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Swordfishy/ASPEN FETZILLA power amp

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#483
scooperman said:
I checked a few discount/surplus places like mpja.com but I think the cheapest sources for magnet wire are going to be sites like Amazon and Ebay. Just Google-search, e.g. "18 gauge magnet wire" and you get a lot of hits.
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You can simply find nearest diy speaker shop or loudspeaker service and get 0.9-1 mm loudspeaker crossover coil. One coil will be probably enough for many Fetzillas zobels 😀
 
#486
Mr Annaji,

That is marvellous!! Thank you for letting me know.... let us hope that Keith receives his package very soon in Mumbai..... I guess since India has only recently liberalised it's mail order policy there is still some fine tuning to be done to ensure quick deliveries!!

Cheers,

Hugh
 
#487
JKC said:
Hugh,

Thanks. I have made some temperature measurements and they are OK too. The hottest spot on the heatsink close to the MOSFET is at 41C (22C ambient) after few hours of running at 400mA. PCB itself has temperature of 34C measured on GND spade in the middle of the board. Those measurements are taken with heatsinks sitting on the bottom cover without front and back panels and without top cover.

Here is the picture of work progress so far.

George
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George,

Maybe I missed something (or in your case both currents compensate), but you might want to look out for shorted current loops through your torodial transformers by the way you sandwiched them in your housing with a metal plate..
 
#488
Good point, Berny,

George, I'd missed that, however, I suspect it wouldn't work at all if there was a shorted turn about each toroid; I suspect that by having it fully enclose both toroids, and one of them reversed primary phase wrt to the other, there would be a nulling anyway..... but don't ever connect the center of the Al platform to the enclosure!!

Cheers,

Hugh
 
#489
Berny, Hugh,

There is no problem with that plate at all and everything is working fine. This plate is made of nonmagnetic aluminum and there is not closed loop of any kind.

I almost done with burning-in stage. First I run it without the load for 14 hours just to form all electrolytic caps. After that I decided to lower temperature on VAS device and added heatsink to it which knocked temperature down by whole 9C and I happy with that. Before this modification temperature on the case of T2 was 48C (22C ambient) which is too high for my taste and this was without any signal on the input. Now temperature on T2 is around 39C with 48W on the output. I can post the picture of that mod if anybody is interested.

After this modification I have increased VAS current to 14mA and bias current to 500mA. I run it for 16 hours with the dummy 7.5ohm load made of 3 non-iductive 50W resistors mounted on heatsink. As input souce I used function generator at various frequencies. Unfortunately I have no scope to tell you more at this point. The acid test with the speakers is coming soon.

George
 
#490
JKC said:
Berny, Hugh,

There is no problem with that plate at all and everything is working fine. This plate is made of nonmagnetic aluminum and there is not closed loop of any kind.

George
Click to expand...

Magnetic or not, you are just lucky.. A conductive loop through your toroidal is all it takes for a blown fuse, that's it. You have one through both of your transformers: chassis, screw, aluminum plate, screw and chassis again.. Anyway, if it works, it works.. ;-)
 
#493
I will ,In the end when all adjustments have settled in, replace the pots P1, P2 and maybe p3 with fixed resistors. You can do that by measuring the pot's value and replace it with your favorite resistors left en right from the wiper, maybe in parallel to get the right value. IMHO it benefits the sound and also the thermal stability.
(tried it with twisted pear Legato 3.1 and Ventus)

I learned something from working with Salas his shuntboards and what brings the noise from LED's/Diodes/ Zener's down, so could I play with the value of C9 ?

Thanks, Erik.
 
#495
George,

My thoughts are that the existing inductor specced, 27T single layer, is best. The larger inductor seems to slow things down a tad, and blows out the bass, which starts to dominate.

I'm now working on Compensation and VAS degeneration. I will get back to you!!

How is yours sounding, now you have it running? Pleased?

Cheers,

Hugh
 
#496
Hugh,

Thank you for an update. I am in no rush to connect the speakers. I am waiting for you guys to finish the testing so I can easily change components before everything is boxed up. So far no surprises, the amp is running with dummy load for 3 days now with VAS at 14mA and 500mA bias. VAS is not overheated anymore with the heatsink I put on it.

George
 
#497
George,

Could you give us a photo of the VAS with heatsink?

I have not noticed any heat issues with my VAS, the padding is generous, and am a little surprised you feel it's necessary to add extra cooling. By my reckoning it's dissipating around 430mW with 12mA current; your 14mA is a tad more, I suspect you have increased it?

Cheers,

Hugh
 
#498
Hugh,

Just to clarify, it is not necessary to do this modification and your 430mW measurement is correct. It is just me, I prefer lower temperatures for active components. I got similar measurements of 420mW running without input signal and 550mW with 48W on the output. With the signal case temperature was about 48C which is still within the spec. Here is the picture.

George
 

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#499
My golly, George,

You should have been in charge at Fukushima - your policies would have averted disaster!!

You have glued the Al rod onto the case with epoxy, I presume?

Now, how are people going with the sound, any reviews yet?

Don't be afraid to use golden speak, my favorite is:

'I noticed a hermetic quality to the sound stage, as though it were not so much open, as expansively constrained, with strong billowing qualities to the sound as it wafted through my consciousness'.

Comment like this makes this game a hilarious entertainment, so let's have 'em......

Hugh
 
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