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Old 2nd July 2013, 05:48 AM   #411
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Quote:
Originally Posted by gaborbela View Post
Yes Renesans is still available but I do not like them.
Compare to the good old Hitachi they are no longer the same quality.
These not just my opinion (I did some A-B test) many other users wrote the same.
May be for that reason no longer so popular like was when Hitachi produce them.
I built some Pass amplifier using hexfet. According to Mr. Pass and many other who used hexfet need high bias to give you good performance.
I never used hexfet in Class A-B circuit ....
Even under class A bias it has a bit week bass.
They just came up with a bipolar circuit to. I will follow that thread to see if their BJT version will be stable all do they use les than 50mA bias. At that bias the darlington stable enough to.
It would be good if you could do some measurement on the darlington device if is oscillate etc.
I blew up many BDW93D & 94D darlington produced by ISC even with low bias, after a few minutes, not even warm up.
Probably it oscillated or just junk device, who knows.....
Funny think after I switched to BDW93C & 94C (about half the power ) and those newer blew up even under 100mA bias at 40V rail voltage.
One think is sure I do not give up on these amp with the power darlingtons.
Even if I have to use large size heatsink like Class A amps.
I double up the darlington and let the bias move up and done. My friend used the amp with one pair darlington over 9 years with high 300mA bias..
Actually the Monster Hiraga has the same bias drifting issue, I set up the bias 800-900mA and after warm up I get 1.5A. The reason it cause less problem because it run only on 12V rail voltage..
I need that sound I got from these amp.
Greetings
Hi gaborbela,

I following this thread, I've been test it. I like the sound and almost the same with vssa. my problem is thermal stability. I've experiment also using vssa schematic value and your's schematic and some modes, the results sound great. Sounds very clear and bass is there. I like the sound of darlington over lafet. I even used very small heatsink in normal listening. I used +32v-32v 1 4700uf per rail. I even used also +12v-12v with very good sonic result. I agree to you that darlington has a good bass. So far for now of my experience, this is a very good i've ever built amp.

Regards,
Boyet
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Old 2nd July 2013, 08:40 AM   #412
Bigun is offline Bigun  Canada
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I don't know if you don't like my solution for bias - I did mention it earlier. I built my own version of the VSSA (called TGM5 - a thread here somewhere) with fast Toshiba BJT outputs. Bias was rock solid. The solution I used was to use generous emitter degeneration on the VAS (what I used was too high, I would suggest less but I haven't experimented with the value, I also want to try a bypass cap on the emitter resistor) and I used a bias spreader with better tolerance to variations in the VAS standing current - a design from Hagerman.

It is extra trouble though and I suspect that good LATFETs are the best option overall.

Still, when I get back from holiday (I'm cooling off in Hong Kong today, boy is it hot) I may have to build Gabors circuit with Darlingtons, otherwise how will I know for myself how it sounds ?
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Old 2nd July 2013, 10:57 AM   #413
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Originally Posted by boyet0173 View Post
Hi gaborbela,

I following this thread, I've been test it. I like the sound and almost the same with vssa. my problem is thermal stability. I've experiment also using vssa schematic value and your's schematic and some modes, the results sound great. Sounds very clear and bass is there. I like the sound of darlington over lafet. I even used very small heatsink in normal listening. I used +32v-32v 1 4700uf per rail. I even used also +12v-12v with very good sonic result. I agree to you that darlington has a good bass. So far for now of my experience, this is a very good i've ever built amp.

Regards,
Boyet
Happy to read another build with good sonic result.
If you have time please post your transistors list and other parts U use so we can see what kind of modification you made..
If you could use a bit more caps in your PS and make it CRC that would be better..
4700uF a bit to low.
Sometimes we forget these amplifier at 35-40V rail voltage produce over 60W or so..
Adequate heatsink must!

Also I would like to ask Bigun, Ashok when you came up with an idea and you have time please make a sketch that way easier to follow, to understand.
To be honest many people does not take the time to read all posts.
I do read every post here because I started the tread.
The same time I follow some other project with same topology, to be honest I do not read each post.
Simple reason I do not have enough time to do so but when I se a circuit, a picture etc I do take a look..
I think we would have more comments, idea etc. if we would post more sketch, pictures etc...
Of course only if and when you have time!!!
Thank you
Greetings G
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Old 2nd July 2013, 02:37 PM   #414
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Quote:
Originally Posted by gaborbela View Post
Happy to read another build with good sonic result.
If you have time please post your transistors list and other parts U use so we can see what kind of modification you made..
If you could use a bit more caps in your PS and make it CRC that would be better..
4700uF a bit to low.
Sometimes we forget these amplifier at 35-40V rail voltage produce over 60W or so..
Adequate heatsink must!

Also I would like to ask Bigun, Ashok when you came up with an idea and you have time please make a sketch that way easier to follow, to understand.
To be honest many people does not take the time to read all posts.
I do read every post here because I started the tread.
The same time I follow some other project with same topology, to be honest I do not read each post.
Simple reason I do not have enough time to do so but when I se a circuit, a picture etc I do take a look..
I think we would have more comments, idea etc. if we would post more sketch, pictures etc...
Of course only if and when you have time!!!
Thank you
Greetings G
Hi gaborbela,

Here my current setup. If you want you can try this. Now beautifully singing even with small heatsink. Sorry for pics is not clear. This topology based on your schema Gaborbela,LC and shaan. I want to thanks to DACZ for PCB designed for me..


Regards,
Boyet
Attached Images
File Type: jpg GABOR VSSA DARLINGTON-BOYET.jpg (96.4 KB, 256 views)
File Type: jpg IMG_070213_0034.jpg (42.2 KB, 213 views)
File Type: jpg IMG_070213_0037.jpg (38.5 KB, 206 views)
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Old 2nd July 2013, 02:46 PM   #415
AndrewT is online now AndrewT  Scotland
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Why is D1 & 2 UF as described on schematic?
If the output pulls the supply low enough that the diode becomes reverse biased, does it matter whether it's a 1N, or UF type?
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Old 2nd July 2013, 03:06 PM   #416
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Quote:
Originally Posted by AndrewT View Post
Why is D1 & 2 UF as described on schematic?
If the output pulls the supply low enough that the diode becomes reverse biased, does it matter whether it's a 1N, or UF type?
Hi AndrewT, I used UF because i dont have 1N diode.
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Old 2nd July 2013, 03:07 PM   #417
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Thank you
Some advice
BD136 and your power transistors must be mounted together in one heatsink...
Your heatsink way too small for these project, be careful you can have thermal runaway at any time and that may take out your speakers to!!
To be honest I would be afraid to connect my speaker and play music at any level like that without speakers protection.
Otherwise nice work!

Greetings G
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Old 2nd July 2013, 03:11 PM   #418
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by boyet0173 View Post
Hi AndrewT, I used UF because i dont have 1N diode.
why the note
Quote:
Diode: ultrafast UF4007
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Old 2nd July 2013, 03:25 PM   #419
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Quote:
Originally Posted by gaborbela View Post
Thank you
Some advice
BD136 and your power transistors must be mounted together in one heatsink...
Your heatsink way too small for these project, be careful you can have thermal runaway at any time and that may take out your speakers to!!
To be honest I would be afraid to connect my speaker and play music at any level like that without speakers protection.
Otherwise nice work!

Greetings G
Thanks for the advise G. But the heatsink is low temperature around 37-40C. I set R15 to 1.3K to make temperature low and R5.R6 47 ohms. And also feedback resistor plays important role in balance temperature both output. That is based on my observation. Any comments are welcome.
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Old 2nd July 2013, 04:17 PM   #420
Vostro is offline Vostro  South Africa
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Quote:
Originally Posted by AndrewT View Post
why the note
Andrew would a slow diode be better ?
I can't see it matter.
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