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I'm in the process of replacing the coupling caps on the output of my McCormack Micro phono drive. The stock caps were a 1.0 mfd Kimber, paralleled with a 0.47 mfd (100 V) Wima.
The 1.5 mfd (450 V) Auricaps would seem the natural choice (by value, not necessarily brand), but there's also a 1.8 mfd (200 V) available which is over 1/4" smaller. This would make for an easier fit.
Do I need to concern myself with using a 0.3 mfd larger value cap?
Thanks.
Follow Ups:
I found the 1.5 mfd 200 V Auricaps I was looking for on the Sonic Craft site. They're having a 20% off everything sale until the end of October. No affiliation, of course.
Thanks for everybody's feedback.
What's the input impedence of the component you're feeding with this unit?
Post when you have this done, OK? Would be curious to know whether it ends up being worthwhile.
I changed the op-amps in my Micro Phono Drive and was glad of it. Have you done this?
Steve.
I have not touched the op-amps yet. I bought a pair of the OPA627 modules on the Brown Dog adapter boards, but have yet to try and fit them in. What op-amps did you use? I heard somewhere that the op-amps are only used for the high gain, m/c section. Do you know if there's any truth to that?
Last night I replaced all the caps in the power supply with Panasonic FM's and FC's. I bought Black Gates, but they were too large to use. On the main board I replaced the 1000 mfd 16v caps with FM's (again no room for BG). I put Black Gate bi-polars in place of the Muse's which were there.
Lastly (for now)I replaced the 100 ohm Holco output resistors with Rikens. I'll put the Hovland's I have in as I button it up, then switch to the Auricaps after the Hovland trial.
Too many changes all at once to pin point what's doing what, I know. I'll keep you posted, IF it works at all. I'm concerned I damaged the circuit boards, but I'll post that separately.
> > I have not touched the op-amps yet. I bought a pair of the OPA627 modules on the Brown Dog adapter boards, but have yet to try and fit them in. What op-amps did you use? I heard somewhere that the op-amps are only used for the high gain, m/c section. Do you know if there's any truth to that? < <
I had not heard that. Let me know if you learn anything further.
I ended up using 604s and also replacing the dual parts with 2604. I tried the 2134 and its single version, but to my surprise I ended up liking the 604/2604 better. I was also surprised that there seemed to be an improvement with the 2604 over the stock dual part.
These BB op-amps are no more expensive than the ones Steve used to begin with. I felt there was more clout, better dynamics, with the BB chips. That was my one complaint when I first starting listening to the Micro Phono.
I stuck with the BB alternatives because of their easy implementation.
Recently put together, too, a toroid transformer with the help of suggestions from inmate Rob Thomas. The change was less than dramatic, to my ears, but probably worth doing.
Steve.
I just ordered some 2604's to use in the MPD. I'm using the 627 modules in my CD player at the moment. I think those op amps Steve used were the cause of the harshness some reviewers found with this phono stage.
I'll keep you posted.
> I just ordered some 2604's to use in the MPD. I'm using the 627 modules in my CD player at the moment. I think those op amps Steve used were the cause of the harshness some reviewers found with this phono stage.
> I'll keep you posted. <
Please do.
Are you not planning to replace the single op-amps as well? Those are the ones Steve replaces in the (pricey) upgrade that he does. (Maybe they're solely for the MC circuit??)
BTW, there is something you may want to know before you start on this job. The way the board is built, these op-amps are harder to desolder than most. Per chip there is (I think just one) -- blind hole, or socket, rather than a complete perforation of the board. No doubt there is a formal name for that, but I don't know what it is.
You want to do one of two things. If you can actually determine which hole is the blind one (I'm sure it's at one of the 4 corners), then cut the chip's pin for that hole and desolder the other pins conventionally. Secondly, you can just cut all 8 pins, then heat the holes and remove what's left of each pin with a needlenose.
For the blind hole, you'll have to work from the top, although you can heat from below. There won't be much left of this pin, and you may have to just poke it out with a needle, icepick, etc.
You'll probably be soldering sockets to the board. You'll have to shorten the pin that goes into the blind hole.
Steve.
Changing cap values, types, and even brands will change the frequency response.
For better or worse is up to you to decide.
Your point is well taken. And if I were a "hardcore" tweaker I'd follow your suggestion. The "better" would be the perfect cap for my system, but the "worse" would be an empty wallet and a drawer full of caps!
After reading your reply, it would seem the logical thing would be to use what Steve McCormack designed the circuit to use and go with the 1.5 mfd. I'll squeeze them in there. He's using Auricaps in his upgrade of this unit, so I'm following his lead as far as cap brand goes.
Thanks!
Coupling caps are usually well outside of the 3 dB rolloff point so raising it 20% probably won't have much effect. It will allow more low end to pass through, slightly widening the pass band. Unless the coupling cap also is implementing a low end rolloff for subsonic suppression, it shouldn't matter. 1973 shovel eh? How do you get it to last through 34 winters of shoveling snow and salt? Just kidding, I've got a '77 XLH.
Why you old Iron Head you! Actually you're not far off with the winters and salt question. The Shovel spent many of those years in Buffalo NY, so it did see its share of salt.
Thanks for your call in the caps. I really hadn't calculated it out, but you're right, it's a 20% increase. I think I'll go with the 1.5 mfd's. It's not a major fit issue. I've got a pair of 1.5 mfd Hovlands waiting to go in before I try the Auricaps, and they're friggin' huge. If they fit, the Auri's will.
I was looking for the answer so I could order the Auricaps today. Parts Connexion is having a 15% off sale thru the end of the month.
Thanks for your reply, and good luck with that Iron Head.
Ride safe.
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