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Old 26th December 2010, 07:12 PM   #1
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Default Quasi complementary outputs in a full complementary circuit

Hi guys,
Am rebuilding an amp which was originally full complementary.Am through with a pair of 2sa1943/2sc5200 with a supply of +/-50v.I intend to use the amp on a 4 ohm load so i needed to add another pair to the output stage.The (only)seller tells me that she wouldn't be stocking any of that stuff in small silicon packs this coming year.She has run out of genuine 2sa1943's,just the 5200's.Am on student budget and can't buy them online(who knows?they might as well be fake!).I have a crazy idea about my situation:i did something that none of you would do.I 'fixed' the trannys onto the heatsink with epoxy since i couldn't get thermal grease.Am not about to hammer a 1943 out so i was thinking maybe i could have the first pair in full complementary and the second pair in quasi complementary...like in ampslab's c200.1 quasi complementary.What do you think?Am just doing this out of necessity and don't know if it can work,can it?
If not,what changes do i need to make on the circuit to make it a quasi complementary amp?
Regards.
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Old 27th December 2010, 12:34 AM   #2
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"B" (attachment 2 - quasi) is directly "swappable" with "A" (attachment 1 - standard). Only built 1 quasi ...merely as a exercise , it worked. No need to here in "semi infested" mouser land , lots of pnp's available .
OS
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File Type: gif ef2.gif (22.3 KB, 384 views)
File Type: gif quasi.gif (31.6 KB, 380 views)
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Old 27th December 2010, 04:25 AM   #3
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Whats up with the red arrows?
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Old 27th December 2010, 04:33 AM   #4
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Have you checked the power bandwidth? 2N3773s are mud slow transistors.

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Old 27th December 2010, 07:16 AM   #5
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Quote:
Originally Posted by xeclipse View Post
Whats up with the red arrows?
That what you have to change/add , if you started out with a standard EF2 ... you didn't specify your original design.

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Have you checked the power bandwidth? 2N3773s are mud slow transistors.
#1 - this is just audio , we aren't transmitting AM band .. #2 -I don't use those Just an example #3 - ya mean a builder would have to wait till the new year to hear the first note out of his new amp??

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Old 27th December 2010, 07:42 AM   #6
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The original design look exactly like attachment 1 with a 220 ohm resistor in place of the 100 ohm R89.
How will it affect the performance if i solder the drivers' emitters resistors to the feedback instead of the original 220ohm resistor across the emitters?
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Old 27th December 2010, 08:24 AM   #7
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Quote:
Originally Posted by xeclipse View Post
The original design look exactly like attachment 1 with a 220 ohm resistor in place of the 100 ohm R89.
How will it affect the performance if i solder the drivers' emitters resistors to the feedback instead of the original 220ohm resistor across the emitters?
Well , the drivers won't be running class A like a EF2 does. Performance should be on par with a fully complimentary OPS. For a closer match in operating point (voltages), 3- 56-68R resistors(instead of the 39R's) would be a close match for your present 220R Re driver stage. This means your Vbe (Bias adjust) would still be in the proper range. Start with just 1 pair outputs to perfect the "swap".

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Old 28th December 2010, 08:22 AM   #8
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Thanks Ostripper.
I hope you understand this idea i have and please let me know if it can work.
I'll use attachment 2 as an example. The first pair being full complementary,the base of the 1943 is soldered to the emittes of the driver(15031).The second pair being quasi complementary,the base of the 5200 is soldered to the collector of the driver.
What do you think? Can it work without a significant rise in distortion?
Regards.
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Old 28th December 2010, 08:28 AM   #9
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Originally Posted by xeclipse View Post
Thanks Ostripper.
I hope you understand this idea i have and please let me know if it can work.
I'll use attachment 2 as an example. The first pair being full complementary,the base of the 1943 is soldered to the emittes of the driver(15031).The second pair being quasi complementary,the base of the 5200 is soldered to the collector of the driver.
What do you think? Can it work without a significant rise in distortion?
Regards.
No - no , NO... don't mix the 2 topologies. Either FULL quasi or full complimentary. (All 5200's)

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Old 29th December 2010, 12:52 PM   #10
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Thanks!
In attachment 2,what is the use of R20?I've seen many designs without it.
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