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WANTED: Futterman H3 OTL project - Harvard Electronics or Tech Instruments

198.144.203.97

Posted on August 7, 2020 at 07:34:42
rogerh113
Audiophile

Posts: 317
Location: San Francisco South Bay
Joined: October 20, 2014
I have now finished a couple of CD player fixes, and am still looking for a Futterman H3 to bring back to life. If you have an old one sitting around, please let me know.

I am looking at it as a chassis, transformer, some tubes, maybe some tube sockets, and the circuit schematic (which I will have to extract from the existing wiring and components). The electrolytics and resistors are well past their lifetime, so a complete rebuild will be needed to bring it up to some level of performance and reliability.

If you step up fast, you may be able to get a Classe CDP-1 or Audio Note AN-CD2 in trade (both are already listed for sale).

regards -- Roger

 

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Why not just get a Atma-sphere amp..., posted on August 7, 2020 at 16:54:57
Charlie8521
Audiophile

Posts: 794
Location: South East Michigan
Joined: October 2, 2004
new or used and be done with the screwing around? State of the art circuit design, high quality components, with factory product support. Just a thought for consideration.

 

RE: Why not just get a Atma-sphere amp..., posted on August 8, 2020 at 07:11:36
rogerh113
Audiophile

Posts: 317
Location: San Francisco South Bay
Joined: October 20, 2014
Sometimes the journey is as entertaining as arriving at the destination.

The Futterman is interesting by way of circuit design, and if it sounded very good with vintage components, I am curious to hear how it sounds with more modern (less vintage) components. For me, this would also be a learning experience as I go through the amp.

I am certainly not taking anything away from Atma-sphere. I have heard they are wonderful amps. You could say they are the same, as they are both OTL, but they are also very different.

 

Well then, why not jump in with..., posted on August 9, 2020 at 09:56:28
Charlie8521
Audiophile

Posts: 794
Location: South East Michigan
Joined: October 2, 2004
both feet. Build one from scratch. I would think you could get someone like Heyboer Transformer to build the Power Transformer, get a schematic with all of the recommended changes, and then utilize high grade components and wiring. Everything brand new, and it would be an experience with something in the end to talk about for years.

 

RE: Well then, why not jump in with..., posted on August 10, 2020 at 07:52:20
rogerh113
Audiophile

Posts: 317
Location: San Francisco South Bay
Joined: October 20, 2014
I have actually considered that, but there are a couple of reasons I opted not to go that way.

I have built a large tube amp from scratch, and enjoyed it a lot. There is a LOT of work in properly setting up the chassis. I simply am not so interested in doing that again. I do enjoy component sourcing, wiring, and learning about circuit operation, and would prefer to concentrate on that. At close on to 67, best to spend your time how you like to....

The various Futterman implementations seem to have variation from amp to amp, and not just the tube complement. Taking a working (or at least formerly working) example at least gives me a functional starting point.

 

OK, maybe post an Ad..., posted on August 10, 2020 at 11:31:35
Charlie8521
Audiophile

Posts: 794
Location: South East Michigan
Joined: October 2, 2004
on the AudioAsylum Trader section, Wanted Futterman. Or do the same on Audiogon site. Good luck in your quest.

 

RE: Why not just get a Atma-sphere amp..., posted on August 10, 2020 at 12:35:28
airheadair
Audiophile

Posts: 371
Location: California
Joined: October 18, 2010
I can say that the NYAL OTL3 sounds fantastic with Stax F83 speakers. But these are probably "vintage" components now. Interestingly, they run rather cool, compared to what I have heard about the Atmosphere amps. As you say, the circuit is very different. Some people prefer one, some the other. It probably depends also on the application.

 

Jon Broskie says they are the same, posted on August 14, 2020 at 11:54:37
Lew
Audiophile

Posts: 10406
Location: Bethesda, Maryland
Joined: December 11, 2000
If you read Tubecad, Broskie, who doesn't shy away from making provocative generalizations, says the circlotron and the Futterman output stages are fundamentally the same. I personally cannot see how that could be true, but I'd love to see Ralph's take on the idea. My last pair of Futterman amplifiers were Prodigy amplifiers, out of Texas. They sounded excellent driving the Sound Lab M1s I owned at that time (early 90s). Arguably, the Sound Labs are "modern". However, they presented a booby trap for either type of OTL, there was a very low impedance dip at midrange frequencies, as low as 2 ohms at between 1kHz and 2kHz. Neither Futterman nor circlotron is happy with that load at those frequencies.

 

RE: Jon Broskie says they are the same, posted on August 14, 2020 at 13:50:03
airheadair
Audiophile

Posts: 371
Location: California
Joined: October 18, 2010
The Stax F83's have a strange impedance curve: about 4 ohms at both frequency extremes, about 160 ohms in the middle. I now use a subwoofer for the bass (crossing over at 100 HZ), so that part of the story is out of the picture. I guess the remaining high impedance makes up for the very low efficiency, making the NYAL OTL a good match.

 

Heard it before., posted on August 18, 2020 at 10:11:07
Ralph
Manufacturer

Posts: 3931
Location: Minnesota
Joined: April 24, 2002
But its not the case. You get a little bit lower output impedance with a Circlotron, and you certainly get to use a lot more intuitive circuit to drive it :)

But you're right, he likes to be provocative.

 

RE: Jon Broskie says they are the same, posted on September 21, 2020 at 07:58:48
cpotl
Audiophile

Posts: 947
Location: Texas
Joined: December 6, 2009
"If you read Tubecad, Broskie, who doesn't shy away from making provocative generalizations, says the circlotron and the Futterman output stages are fundamentally the same."

That's not quite what he says. His whole point in that article is that what really matters, when you analyse the circuits, is where the signal reference point is in the output stage. As he says, the signal ground reference point is different in the circlotron and in the totem pole, and so they behave differently. However, he also points out that with a small change in how the ground reference point is set (by taking the signal ground to be at the midpoint between the two speaker terminals rather than at one end), then the totem pole would become operationally equivalent to the circlotron. I think that is an uncontroversial point.

 

Thanks for the correction,,,,, posted on October 10, 2020 at 13:58:03
Lew
Audiophile

Posts: 10406
Location: Bethesda, Maryland
Joined: December 11, 2000
Perhaps I faded out before completely comprehending Broskie's thought on this subject. As an OTL devotee, I want to understand it, so I will search it out and re-read it.

 

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