2. amps-preamps
  3. 128359-41

Amps Atma-Sphere M-60 Mono blocks OTL design

I just purchased a used OTL Atma-Sphere M-60 mono blocks that I have sent to Atma-Sphere to be upgraded to the current model 3.3 and I also added the option of a higher quality power supply and V caps.

I have sold my old trusted Eggleston Andra 2’s speakers and have built some monitors using Aurum Cantus ribbons (102db) and Aurum Cantus midwoofers (90db) that are both rated as 8 ohm nominal. I have a DEQX Premate and will be crossing over to (2) JL Audio F-113 subs at 80hz.

Currently I am using a solid state high power stereo amp (Pass Labs) that I used with the Andra 2’s.

The Atma-Sphere M-60 is rated at 60 watts class A and is said to work better with higher impedance loads.

It will probably be a few weeks until I get the M-60 and was hoping someone could provide opinions of what to expect.

I listen to late 60 early 70’s classic rock music mostly. Sometimes loud.

ozzy

128x128ozzy
charles1dad's avatar
charles1dad
10,250 posts
 

Hi Ozzy, I certainly acknowledge and give  credit for a well thought out long term upgrade/updating pathway.

Charles

sdrsdrsdr
196 posts
 
Doesn't using zero transformers defeat the whole point of an OTL amp? It's putting  a transformer in and makes it similar to a non OTL push pull tube amp.
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Doesn’t using zero transformers defeat the whole point of an OTL amp? It’s putting a transformer in and makes it similar to a non OTL push pull tube amp.
That’s a logical question, which has been stated here in a number of other threads in the past, but basically the answer is "no." From a technical standpoint the following statements quoted from the FAQ at the zeroimpedance.com site are good ones IMO:
12) What is the difference between the ZEROs autoformer and a typical tube amplifier’s transformer?

The ZEROs have a few advantages over "typical" tube amp transformers:

A) The music comes out on the same winding wire that it goes in on so the music does not have to pass from a primary winding to a secondary winding.

B) There is no DC current to contend with. When a transformer is made to accommodate a DC field, its audio transparence is compromised.

C) The impedance ratio is very small (16 ohms to 4 ohms, compared to a few thousand ohms to 4 ohms). This simply means that it is much easier to achieve things like, frequency response extremes, than with a "typical" tube amp transformer. The ZEROs sport a frequency response of 2 Hz to 2 MHz.

13) Doesn’t adding the ZEROs to my Output-Transformer-Less (OTL) Amplifier defeat the benefits of the OTL design?

The ZEROs were originally designed to maximize the full benefits of the OTL amplifier by changing the speaker’s load impedance to the Maximum Power Transfer Region of the amplifier being used.

The ZEROs are not an amplifier fix, they are a speaker fix. It is a great disfunction to music loving audiophiles for speaker manufactures to be making 4 ohm speakers with 3 or 2 ohm impedance dips, and then expect amplifiers and speaker cables to be able to transfer music into a load approaching a dead short. The ZEROs simply multiply the impedance of the speaker in use, and do it so transparently they provide greater benefits than the "penalty" of an added component.
As I said, from a technical standpoint that all makes sense to me. Basically, all transformers and autoformers are not created equal :-)

Regards,
-- Al

atmasphere's avatar
atmasphere
11,806 posts
 
Doesn't using zero transformers defeat the whole point of an OTL amp? It's putting  a transformer in and makes it similar to a non OTL push pull tube amp.
'Defeat' as used in the question above suggests that an OTL is trying to do something that is somehow in opposition to a normal amp with a transformer?

It isn't. What we are trying to do is get as close to the music as we can.

The fact is that the ZERO has a very low turns ratio. Because of this it has very wide bandwidth- wider than almost any amplifier made, tube or solid state. You can't do that with a regular tube amp with an output transformer. You need to start with an amp that already has a fairly low output impedance, and a circuit that is not putting DC through the transformer winding.

The ZERO is really a problem solver- for example, here in Minnesota a lot of people want to use the M-60 with Magnaplanars. Usually they have smaller Maggies, but the M-60 is usually challenged when presented with a 4-ohm load. The ZEROs fix that and you don't loose the transparency of the amp. My rule of thumb is that when using the ZEROs you don't encounter any serious sonic tradeoffs. If the amp sounds better without the ZEROs then you just don't need them.

I think its better if the amp doesn't need the ZEROs. That usually means the speaker load is 8 ohms or more as in the case of ozzy's speakers.
bdp24's avatar
bdp24
9,792 posts
 
Too bad more Maggie lovers who want to drive them with M-60's aren't aware of the Eminent Technology LFT-8b loudspeaker. It like Maggies is an inefficient planar-magnetic design, but the LFT-8's impedance is nominally 8 ohms, and if bi-amped the m/t panel (frequencies below 180Hz are handled by a sealed-enclosure dynamic woofer) has an impedance of 12 ohms, much better for a tube amp than the 4 ohm Maggies.
More to discover