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Old 22nd February 2013, 01:37 AM   #3991
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Esperado View Post
Jay, i would not like to be in a plane driven by a pilot only experienced as a flight simulator player.
Well, I build amps. I don't care how good or how bad amps are in simulations or even in measurements. I have faith in my ears. Simulators only tell me which amp to build.

If you can find people here who cares only with the real things, surprisingly it's me. I don't need to design my own amps if people can provide schematics as fast as I can build (and of course, I feel that I know how an amp should be built, I just not skillful yet to get it exactly perform the way I want it).

I have more than a hundred amps, but I tell you, none is enclosed in a box (I don't have time for doing PCB or boutique enclosure )
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Old 22nd February 2013, 02:42 AM   #3992
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Originally Posted by Jay View Post
(no amp is 100% stable under all conditions anyway.

Not entirely true, when you use a true open loop buffer designed correctly without its own loop feedback the reactive load of the speaker becomes invisible to the gain stage resulting in the need for minimal compensation. Also more importantly this can result in 100 percent stability into any load provided you can live with the sims of higher thd.


Colin
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Old 27th March 2013, 09:08 PM   #3993
maxente is offline maxente  Romania
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Hi everybody
I decided to build SSA with BIGBT
I have some BC546 and BC556 with extremely close hFE 303 and 304 measure with normal DMM
BF471 and BF472 are not close hFE, 160 and 125,
Can i use common heatsink on both BF ?
On output i will use NJW1302 and NJW3281 with hFE 101 and 91
Suggestions are welcome
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Last edited by maxente; 27th March 2013 at 09:19 PM.
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Old 27th March 2013, 10:54 PM   #3994
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It is probably more relevant to make sure that there are no shorts on the PCB than to match the Ts...

Good luck,
M.
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Old 27th March 2013, 11:06 PM   #3995
maxente is offline maxente  Romania
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Thanks for your concern, no short on the pcb, the photo is taken with my phone camera that's why it looks bad

Last edited by maxente; 27th March 2013 at 11:20 PM.
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Old 29th March 2013, 10:21 AM   #3996
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Quote:
Originally Posted by maxente View Post
Hi everybody
I decided to build SSA with BIGBT
I have some BC546 and BC556 with extremely close hFE 303 and 304 measure with normal DMM
BF471 and BF472 are not close hFE, 160 and 125,
Can i use common heatsink on both BF ?
On output i will use NJW1302 and NJW3281 with hFE 101 and 91
Suggestions are welcome
Yes you can use common heatsink for BFs, but it has to be on GND potential and both BFs isolated by means of mica/kapton washers. Be careful that it will be big enough to dissipate 2 W from both BFs at less than 50C.

Inform us about results when finished.
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Old 29th March 2013, 01:19 PM   #3997
maxente is offline maxente  Romania
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Originally Posted by Lazy Cat View Post
Inform us about results when finished.
I certainly will
I like this combination of power transistors that form BIGBT, very interesting
In the meantime some progress
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Last edited by maxente; 29th March 2013 at 01:30 PM.
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Old 2nd April 2013, 11:34 PM   #3998
maxente is offline maxente  Romania
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Job done !
Before i will power up this amp I have to check some things
- on the output I mount a Boucherot 10 ohm + 0.1uF
- i connect to GND L braket and BF's heatsink
- power supply is a half bridge SMPS that i made two months ago, +/-58v with no load
- what is the optimum bias for BIGBT output?
If you already explained about bias the BIGBT i apologise, but there are 400 pages to read and i can't wait to power up this amp
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Last edited by maxente; 2nd April 2013 at 11:39 PM.
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Old 2nd April 2013, 11:48 PM   #3999
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Very nice looking PCB, just great.

Well VAS/TIS TO-126 should have 10-12 mA bias, each output BJT 100 mA, and IRFs will consequently set up at 30 mA if you use 22 ohm Rbe for the outputs.

SSA is completely DC coupled so expect some DC offset traveling if you don't have some sort NTC, DC servo or other temp tracking for the input stage. Bias spreader for the outputs sense and regulates only main heatsink conditions.

Regards, L.C.

BTW cool SMPS you have there.
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Old 3rd April 2013, 03:08 AM   #4000
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Esperado View Post
Point 2, you have other choices than electrolytic, in the signal or feedback path. On my side, i use film one for the input, and electrolytic in the feedback with no negative issue on the sound. Tried servo: no real change on the signature of the amp, and nothing witch destroy its transparent and fast aspect.
Try a bipolar electro in place of polar-electro. they offer better meaureable performance in low thd audio circuits.

Thx-RNMarsh
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