How good is the McIntosh MC-2300 vs modern SS amplifiers?

HI George,

I have not listened to one but I like the circuit, especially for its day when Phase Linear and Crown were the alternatives. I just appreciate a good design for the parts that were available at the time. Transistors have come a long way since then. This amp used a MJ15001 series part. Although they could have used the compliment they went with same sex devices. Its a really clever design,

As far as I know The Dead bought all those amps. There is even a story where they took a helicopter and $6000 to pick up some amps at the factory on a Sunday.

Did it really sound that bad? Anyone else heard one?

I was hoping someone would compare the fine engineering of this amplifier compared to what Phase Linear, Crown, Quatre and otheres were doing at the time. 

Auto transformers made this design extremely relaible. Ive never been a Mac Man but I have to appreciate good design when I see it. I don't like everything they build and I have worked on much of it. Their preamps have too many buttons in the signal path. But if kept clean they are not a problem.

I just wanted to share my discovery with others who might also appreciate it. In an earlier thread there were posts that called the autotransformer a bandaid for a poor design. It is the essence of this design. Anyone who understands safe operating area of transistors will appreciat this. Most amplifiers that fail are due to engineers who do not. Mac knew.

How an amplifier sounds is subjective and may depend as much as someones mood, their perception of value and cost and build. 

George, I respect your posts here. However you are comparing the Gryphon on Wilsons to the Mac on what speaker? How many years between the comparisons? How many years between the amplifier designs...50 Years!

Do readers here know that almost all modern SS amps are a basic op-amp circuit done over and over again with fancier metal, more capacitors, where are we going with this?

I built many solid state amps in my youth, not knowing of the AutoTransformer Macs. But then I was just a child. I did however get a firm understanding of how transistors fail and the circuits necessary for them to be protected against shorts and reactive loads. I learned about safe operating area (SOA). I saw that at the voltages required just to make a 100 watt amplifier would intrude into the SOA of all power transisitors and still does. So the designer has to protect the transistors. I found most of the protection schemes would cause premature clipping into reactive and low impedance loads. 

When an amplifier sounds very bad on a particular speaker and good on others I contend it is misbehaving into that load. Two common examples are current limiting (load line limiting) and outright instabilitiy usually in the form of birdies (small HF oscillations on the wave that look like a bird on a wire). Birdies sound like the worst kind of clipping, yet the amp may be far from clipping. 

This concept of matching speaker and SS amplifier appears to be misunderstood and a bit overrated. As stated above the particular speaker may make the amplifier unhappy. If the amplifier is happy then one may consider impedance variations that are exaserbated by high output impedance. 

If I were to make SS amps I would like likely use autoformers because:
  
1. I know how to make them
2. They allow me to use the full rating of the transistors.
3. They allow me to use same sex transistors
4. They protect against DC faults
5. They present the optimum load to the amplifier via their taps

Can we agree that good amplifiers drive a large number of speakers very well and changing to another "good" amplifier will drive the chosen speaker just as well? These amplifiers have certain common characteristics that make them sound very similar on a wide variety of speakers. 

Can we further agree that some amplifiers have (rather undesirable) measurable characteristics that will make a given speaker sound uniquely different on this amplifier. And though we might like the coloration this combintion produces, it is not what the speaker designer had in mind? 

If the right amp has to be found for just some one speaker, I would say that is a bad amplifier waiting to find a home. How is one to find this perfect match?  How many of these colored amplifiers would one have to audition? Take the current OTL amps which all have high output impedance. They can properly drive less that 10 % of the speakers out there. How about an OTL that can drive a wide variety of speakers properly?

How about an OTL that can drive a wide variety of speakers properly?


No such thing, unless you stick an autoformer band-aid on it for the hard to drive ones. Then you ruined the whole advantage of the OTL design and what it can do.
Your better off getting one of your amps to do the job if you wish to stick with tubes, or putting a proper output transformer on the OTL, again a backward step to what an unhindered OTL is capable of giving with the right speaker.

Here is an interesting story that happend to me. Jim Jordan, the designer of Vaughn speakers fell in love with the Wavelength 300B Cardinal with silver transformers and all. Big bucks for a 7 watt amplifier. This amplifier has rather low damping, but within its power range I assume it to be a good amplifier. He named his speaker after the amplifier. In this case the amplifier came first and he designed a speaker he felt worthy of it as other speakers he tried were not.

https://www.vaughnloudspeakers.com/story

Then he met me, actually I went to his house to hear his speakers. I took along a rough prototype of my OTL for him to hear. Somehow he convinced me to make one for him and one for his customer in stereo on a nice chassis. Now he uses my AUTOFORMER OTL all the time. It has very low distortion very low output impedance. It is of the Futterman School which always has low output impedance. Mine only two output tubes, triode connected, and one driver tube per channel. Most OTLs have 6-12 output tubes per channel. Lots of heat, lots of matching.

The autoformer has no special materials, I make them of standard copper magnet wire and M6 Iron. It is very small, costing a fraction of a silver 300B transformer. It is partially in the feedback loop or not, as desired. Id does effect the sound and Jim moves it from time to time for different listening. He likes the subtle changes it makes.

I wound 4, 8, 16 ohm taps and 32 ohms is direct output. At 32 ohms the amplifier puts out 30 watts into a 32 ohm load. An 8 ohm load connected to the 32 ohm tap produces 3 watts because the tubes can only provide that much current (about 1 amp). But any load connected to its proper tap will put out 30 watts. To my suprise the Autoformer extends the high frequency frsponse from 120 KHZ direct to 160 Khz using the 8 ohm autoformer tap into an 8 ohm load, or 4 into 4, etc. All the taps produce the same results into their specified load.

I arrange a feedback wire on a lug and tell the user to move the feedback wire to whichever tap they are using so the feedback is always on the tap looking right at the speaker. Sometimes the put it on a different tap and like that better. Its all good, the amp is stable and happy.

In closing the SA-6 I deisgned for Counterpoint and the large Futtermans will drive a wide variety of speakers with 100 watts per channel with very low distortion and high damping. Keep in mind that the Circlotron amplifiers are an entierly different animal. They do not have low output impedance of a lot of current. All OTLs are not the same

I invite George and others to take a little time and learn about the Futterman style amplifiers and then say something. Little by little I will get around to all of it, but it took me years to fully appreciate his work, the man was very smart and I am happy I got to spend an afternoon in his shop. 

So what your saying is an amp that can drive the Wilson Alexia’s known impedance of down to 0.9ohm is a bad amp?????

No you’ve got that arse about face, the speaker is the problem being too hard to drive and the amp that can do it is a great amp, and will not only drive it but anything else as well. Definitely not a bad amplifier waiting to find a home.

Cheers George

I hope I didn't imply that. An amplifier that drive 0.9 ohms would be a very good amp if all other things were up to snuff. There are lots of both good an bad ways to drive an ohm.

Speakers are the designer's sonic goal, his taste, his dream. In many cases he doesn't care how he gets there. Some care and some do not care about the difficulty of their load, not their problem. I would suspect most people who are serious about speaker design have good rather universal amps with high damping, lots of current and voltage. Why wouldn't they? Therefore if you buy their dream you had better ask its characteristics or how they drove it. 

On the other hand if someone is interested in 300B amps, like Jim Jordan, the speaker choices are limited and one is playing in an entirely different field which is not universal but has limitiations. Here the speaker/amplifier interactions are going to be important, obvious and likely hit you in the face like the Circulatron that produced a 8 db peak at 50 Hz and a marked loss of highs in my QUAD 63. The 8 dB peak surprised me so much I got a oscillator and meter and measured an 8dB rise at the speaker terminals at 50 Hz and many dB fall off about 400 Hz. The 63 was not longer Mr. Walker's 63.

In the  HI FI world some people design speakers that are hard to drive, yet there are many amps capable of driving them. At a wide range of prices. So what is all the fuss about? 

However what do we do with amplifiers that have high output impedance and limited current? People buy lots of them.

May I remind all that the topic of this thread is about what an autotransformer can do for matching the load to the amp. Whether or not a Gryphon sounds better than the old Mac is not the issue and certainly not the money which few can afford. I also find it odd that Gryphon is not in Stereophile Rec Components, nor could I find a review or any mesurements. If someone has a link I would love to see this amp's performance. Perhaps is all just a pretty face.

Well EXCUSE ME (Steve Martin). I guess its too much to ask to clean the pots of a 40 year old amplifier. FYI dirty pots can cause lots of contact (diode) distortion. You must have some very nice looking MIG welders. how do they sound?

How impartial of you to listen to and judge an amplifier that obviously has dirty pots. Any amp of that many years deserves a full checkout and bench test given its age. I have measured distortion go down by 100x just cleaning a pot. It also deserves respect for still working.