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Simple Symetrical Amplifier
Simple Symetrical Amplifier
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Old 3rd February 2012, 07:25 AM   #1851
Lazy Cat is online now Lazy Cat  Slovenia
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Quote:
Originally Posted by guitar89 View Post
I'm thinking is it possible to integrate this VAS to SSA ? I think it is known as complementary darlington VAS.

It seems have good properties, but I have no idea what value should be CC1, CC2, R1 & R2. Is possible to use without those capacitor ?
If you don't want to use cascoded VAS this is also very good solution for high current gain "single" VAS device regarding input stage isolation from output load impedance influence.

Omitting CC1, CC2 would be unwise-impossible cause amp without them would certainly oscillate. Their values depends on many factors but it would be somewhere in between 20-100pF.
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Old 3rd February 2012, 09:21 AM   #1852
guitar89 is offline guitar89  Malaysia
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hm.... being said so, the situation now best is to use cascode ? (to use 2SA1707/2SC4487)
What would you recommend now ? or is it still possible to use the complementary darlington VAS ?
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Old 3rd February 2012, 09:33 AM   #1853
Lazy Cat is online now Lazy Cat  Slovenia
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In any case you'll use 2SA1707/2SC4487, you will need cascodes or power supply lower than +/-25V.

Why not use 2SA1209/2SC2911 instead?
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Old 3rd February 2012, 09:46 AM   #1854
guitar89 is offline guitar89  Malaysia
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well.. one of the reason is I brought it X.x haha
And the dealer i brought from doesn't have alot of sanyo transistor.

Is there any other manufacturer that produce high ft transisitor ? Sanyo have poor SPICE library..
which i cannot test before built...

Last edited by guitar89; 3rd February 2012 at 09:59 AM.
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Old 3rd February 2012, 10:40 AM   #1855
guitar89 is offline guitar89  Malaysia
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LC, there is a funny thing on my power supply too. Although it is +-40V but it is only 120VA, means for stereo, only 60VA each channel. With load variation from 2ohm - 16ohm, the maximum voltage swing is only +-20V before my trafo gone heaven. (Hope my calculation is correct)
So i guess the 2SA1707/2SC4487 is still suitable for use ? since I have no hope to reach higher....
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Old 3rd February 2012, 12:57 PM   #1856
guitar89 is offline guitar89  Malaysia
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LC, what i'm thinking is such design as attached.

By using those, I get very high open loop gain and low THD.
The VAS are biased as 0.7mA & 10mA
The driver is biased to 1-2mA & 20mA to Output device.

what could be the good number for C13, which is around the OPS, between the Drivers ?

I intend to change those drivers to the 2SA1707/2SC4487 (didn't do in SPICE because no model.....)
and the OPS change from 0281/0302 to NJL4281/4302. (In SPICE, the number is quite outrages......)

Hope it will turn out into a very nice X.x
Attached Images
File Type: jpg SSA TT - Darlington EF.jpg (108.5 KB, 574 views)
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Old 3rd February 2012, 01:07 PM   #1857
Esperado is offline Esperado  France
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Quote:
Originally Posted by guitar89 View Post
Sanyo have poor SPICE library..
which i cannot test before built...
How did we lived before Spice ?
Well, very simple: calculating ;-)
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Old 3rd February 2012, 02:10 PM   #1858
guitar89 is offline guitar89  Malaysia
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Quote:
Originally Posted by Esperado View Post
How did we lived before Spice ?
Well, very simple: calculating ;-)
haha.... more than just calculating i guess.... involve experiment to explode, etc etc

Well... I just being more caution X.x afriad to test out physically X.x
Maybe my maths aren't that good for amplifier, need to work up.

Secondary purpose using SPICE is to get those THD values easily. (I don't have those instruments)

Edit : Modern people are too replied on technology......... including me, haha
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Old 3rd February 2012, 02:14 PM   #1859
Esperado is offline Esperado  France
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Quote:
Originally Posted by guitar89 View Post
LC, what i'm thinking is such design as attached.
There is something I dont understand: how can your Q3, Q4 bases be at +15V and -15V while their emitters are at 0V ?

[edit] Yes, experimenting in real world and listening seems to me the only way to increase his experience and make-it part of yourself. I'm not sure that all this virtualisation gives no good. It saves time, (money) but kill the soul. (Yes, amps had some kind of soul when they were handcrafted)

Last edited by Esperado; 3rd February 2012 at 02:21 PM.
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Old 3rd February 2012, 11:29 PM   #1860
Sheldon is offline Sheldon  United States
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I've got one channel of ThermalTrak Basic built: http://www.diyaudio.com/forums/attac...rack-basic.jpg

Only significant difference is 2SA1360/2SC3423 for the drivers. Resistor values are as shown, except 2.2R base stoppers for the output devices. Before I fire it up, I could use some guidance on a starting point for the 5K trim pots that parallel the 2.2k resistors into the feedback network. How much current do we want through the zeners, and how much into the feedback network?

Sheldon
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