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Old 7th August 2011, 04:48 PM   #81
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Default Here too.... a short form of Eduardo (Edward)

regards,

Carlos
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Dx Blame ST with a tube preamp. recorded with Xperia cell phone, https://www.youtube.com/watch?v=Qjs32J0gdj0; https://www.youtube.com/watch?v=nhrZ...vDnDhEpNv_XVxg
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Old 7th August 2011, 05:01 PM   #82
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Default Please Lazy Cat... publish a more evoluted circuit for us

I suppose lineup may be already working on that...i would like to see your work fellows.

regards,

Carlos
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Dx Blame ST with a tube preamp. recorded with Xperia cell phone, https://www.youtube.com/watch?v=Qjs32J0gdj0; https://www.youtube.com/watch?v=nhrZ...vDnDhEpNv_XVxg
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Old 7th August 2011, 06:20 PM   #83
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Quote:
Originally Posted by Lazy Cat View Post
Can you make sim as proposed, turning the output mosfets to IGBT's?
Quote:
Originally Posted by Nico Ras View Post
Yes I can. Which ones did you have in mind?
... or maybe just add this output buffer in microCAP to see if THD will lower substantially. If yes than we'll know that current feedback amp basic configuration cannot be easily to overcome.
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Old 7th August 2011, 07:40 PM   #84
jaycee is offline jaycee  United Kingdom
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What about a low power version for headphone use?
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Old 7th August 2011, 07:50 PM   #85
juma is offline juma  Serbia
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Quote:
Originally Posted by Lazy Cat View Post
... or maybe just add this output buffer in microCAP to see if THD will lower substantially. If yes than we'll know that current feedback amp basic configuration cannot be easily to overcome.
Nice, but with HEXFET + BJT output stage the thermal compensation circuit (Vbe/Vgs multiplier) will have to replace the simple 1k trimmer...
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Old 7th August 2011, 07:56 PM   #86
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Originally Posted by jaycee View Post
What about a low power version for headphone use?
No problem it can be voltage/current scaled down and used with BC signal transistors only and IRF's at the output. But please wait untill we set the right topology with lower THD levels, than any version can be properly settled and calculated. Just wait what Nico will say ...

Last edited by Lazy Cat; 7th August 2011 at 08:02 PM.
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Old 7th August 2011, 07:59 PM   #87
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@juma
yeah I know that ... in my posted picture you can clearly see it sitting there on the top of the BIGBT
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Old 7th August 2011, 08:12 PM   #88
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Lazy Cat that does not work. You substituted a Lateral MOSFET with a HEXFET. Biasing it is impossible. It switches between 22pA and 82 Amp. I will have to analyse it properly to find the solution. But personally I do not know why you want to mess with the schematic, rather make some real life measurement of what you have and give it a good listen. I will do the same during the week. I remain confident in what you have here is a very good amp.

Jaycee, a low power version is feasible, but you cannot just scale it. You would probably use BD139/140 for the output devices and run it off a +-6V supply, but there would be a number of value changes required. SIM predicts that it could work quite nicely as a headphone amp.

It is Lazy Cat's design so I leave it to him to decide.

Nico
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Old 7th August 2011, 09:20 PM   #89
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Originally Posted by Nico Ras View Post
Lazy Cat that does not work. You substituted a Lateral MOSFET with a HEXFET. Biasing it is impossible. It switches between 22pA and 82 Amp. I will have to analyse it properly to find the solution.
I know, you would need source resistor to stabilise IRF's drain current but it works perfectly cause I have tested and listened them. Now I know that my BIGBT's acted like an output buffer so distortion was infact low in my test amp. I have 100mA per each output BJT and it is very stable, also as you can see in previously posted pic that there is no heatsink at all and I could listen exact BIGBT combo for a few minutes before temperature went over 60C.

The problem is that I write these lines from the sea and can not perform any tests right now, only communicate.

OK we'll try to stick to basic sch, fine tune the values and than make PCB.

As you probably know common topology to all current feedback amps is similar and combined from an input current diff amp, I/V conversion and output buffer, so the last is somehow missing in our primary sch.
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Old 7th August 2011, 09:24 PM   #90
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Lazy Cat, Don't get carried away now. We can reduce THD by two orders of magnitude by using a pre-driver, very little change and remains simple. I am going to bed now but will do some more work and let you know.

Nico
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