs in the 2nd position of these amps.
I'm sort of working on a pair of Music Reference EM7 SETs and probably will use SoniCap Platinums as couplers.
W, if I started soldering on opamps, probably the unit wouldn't work when I finished. I just stay away from them. Both my Denon 2900 multidisc and my Toshiba HD DVD players are absolutely stock.
-------------------------------------------------------
Tin-eared audiofool and very parttime fotografer.
http://community.webshots.com/user/jeffreybehr
hi Jeff,
nice woodbase for the caps! yes the motor oil cap is very nice indeed! I also use the Russian Teflon cap in the PS and it will always clean up the sound as if all the exisitng caps were not working well!
For CD players I found that the usual problem outside the op amps are the AC filter, the lytics in PS, and the output muting that many have discussed here. Often the AC line filter uses such a big filter caps that kills all the minute details in the music!
Bets rgds
William
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