Jwm, just for the record, all ESLs have an input matching transformer. So if you used a set of ZEROs with a transformer coupled amp you would be passing the signal through three transformers if you were using ZEROs.
Even though we are an OTL manufacturer, (IOW if I say so myself) the use of the ZEROs **does not** defeat the purpose of the amps! A transformer like the ZERO would not even be possible if you did not also start with an amplifier that already has a low output impedance, since the ZERO loads the amps at 16 ohms.
Because of the very low turns ratio, the bandwidth of the autoformer is from 2Hz to about 2MHz- wider than almost any amplifier made. Even transistor amplifier manufacturers report that their amps sound better driving 4 ohms through the ZEROs rather than direct. The lesson here seems to be that while a transistor amplifier might double its power while driving 4 ohms, that is not the same as saying it sounds its best while doing so.
The same is true of tube amplifiers- the ZEROs can be regarded as a problem solver or assistance to any amplifier that has to drive a low impedance (so long as that amplifier does not make power too excessive for the ZEROs). So, it would be one thing if only OTLs benefit from ZEROs, but when **all** amplifiers do, its hard to say that they defeat a purpose :)
In the case of the MA-1s, they are a big enough OTL that it is hard to say if the ZEROs will help. Certainly with M-60s they do- the later Quads tend to have a generally lower impedance curve than the earlier 57s and 63s (which don't seem to need the ZEROs).
Have a Happy New Year!
Even though we are an OTL manufacturer, (IOW if I say so myself) the use of the ZEROs **does not** defeat the purpose of the amps! A transformer like the ZERO would not even be possible if you did not also start with an amplifier that already has a low output impedance, since the ZERO loads the amps at 16 ohms.
Because of the very low turns ratio, the bandwidth of the autoformer is from 2Hz to about 2MHz- wider than almost any amplifier made. Even transistor amplifier manufacturers report that their amps sound better driving 4 ohms through the ZEROs rather than direct. The lesson here seems to be that while a transistor amplifier might double its power while driving 4 ohms, that is not the same as saying it sounds its best while doing so.
The same is true of tube amplifiers- the ZEROs can be regarded as a problem solver or assistance to any amplifier that has to drive a low impedance (so long as that amplifier does not make power too excessive for the ZEROs). So, it would be one thing if only OTLs benefit from ZEROs, but when **all** amplifiers do, its hard to say that they defeat a purpose :)
In the case of the MA-1s, they are a big enough OTL that it is hard to say if the ZEROs will help. Certainly with M-60s they do- the later Quads tend to have a generally lower impedance curve than the earlier 57s and 63s (which don't seem to need the ZEROs).
Have a Happy New Year!