John Curl's Blowtorch preamplifier - Page 20 - 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
Closed Thread
 
Thread Tools Search this Thread
Old 24th February 2006, 02:14 PM   #476
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
It is your problem, Elso....
 
Old 24th February 2006, 02:41 PM   #477
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Question Wizard?

Quote:
Originally posted by Upupa Epops
It is your problem, Elso....
Hi Upupa Epops,
Is a wizard synonymous with a Guru?
Are you a Guru Upupa? Or a wizard?
 
Old 24th February 2006, 04:29 PM   #478
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
Guru and wizards are two things, Elso.... And what am I ? It is not question for me...
 
Old 24th February 2006, 05:47 PM   #479
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
It’s better than Dallas! Don’t know more recent examples, … no TV set!

Quote:
Originally posted by Justcallmedad
Speaking about fets, and specially about the 2SK170/2SJ74 or the 2SK389/2SJ109 pairs, I notice than using them at low Vds, lower than 12V give the best results, even M. Borbely uses them in the saturation region, I guess around 1V in his fet/fet cascode configuration, can someone enlighten me on this subject? Igsx maybe?
Igsx.

No idea, no one ?
__________________
Richard Perez
 
Old 24th February 2006, 06:13 PM   #480
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
I usually run fets around 15V, or about 1/2 their voltage rating. I do this because they become more linear at high frequencies with MORE voltage, but then they will start to leak gate current, if too much voltage is applied. Look at the detailed data sheets of specific fets and the change of Cgs and Cdg with voltage. You will find the 'rate of change' to level off after several volts. Very low voltage operation gives you high value, non-linear capacitance from inside the fets.
 
Old 24th February 2006, 06:34 PM   #481
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Thanks M. . It's what I suspected, but not as much for Cgs and Cdg.

I have another question about a fact that I can’t explain completely and of which I partially talk here during the discussion on dc-servos : Carrying out some tests on the input stage (fig 1) and the dc-servo of a power amp (in spite of the fact that I used a small value resistor for R after the integrator), I get much better results with the (fig 2) and a quite softer sound.
I thought that the problem could come from mixing 2 references, input ground and dc servo ground, then I tested the (fig 3) imagining that it could be a problem of ground currents and ground loops (I talk here about a power-amp), and in this case the sound was much more softer and more “live”. Do you think as I it suspect but I am not completely sure that it is a ground problem , have you another or better explanation?

Fig1-fig2-fig3
__________________
Richard Perez
 
Old 24th February 2006, 06:38 PM   #482
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Sorry the link is wrong! Here it is.

Click the image to open in full size.
__________________
Richard Perez
 
Old 24th February 2006, 06:49 PM   #483
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
You must imagine output of integrator like " floating ground " ( in look of AC signal ) . Value of output resistors are compromise between good SNR and good distortion, as you understand me...
 
Old 24th February 2006, 07:26 PM   #484
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Hi Upopa,

So you agree that a floating ground improves the naturalness, and the fidelity, as long as the ground reference for the integrator and the virtual ground op amp is the same and clean.

As you seem to know well the Borbely stuff, do you know the advantage of using his fet/fet cascode configuration even if the lower fet Vds is only about 1V.
__________________
Richard Perez
 
Old 24th February 2006, 07:37 PM   #485
Account Disabled
 
Join Date: Apr 2004
Location: Cysoing, near Lille
Hello, Upopa,

For sure that wizzards and gurus don't exist.... I built lots of amps and preamps, and also tested/upgraded some more for friends... Nothing to do with Black Magic, eh ! I don't think that my current scope and meter were on a vaudou influence too... But I can be wrong with these ones...

All I know is that John Curl NOT only is an engineer. He also collaborated to theory works... I have the works here at home. And I sometimes wonder what would audio world would be just juggling with uA709 & 741, and bad capacitors, Upopa. Seriously...

Was not so big a crowd of engineers advocating against poor opamp performances. Not defending special topologies... Still to see from other names you have in head associated with that.... NOW they are sharing data, but I didn't hear any in the business 25 years ago... Now, we have rather large access to patents and so on... Wasn't the case some years ago.

And it is the reward of sharing : Nelson Pass himself had to drop off his VERY interesting site. Guess why.

And because you seems to put me a lesson in testing here, I favourite Class A running, and experimented with almost all active parts available through years, from bipolars to IGBT with Mosfets in the middle and some others... Vfets as an exception ! And also experiences like Alexanders one ...

But sorry, Upopa, you can't read in my head nor put more in my words much that it is ! I am just advocating John Curl's work... What happened to him with time is out of my current thinking. And I already know that some guys just think him as a pretentious guy, guru like and very hard to deal with.... Perhaps. But I won't certainly judge nobody on a single word... On repeated facts, perhaps ...(Upopa, you don't know it, by I am formerly a lawyer... Hence my "special analysis" of things that happen... And please have my apologies for these rude words, John !!!). But that doesn't change anything in the full story...

Now, what am I doing here, in this forum ? For sure NOT having crusades against guys that just think different,, like you... But frankly, I am trying to see why some Curl's backworks are made for... And just to point any word against others "gurus" you have perhaps associated with my own mind. So, the debate is closed with you on my side, Upopa. Still to hear of you on a more cinstructive basis, and NOT a mind justice...

My current project ? Oh, yeah ! "The Flame Thrower" ! Guess why !

Jbaudiophile
 
Old 24th February 2006, 07:47 PM   #486
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
A self referenced cascode is a good compromise design component. This is where the cascode is made by a fet with its gate tied back to the input fet's source.
Usually, we use 2 different fet types for this. A short gate, low Vg part (hi transconductance) for the input part and a long gate (low transconductance) part for the cascode part. Identical parts may be an interesting solution, but I tend to avoid it. The input capacitance will be very high, BUT the change in drain-gate voltage will be very small, so the non-linear capacitance will be essentially invisible. This is not true with a non cascode fet that has to swing significant voltage at its output. Here, operating voltage across the fet is very important. Of course the best is to operate the fet with a reasonable voltage, and then cascode it as well. Best of both approaches.
 
Old 24th February 2006, 08:09 PM   #487
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Oh yes his cascode configuration is very attractive! I agree, but as I said, in this case the “active“ device only sees something like 1V or so, if it where a BJT no problem, but in the saturation region? A lot of parameters seem to be less interesting, Cgd Cgs Yfs, but I guess that as the active device doesn't sees the signal, it doesn't matter...
__________________
Richard Perez
 
Old 24th February 2006, 08:09 PM   #488
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
Inpact of DC servo to sound is more complicated and isn't based only on ground " problem " . You must imagine, that this output's resistor is connected in parallel with feedback resistor and output of integrator substitute true ground for AC signal. If integrator will be forced, thanks to uncorrect condition ( for example too high output current ), to work at his own parameter border, will injected into feedback loop own distortion ( virtual floating ground will be not perfect ). So by another words spoken : we must be very careful with value of components and type of this circuit at this position. By my opinion most of objections against this solution are cause by this reason.
 
Old 24th February 2006, 08:21 PM   #489
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Yes Upopa, but in my tests the fig2 circuit was better than the one of fig1. I didn't use feedback in this amplifier.
I am also agree now that a larger value resistor will be better, but for my tests as the resistor sets the gain in fig2 circuit ...
__________________
Richard Perez
 
Old 24th February 2006, 08:39 PM   #490
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
I don't know DC condition off all discrete circuit - 'cos you have at fig. 1 at output voltage divider, output of opamp can be overloaded...
 
Old 24th February 2006, 08:48 PM   #491
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
BTW, do you know, what cut man on this record ( at RW's ) ?
 
Old 24th February 2006, 09:19 PM   #492
Account Disabled
 
Join Date: Apr 2004
Location: Cysoing, near Lille
Hi, JustCallMeDad

If your schematics refers to the Blowtorch, please consider that it works BOTH BALANCED and UNBALANCED... So, it is just much more complex that the usual interator way.. . That is ways off the real problem...

And here we are not in the books guruing (as I ever heard from somes), but in real engineering... An answer to this differential problem, anyone ?

Still to hear from your own studies, Upopa... Sorry for, but pressure will increase A LOT from my side... Want to see your proposal first... Mine second only... And guess who is the lessons on that I took from ? Any Guriu ? NO !

Go for the challenge, Upopa ???? Good .... But if your question was off thsi topic, please consider I haven't said a single word...

Jbaudiophile
 
Old 24th February 2006, 11:02 PM   #493
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Quote:
Originally posted by Upupa Epops
BTW, do you know, what cut man on this record ( at RW's ) ?
Sorry Upopa I don't understand "cut man". By RW you mean Roger Waters? Could you develop.
__________________
Richard Perez
 
Old 24th February 2006, 11:02 PM   #494
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Looking at those servos, I see a BIG problem. You should not create an artificial ground and then run audio through it. It will map itself into the audio signal itself, i.e. any impurities generated by the servo IC will be part of the audio path. No wonder you can hear these servos so easily. Always separate the servo from the audio thru-path. This can be done by adding a low value resistor to ground, and the servo resistor high valued. Then a small imperfection in the servo will be attenuated many times before it is added to the audio path.
 
Old 24th February 2006, 11:10 PM   #495
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
In the song, where goes horses, some man cut something by axe. What he cut ?
 
Old 24th February 2006, 11:11 PM   #496
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Yes John you are completely right, it's exactely what I thought doing the test, and I was very surprised In listening to it and discover that circuit 2 and 3 where better than circuit 1! Essentially the third one!

Il
__________________
Richard Perez
 
Old 24th February 2006, 11:15 PM   #497
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Ah YES! Ahem.... Really don't know, jb...maybe ? , In vinyl it's marvelous Upopa
__________________
Richard Perez
 
Old 24th February 2006, 11:18 PM   #498
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
None of these circuits is optimum. Circuit one does not have enough attenuation to remove the servo imperfections. The other servos should do even more change to the sound.
 
Old 24th February 2006, 11:22 PM   #499
diyAudio Member
 
Justcallmedad's Avatar
 
Join Date: Jun 2004
Location: Paris
Some day I will test again these 3 configurations WITH A BIG R! after the servo John , What is possible also is that something else has change, during the listening, in the circuit a contact or a bad welding and disturb the test.
__________________
Richard Perez
 
Old 24th February 2006, 11:28 PM   #500
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
He cut eis, Richard...listen closely ...
 

Closed Thread


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



New To Site? Need Help?

All times are GMT. The time now is 11:46 AM.


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