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Old 25th October 2012, 09:29 AM   #1291
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Hi LC,

Since i am waiting tssa_bigbt_hp new filtering/smoothing caps for firste stage building, i have little to study new possibility for using my good matched pair of MJL3281 and MJL1302 (No BIGBT possibility since NPN/PNP matching is over 5%). I try to swap from BIGBT to BJT... (I say try....) base for moment on +-35Vdc

Marc
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Old 25th October 2012, 09:36 AM   #1292
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Quote:
Originally Posted by Lazy Cat View Post
Where did you vanished Marc?
In word format as you advice me to keep it for me until TSSA_BIGBT_HP is runnig. I have to purchase new smoothing/Filtering caps. Mine are coming from salvaged power supply and got some strange sounding behavier on other project.

Marc
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Old 25th October 2012, 09:37 AM   #1293
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Hi Marc, no problem if it is triple BJT output stage, VAS isolation from the output current would be great, so no other change required.

But as you remember we didn't pass the first task of setting CCS to correct current levels, or you already did it in the mean time?

Regards Andrej
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Old 25th October 2012, 09:45 AM   #1294
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Thanks to all for your responses - actually now after the measures I took the noise in the modified channel is very low - almost inaudible with my ear actually touching the face plate of the tweeter and CLG of 23 - so for now I am satisfied with this.

I am looking forward, when I have converted the other channel, to make another comparison of noise & music between TSSA 1.6 & my amp - but already both sound very good.

I think I will have to stop calling my amp Fetzilla to avoid confusion with Hugh's design from which it differs in several ways and also because it now it is not exclusively made with fets so from now on I will call it Simple S.E.A.

I also look forward to make a comparison with SSA ASAP but first I have to build it !

I think TSSA, SSA & Simple SEA are like 1st cousins and I am grateful to Andrej & Sonny because I set you very high standard in design that inspires me to understand and improve my own design efforts.

Last edited by mikelm; 25th October 2012 at 10:11 AM.
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Old 25th October 2012, 09:46 AM   #1295
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Quote:
Originally Posted by Lazy Cat View Post
Hi Marc, no problem if it is triple BJT output stage, VAS isolation from the output current would be great, so no other change required.

But as you remember we didn't pass the first task of setting CCS to correct current levels, or you already did it in the mean time?

Regards Andrej
HI LC that's just "paper job" or "computer job"....i explain why i have not proceed to TSSA_BIGBT first test. I do not trust enough my actual smoothing/filtering caps and wait on some new. The soft start/speaker protection board is ok and functionnel so LTP327 can be feed.

Can you developpe :

Quote:
VAS isolation from the output current would be great
I choose your TSSA shématic beacause you provide the table with Vrail conversion value. I just have interrogation about value toward Vrail amout on the resistor feeding Driver (MJE15030/15031)base : 100R in my schematic.

Marc
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Old 25th October 2012, 10:23 AM   #1296
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VAS isolation from the output current means, that ratio (current gain) between output current level (speaker load current) and VAS loading current or base current (Ib) to input BJT of the triple output stage is enormous. Let say for 10 A load current, VAS loading current would be only few mA, ratio more than 1000, current isolation more than 60 dB. Clear now?

100 ohm sets too low bias current for driver (second BJT in triple) it should be 22 ohm for app. 30 mA driver's bias.
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Old 25th October 2012, 12:37 PM   #1297
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Reduced at Hf with the mosfets, because the parasitic caps of those devices ?
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Old 25th October 2012, 02:45 PM   #1298
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Quote:
Originally Posted by Idefixes View Post
i have little to study new possibility for using my good matched pair of MJL3281 and MJL1302 (No BIGBT possibility since NPN/PNP matching is over 5%)

Marc
Not 100% right i look foward and think i found one more new BIGBT possibility by new project devices repartition

Marc
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Old 26th October 2012, 07:56 AM   #1299
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Quote:
Originally Posted by Lazy Cat View Post
See the analogy now? Just parallel bipolar devices as many as you need same way as on the picture. Now all bipolars around one mosfet driver have to have the same current gain hFE (+/-5%)

P.S. IRF610/9610 mosfet drivers from your TSSA sch stays on positions as they are, so please ignore reversed mosfet positions on this pic because in Maximus it was completely different configuration of an output stage.
LC thanks - I get it.
The extra components on the first drawing confused me.
Now to order parts from Mouser.
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Old 26th October 2012, 10:21 PM   #1300
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Quote:
Originally Posted by Idefixes View Post
Not 100% right i look foward and think i found one more new BIGBT possibility by new project devices repartition

Marc
Yes, these BJTs are more than adequate for BIGBT application.
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