Disappointing Audiolab

[Greg.]

But if you alter the operating temperature of mosfets, my understanding is you interfer with their optimum operating point. I thought designs incorporating mosfets include the consideration of operating temperature to establish the values of corresponding components to allow them to work optimally. Sorry, this is probably a bit simplistic, even inaccurate, but I would have thought the addition of external after cooling of a mosfet design would require an understanding on how much hotter than designed the unit was trying to operate at and then a regulation of external fans for cooling to bring them back into their intended operating range. Of course, as I am pretty much an ignoramous on this, what I have written may be absolute rubbish. I’d be interested in any thoughts from someone who knows.

[Black Stuart]

Greg,
I've seen loads of posts about on different forums that state - mosfets are best when run hot. What I've never seen is any empirical evidence to back this up or any empirical evidence to show that when run 'relatively' cool the resulting sound is bad.

It was my Dutch mate Harry that first suggested using a computer fan beneath our hybrid h/amps with the base plate removed.

We listened to the sound of our amps run conventionally and with fan cooling. We both found that the fan assisted cooling gave a slightly liquid sound difference that we both liked.

Just as important it also meant that all components in the amps were operating at a lower temperature. If casings were made to create convection currents then operating temperatures would drop considerably and components would last a lot longer. Of course it's not in their interests to have equipment that lasts and lasts but the diy community should be experimenting.

[Black Stuart]

Just tonight saw that Massdrop is doing an Alex Cavalli designed h/amp @ $250. and designed in - convection cooling,it's about time. It has an ss and a valve section and uses a single 6992 valve.

[Greg.]

Stuart, your post supports what I say. This Massdrop has ‘designed in’ cooling. I hope it has been done taking into account the optimum operating temperature of any transistor being used. My point is that simply using fans to cool an amp where this was never intended in the design does not necessarily cause the amp to operate optiminally. Living in a warm country, adding fans to an amp not designed to work in higher ambient temperatures may well work, but there is no science in it and it certainly does not ensure optimum performance, albeit might prevent the amp from breaking with the immision of magic smoke.

[colin.hepburn]

Each to their own here I think
If an amp is designed correctly it will have the correct heatsink sizing and work as intended without fans at the powers Wattages. we use in a home inverment and fans will always inject noise across the power rails this is why I don’t use a pc for music anymore but that another story

I Use my pioneer amp as headphone amps with my HD650s but I run them a little hotter running them in Class A for a bit longer before they go into class B and they sound very good indeed only topped by my 5751/12BA4 single ended h/amp no fans
Pioneer SA-500A Quasi Complementary and the pioneer SA-6200 both recapped of course
Just my view others may differ

[Black Stuart]

Both of you are missing the point - the audio world, especially analogue are trapped in the past. Active cooling didn't exist in any form as little as 15 years ago and now it does.

Greg - the h/amp in question was designed by Alex Cavelli, not Massdrop, they are just an internet retailer, mainly driven by consumer polls.Check out his work.

Richard brought up the point that as early as the 1950s it was known that dropping the operating temps by 10C doubled the life of components. What a shame that listening tests weren't carried out at the same time.

Neither of you have ever used equipment that was actively cooled so your both talking from theory not practice. Isn't it time for the analogue boys to climb out of their self made boxes and experiment. Can either of you point me toward actual tests carried out on actively cooled equipment to back up your arguments, well can you?

[bob orbell]

Stuart, I don't think Greg or Colin are arguing, you posted to me, that I should change my attitude, maybe you should practice what you preach, . BOB

[colin.hepburn]

Originally Posted by bob orbell

Stuart, I don't think Greg or Colin are arguing, you posted to me, that I should change my attitude, maybe you should practice what you preach, . BOB

Hi all
BOB is right Greg and I are not arguing on anything
I just posted my views on my preferences on Amplifiers that I prefer i.e. for me which are older solid-state and my Valve amps single ended headphone and my JE.labs single ended 6SL7/KT66 with back loaded horns
that’s how I like my music played sorry but don’t want fans in the system but thats me
PS. I have used many actively cooled systems but this was back in the day when I worked with Band PA systems using In excess of 5k by that brings back fun memories

[Phil Y]

Well,

8 months on and I opened the case again. I ended up changing about half the caps before, leaving a lot of the small (mostly 100u 25v) ones as there was no sign of them leaking/bulging at the time. Sadly, one of them is now leaking brown gunk so it looks like it was not just the large ones. Time to change the rest.

Question,

Near the output, there is a pair of 2.2uF 63v Wima MKS4 caps. I am assuming these are the o/p coupling caps (I will check properly when I have it fully apart). This being the case, I was wondering about changing these when I do the job, as they are not great sounding caps. Does anyone have any suggestions for similar, small, radial package caps that they consider to be a better sounding alternative to the Wimas?

Regards, Phil.

[Richard]

Annoying about the electros Phil.

The coupling caps may depend on what space you have available as polyprops seem only to be available in higher voltage and physical size. Much of audio seems to use those layer polyesters.

I had a similar choice to make when I re-capped the Quad pre. It had 2.2uF bipolar electros as coupling in the phono so I used those Wima layer polyesters instead and they sound ok to me but I haven't done an A-B listen. Why do you think they are poor?