Oh geez... my friend, you certainly mentioned your personal preferences:
- russian military tubes
- regulated supplies
But, the topic is what made McIntosh's OLD stuff so good!
The fact remains that their design, especially the output stage remains quite unique and special, outperforming almost any standard output stage with ease, even today. The main downside of the McIntosh output stage is the demand upon the driver to make the same voltage swing as the B+ supply requires (much like some solid state output stages requiring more B+ on the driver than the outputs). This led to the earlly high-power units mentioned earlier requiring tricky bootstrapped driver tubes to make that swing... but other than that it is a simple design, simple idea and it really does work tremendously well.
Imo, the "soupy" and "warm" McIntosh sound may have come not from the topology as much as from the use of carbon comp resistors, sloppy power supplies and paper caps... fix that and you kill the vintage collector's value, but transform the amp.
Compare the McIntosh to the Dyna ST-70. The ST-70 can be modded to sound very good, and it starts out as a very flawed design, with good, not great output iron. The McIntosh starts out with a not very flawed input/driver design, great output stage and "top of the food chain" output iron. So... draw ur own conclusions. 😀
_-_-bear
- russian military tubes
- regulated supplies
But, the topic is what made McIntosh's OLD stuff so good!
The fact remains that their design, especially the output stage remains quite unique and special, outperforming almost any standard output stage with ease, even today. The main downside of the McIntosh output stage is the demand upon the driver to make the same voltage swing as the B+ supply requires (much like some solid state output stages requiring more B+ on the driver than the outputs). This led to the earlly high-power units mentioned earlier requiring tricky bootstrapped driver tubes to make that swing... but other than that it is a simple design, simple idea and it really does work tremendously well.
Imo, the "soupy" and "warm" McIntosh sound may have come not from the topology as much as from the use of carbon comp resistors, sloppy power supplies and paper caps... fix that and you kill the vintage collector's value, but transform the amp.
Compare the McIntosh to the Dyna ST-70. The ST-70 can be modded to sound very good, and it starts out as a very flawed design, with good, not great output iron. The McIntosh starts out with a not very flawed input/driver design, great output stage and "top of the food chain" output iron. So... draw ur own conclusions. 😀
_-_-bear
No, it is your personal preferences to read my mind such a way. My personal preference is what works better for best result. Best result for me is set of criteria of optimization. Are tubes military or civil, are they Russian or Chinese, I don't care. I care for higher quality, especially if price is lower. And, of course, I prefer regulated power supplies when they help to achieve significantly better results for lower price than other ways, like selecting 8 matched MOSFETs from batch of 1000'th, like you prefer, in order to avoid degradation of output devices, that you prefer to dislike. 😀
Or, do you prefer warm vodka and spoiled fish, my friend? Oh geez... 😉
What standard output stage do you mean? Who decides what is standard? Is my Pyramid output stage standard? Does it outperform it?
Bear, I know you are the master of arguing with no facts in hands, using sentences with zero semantic. It is not my game, I am out.
hey-Hey!!!,
The McIntosh does not have 'top of the food chain' output iron. What it has is a power stage that does not require it. The whole thing works well together, and modifying it requires understanding of those workings. With the even split between plate and cathode loading one does not need any more NFB, and the global loop just doesn't have to be there. Building an OPT that has just a little bit more careful attention to interleaving would help.
Take for example that 12BH7 driver stage and its positive FB. Replace those 12K resistors with a CCS and you get the same effective B+ headroom without the positive FB. Get rid ov that nasty 12AU7 and re-wire for a 6CG7. Employ a CCS instead of the 18k tail load and equalize the plate loads. Add adjustable bias circuits to the cathode follower grids...this fantasy surrounding the 'doesn't need matching tubes/idle current' is just that: fantasy.
cheers,
Douglas
Bandersnatch, imo, you are just plain wrong. Have you measured any McIntosh style output iron in terms of bandwidth??
Have you looked at what the square wave looks like on a typical McIntosh compared to a typical tube amp?? Do you think you can achieve the same lack of ringing without output iron of wide bandwidth??
Not sure what you mean when you say "it has is a power stage that does not require it."?? What is "it", and what do you mean by "power stage"??
One does not need extra headroom on the standard power McIntosh amp's driver stage, it was needed on the the K-104 with the 810 (hope I have the number right) tubes in the output stage, there positive feedback was needed since the B+ was iirc over 1kv...
dunno who or what you are addressing with the comments on adjustable bias circuits... or matching tubes, etc...
And, I am certainly NOT saying that one can not build an even better McIntosh type output iron than the early factory units, one can today...
I am talking about the original McIntosh tube design, not the later Nestrovich designs here.
_-_-bear
Have you looked at what the square wave looks like on a typical McIntosh compared to a typical tube amp?? Do you think you can achieve the same lack of ringing without output iron of wide bandwidth??
Not sure what you mean when you say "it has is a power stage that does not require it."?? What is "it", and what do you mean by "power stage"??
One does not need extra headroom on the standard power McIntosh amp's driver stage, it was needed on the the K-104 with the 810 (hope I have the number right) tubes in the output stage, there positive feedback was needed since the B+ was iirc over 1kv...
dunno who or what you are addressing with the comments on adjustable bias circuits... or matching tubes, etc...
And, I am certainly NOT saying that one can not build an even better McIntosh type output iron than the early factory units, one can today...
I am talking about the original McIntosh tube design, not the later Nestrovich designs here.
_-_-bear
Alright bear...If I take a schematic of a tube amp...let's take the MC30 as an example...lay it on the table and ask you to point to the phase splitter stage, what do you point at?
cheers,
Douglas
The Mac OTs that I have seen frequency specs on were quite impressive. I don't recall any figures off hand, but they were many times better than an Edcor or Hammond OT.
Edcor transformers with parallel feedback across output tubes look no less impressive than McIntosh transformers with feedback in series. Just different ways to skin the cat, but results are similar. McIntosh needed higher voltage swing to drive output tubes, I need higher current swing. No principal difference, end results are similar. As soon as finish with current toy I am playing with currently (DHT triode output with zero feedback), I am going to build 200W monoblocks using Edcor output transformers, then report the results. I am pretty sure they will be quite impressive.
At only 20 KHz bandpass, you have no choice but to use local feedback with such an OT. This does not allow one to correct for the imbalance between P-P sides from unequal leakage inductance or winding resistance in the OT (quite prevalent in non split bobbin OTs, particularly in high Z primary ones), which is in series with the output (so only global FDBK can fix it). Producing HF distortion. Fortunately most older people cannot hear it.
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How do you figure that? What are you going to do with the tri-filar primaries from a MC75 for example?
cheers,
Douglas
Right!
The shorted MC275 OPT I dismantled some time ago had no interleaving at all. Only isolation between primary high voltage sections and and secondary output sections (loudspeaker) was the wire enamel. Brrrrr.
Or take a look at Lockhard's schematic (1956 or so, to be found on Pete Millet's site). This one is based on the same output stage topology, but respecting the correct primary impedance instead of McIntosh's lowish 2k (to squeeze out that 75 watt). Relies on inductive loads for voltage swing and sensible amount of (local) feedback. A well built amp along these lines would outperform a stock McIntosh IMHO.
It was just a reference to the basic unity split primary configuration being reconfigured to a standard PP primary. I'm newb to McIntosh, hence the 'mac' moniker, so not up with all the winding nuances of all the models - sorry.
Tim
Tim
You can not compare Mac OPT's with whatever other brand.
These Mac OPT's are specially wound (equal plate and cathode load).
The impressive frequency specs are the result of the cathode feedback; the Rp of the tube is very much lowered by this, giving these specs.
Out of experience I can tell you that nowadays Mac OPT's are, apart from the cross coupling winding technique, nothing special. From what I have seen I would say they are very mediocre (no interleaving - see other post), using EI cores instead of the early generation Mac's using c-cores.
Please explain why the McIntosh output stage would not need more from the driver stage compared to a "standard" output stage of whatever pedigree.
It does need more.
The unity coupling output stage of the standard McIntosh tube power amp consists of a pair of output tubes each working like cathodyne phase splitters (equal plate and cathode load). Therefore each tube (phase) will have a theoretical voltage gain of 2, lowered to around 1,5 because of the secondary load. Therefore almost all of the voltage gain must be produced by the input and driver stage as the output stage hardly amplifies voltage.
I have an original MC275 and use it on a semi-regular basis. When I first got it, I used it daily for ~6 years. It came from a commercial installation where it had been in place for ~20 years seeing infrequent use in a conference room. It had all McIntosh marked front-end tubes and a set of Genalex Gold Lion KT88's in it. They are not McIntosh marked and are likely replacements. Upon getting it I checked all the tubes in my Hickok 539C and they all tested as new. Today, ~20 years later, those tubes still test as they did then. In operation, the KT88's get very warm but not so that you cannot put your fingers on them. (The Dynaco MKIII's I used to have on the other hand would take skin off if you tried that.)
In the time I've had my MC275 I've done exactly 1 mod to it. I disconnected the primary tap on the power transformer from 117 to 125 only and the switch functions as ON/OFF now. It looks like the filter caps were changed somewhere along the way before I got it though. I was not too happy with the audio quality when I started using it. Ultimately I found a set of speakers that work well with and I've stayed with that combo ever since. To me it reminds me of high-end solid-state and not so much as a tube amp. My Citation II's hit me the exact same way and I like both amp's presentations. (My MC30's have more of the sound one would associate with a tube amp to me. I like them too.) I would never say original McIntosh was the ultimate but it certainly was an amazing business accomplishment. I cannot think of any US audio company that compares to it.
In the time I've had my MC275 I've done exactly 1 mod to it. I disconnected the primary tap on the power transformer from 117 to 125 only and the switch functions as ON/OFF now. It looks like the filter caps were changed somewhere along the way before I got it though. I was not too happy with the audio quality when I started using it. Ultimately I found a set of speakers that work well with and I've stayed with that combo ever since. To me it reminds me of high-end solid-state and not so much as a tube amp. My Citation II's hit me the exact same way and I like both amp's presentations. (My MC30's have more of the sound one would associate with a tube amp to me. I like them too.) I would never say original McIntosh was the ultimate but it certainly was an amazing business accomplishment. I cannot think of any US audio company that compares to it.
I agree that the MC amps can sound a bit bloomy for some audiophiles...
I do two simple things to my McIntosh amps and makes a big difference...I made believers out of some people who normaly did not like McIntosh amps..
First...get rid of the input cap...either replace it with something good or simply bypass it as I prefer...this will open up the soundstage and improve imaging.. I just make sure I do not have a pre-amp with any DC offset on it's output...
The second thing I do increase the value of the global feedback resistor slightly... This will give it just a bit more air and make it breath a bit better without being clinical... of course I mean just a little bit or else you will increase distortions..
Of all the speakers I have tried on the MC amps...such as MC30's, up through MC75's... I find the Vandersteen 2Ci or 2Ce bring out the best in the McIntosh amps....
Regarding the other post discussing the MC75 output transformers...
The first early series of MC75 Outputs, M-212, were more prone to shorting due to the #31 AWG used in the driver winding.... Sidney Corderman at McIntosh made the change to #29 AWG sometime in the mid 60's...
The way to tell if you have the older or newer output is to measure the DC resistance of the winding... The early version will be roughly 50 Ohms per side while the later version is roughly 30 ohms per side.... Or simply double these numbers and measure measure pin#1 to pin#6 of the driver tube for the full winding end to end...
When I wind these outputs I use the same gauge# for all three of the tri-filar windings....this way the wire layers are even and less strain on the wire...The original used 3 different wire gauges and had a very lumpy build of layers..of course I use the largest wire for all three..this would be 15 ohms per side...making all three winding now interchangable.... The only time I would use the original wire gauges is if it is a rewind that needs to match with it's mate ....The MC75 uses just one big C-core...
Chris
I do two simple things to my McIntosh amps and makes a big difference...I made believers out of some people who normaly did not like McIntosh amps..
First...get rid of the input cap...either replace it with something good or simply bypass it as I prefer...this will open up the soundstage and improve imaging.. I just make sure I do not have a pre-amp with any DC offset on it's output...
The second thing I do increase the value of the global feedback resistor slightly... This will give it just a bit more air and make it breath a bit better without being clinical... of course I mean just a little bit or else you will increase distortions..
Of all the speakers I have tried on the MC amps...such as MC30's, up through MC75's... I find the Vandersteen 2Ci or 2Ce bring out the best in the McIntosh amps....
Regarding the other post discussing the MC75 output transformers...
The first early series of MC75 Outputs, M-212, were more prone to shorting due to the #31 AWG used in the driver winding.... Sidney Corderman at McIntosh made the change to #29 AWG sometime in the mid 60's...
The way to tell if you have the older or newer output is to measure the DC resistance of the winding... The early version will be roughly 50 Ohms per side while the later version is roughly 30 ohms per side.... Or simply double these numbers and measure measure pin#1 to pin#6 of the driver tube for the full winding end to end...
When I wind these outputs I use the same gauge# for all three of the tri-filar windings....this way the wire layers are even and less strain on the wire...The original used 3 different wire gauges and had a very lumpy build of layers..of course I use the largest wire for all three..this would be 15 ohms per side...making all three winding now interchangable.... The only time I would use the original wire gauges is if it is a rewind that needs to match with it's mate ....The MC75 uses just one big C-core...
Chris
There are obviously different types of McIntosh output transformers.
The one I unwound came from an MC275, EI core, bifilar windings for plate and cathode (well maybe bifilar for the first layer...), separate centertapped winding for feedback, no interleaving.
The one I unwound came from an MC275, EI core, bifilar windings for plate and cathode (well maybe bifilar for the first layer...), separate centertapped winding for feedback, no interleaving.
I don't know any of the details of the Mac OT winding technique other than the multi-filar bit, but would like to point out that a high performance OT does not necessarily use machine layer winding. A progressive wind, for example, would look quite random unless you knew what to look for when unraveling it. Carver's OTs apparently use hand wound Pi windings, another high perf. technique that is not layer wound. And there are very high performance insulations now that would allow skipping the layer insulations and still meet UL safety approval. (routinely used in switching supplies)
The real performance indicator of an OT is its resonant frequency, you can not fake that with CFB. I recall the specs I heard were relating to the OT resonance freq. In contrast, the resonance freq on Edcors I have measured were only 30 KHz, totally inadequate for global feedback. I have heard of some high performance OTs that have resonances up in the 100 KHz to 250 KHz region, these are what would be required to use global feedback with good results. C cores (grain oriiented) would certainly be an improvement over standard scrapless E-I, but require the windings to be split on the core sides for high bandwidth (not using two C loops and a winding in the middle). Long E-I laminations, on the other hand, are what were used on most of the very high performance legendary OTs. You don't find them on anything currently made. Also, a split bobbin, with equal windups on each (for P-P), and using primary side crossovers is essential for balance between the two tube phases. This is also very rare on current offerings.
The real performance indicator of an OT is its resonant frequency, you can not fake that with CFB. I recall the specs I heard were relating to the OT resonance freq. In contrast, the resonance freq on Edcors I have measured were only 30 KHz, totally inadequate for global feedback. I have heard of some high performance OTs that have resonances up in the 100 KHz to 250 KHz region, these are what would be required to use global feedback with good results. C cores (grain oriiented) would certainly be an improvement over standard scrapless E-I, but require the windings to be split on the core sides for high bandwidth (not using two C loops and a winding in the middle). Long E-I laminations, on the other hand, are what were used on most of the very high performance legendary OTs. You don't find them on anything currently made. Also, a split bobbin, with equal windups on each (for P-P), and using primary side crossovers is essential for balance between the two tube phases. This is also very rare on current offerings.
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