Sziklai pair - 1fet+1bjt. - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd February 2006, 10:50 AM   #11
beppe61 is offline beppe61  Italy
diyAudio Member
 
Join Date: Feb 2005
Location: torino
Quote:
Originally posted by Justcallmedad
beppe,
"The only schematic I have seen with only 2 fets are those nice buffers designed by E.Borberly."
Yes you can read on his site:
http://www.borbelyaudio.com/adobe/ae599bor.pdf
http://www.borbelyaudio.com/adobe/ae699bor.pdf
All is in Pages 18/19 (second part) of the Audio Electronics paper.
Thank you again.
I meant BORBELY of course. Sorry for the mistake.
Did you build them? which do you recommend ?
Kind regards,
beppe
  Reply With Quote
Old 23rd February 2006, 02:37 PM   #12
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Default Re: Sziklai pair - 1fet+1bjt.

Quote:
Originally posted by beppe61
I understand that with a fet at the input I could do without an input coupling cap.
I would maintain the output coupling cap to be safer (my current power amp does not have an input DC blocking cap).
I am pretty sure this very simple topology has the possibility to sound extremely nice.
Beppe,

here is a possible schematics and results of FFT simulation for 1V RMS output - the gain here is about 7. I did use similar gain stages in the past and if you have time to select JFETs, it could be a very good circuit.

Input here is directly coupled, however in real life you may decide to add a simple RC filter to remove RF, say 10K and 100pF.

Cheers

Alex

P.S. - I've edited the schematics to add the filter.
Attached Images
File Type: gif jfet_bjt_s1.gif (4.8 KB, 643 views)
  Reply With Quote
Old 23rd February 2006, 02:39 PM   #13
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
I couldn't attach two files for whatever reason, so here is the FFT graph:
Attached Images
File Type: gif jfet_bjt01.gif (5.9 KB, 525 views)
  Reply With Quote
Old 23rd February 2006, 02:45 PM   #14
beppe61 is offline beppe61  Italy
diyAudio Member
 
Join Date: Feb 2005
Location: torino
Default Re: Re: Sziklai pair - 1fet+1bjt.

Quote:
Originally posted by x-pro

Beppe,
here is a possible schematics and results of FFT simulation for 1V RMS output - the gain here is about 7.
I did use similar gain stages in the past and if you have time to select JFETs, it could be a very good circuit.
Cheers
Alex
Dear Alex,
thank you so much for your extremely kind and much valuable reply.
That is indeed what I was thinking about !
I still have two question:
1) as I intend to build a line stage gain= 7 is a little too much.
Could you think it could be possible to arrange the resistors value to get let's say a voltage gain of 3 ?
2) would you think that increasing the voltage supply could give some nice improvements in dynamics?
Please excuse my silly questions but I have been too many times said that the higher the voltage supply the better that I am become almoct obsessed with high voltage value.
Anyway this is what I was looking for on principle.
Have you actually built it ?
Very very interesting indeed.

Thank you again.
Kind regards,

beppe
  Reply With Quote
Old 23rd February 2006, 03:10 PM   #15
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Default Re: Re: Re: Sziklai pair - 1fet+1bjt.

Quote:
Originally posted by beppe61
I still have two question:
1) as I intend to build a line stage gain= 7 is a little too much.
Could you think it could be possible to arrange the resistors value to get let's say a voltage gain of 3 ?
2) would you think that increasing the voltage supply could give some nice improvements in dynamics?
Please excuse my silly questions but I have been too many times said that the higher the voltage supply the better that I am become almoct obsessed with high voltage value.
Anyway this is what I was looking for on principle.
You can do gain of 3, however as it is indeed a very simple circuit you have to understand the limitations and requirements of it to get a good result. I will try to give here a brief explanation. The R1 and R2 chain gives you the gain value, however to get high open loop gain R2 needs to be relatevely small as it provides a local NFB for J1. On the other hand the DC condition of this circuit would be set by the Vgs of the JFET for a given drain current. This current is defined by R3 and Vbe of Q1, and in the illustration equals about 0.7-0.8 mA . Vgs defines the current through R2, which is in turn the sum of currents through both transistors Id+Ic. Hence the DC voltage on the collector is more or less defined by the Vgs and gain. In the example Vgs is about 1.7V but it would obviously depend on the cut-off voltage of the JFET. If you'll choose a JFET with higher Vgs for the same current the gain will be lower. That why I've said about selecting JFET's - as you'll need two matched FETs with required parameters (for two stereo channels) to get the gain you want. Higher voltage is usually a good thing, but in this circuit you need to get about a half supply on the collector of Q1 and as this is Vgs and gain dependent you'll need to find a good compromise... .

Quote:
Have you actually built it ?
Very very interesting indeed.

Thank you again.
Kind regards,

beppe
Yes, I did build circuits of this topology in the past many times with very good results. However the resistor values in the picture are for a simulation only . You'll need to change them to adjust for a particular FET, gain and supply voltage. There are not that many resistors, thought .

Alex
  Reply With Quote
Old 23rd February 2006, 06:03 PM   #16
beppe61 is offline beppe61  Italy
diyAudio Member
 
Join Date: Feb 2005
Location: torino
Quote:
Originally posted by x-pro
I couldn't attach two files for whatever reason, so here is the FFT graph:
Dear Alex,

I am everything but an expert, but I would call this performance quite good , don't you?
Nevertheless I would not dismiss it because "too simple".
On the contrary I understand that even very famous audio designers have abandoned complex topologies in favour of simpler ones.
I well understend that the quality of the execution matters, but I have the strong feeling that the simplest topologies have the biggest chances to sound phenomenal.
Then I have to be honest with you.
I am very very ignorant in electronics.
I tried to learn the basics in audio design (I mean how to calculate a simple one bjt buffer for instance) but failed.
I must tell you this because your explanation are targeted to an educated expert.
I cannot explain how sorry I am not to understand them well.
Because if I were smarter I would have tried to become an audio designer, in the hope to marry passion and work.
Unfortunately this has not happened.
So any judgement I make on a circuit is from an aesthetic point of view (no, I am not an architect), and your is wonderful in its simplicity.
It is not clear to me which type of fet do you propose in the schematic.
I could not find any U309 fet.
My final solution would be, as I said, your topology with 48V voltage supply and a volatge gain of 3.
If you have any idea on how implement such a circuit I would be very interested in it. That would be my future line stage.
I am sure that this kind of circuit could be a real nice surprise for sound.

Thank you sincerely for your extremely kind and valuable advice.
I appreciate it very much indeed.

Best wishes,

beppe
  Reply With Quote
Old 26th February 2006, 12:51 PM   #17
beppe61 is offline beppe61  Italy
diyAudio Member
 
Join Date: Feb 2005
Location: torino
Quote:
Originally posted by x-pro
I couldn't attach two files for whatever reason, so here is the FFT graph:
Dear Mr. Alex,

may I ask you wich software have you used to simulate the circuit ?
I would like to ask you another thing.
Do you think that "playing" with the value of R1, R2 and R3 and/or the V2 value it would be possible to get an even better distortion spectrum ?
I would like to thank you very much again for this very interesting circuit.
I like it very much indeed.

Kind regards,

beppe
  Reply With Quote
Old 26th February 2006, 02:51 PM   #18
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally posted by beppe61
Dear Alex,

I would call this performance quite good,
don't you?
Yes, it is very good for such a simple circuit.
2nd harmonic is dominant: -80dB
3rd harmonic distortion is low: -100dB

These are very nice numbers!
I would call it Hi-fi, out of 2 transistors.


One thing, as circuit is now,
we have not added 1 more output buffer transistor.
So best is to keep a light load.
I would suggest 22kOhm or higher load impedance.

With a suitable added NPN follower output stage, it will drive any load.
Like a 5 kOhm potentiometer.
With almost same performance.
__________________
lineup
  Reply With Quote
Old 26th February 2006, 03:08 PM   #19
beppe61 is offline beppe61  Italy
diyAudio Member
 
Join Date: Feb 2005
Location: torino
Quote:
Originally posted by lineup

Yes, it is very good for such a simple circuit.
2nd harmonic is dominant: -80dB
3rd harmonic distortion is low: -100dB
These are very nice numbers!
I would call it Hi-fi, out of 2 transistors.
...

Thank you very much Sir.
I would like to get your opinion on the spectrum distortion graph.
Do you think it is the most dependable way to assess by instruments the quality of an amplification device?
This question about the ultimate measurement to assess the sound quality of an audio equipment will accompany me till my old age.
I mean, someone say these graphs tell nothing.
Others propose them as valuable.
I do not know who to trust.
What makes me crazy are units that measure worse and sound better !! how can this be ? but it seems it is.


Thank you very much.
Kind regards,

beppe

P.S. I could not enter your web site. Is it for Members only?
  Reply With Quote
Old 26th February 2006, 03:31 PM   #20
MikeB is offline MikeB  Germany
diyAudio Member
 
MikeB's Avatar
 
Join Date: Apr 2004
Location: GŁtersloh
Quote:
Originally posted by beppe61

What makes me crazy are units that measure worse and sound better !! how can this be ? but it seems it is.
Typically the absolute wrong stuff is measured... To get very good specs for 1khz measurings you have to sacrifice HF qualities.

Mike
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
a wonderfull sziklai east electronics Solid State 266 27th November 2012 02:34 PM
Sziklai pair as Vbe Multiplier? sam9 Solid State 12 15th September 2009 02:11 PM
Hybrid Sziklai CFP Stee Solid State 0 27th December 2008 10:53 AM
Negative Sziklai timH Solid State 17 30th July 2007 10:13 PM


New To Site? Need Help?

All times are GMT. The time now is 12:47 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2