SOZ virgin needs help!

[Lenin]

Oh Brian, setting up the heatsinks.

No, I'm not using one heatsink for output devices and one for resistors in each monoblock. I've picked up bits and pieces in the forum on this issue (and the often repeated advice to mount them seperately for best sound quality). I don't doubt that there is an audible effect, but I suspect that what people are hearing is the resistors 'cooking' the output devices.

Paying proper attention to the arrangement of devices and resistors on the heatsink should minimise this problem for those running everything (heatsinks - and the devices junction temperature) pretty high. As I say, I'm aiming to have a 'cool' running (I know this is a relative term!) 20w SOZ, so this problem shouldn't arise.

[grataku]

Lenin,
are you sure you want to pop your cherry with the SOZ? Oh, by the way I think you will soon realize how off you are on your temperature rise estimates.
I would wait a couple of weeks for the new and hopefully better SOZ with CS. You maybe able to squeeze a few extra watts out of your trafo or save some $ on the electric bill.

[Lenin]

A new SOZ with CS?!!! (Candle Sticks? Custom Spraypaint?)

You mean to say that Mr NP has been developing CS for the SOZ on the QT!

I didn't know anything about this. I guess it explains the absence of any detailed reference to SOZ on the Pass DIY site. Of course I'll wait. Thanks for the tip. And seriously, what is CS, by the way?

I don't suppose you could tell me whether 600VA/300,000u SOZ monos are just too wimpy.

Thanks

[BrianGT]

The SOZ is on the pass website, under the legacy section:

Legacy section on PassDIY

As for the 600VA and the 300,000uF, 300,000uF sounds like overkill for one channel. If you are going for overkill, why don't you just get 1kVA for each channel?

--
Brian
gte619j@prism.gatech.edu

[Peter Daniel]

I don't know if you thoght about it but if it's going to be a miniature SOZ with dimentions you specified are you sure you will fit 600W transformer and 300,000uF of caps inside the chasiss?
If you covered that side than my best bet is to use cooling fan and possibly variac if you have access to one and then you might even like your cake.

[Lenin]

Thanks Brian. Problem solved.

And hey, Grataku what do you mean " you'll soon realise just how off you are with your temperature rise estimates"? Don't tease me - tell me where I'm going wrong!

[Lenin]

My original post starting this thread explained that the (stereo) spec is: 1.2KVA and 300,000u.

Somewhere in the twists and turns of the thread I decsribed the monoblock as being 600VA and 300,000u. Of course, that should have read 600VA and 150,000u. My silly mistake.

Yep, there is space (just) for 600VA - it's actually arranged as 2 300VA transformers. The intention is to independently rectify and feed each half of a balanced configuration arranged on 2 signal boards (hence 2 heatsinks per monoblock).

And finally, I'll come clean. Yes, it is a fan cooled arrangement. I've simply not mentioned it up till now because of the derision which seems to meet the idea of fan cooling whenever it is raised on the forums.

Personally, I feel fan cooling has had a bad press from the audio community and implemented correctly, is the answer to most class-A heat dissapation headaches.

Yes, fans are often noisy (Purchase a low noise fan)

Yes, a poor implementation can leave you injecting noise into the system (imlement some decent isolation for the power supply - incorporate it into the regulator even!)

Run the fan at a lower voltage. (Noise tends to increase logarithmicly with fan motors, running them at half voltage works a treat)

Finally, isolate the fans from the heatsinks and the chassin with an appropriately large guage of sorbothane or similar, to finally kill any remnants of noise.

I tried this out of desperation about 7 years ago, just accepting that the end result would probably be noisy, but that it was the only way to get my high bias power amp projet at the time on the road.

The end result (complete with sorbothane mounts, etc) astounded me. For about 5 years now, I've been using some truly incredible 12db fans from Papst (sorry, I don't have the web address, but they won't be hard to find). These really are the icing on the cake and surely it's just a matter of time before Class-A afficionados release that as long as class-A amplification is associated with scalding hot mini power stations dominating peoples homes, it will never reach mass acceptance. Fan cooling is the missing link, in my view. Unfortunately, it will only shake off it's unfair reputation as unthinkable for high end audio, when others on this forum are far-sighted enough to point out that it has generally been poor implementation that has led to the audiophile 'truth' that fans are too noisy for high end audio.

Now that should put the fan-cooled cat amongst the scorched pidgeons...

While I'm at it, why doesnt someone (with far more technical ability that me) come up with a nice little schematic that solves most peoples electronic objections? I'll certainly post mine as soon as I've got to grips with just how to do it!

[GRollins]

CS is an abbreviation for current source.
A current source can lower the heat dissipation by allowing you to lower the rail(s). I did a thread on this a while back.
Whether you like the sound of current sources (current mirrors, et. al.) is another ball of wax...
(Jam will show up shortly to defend current sources.)
Don't judge a power supply on the number of microfarads, judge it by Joules of storage/output Watt. Low voltage rails require far, far more capacitance to equal the J/W ratio of an amp with higher rail voltages--something tube folks have known for years.

J=1/2*C*V**2

where:
J= Joules
C= capacitance in Farads
V= Voltage

Note that the voltage is squared. Assuming that the capacitance remains the same, going from 40V to 400V makes a <i>BIG</i> difference. Conversely, dropping the voltage to 20 or 30V requires a fairly hefty investment in caps to retain the same number of Joules of storage.
I've used fans...and not, depending on the project, the phase of the moon, and how much money I had on hand at the time. I generally prefer not to. If you really want to get serious about dissipating a lot of heat in a small area, go water-cooled.

Grey

[Lenin]

Thanks.

I've got one final question. I'm a bit perplexed at Nelsons advice to add approx 20% onto the transormer secondary voltage in order to get the rail voltage figure. Shouldn't we be multiplying by 1.414 (and swallowing rectifier and other losses?)

I suppose one of the reasons I ask this is that I'll be using shcottky rectifiers in my SoZ project (with thier lower voltage drop, absence of switching spikes, etc). With this in mind, what do you guys reckon I need to be specifying as secondary voltages for the transformer? I'm guesstimating I'll need 30V secondaries, for a theoretical, lossless 42V, or a real world 40V.

(I'm now after a 40V rail, having found a way to fit a 1.5KVA toroid into each chassis).

Or should I just stick to Nelson's recommended 32V?

[BrianGT]

> having found a way to fit a 1.5KVA toroid into each chassis

1.5kVA for each chassis??? That would mean that you would have 3kVA for the amplifier. That just seems like overkill to me.

Good luck keeping those things cool, and I wonder how much your monthly electric bill will increase.

--
Brian
gte619j@prism.gatech.edu