Levinson ML-3 mono parallel configuration

[BrianEno]

Could I safely make out of two Levinson ML-3 stereo amplifiers two mono-amps by shorting the left and right speaker output binding posts and drive them with the two outputs from a Levinson ML-7preamp? (Two left connections two one amp and the right to the other) Or should I be worried about DC offset differences between the to shorten channels, gain differences and/or feedback problems?

Is it maybe saver to bridge them or would that induce other problems with something like instability/oscillation in the high frequencies of mt Acoustat model 2 + 2 electrostatics.

Thanks in advance for "feedback"

[Dang. Amateur]

No, you can't short the outputs together! Each amp would see the output impedance of the other, which in a high-damping factor amp is practically zero. I don't know enough about it to tell you what to do otherwise. Some amps can't be bridged. If I were you I would try to get the manufacturer to answer the question.

[PAM]

Look in the manual of No 29. (You can download it) or other power amps.
There is a chaper about bridging power amps and how to connect it to the preamp
Maybe in the manual of the No 3 too

I think it is possible.

[PAM]

No 23.5 27.5 29 331 332 333 334 335 336 can all be bridged.
See manuals.

[Nelson Pass]

If you can trim the output DC offset and the gain to be equal,
you probably can do it, but to be on the safe side, I would
put about a .22 - .5 ohm power resistor in series with each
output before they are paralled also.

Perhaps John Curl would further enlighten us.

[BrianEno]

Originally posted by Nelson Pass
If you can trim the output DC offset and the gain to be equal,
you probably can do it, but to be on the safe side, I would
put about a .22 - .5 ohm power resistor in series with each
output before they are paralled also.

Perhaps John Curl would further enlighten us.

DC offset can be trimmed internal and gain can be finetuned at the balancepots of the ML-7. I'm mostly worried about the feedback I mean that the feedback circuits from the paralled channels are going to errorcorrecting eachother.
The only statement I can find about the use of feedback with this amp that large amounts of feedback are unneccesary due to the use of selected discrete components, for what is worth. In a German publication from september 1980 ("Hifi Exklusiv Nr. 9) a pair of Threshold Stasis 1 is compared with a ML-3 were the Thresholds are designated as the NFB (globally) type of amp.

Bridging would be an alternative (easier to manage when I had a balanced output at the ML-7A) but as said I'm worried about the low impedence at high frequencies.
The No. serie of Levinson have allready balanced inputs and only the ML-2 had as only member from the ML (MLAS) serie XLR's so it was possible to bridge two ML-2 for 100 Watts instaed of 25 Watts at 8 Ohms. The Threshold S/1000 was also a bridged amplifier as I recall and John Soderbergh had his reservations about the stability with electrostatic loudspeakers. A pair of S/1000 Series II I had was converted to SA/1 so was converted from a bridged to a massive parallel configuration.

So I think that amps with no global feedback circuit that calls upon the predriverstage to correct errors at the output stage like Thresholds and Rowlands are maybe saver to convert in a mono parallel configuration then Levinson's and/or maybe Krell's from that era that use more feedback.

[BrianEno]

In a German publication from september 1980 ("Hifi Exklusiv Nr. 9) a pair of Threshold Stasis 1 is compared with a ML-3 were the Thresholds are designated as the NFB (globally) type of amp.

That must be NON NFB for the Stasis 1 of course

I'm not sure if John Curl was responsible for the basic design of the ML-3. Could be Tom Colangelo also or some construction like the JC-3/ML-2.