OTL amp owners

Ron Resnick

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Duke LeJeune

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This is incomplete imo as OTLs have other idiosyncrasies. See the common recommendation of Speltz autoformers in order to increase speaker impedance (which can't be 100% transparent of course). OTLs are often lacking in bass too. So is this complete neutrality? Not so sure.

Every time I have been able to examine in detail a situation where an OTL amp was introduced into a system and the results were disappointing, I have found a plausible explanation in the speaker's impedance curve.

We must consider that OTLs have high output impedance and some speakers have very severe dips in the impedance in the bass frequencies - this can create dips in bass response. Some speakers are adequate for OTLs, some are not. XLF's are good candidates ...

Excellent points.

Compared to a voltages-source amp (most solid state amps), an OTL will deliver more power into an impedance peak and less power into an impedance dip.

So... OTL amps (and any high-output-impedance amps) will deliver more power into the bass peak(s); less power into the typically fairly broad upper-bass/lower mid impedance dip (ime this explains cases of "leanness"); and more power into impedance peaks associated with the crossover region. The net result can be an unacceptably colored frequency response if the speaker's impedance curve is a poor match for the amplifier. This is why, in my opinion, the amp manufacturer and/or speaker manufacturer should be consulted about compatibility before money changes hands if OTL (or SET) amps are involved.

It is not too difficult to design a speaker for compatibility with an OTL amp, but you have to keep one eye on the impedance curve in the design stage so that you don't paint yourself into a corner. Fortunately OTL amps tend to be more powerful than SET amps, so extremely high efficiency generally isn't as essential. I design for OTL amp compatibility and my efficiencies are typically in the lower 90's.

I can't speak to other OTL designs, but Atma-Sphere offers noise-floor-lowering options for users with extremely high efficiency speakers. I have a friend who has been driving his outrageously efficient Avantgardes with Atma-Sphere amps for close to two decades.
 
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CKKeung

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Every time I have been able to examine in detail a situation where an OTL amp was introduced into a system and the results were disappointing, I have found a plausible explanation in the speaker's impedance curve.



Excellent points.

Compared to a voltages-source amp (most solid state amps), an OTL will deliver more power into an impedance peak and less power into an impedance dip.

So... OTL amps (and any high-output-impedance amps) will deliver more power into the bass peak(s); less power into the typically fairly broad upper-bass/lower mid impedance dip (ime this explains cases of "leanness"); and more power into impedance peaks associated with the crossover region. The net result can be an unacceptably colored frequency response if the speaker's impedance curve is a poor match for the amplifier. This is why, in my opinion, the amp manufacturer and/or speaker manufacturer should be consulted about compatibility before money changes hands if OTL (or SET) amps are involved.

It is not too difficult to design a speaker for compatibility with an OTL amp, but you have to keep one eye on the impedance curve in the design stage so that you don't paint yourself into a corner. Fortunately OTL amps tend to be more powerful than SET amps, so extremely high efficiency generally isn't as essential. I design for OTL amp compatibility and my efficiencies are typically in the lower 90's.

I can't speak to other OTL designs, but Atma-Sphere offers noise-floor-lowering options for users with extremely high efficiency speakers. I have a friend who has been driving his outrageously efficient Avantgardes with Atma-Sphere amps for close to two decades.
Hello Duke,
Does the principle apply also to OTL headphone amps?
Thanks.
 

Duke LeJeune

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Hello Duke,
Does the principle apply also to OTL headphone amps?
Thanks.

Yes the same principle applies, but without knowing the specifics I couldn't say whether it's a significant consideration or not... I'm not a headphones guy, so I don't know what sort of amplifier output impedances and headphone input impedances we're talking about.
 

Kcin

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Futterman H3 with ESLs

IMG_1802.JPG
 
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DetroitVinylRob

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Atma-Sphere MA1 Mk.3.3 OTL Silver Edition mono blocks

Classic Audio T-3.4 fully field-coiled

With that and the Atma-Sphere MP1 3.4 this is the best sounding music machine I have ever owned. Ah...
 

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microstrip

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Atma-Sphere MA1 Mk.3.3 OTL Silver Edition mono blocks

Classic Audio T-3.4 fully field-coiled

With that and the Atma-Sphere MP1 3.4 this is the best sounding music machine I have ever owned. Ah...
Great system. What are the differences between MP1 mk3.4 and the mk3.3?
 
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LL21

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Atma-Sphere MA1 Mk.3.3 OTL Silver Edition mono blocks

Classic Audio T-3.4 fully field-coiled

With that and the Atma-Sphere MP1 3.4 this is the best sounding music machine I have ever owned. Ah...
Great system!
 
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DasguteOhr

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I think that must be fun ;)otl driven quad esl 57
 

BruceD

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Yes the first time I experienced the Superb Atma-Sphere OTL's was at this dear friend's house--also Stacked Quads with Entec Woofers.

The sonic presentation I still recall to this day.

Kudos indeed :)

BruceD

Magnan1.jpg
 

DasguteOhr

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With a second Stacked Quad you add + 6dB at bottom and+3 dB overall.
Alone one One Esl 57 mesasurment
QUAD2-FRQ.gif

Stacked Quad esl57 two each side
DBLQ-FRQ.gif

Here comes the Trick you add no woofer, you add another quad of course only the bass panel of a quad esl 57 like in the video.
Then you have a real fast and deep playing Speaker.
If like you can add a Supertweeter,i have seen some use Mark Levinson ribbon tweeter finished is great speaker.;):cool:
P.S bass panel can also stand behind it does not matter
 
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BruceD

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What year? Looks like 1978?
Ha!-- the owners would not know whether to laugh or cry--but I did spare a chuckle :p

No, that pic was actually --I think 1990/91--Ralph would possibly know the setup and the Gentleman pictured.

I spent some great listening sessions there!

Incidentally not 78 but 1981 when I was on a working stint in NY I caught up with an old buddy ,John Syder he was working with Dr Gizmo on the

NYAL OTLs --we had some top listening sessions --one especially, when we visited Stew Hegeman in his studio and spent the day musing with him

on his work on the Citation Amps and his unusual speaker ( if I recall the cone, I think an 8inch faced upwards )listening to his wonderful

Westminster Master tapes he produced.We heard his Hapi one Phono pre--I bought it;)!

Fun times,

BruceD
 
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tima

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Had not seen this thread until its resurfacing in the last few days.

I've had a nice amount of time with Atma-Sphere gear and a few weeks with David Bernings big Quadrature Z's. Others can debate if the latter is an OTL but they were the most resolving amps I've ever heard - they will tell that Dusty brushed with the Ipana, not the Colgate.

The Atma-Sphere M60s were in-house for several months and I wrote about them here. I owned a pair of MA-1 mk3s and wrote about them getting upgraded to 3.1 status. I owned the MP-1 mk3.1 preamplifier (a true preamp !) and wrote about it here.

I used the Atma-Sphere gear with my Audio Physics Avanti Century speakers and with the original Wilson Sasha - with and without Paul Speltz's autoformers. No doubt there are nay-sayers and technocrats wrt the Wilsons, but the reality was the MA-1 + MP-1 combo was surprisingly satisfactory with them. Together they presented information from LPs that neither ARC 250SE monoblocks, C-J Premier 140 nor Lamm M1.2 monoblocks did not.

P1000751.JPG
ooooo, aahhh -Two 7-inch woofers! My pre-Mahler days.

Atma-Sphere_MA-1_Tim_4.jpg
Only 10 years ago - it sure seems a lot longer than that.

Atma-Sphere_MA-1_Tim_6.jpg
Super good point-to-point wiring from Ralph's shop.


MP-1 Volume Control.jpg
Want to know if your preamp is a true balanced design or one that just converts signal from XLR inputs to single-ended and back? Check if its volume control is a true four-pole device. That's the MP-1 above - hand built, lovely workmanship.
 
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microstrip

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Had not seen this thread until its resurfacing in the last few days.

I've had a nice amount of time with Atma-Sphere gear and a few weeks with David Bernings big Quadrature Z's. Others can debate if the latter is an OTL but they were the most resolving amps I've ever heard - they will tell that Dusty brushed with the Ipana, not the Colgate.

The Atma-Sphere M60s were in-house for several months and I wrote about them here. I owned a pair of MA-1 mk3s and wrote about them getting upgraded to 3.1 status. I owned the MP-1 mk3.1 preamplifier (a true preamp !) and wrote about it here.

I used the Atma-Sphere gear with my Audio Physics Avanti Century speakers and with the original Wilson Sasha - with and without Paul Speltz's autoformers. No doubt there are nay-sayers and technocrats wrt the Wilsons, but the reality was the MA-1 + MP-1 combo was surprisingly satisfactory with them. Together they presented information from LPs that neither ARC 250SE monoblocks, C-J Premier 140 nor Lamm M1.2 monoblocks did not.

View attachment 75170
ooooo, aahhh -Two 7-inch woofers! My pre-Mahler days.

View attachment 75166
Only 10 years ago - it sure seems a lot longer than that.

View attachment 75167
Super good point-to-point wiring from Ralph's shop.


View attachment 75169
Want to know if your preamp is a true balanced design or one that just converts signal from XLR inputs to single-ended and back? Check if its volume control is a true four-pole device. That's the MP-1 above - hand built, lovely workmanship.

The Atmasphere's are great sounding amplifiers - and the factory upgrade policy is one of the best in the audio industry.

If it was not for the 1600W idle of the MA2 pair I would surely still own them. And once we try the MA-2's we do not want MA-1's - the MA-2's are a class apart. I would love to listen to them with the Vivaldi stack - in my experience it smells a great match!
 
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Ron Resnick

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Thank you for posting those photos, Tim!

What drove the switch from Atma-Sphere to Lamm?
 
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DetroitVinylRob

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Great system. What are the differences between MP1 mk3.4 and the mk3.3?
Oops. I believe that’s a typo, should be Mk.3.3. Nice catch
 

morricab

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The Atmasphere's are great sounding amplifiers - and the factory upgrade policy is one of the best in the audio industry.

If it was not for the 1600W idle of the MA2 pair I would surely still own them. And once we try the MA-2's we do not want MA-1's - the MA-2's are a class apart. I would love to listen to them with the Vivaldi stack - in my experience it smells a great match!
That is ultimately what led me to sell my Silvaweld OTL reference monos...the heat... oh boy the heat! Also a real pain to keep biases correctly.
 

DetroitVinylRob

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OTLs in the great white north make a home cozy.
 
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