Fast996 Posted August 1, 2021 Share Posted August 1, 2021 I purchased a McIntosh C20 preamp on Epay. I was looking for a tube preamp to run with my new to me Khorns. My first Mcintosh piece of gear and I knew the C20 would need some work. People say...oh keep it original and keep the "bumble bee caps", well that ain't necessarily a good idea. Some might look at the "before specs" and say that the measured performance wasn't that bad,but the McIntosh factory baseline for THD is 0.2 or better. I see tons of vintage Mac gear but the sellers never post figures,so I thought I would post these. When I receive the C20 back from the McIntosh authorized factory dealer service center I'll post my thoughts on the sound with the Khorns. The tech said "it sounds wonderful and "warm as it should". I can't wait. 1 Quote Link to comment Share on other sites More sharing options...
Bubo Posted August 1, 2021 Share Posted August 1, 2021 You replaced the bumble bee caps, with what ? any difference in measurement ? 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted August 1, 2021 Share Posted August 1, 2021 Guessing you ran the unit before having the service work and will be able to hear the difference. 2 Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 1, 2021 Author Share Posted August 1, 2021 1 hour ago, Bubo said: You replaced the bumble bee caps, with what ? any difference in measurement ? Lol...I chuckled,,,sorry. The bumble bee caps are VG candidates to leak and crack. I'm sure though if a put them on ebay somebody will buy them. The Arizona Capacitors Blue and Red have that classic sound. I tried to voice the preamp with mostly copper foil. I've had the 4 teflons for years and was glad to use them. The same with the Japanese resistors and the Black Gates. This unit gobbled up a bunch of stuff I've had for quite a while.... https://jeffsplace.positive-feedback.com/the-vintage-mcintosh-mx110-adventure-omg-stop-the-presses-up-next-the-a5-vott-project/ I used mostly pieces that I had left over from my other builds. Mundorf,Miflex KPFM,TFT teflon JDM Duelund,Arizona Capacitor,and Mundorf 4700uf 40v I purchased the JDM's, the Arizona caps,and the Mundorf filament cap.The rest I had leftover Takiman and shinko 1 watt resistors both carbon and metal film Silver micas 4-47uf 16v black gate FK The tech upgraded the power supply... low esr 105c caps...C1 50/50/50/50 uf electrolytic B+ cap 1 C2 50/50/50/50 uf electrolytic B+ cap IIRC the original can cap values were like 40,40.40,20,20,20 The original filament cap was a 2000uf 15v replaced w the 4700uf 40v You can upgrade these C20's with improved performance and yes my build is over the top,You can spend 5 bucks each on caps and no doubt retain the original sound. I just like to experiment. So if I have 4k invested I'd rather do that then spend 10K to each their own. Will all this make a SQ difference? In my experience yes. I had 4 .022uf Jupiter caps that I was hoping to use but the schematic I grabbed off the web showed them,but they weren't used in the model. McIntosh built 3 versions of the C20...early,mid,and late. Mine is a mid unit with a unpotted transformer and glass faceplate. Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 1, 2021 Author Share Posted August 1, 2021 1 hour ago, billybob said: Guessing you ran the unit before having the service work and will be able to hear the difference. No....from the Ebay seller direct to the largest and most respected Mac dealer in the world. The preamp is 60 years old...I voice all my vintage RTR's,Accuphase,and the rest. It's just how I roll. 2 Quote Link to comment Share on other sites More sharing options...
Bubo Posted August 1, 2021 Share Posted August 1, 2021 If they had better components 50 years ago they would have used them So why not replace with 1% and better temp and performance ratings. Carbon resistors probably don't find their way into many new designs Same goes for rectifier tubes etc Mac transformers tend to be well engineered. I believe 2 of the 4 founders were transformer engineers 1 Quote Link to comment Share on other sites More sharing options...
Pondoro Posted August 1, 2021 Share Posted August 1, 2021 I read the before and after specs, what happened in between? 1 Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 1, 2021 Author Share Posted August 1, 2021 1 hour ago, Bubo said: If they had better components 50 years ago they would have used them So why not replace with 1% and better temp and performance ratings. Carbon resistors probably don't find their way into many new designs Same goes for rectifier tubes etc Mac transformers tend to be well engineered. I believe 2 of the 4 founders were transformer engineers Everything I specified and provided was 1 pct and I used all caps that give a mix of detail,warmth,transparency and no harshness or edge to the music. The preamp should despite the tube rectifier should sound better than new. Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 1, 2021 Author Share Posted August 1, 2021 53 minutes ago, Pondoro said: I read the before and after specs, what happened in between? Restoration Quote Link to comment Share on other sites More sharing options...
Bubo Posted August 1, 2021 Share Posted August 1, 2021 28 minutes ago, Fast996 said: Everything I specified and provided was 1 pct and I used all caps that give a mix of detail,warmth,transparency and no harshness or edge to the music. The preamp should despite the tube rectifier should sound better than new. Can you stuff 2 diodes in the socket for the tube rectifier ? Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 1, 2021 Author Share Posted August 1, 2021 40 minutes ago, Bubo said: Can you stuff 2 diodes in the socket for the tube rectifier ? In my instructions for the rebuild I mentioned that,but it was never addressed by the tech I'm alright with the 6x4 as the C20 doesn't sound like the C22 . I didn't want to make a change away from original.anyway At some point ill.probably pick up a C22 and then ill.see which one I prefer. Quote Link to comment Share on other sites More sharing options...
Pondoro Posted August 2, 2021 Share Posted August 2, 2021 18 hours ago, Fast996 said: Restoration So it isn’t clear from the page you posted. Did they replace all the caps? The page just talks about cleaning and retensioning the tube sockets. The performance clearly improved, I can’t tell if the caps were changed. Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 2, 2021 Author Share Posted August 2, 2021 56 minutes ago, Pondoro said: So it isn’t clear from the page you posted. Did they replace all the caps? The page just talks about cleaning and retensioning the tube sockets. The performance clearly improved, I can’t tell if the caps were changed. Hi , Here is the list of changed parts,all of the capacitors,all the electrolytics,including the power supply which was upgraded to about double the uf. All original spec'd low noise resistors and others upgraded to 1 pct 1 watt and all caps were 1 pct also. Some in spec carbon resistors were left in place. The best published specs after a recap I could find on the web was a unit done by Terry Dewick a master McIntosh tech. The unit Terry recapped which he called "virgin" was 0.02 THD Am I happy with .05/.06 absolutely because mine was electronically far from virgin. Also the new caps should have a very positive effect on the sound...though still having the "Mac" signature. I'm glad I had it done. It will last me the rest of my lifetime. 1 Quote Link to comment Share on other sites More sharing options...
Pondoro Posted August 2, 2021 Share Posted August 2, 2021 3 hours ago, Fast996 said: Hi , Here is the list of changed parts,all of the capacitors,all the electrolytics,including the power supply which was upgraded to about double the uf. All original spec'd low noise resistors and others upgraded to 1 pct 1 watt and all caps were 1 pct also. Some in spec carbon resistors were left in place. The best published specs after a recap I could find on the web was a unit done by Terry Dewick a master McIntosh tech. The unit Terry recapped which he called "virgin" was 0.02 THD Am I happy with .05/.06 absolutely because mine was electronically far from virgin. Also the new caps should have a very positive effect on the sound...though still having the "Mac" signature. I'm glad I had it done. It will last me the rest of my lifetime. So this is very interesting. Lots of people say, “replace the capacitors” but here is actual before and after test results. Thanks! Quote Link to comment Share on other sites More sharing options...
Audible Nectar Posted August 3, 2021 Share Posted August 3, 2021 I've walked the walk with vintage Mac for actual operational purpose, where best sonics are a consideration, and I can tell you without question that these pieces benefit from the rework. Collectors who have these sitting on a shelf might well do just fine leaving them original, because after all they are doing it for the collecting, but for actual operational use - not to mention safety - an electronic restoration by a competent technician well versed in reworking these pieces is highly recommended. In this case, we have one who can do their own work and have gotten the requisite excellent results. There's certainly room for discussion as to exactly what parts should be used to best keep the "signature", but I've found that there's more leeway than you might think, just listening to the different builds that I have, but certainly know that a good build does wonders for the pieces. C22 has a solid state rectifier where the C20 is tube rectified, and that seems to account for the obvious difference in its signature......more authority in the bass response the C20 a bit more "rounded". Both really have a magic about them, though...... 1 Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 3, 2021 Author Share Posted August 3, 2021 4 hours ago, Audible Nectar said: C22 has a solid state rectifier where the C20 is tube rectified, and that seems to account for the obvious difference in its signature......more authority in the bass response the C20 a bit more "rounded". Both really have a magic about them, though...... My C20 will be paired with a PS modded and upgraded Accuphase P300 which is a great SS amplifier....when I upgrade them. I will be interested if a synergy will exist and if the tube rectified C20 will deliver some punch in the bass. One can hope....overall the pairing should deliver some magic. I have tube amps but I'm going to try the Accuphase first. Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 5, 2021 Author Share Posted August 5, 2021 Here are some photos of the finished C20. Came out pretty nice for 60 years old. But how does it sound? I have to wait a little while for my Accuphase P300 to return. 2 Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 5, 2021 Author Share Posted August 5, 2021 Low and behold I didn't notice that the tech did read all of my instructions and replaced the 6x4 tube rectifier with a solid state rectifier. What difference can I expect to hear. There was a reason he upgraded the power supply. Quote Link to comment Share on other sites More sharing options...
Fast996 Posted August 8, 2021 Author Share Posted August 8, 2021 A little McIntosh C20 porn....my vision of a beautiful C20.... Quote Link to comment Share on other sites More sharing options...
Searing75 Posted August 13, 2021 Share Posted August 13, 2021 The solid state rectifier will tighten up the low end. As as far as recapping goes.....I have recapped five vintage McIntosh components. An MC2105, C32, C34v, and two MC50 ‘s, and all of them came alive afterwards. Huge difference in sound. Much cleaner, quieter, and more detailed. Quote Link to comment Share on other sites More sharing options...
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