Simple Mosfet SE amp ?

Mike H · Post by **Mike H** » Thu Jun 18, 2009 10:32 pm

Oh right cos it leaves a charge on when you turn it off? Or just takes a long time to go off?

How fast do you want it to discharge?

Otherwise 1mA is fine.

pre65 · Post by **pre65** » Thu Jun 18, 2009 11:23 pm

Yes,I think 1ma should do, just to discharge the caps after switch off.

Thinking about the choke input PSU discussions,is there any reason not to use one on a mos-fet amp ?

The PSU voltage is "only" 24V and 12V at the mos-fet end.

Post by **Nick** » Fri Jun 19, 2009 12:24 am

As MJ points out there is if anything more reason for low voltages. The charging current of cap input supplies can be huge and replacing with a constant flow through a choke should be good. only small values of chokes are needed, and hammond seem to have some high current "reactors" in their range.

pre65 · Post by **pre65** » Fri Jun 19, 2009 9:16 am

Nick wrote:As MJ points out there is if anything more reason for low voltages. The charging current of cap input supplies can be huge and replacing with a constant flow through a choke should be good. only small values of chokes are needed, and hammond seem to have some high current "reactors" in their range.

The one specified in the circuit write up (and the one I use !) is a Hammond 159 ZJ 10mH @ 5 A which Bluebell had in stock.

Will look into the figures (PSUD) after Monkey is finished.

pre65 · Post by **pre65** » Mon Jun 22, 2009 3:12 pm

The front heat sink has been swapped for the ones on the Monkey and the resistor now runs a bit hotter, but not too muchly so.

The bleeder resistor turned out to be 12K which givea a 2ma draw.

Whilst it was on the bench I took the 33uf cheapie cap off and replaced it with a Rifa that was previously used on 832a PP.

The power of these is miniscule,although on the MC2 they dont do bad as the speakers are only 3 ft from my ears. On DTB Sabs at Eggy they struggled to get much loudness without distortion,but they may fare better in Daves living room on Saturday.

Dave the bass · Post by **Dave the bass** » Mon Jun 22, 2009 4:02 pm

Yeah, it was cranked up a bit though weren't it at Eggy, we didn't give it enough time to redeem itself.

Bring it round and we'll see how it sounds.

DTB

pre65 · Post by **pre65** » Sun Jun 28, 2009 2:39 pm

Dave the bass wrote: Bring it round and we'll see how it sounds.

DTB

In action with Daves Subaros they performed reasonably well,so I was fairly pleased.

Andrew I has borrowed them for a while to see how they work at his abode.

andrew Ivimey · Post by **andrew Ivimey** » Sun Jun 28, 2009 2:49 pm

I actually thought they sounded better than Dave and Philip thought.

fast and noticeable attack transients (good for sub bass driving!) oh maybe there was a hint of greyness that we tend to find in SS amps but the clarity was good and the music washed over us in a way like its supposed to do.

andrew Ivimey · Post by **andrew Ivimey** » Sat Jul 11, 2009 12:19 pm

Sooooooooo Philip, having kindly loaned his monoblock simple mosfet monster to me, I set about 'avin'a lissen.

To get me in the mosfet groove, I resurrected my er 'F5', which has a passing resmblance (SWIDT?) to Nelson's design (if you only have one eye, perhaps). This er 'F5' was a kit from Hongkers. It works and over a couple of weeks I have enjoyed it.

But, hands down, Philip's simple mosfet amp beats it. Now its maybe that the er'F5' sounds better with low impedance, with a bit of current, input but against the same Denon CD/FM/amp I used at EggyB and use a great deal of the time (oh the joys of remote control), the simple mosfet sounds much more musical and gutsy than the 'F5'.

pre65 · Post by **pre65** » Tue Nov 24, 2009 9:49 am

The GM70 amps need a couple of minor mods so "simple mos-fet" is now in place in the main system.

Connected to 26 pre the "noise" is not too bad and the resulting combination has pleasantly surprised me.

Now playing "Ladysmith Black Mambazo" CD which DTB introduced me to (thanks again Dave) and enjoying it enormously.

Dave the bass · Post by **Dave the bass** » Tue Nov 24, 2009 10:31 am

My pleasure.

Check this out...

I taught 'em how to dance...

DTB

Post by **Nick** » Tue Nov 24, 2009 2:08 pm

When I read Phils post, the thought of him high kicking filled me with a feeling of dread.

Hmm, "feeling of dread", must go and listen to some Aswad.

pre65 · Post by **pre65** » Tue Nov 24, 2009 2:25 pm

Nowt wrong with my high kicking !

Two gallons of Immac and sheer stockings (Ann Summers) make for an unmissable experience.

Pass the sick bucket

pre65 · Post by **pre65** » Tue Nov 24, 2009 2:31 pm

Dave the bass wrote:My pleasure.

Check this out...

I taught 'em how to dance...

DTB

Here is one of my relations singing with them.

Mike H · Post by **Mike H** » Tue Nov 24, 2009 3:31 pm

pre65 wrote:Nowt wrong with my high kicking !

Two gallons of Immac and sheer stockings (Ann Summers) make for an unmissable experience.

Pass the sick bucket

.

audio-talk

Simple Mosfet SE amp ?

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