Building an amp

[Rocker]

Fran, there are detailed and fairly heavy articles on power supplies on www.TNT-Audio.com/clinica/tweaks.html which may be of help in understanding what is going on.

[Fran]

Hi Rocker,


yes theres good stuff on TNT - including some nice simple regulators.


So hows about an update? Well I only got to take some pics last night - first up here is the transformer. This is pretty massive!!

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Next is the capacitors and resistors for the power supply (CRC filter). The big resistors at the bottom of the case are 10R and these get pretty warm!

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More pics later!


Fran

[Fran]

Now, next up is the actual circuit on a bit of perfboard. Its not too easy to see this exactly, but you can make out the mosfet at the bottom and the source resistor attached to the heatsink on top. The big brown capacitor with the gold stripe is C3 from the earlier schematic - and this is paralleled with the yellow film cap to improve the highs a bit.

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This is how I used the light bulbs to set the bias current - 3 bulbs per channel, in parallel, and these set the bias for the mosfet.

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Zooming back out a bit, you can see the 2 heatsinks on the back of the case and the way each circuit is held to them.

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And a bit further back, this is the whole amp:

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Lastly, although this is a solid state amp, there is some glowing goodness in there too!!

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Fran

[Fran]

Few things I reckon I should add:

My builds nearly always end up like birds' nests. Just because what happens is that I'm building them to try out, then need to swap in or out this component or some other thing, and before I know it, it looks like that!! Having said that, there is no hum from it (apart from a small transformer buzz that is only audible up close to the amp).

This thing gets hot. Good and hot. I reckon the heatsinks get to 60deg C (you'll put your hand there for about 5 secs, although it won't mark or burn you) and the internal about 5 deg C less. Ideally, bigger heatsinks are called for.....

This thing sounds gooooood! I can only comment with horns, but its a tad warmer than my Pass F5 - but still dynamic as hell and very resolving. Probably a little more resolving than the F5.

The gain isn;t too high - so probably a passive/unity gain preamp may not be the best idea, depending on what volume you need.

I need to do more testing with other speakers. First up will be my ESL57s.


Fran

[fergus]

Excellent stuff Fran and very good photos too....that really helps!

[Ivor]

Fantastic stuff Fran.

[cybot]

You are telling it as it really is! Most people never get to see what you are doing fran because they usually just follow the perfect 'how to' manual. Yours is the real diy deal.... I recall highly qualified lecturers in college who were brilliant at the theory end of things but hadn't a notion of the practical side;in fact, and this is true, they couldn't even wire a plug! That's why I always admire a guy who can do both...Practical adeptness requires far more intelligence than certain people realise or give credit for.....

BTW I love the way you have the bulbs set up :-)

[jaybee]

I'm delighted to see the old girl getting a new lease of life.... It's like watching a hermit crab move into a new house!!

are those the original transformers?? If so they always had a humm....!!

[Fran]

Thanks jaybee,

Good to hear that about the transformer - I was a little,worried that I was putting too much of a load on it. We'll have to get you down for a listen soon....


Fran