Air Tight ATM 1 and 4 ohms
 

Hi, any know if this model ATM-1 can work with 4 ohms speakers ?

What speakers are you thinking of ?

I've heard them with Sonus Faber's and there was no issue at all.

Yes -- the ATM-1 sample I saw years ago had both 4 & 8 ohm taps.

As for the ATM-1S -- it only has 1 tap -- John Atkinson said in his measurements overview that the amp appears to be optimised for 4 ohm loads:

Air Tight ATM-1S power amplifier Measurements | Stereophile.com

thank you :yes:

Greetings from Berlin,

the Air Tight ATM1 had output tabs for 4 ohm and 8 ohm.
The newer ATM1S has a configuration normally set to 8 ohm. It has only one pair speaker tabs per channel.
But you can change that.
To change the output impedance setting, you have to unscrew the copper bottom plate.
After that you lokate the output trannies.
On the trannies you will see scrips, which let you determine on which of these you will find the 4 ohm tap.
You need now only to soldier the Cables from 8 Ohm to 4 Ohm - all other connection will be untouched.
This means a work for less than 45minutes.
After that your ATM1S is connected and able to work with 4 Ohm Speakers.
The output tabs are now handling 4 Ohms.
If desired, you can also configure the amp to 16 ohms - the Hashimoto output trannies have also for 16 ohms a connection.
But keep in mind - a EL 34 is not a KT88 - means, there are not so many 4 Ohm speakers out there, where I can see a benefit in driving with an ATM1S.
The amplifier has 2X 36w - which is not too much - and it does not like heavy loads.
The 2X36w are also measured with much more than 1% distortion - so in real live it is much less!

A fantastic combination with the ATM1S is for example the LS3 5a with 11 ohm or the older 16 Ohm version, also Harbeth P3 ESR is a very good combination.

Hope I could help - I have 3 Air Tight systems - one with Air Tight ATM1S and ATC1 HQ with the ATH2A Step Up.
The other wit ATM4 (6l6GC) together with ATC2 HQ and ATE2005 RIAA, and finally a setting with ATM2 and modified ATC3 HQ (with Output transformers) and also ATE 2005 RIAA.
Alle 3 systems showing a very different character, and al are fitted with NOS tubes.
If you have any more question, feel free to ask.

Hope this helps

Ekki

PS: The Stereophile test has a lot of mistakes in the description of the amplifier......;-((((