Another MoFo

[pre65]

I'm still very happy with the amps.

The lack of background noise is nice as well, but perhaps solid state amps are like that ?

The only noise is from the 22v transformers, but it's only noticeable close up. There are a couple of mods to try and negate, or diminish that noise which I will implement next time the amps are on the operating table.

[izzy wizzy]

The lack of background noise is nice as well, but perhaps solid state amps are like that ?

Another satified MoFo owner which must be nice.

Your statement above made me curious. Can you explain more?

[pre65]

Well, it seems (to me) quite difficult to get a valve amp totally silent. Perhaps it's the way I build things ?

Anyway, having silence when silence is needed, seems good to me, and a lower noise floor means quiet detail is not obscured.

The a cappella discs I have played recently really do show off human voice at it's best.

[pre65]

I've finally got round to getting more gain into the MoFo amp.

I have got a cheapie Chinese ( ) valve pre amp, and I have inserted that between my main pre amp (Audionote copy) and the MoFo.

Not quite sure about the quality, but got volume galore now.

[pre65]

Now I have two proper chokes for these amps, I suppose it's only fair to install them and see if I like what they do.

I'd forgotten how to set the choke current, but re reading the original paperwork has refreshed my memory. It says bias the "big" version at 2.5A, but I seem to think I went up to 3A on mine, but I can check that before removing the MOT's (microwave oven transformers).

[pre65]

I've swapped over the new chokes.

I've set up the voltage to 1.7V, which is under 3A (not a lot) and time for testing.

A quick play reveals they make a noise, but I can't do a proper test at the moment.

I'll leave them to warm up and check the voltage again.


EDIT.

Playing a bit of Dean Martin to start with. Expectation bias would want me to say they are a vast improvement, but nevertheless, to me, they are "more listenable", and the lower notes seem a smidge more distinct but still integrating with everything else.

I need to vary my listening material to get a broader view.

[Nick]

I've set up the voltage to 1.7V, which is under 3A (not a lot) and time for testing.

Just checking, how did you measure the choke DCR accurately enough to know the current with any certainty.

[pre65]

I've set up the voltage to 1.7V, which is under 3A (not a lot) and time for testing.

Just checking, how did you measure the choke DCR accurately enough to know the current with any certainty.

Well, to be honest I didn't.

I relied on the manufacturers spec and our Ed saying they measured up well.

At 1.7V the chokes remain cool, and the heatsinks are getting warmer.

[simon]

Ay 1.7V the chokes remain cool, and the heatsinks are getting warmer.

1.7V or 17V Phil? Or have I misunderstood?

[simon]

I need to vary my listening material to get a broader view.

(Just in case our Dave isn't about)

[pre65]

Ay 1.7V the chokes remain cool, and the heatsinks are getting warmer.

1.7V or 17V Phil? Or have I misunderstood?

1.7V across the choke DCR, set by varying P1 (20K) on the PCB.

The toroids I use are 22V.

[ed]

I relied on the manufacturers spec and our Ed saying they measured up well.

I measured mine, not yours.

[simon]

Ay 1.7V the chokes remain cool, and the heatsinks are getting warmer.

1.7V or 17V Phil? Or have I misunderstood?

1.7V across the choke DCR, set by varying P1 (20K) on the PCB.

The toroids I use are 22V.

Ah okay. With you discussing voltage rather than current through the choke I wondered if you were referring to V+.

[pre65]

I relied on the manufacturers spec and our Ed saying they measured up well.

I measured mine, not yours.

Yes Ed, I realise that.

[ed]

there are a confusing number of mofo threads on the go at the mo. It's difficult to know where to add stuff...but I'll plump for this one as it has a meaningfull title....

Simon's boards took 8 days from order to delivery...mine took 20 days. Considering all the reports of lockdown in China I think that may be a result....anyway, these arrived this morning....

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