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McIntosh MC275 MK VI Clone

Now comes the populated board being offered.

...And the output and power transformers...

See attached MC275 MkVI board layout. AFAICT is identical down to the part layout and part IDs. Only the J numbers for the jacks seem to be changed.

See attached Vanderveen VDV-1070-UC Unity Coupled transformer specs. What I find interesting and did not realize until now is that the Mark VI (the att schematic may indeed by the Mark IV) and does NOT include an extra set of windings for the tubes that drive the output KT88's. Neither does the VDV transformer. Based on my prior work, I bet the VDV will drop right in this board (VDV does not have a CT feedback winding so no balanced input). The VDV is half the price of the aliexpress clone, and is a known good one in my experience. Redesign some to make up for the VDV operating into a higher 6.4K load into 8 ohms...hmm...yes, I asked if a bare board could be purchased.
 

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rustnrot said:
Now comes the populated board being offered.

...And the output and power transformers...

See attached MC275 MkVI board layout. AFAICT is identical down to the part layout and part IDs. Only the J numbers for the jacks seem to be changed.

See attached Vanderveen VDV-1070-UC Unity Coupled transformer specs. What I find interesting and did not realize until now is that the Mark VI does NOT include an extra set of windings for the tubes that drive the output KT88's. Neither does the VDV transformer. Based on my prior work, I bet the VDV will drop right in this board (VDV does not have a CT feedback winding so no balanced input). The VDV is half the price of the aliexpress clone, and is a known good one in my experience. Redesign some to make up for the VDV operating into a higher 6.4K load into 8 ohms...hmm...yes, I asked if a bare board could be purchased.
Click to expand...
:idea:...I like it.
 
Tubes in and lift off tonight. We are at 100hrs with the New updated board, and all is sounding good. Let's give this another 100hrs for a Sound and Temp Check.

MC275m.png
 
120hrs and counting. I have put back the EH KT-88's as I'm finding these "Livelier" then Genalex :idea:. I am pleased on the Openness and Space the Mundorf's are sounding (200hrs at least needed).
Not sure on the position the 12AT7's have to the overall sound by using Brimar, HP, Genalex, etc?

MC275n.png
 
On the actual Mark VI, I think the LEDs can also be used as indicators for warm-up or something like that. Do the clone LEDs do that or is there just a simple ON-OFF switch (assuming they can be turned off).
 
rustnrot said:
On the actual Mark VI, I think the LEDs can also be used as indicators for warm-up or something like that. Do the clone LEDs do that or is there just a simple ON-OFF switch (assuming they can be turned off).
Click to expand...
I had asked and this one is On only, with a Tube failure or Over Volts then relays kick in.
 
rustnrot said:
On the actual Mark VI, I think the LEDs can also be used as indicators for warm-up or something like that. Do the clone LEDs do that or is there just a simple ON-OFF switch (assuming they can be turned off).
Click to expand...

On the "real" Mc the LEDs start out orange and change to green when the amp is ready to go.

.
 
RickB said:
On the "real" Mc the LEDs start out orange and change to green when the amp is ready to go.

.
Click to expand...

Yes, part of the power on self test "boot up", at least on my untouched and original (4) 12 yr. old 275LEs.
And always nice to watch them go from orange to green after powering them up every weekend evening, knowing that their still heathy and happy.
 
Thanks CohibaJoe, for sharing your experience with this amp. You are the only one I can find on the internet that has actual experience. Strangely absent are any YT videos or reviews. Only chats with lots of unqualified opinions. Also interesting, ebay listing photos show a bright green PCB. I wonder if there are different builds or versions from different sources.
 
Jimsaku said:
Thanks CohibaJoe, for sharing your experience with this amp. You are the only one I can find on the internet that has actual experience. Strangely absent are any YT videos or reviews. Only chats with lots of unqualified opinions. Also interesting, ebay listing photos show a bright green PCB. I wonder if there are different builds or versions from different sources.
Click to expand...
Maybe this would push me to Post this in Action on YouTube:idea:. And a side note..Maybe the YouTube Commets should be turned off as you can see in my thread a few of the "Kings/Queens" beating their chest :rflmao:. Said the Green board is a Basic Model with Standard parts.
 
150 hrs. and going. I did switch back to the GL KT-88's and HP 6201... Now we are sounding what the GL should sound like.
The EH KT-88's do have an upper range "Sparkle" that I do like...Maybe not the best choice for jittery tweeters.
 
CohibaJoe said:
Maybe this would push me to Post this in Action on YouTube:idea:. And a side note..Maybe the YouTube Commets should be turned off as you can see in my thread a few of the "Kings/Queens" beating their chest :rflmao:. Said the Green board is a Basic Model with Standard parts.
Click to expand...
I think there are many that would be interested in buying if they had a reference point (video) showing that it is real and how good it is. I wonder if McIntosh gets YT and other sites to remove reviews. As for as buying a real one, McIntosh doesn't make it easy. I would have to drive to another state to pick one up. Online dealers won't ship (maybe Audio Classics would). I am not interested is spending that much anyway on something like that. My brother used to make fun of my McIntosh equipment by calling it McIntush. If I could only find a logo like that! I bought a C24 preamp for $50 and didn't like the sound, especially the contour knob, but I can't seem to part with it. My 2100 really punched with Klipsch for DJ use, but it broke down several times later over the years without any use (they don't always last "several lifetimes"). I bought a MAC1700 with wood cabinet for $3 at a thrift store, working with McIntosh branded tubes. Sold that one.
 
Jimsaku said:
I think there are many that would be interested in buying if they had a reference point (video) showing that it is real and how good it is. I wonder if McIntosh gets YT and other sites to remove reviews. As for as buying a real one, McIntosh doesn't make it easy. I would have to drive to another state to pick one up. Online dealers won't ship (maybe Audio Classics would). I am not interested is spending that much anyway on something like that. My brother used to make fun of my McIntosh equipment by calling it McIntush. If I could only find a logo like that! I bought a C24 preamp for $50 and didn't like the sound, especially the contour knob, but I can't seem to part with it. My 2100 really punched with Klipsch for DJ use, but it broke down several times later over the years without any use (they don't always last "several lifetimes"). I bought a MAC1700 with wood cabinet for $3 at a thrift store, working with McIntosh branded tubes. Sold that one.
Click to expand...
If you have a Best Buy (Magnolia) by you, they sell McIntosh. I had 1900, 6100, C32, 4100 & M-78 (still have) and like any electronic piece the older gear "Needs TLC". I'm not a 1 Brand loyalists (boring) as like to mix brand sounds signatures throughout my setup.
In this thread, I'm having Fun messing around with this unit and that is that.
 
CohibaJoe said:
150 hrs. and going. I did switch back to the GL KT-88's and HP 6201... Now we are sounding what the GL should sound like.
The EH KT-88's do have an upper range "Sparkle" that I do like...Maybe not the best choice for jittery tweeters.
Click to expand...
I would be interested if only someone did a distortion measurement over frequencies and at various power levels to confirm that the transformers are really as good/better than the original MC275 Mk1. I maybe mistaken but I think only the Mk1 and Mk2 of the MC275 had C-cores.
I'm sure I would want to get a pair of good new copies of the MC275 output transformers for DIY with different tubes and a simpler topology with less stages. The newer McIntosh uses lower spec EI core.

pictures of actual C-core of older mcintosh transformer:
http://merrenaudio.com/mcintosh

for distortion measurements of the MC240 see https://www.kenrockwell.com/audio/mcintosh/mc240.htm Originally better than 0.1% THD across 20Hz to 10kHz at 1 watt and 0.2% at 20 watts.
 
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nicknack said:
I would be interested if only someone did a distortion measurement over frequencies and at various power levels to confirm that the transformers are really as good/better than the original MC275 Mk1. I maybe mistaken but I think only the Mk1 and Mk2 of the MC275 had C-cores.
I'm sure I would want to get a pair of good new copies of the MC275 output transformers for DIY with different tubes and a simpler topology with less stages. The newer McIntosh uses lower spec EI core.

pictures of actual C-core of older mcintosh transformer:
http://merrenaudio.com/mcintosh

for distortion measurements of the MC240 see https://www.kenrockwell.com/audio/mcintosh/mc240.htm Originally better than 0.1% THD across 20Hz to 10kHz at 1 watt and 0.2% at 20 watts.
Click to expand...
:idea:, Let me contact my tech I use locally to see if he can do this.
 
Update - I have BIAS the unit per the Factory after asking for 3 months (replaced stock EH with Genalex). KT88 Pin 3 at 61V-65V. The right side was 65.5V so now both Left/Right sides at 61.5V-62.0V.
They said KT88's should be Balanced Quad and should not require any further BIAS adjustments.
 
CohibaJoe said:
Update - I have BIAS the unit per the Factory after asking for 3 months (replaced stock EH with Genalex). KT88 Pin 3 at 61V-65V. The right side was 65.5V so now both Left/Right sides at 61.5V-62.0V.
They said KT88's should be Balanced Quad and should not require any further BIAS adjustments.
Click to expand...
Oh that's interesting. How did you set the bias? The original MC275 by the very nature of it's design doesn't require Bias tuning(that's part of the clever design). At least that's what I recall. So this new clone requires bias to be set at least once?
Just re-iterating my interest in this new amp is that if the transformers are really a true McIntosh copy ie Trifilar wound on a C-core, since I did like to build a version of the original MC275 circuit without a phase splitter and one less gain stage since a lot of new DACs can output 3V or even 6V rail to rail with a balanced XLR output that will automatically give the differential drive without the need of the phase splitter circuit.
https://usermanual.wiki/Mcintosh/McintoshMc275UsersManual771578.63537312/view
 
Oh AFAIK the only reliable service-shop that can rewind a McIntosh transformer to it's original winding arrangement is no longer in business(owner passed away). So if anyone has any leads on a reliable shop/service that can rewind a MC275 output transformer to original specification please pass me that info so I can get an old pair repaired.
 
nicknack said:
Oh that's interesting. How did you set the bias? The original MC275 by the very nature of it's design doesn't require Bias tuning(that's part of the clever design). At least that's what I recall. So this new clone requires bias to be set at least once?
Just re-iterating my interest in this new amp is that if the transformers are really a true McIntosh copy ie Trifilar wound on a C-core, since I did like to build a version of the original MC275 circuit without a phase splitter and one less gain stage since a lot of new DACs can output 3V or even 6V rail to rail with a balanced XLR output that will automatically give the differential drive without the need of the phase splitter circuit.
https://usermanual.wiki/Mcintosh/McintoshMc275UsersManual771578.63537312/view
Click to expand...
Set it once with Balanced Quad KT88's at 61V-65V.

MC275Lb.png
 
The original MC275 did not have bias adjustments. But adding them is a net positive. The Unity Coupled design only lessens their need, not necessarily remove it. I added bias adjustments to enhance my Unity Coupled amp referenced earlier in this thread.

The older MC275 OPTs were trifilar wound. The newer ones are not. Trifilar or not still requires a phase inverter.
 
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