a bit different amp front end layout

ergo · 9th January 2002, 06:46 AM

I have been playing around with this basic idea. In theory (at least in my head) the dif amps connected this way would have good current balance without using current mirrors on their collector loads nor the resistors that are not equal. The thing works in SPICE simulation, but I also constructed it in real life and seem to have a lot of problems. The currents are not equal even if I remove the VA stage transistors.....

My question mostly is, if anyone has tried such layout or what thoughts does it provoke in your head. For some reason the idea is attractive to me but as I don't have that much of experience, might be I'm totally overlooking some possible problems..

Ergo

Damon Hill · 9th January 2002, 07:07 AM

Doesn't look like the differential amplifiers can work as such,
since they can't share a common current source. What you
appear to have is an independent current source for each
transistor, so no 'balancing' action can occur. In fact, it looks
sort of like a current mirror, but on the wrong side.

Self and Sloan in their books give some examples of rather
more complex differential amplifiers, some using complementary
feedback pairs, but I found them difficult to understand.

I don't really understand negative feedback either...I just take
it on faith that it works.

TomT · 9th January 2002, 10:15 AM

You've rediscovered the phono stage used in the Hafler DH101 preamp, were the feedback network is the RIAA and the output transistors are darlingtons. The current sources were just resistors to the rails.

Geoff · 9th January 2002, 10:17 AM

Ergo

Have you seen my message to you in the 'Everything Else' section of the forum regarding my attempts to reply to your email?

Geoff

Elso Kwak · 9th January 2002, 02:02 PM

Hi Ergo,
Please have a look at the GAS Thaedra or Thoebe schematic in the link. They used the same idea for there line amp and Ampzilla and Son of Ampzilla poweramp. It is more than 26 years old!
The scheme is also used to some extent by Elantic and Harris(now Intersil) in some of there IC's
http://home.earthlink.net/~narf1/thopho.jpg
I am a happy owner of a Ampzilla and I can tell you the circuit works best if <B>all four</B> inputtransistors are matched. You need a lot of them to find four equal!

mlloyd1 · 9th January 2002, 05:13 PM

Elso:
Thanks for posting that schematic. I'm curious; is there a reason that the current sink/source resistors for the input diff pairs are returned to the emitter of the output device instead of the rails? It appears to be some sort of feedback. Otherwise, it looks very much like the Lin configuration that Borbely likes to use.

mlloyd1

Elso Kwak · 9th January 2002, 05:41 PM

Hi mloyd1,
I have no idea it seems to be a James Bongiorno speciality. He does it all the time in all his circuits.
BTW the HaflerDH200 also uses this scheme but without the detail you described. No wonder as JB worked for Hafler and SAE . SAE also uses the scheme in a lot of there amplfiers.

tvi · 19th January 2002, 02:05 PM

<a href="http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='4853609'.WKU.&OS=PN/4853609&RS=PN/4853609">US Patent 4,853,609</a> Pioneer Electronic Corporation

Regards
James

snowdog51 · 24th March 2009, 03:32 AM

Elso i have thaedra preamp and son of ampzilla i just love them
i know you love your ampzilla

PH104 · 24th March 2009, 03:53 AM

posted by mlloyd1
I'm curious; is there a reason that the current sink/source resistors for the input diff pairs are returned to the emitter of the output device instead of the rails?

I believe that increases the compliance of the current source. Curcio does the vacuum tube equivalent with his Dyna mods.

9th January 2002, 06:46 AM	#1
ergo diyAudio Member Join Date: Mar 2001 Location: Tallinn, Estonia	a bit different amp front end layout I have been playing around with this basic idea. In theory (at least in my head) the dif amps connected this way would have good current balance without using current mirrors on their collector loads nor the resistors that are not equal. The thing works in SPICE simulation, but I also constructed it in real life and seem to have a lot of problems. The currents are not equal even if I remove the VA stage transistors..... My question mostly is, if anyone has tried such layout or what thoughts does it provoke in your head. For some reason the idea is attractive to me but as I don't have that much of experience, might be I'm totally overlooking some possible problems.. Ergo

9th January 2002, 02:02 PM	#5
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	complementary schematic Hi Ergo, Please have a look at the GAS Thaedra or Thoebe schematic in the link. They used the same idea for there line amp and Ampzilla and Son of Ampzilla poweramp. It is more than 26 years old! The scheme is also used to some extent by Elantic and Harris(now Intersil) in some of there IC's http://home.earthlink.net/~narf1/thopho.jpg I am a happy owner of a Ampzilla and I can tell you the circuit works best if <B>all four</B> inputtransistors are matched. You need a lot of them to find four equal!

9th January 2002, 05:41 PM	#7
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	crircuit detail attributed to James Bongiorno Hi mloyd1, I have no idea it seems to be a James Bongiorno speciality. He does it all the time in all his circuits. BTW the HaflerDH200 also uses this scheme but without the detail you described. No wonder as JB worked for Hafler and SAE . SAE also uses the scheme in a lot of there amplfiers.

24th March 2009, 03:32 AM	#9
snowdog51 diyAudio Member Join Date: Jan 2009	gas ampzilla son of Elso i have thaedra preamp and son of ampzilla i just love them i know you love your ampzilla

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9th January 2002, 07:07 AM	#2
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma) Blog Entries: 1	Doesn't look like the differential amplifiers can work as such, since they can't share a common current source. What you appear to have is an independent current source for each transistor, so no 'balancing' action can occur. In fact, it looks sort of like a current mirror, but on the wrong side. Self and Sloan in their books give some examples of rather more complex differential amplifiers, some using complementary feedback pairs, but I found them difficult to understand. I don't really understand negative feedback either...I just take it on faith that it works.

9th January 2002, 10:15 AM	#3
TomT diyAudio Member Join Date: Jan 2002 Location: Central California	You've rediscovered the phono stage used in the Hafler DH101 preamp, were the feedback network is the RIAA and the output transistors are darlingtons. The current sources were just resistors to the rails.

9th January 2002, 10:17 AM	#4
Geoff diyAudio Member Join Date: Apr 2001 Location: UK	Ergo Have you seen my message to you in the 'Everything Else' section of the forum regarding my attempts to reply to your email? Geoff

9th January 2002, 05:13 PM	#6
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	Elso: Thanks for posting that schematic. I'm curious; is there a reason that the current sink/source resistors for the input diff pairs are returned to the emitter of the output device instead of the rails? It appears to be some sort of feedback. Otherwise, it looks very much like the Lin configuration that Borbely likes to use. mlloyd1

24th March 2009, 03:53 AM	#10
PH104 diyAudio Member Join Date: Nov 2001 Location: New Mexico	posted by mlloyd1 I'm curious; is there a reason that the current sink/source resistors for the input diff pairs are returned to the emitter of the output device instead of the rails? I believe that increases the compliance of the current source. Curcio does the vacuum tube equivalent with his Dyna mods.

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