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Chalk this up to the FWIW column. Roughly a couple of years ago several upgrades were recommended/became available for M60s (possibly the Mk. II.3 package, I can't recall for sure). Among the items offered was increased storage capacitance. I decided to implement this change and, following contact with Atmasphere, had it done locally by a qualified tech who is the marquis name on a nationally distributed brand of cables and power conditioners.My reaction to the change was one of ambivalence. It seemed the amps had slowed down some but, otherwise, things were mostly status quo. So back to the tech to fit some bypass capacitors in the hope of restoring the lost speed. Again, results were a mixed bag.
Fast forward to the present. I just got the amps back from the same tech. They have been restored to original condition (added capacitors have been pulled). Well, that old black magic is back in spades...increased purity and transparency and (whodda thunkit) noticably more defined and impactful bass. It's a keeper!
My speakers are 102db sensitive AG Duos and I think this is key to the reason this changeback worked for me. I'm no electronics guru by any stretch but it just seems that the extra storage capacitance was not needed in my case and tended to lend a certain thickening to the overall presentation, almost like what adding an output tranny would be expected to do.
So the message is, if you have high sensitivity speakers, you might want to investigate this relatively quick and easy mod. It's simple to reverse it if it turns out to be not your cuppa.
Thank you, class, for letting me share my 7th grade science project with you all.
Follow Ups:
Opps, pardon the brain fart. Make that "marquee" name.
Okay, I promise, no more. Make that "oops". Gotta quit thinkin' about that Oppo 971 player.
Your impressions are interesting. It may be that, due to space limitations, using caps of larger value is the most practical way to increase total capacitance of the LV supplies. Sometimes large value electrolytics don't sound as good as smaller value ones, all other things being equal. You may find that installing a larger number of the smaller value caps, so as to effect an increase in net capacitance without sacrificing the possibly greater speed of small caps, will give you the best of both worlds. Also, I highly recommend Paul Speltz's mod to the output supply (in the tweaks archives from the old ASOG website, if you can find it): he used a small value lytic right after the rectifiers (in this case say ~1000uF to 2000uF) followed by low value resistors, etc, so as to effect a CRCRC type filter, where the last C can be a bunch of caps in parallel for a very high net capacitance. This works very nicely on my amps and is "all good". R ranges from 0.1 to no more than 0.5 ohms, and you need to use them on both the positive and negative sides of the supply rails. Then there was Harvey Rosenberg's idea of using CLC type filtration on an M60, but in that case, L needs to be very low inductance, very low DCR, and very high current so as not to limit transient performance or cut down the plate voltage to the output tubes.
We've been installing an RC network in the M-60 for some time, mostly to get after the diode noise, especially on horns. It has been helpful (although we found that most of the noise was coming from elsewhere...).With less efficient speakers, a significant impedance in the power supply has been something we wanted to avoid so that the supply could deliver any currents asked of it. When we added the extra filter capacitance as a standard item to the M-60 a few years back, it allowed us the RC ability without sacrifice.
Lew - I have done just that ! - since the old drawing that I have does not show the Output P/S ..I searched around for details & ideas . With Pauls vast experience in this area , I decided to use his principle that you mention * from his notes * . The CRC method drops the ac ripple to a great reduction from the entry to the caps banks .
Ive used 6x 2200 uf caps ..3 per p/s bank ...no extreme caps here - just used low ESR type from the UK - was approx 50 USD each , and CRC them with ( CAP + 0.47 CAP + 0.22 + CAP ) ...I did this on both sections of each cap .... Thanks Paul ! - I am very satisfied with the results . I did mess up with the VA rating of my output section tho - Paul mentioned 470 VA I think ...I have fitted 500 + 500 ! ...so is a 1 KVA @ 100 vac . I took the value of 470 VA as the rating per bank .... And when I had my toroids wound in australia , they made them for me at 500VA per winding . Does take up some precious room . Less is more indeed ...and I have a very uncluttered chassis , and the less components in the build,the better I feel about the results . Stu
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