A re-build of my "bucket list" McIntosh preamp (C11/C22)
- Thread starter DC
- Start date
Thank you! I will look for those references for sure.
I got some more parts in the mail today ...
When I did the re-cap on this, I never changed the coupling caps that route around the rumble filter associated with V6. (They're in circuit when the Rumble Filter is OFF, which means they're always in circuit!
) Russian PIO .022uF caps with Orange Drop .025uF caps now in circuit:
Before:
After:
And an OOPS moment!
I was glancing at the previous work and discovered an UNSOLDERED CONNECTION from last time. DOH! All fixed now ...
When I did the re-cap on this, I never changed the coupling caps that route around the rumble filter associated with V6. (They're in circuit when the Rumble Filter is OFF, which means they're always in circuit!
) Russian PIO .022uF caps with Orange Drop .025uF caps now in circuit:Before:
After:
And an OOPS moment!
I was glancing at the previous work and discovered an UNSOLDERED CONNECTION from last time. DOH!
All fixed now ...
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Fortunately, this one tracks decent. I've considered removing the loudness tap to see if it tracks any different, but since it's OK as it, I've left it alone.
I've got a few more caps coming as well as all new rear-panel RCAs, so I'll be under the hood a bunch more.
I've got a few more caps coming as well as all new rear-panel RCAs, so I'll be under the hood a bunch more.
Looking and sounding better all the time I bet Don. Very well put together thread.
More baby steps ...
Another shipment (this time from Mouser), so another capacitor upgrade. These are the 50uF/3VDC caps associated with V1 and V2 in the phono stage. The old Cornell Dubilier caps were replaced with new Sprague aluminum electrolytics. I ended up using 50uF/16VDC caps as the 3V rated ones were very difficult to find.
Before:
After:
Now, a question for the cognescenti (is anybody actually reading this?): Is it worth the effort at this point to replace the few remaining disc capacitors? There are four (two each L/R) for the loudness compensation, which I won't bother with, but I'm wondering about the rest of them. Four (two pair each) are buried amongst the tube bases and probably are the most difficult components in the entire preamp to get to to replace. If it's probably worth the effort, I'll get some good quality ceramics to replace them; but if it's just chasing windmills, I'm content to leave well enough alone for a while.
Eh?
Another shipment (this time from Mouser), so another capacitor upgrade. These are the 50uF/3VDC caps associated with V1 and V2 in the phono stage. The old Cornell Dubilier caps were replaced with new Sprague aluminum electrolytics. I ended up using 50uF/16VDC caps as the 3V rated ones were very difficult to find.
Before:
After:
Now, a question for the cognescenti (is anybody actually reading this?): Is it worth the effort at this point to replace the few remaining disc capacitors? There are four (two each L/R) for the loudness compensation, which I won't bother with, but I'm wondering about the rest of them. Four (two pair each) are buried amongst the tube bases and probably are the most difficult components in the entire preamp to get to to replace. If it's probably worth the effort, I'll get some good quality ceramics to replace them; but if it's just chasing windmills, I'm content to leave well enough alone for a while.
Eh?
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DOH!
I knew I should have measured the holes, I knew I should have measure the holes, I knew I should have ...
The bag-o-gajillion connectors I bought are about 1/16" too big for the mounting holes in the rear panel, so they don't fit. :grumpy: I guess I'll either need to drill out the existing holes to accommodate these or I'll need to find more appropriate connectors. Hmmm ...
I used a few cheapy ones I had from Radio Shack in the meantime. The low-level inputs (phono only, really; no need for the others anymore) will need a little more delicacy as they are mounted on a floating-ground panel. And since the 47k loading resistors are right there, I'll upgrade them too when the time comes.
Oh well.
I knew I should have measured the holes, I knew I should have measure the holes, I knew I should have ...
The bag-o-gajillion connectors I bought are about 1/16" too big for the mounting holes in the rear panel, so they don't fit. :grumpy: I guess I'll either need to drill out the existing holes to accommodate these or I'll need to find more appropriate connectors. Hmmm ...
I used a few cheapy ones I had from Radio Shack in the meantime. The low-level inputs (phono only, really; no need for the others anymore) will need a little more delicacy as they are mounted on a floating-ground panel. And since the 47k loading resistors are right there, I'll upgrade them too when the time comes.
Oh well.
A recent thread (http://www.audiokarma.org/forums/showthread.php?t=624732) raised the question as to exactly what the differences between the C11 and C22 actually are. Well, the schematics are virtually identical and internally they look like identical twins. However, a quick analysis of the schematic will reveal a few minor/subtle changes, including a couple of component values. One difference is that in the C11 and early C22, C3/C4 are 50uF but are doubled to 100uF in later C22. When I ordered the 50uF caps to replace the old ones, I ordered five, so I still had three left on hand. I simply tacked another 50uF piggy-back on to the existing 50uF for each channel, giving the 100uF value in the later C22 schematic.
I have no idea if it will actually make an improvement in sound, but I'll hope for the best. :thmbsp:
I have no idea if it will actually make an improvement in sound, but I'll hope for the best. :thmbsp:
BillyBatts
ALOHA!
I'm glad I caught this thread. Beautiful work, OP. Simply beautiful.
And what a great rig to keep pristine.
:thmbsp:
And what a great rig to keep pristine.
:thmbsp:
Anybody perhaps more savvy than myself that can take a gander at the schematic (see above) and determine if this 50uF --> 100uF change would likely make any difference in the overall bass response of the phono stage? My ears say that the noticeably lean bass of the internal phono stage (which I've just attributed to the old PEC RIAA devices which I have no interest, at this time, in rebuilding) seems a little better, now - better as in less lean and a little more robust.
Eh?
I assure you, my only "talent" in this regard is the ability to solder reasonably well and follow others' instructions.
I think the real credit goes to Craig Otsby of NOSvalves for posting his C22 rebuild for all us DIY guys to follow and answering several email questions I sent him about component parts. One of these days I'll have him give this a thorough bench-test (he's reasonably local) to make sure there are no hidden problems, but so far my ears approve.
Thanks!
Thanks again!
cduarte
Well-Known Member
A recent thread (http://www.audiokarma.org/forums/showthread.php?t=624732) raised the question as to exactly what the differences between the C11 and C22 actually are. Well, the schematics are virtually identical and internally they look like identical twins. However, a quick analysis of the schematic will reveal a few minor/subtle changes, including a couple of component values. One difference is that in the C11 and early C22, C3/C4 are 50uF but are doubled to 100uF in later C22. When I ordered the 50uF caps to replace the old ones, I ordered five, so I still had three left on hand. I simply tacked another 50uF piggy-back on to the existing 50uF for each channel, giving the 100uF value in the later C22 schematic.
I have no idea if it will actually make an improvement in sound, but I'll hope for the best. :thmbsp:
My tech didn't have either 50 or 100uf caps to replace those so he installed a pair of 150uf/16v tantalum caps and he measured the RIAA curve and here's what he found: "Solid tubular tantalums installed for cathode bypass in the phono section of the McIntosh C-11. Now to see if the RIAA curve is improved..Solid tubular tantalums installed for cathode bypass in the phono section of the McIntosh C-11. Now to see if the RIAA curve is improved... we picked up 1.5dB more gain at 20hz. So the RIAA curve is now within 1.8dB of ideal."
Nice! Overall, I reckon +/- 1.8dB for RIAA spec isn't very good, but it seems to be commonly understood that the waxed PEC devices are the real weak points in these old preamps and maybe that spec isn't so bad, considering.
An enterprising individual should build and market some solder-in replacement devices for the RIAA curve, tone circuits, tape EQ, and the like. I'd buy them in a half-second and I'd bet a lot of other C11/C22 owners would do the same.
Hmmm, maybe even with customizable tone controls, like 1.5-2dB steps +/- instead of the 3-4dB leaps in it's current configuration. Hmmm, and a better loudness curve (which is stupid as is). Hmmm, and ...
An enterprising individual should build and market some solder-in replacement devices for the RIAA curve, tone circuits, tape EQ, and the like. I'd buy them in a half-second and I'd bet a lot of other C11/C22 owners would do the same.
Hmmm, maybe even with customizable tone controls, like 1.5-2dB steps +/- instead of the 3-4dB leaps in it's current configuration. Hmmm, and a better loudness curve (which is stupid as is). Hmmm, and ...