PASS 50W single ended mosfet amp.

[Cressy Snr]

These buggers ought to drive your Quads beautifully.

[pre65]

These buggers ought to drive your Quads beautifully.

Hopefully.

Although when I took them to Owston in 2017 (with the baffles) no one seemed at all interested in them.

[Cressy Snr]

Whaddya expect?... They're TRANSISTORS! (horrors)

Solid state is fine though. My NVA clone is going to Owston and Ed has some interesting SS gear to show, I think. Then there is the terrifyingly expensive Soulution thingy, so you never know ....

[pre65]

Oh the heat !!!!

Anyway, finally got both A & B tested, and now set up in the system with the ESL57s.

I'll need a few hours to get a firm opinion, but first impressions are good.

PS For Eds edification, can't hear the two cooling fans.

[pre65]

Well, after a few hours testing I'm happy that these single ended mosfet amps work well with the ESL57s.

They seem to go louder than the GK-71 amps, no surprise really, but a "bigger" sound as well.

Sitting here, with a glass (or two) of chilled crab apple wine, listening to the Lark Ascending.

Sublime.

[pre65]

I've finally managed to get the amps on my rack.

The amp parts are on the bottom shelf, pulled out frontwards so the heatsinks are not covered by the shelf above, and the overhanging front held in place from the floor by supports made from bits of scrap BBP.

Just got to make up slightly longer connecting wires and plumb in the 12v supply for the (silent) cooling fans.

[pre65]

Two steps forward, one step back.

Got everything in position and wired up now. Great sound.

Trouble is now, got a slight hum on both speakers.

I'm sure it's because of the way the amps are now positioned, the curse of racks.

More thought required.

[pre65]

I've had one of the amp portions on the workbench, have moved the input transformer about three inches further away from the power supply, and tidied up the wiring a tad.

I'ts now on test and no hum is noticeable.

Must do the second one now.

[pre65]

Second one done.

However, there is still a little hum, slightly more on B than A.

[pre65]

On the output of these amps is a 10,000uf cap bypassed with a 10uf cap.

Would these be considered as "floating" ?

This question was asked because of a Nick G post on HFS.

Circuit diagram is on page 24, 3rd post down.

[Nick]

Sort of, yes, but the signal level at that point will be large, so its unlikley that its the cap picking up a hum field. Also the output side of the cap is connected to ground via the 8 ohm of the speaker.

[pre65]

I need to make it easier to couple the two parts of each monoblock together to

A) Minimise floor space.

B) Eliminate transformer field caused hum.

Then they would be easier to set up and use. I'd like to bring them to the next Owston.