Has anyone seen this front-end before? - Page 9 - 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 5th April 2012, 10:17 AM   #81
diyAudio Member
 
Edmond Stuart's Avatar
 
Join Date: Nov 2003
Location: Amsterdam
Default Op-amp vs Super TIS

Quote:
Originally Posted by PHEONIX View Post
Hello Edmond,

Congratulations on your excellent and thorough work ,
Hi Arthur,

Thank you!

Quote:
do you plan to include the Alexander type of front-end or will it be excluded because it uses an opamp and is not discrete.
It will be excluded. Not because it isn't discrete, but simply because it has been outperformed by the Super TIS front-end (in terms of complexity, distortion and slew rate). The reason I started to follow the op-amp route, was because a high-end discrete front-end seemed too complicated (see fig.5 on my website, 28 transistors!).
Also the op-amp based front-end, incorporating a NDFL stage, became quite complex, see this one , for example.
On top of that, I still had troubles with the active clamp.
The Super TIS on the other hand, is self-limiting. That means no active clamp and associated circuitry is needed.
So I decided to abandon the op-amp front-end and proceed with the Super TIS.

Cheers,
E.
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
  Reply With Quote
Old 5th April 2012, 11:16 AM   #82
diyAudio Member
 
Edmond Stuart's Avatar
 
Join Date: Nov 2003
Location: Amsterdam
Quote:
Originally Posted by Bonsai View Post
Edmond,

yes, more excellent stuff from your side - thanks for sharing.
Hi Andrew,

Thank you for your kind words.

Quote:
Any thoughts on using your front end with say 5-8 pairs of bipolar to create a big 200-250W amp, and, same question again wrt mosfets.
At he moment, I'm designing an OPS with four pairs of MOSFETs.
As for BJTs, No, see below.

Quote:
My concerns with bipolars are I have not seen a working design that uses HEC probably because of the low BE forward voltages make it more difficult to implement without losing headroom, or having to provide higher supply voltages to the front end.
Exactly. That's why I prefer vertical MOSFETs.

Quote:
EF3 goes some way to solving the linearity issues, but, my practical experience (both on the Ovation 250 and on my new e-Amp I am working on) shows that thermal lags across the EF3 completely dominate short term distortion - and here I talk about seconds to minutes. I am wondering if HEC can solve this issue (but maybe then we only need an EF2 again ;-)
HEC doesn't solve the thermal delay issue, of course. But it does decrease the associated distortion, that is, to a certain extent. Anyhow, as always, better avoid than cure'.

Quote:
WRT mosfets, how effective is HEC when a lot of devices are paralleled,
Theoretically, that shouldn't make any difference. Practically, I think, it will have some consequences: the more OP trannies, the beefier the driver has to be. It's the latter that might affect the effectiveness of HEC.

Quote:
and what about the current sharing issue in linear mode?
Imperfect current sharing has little effect on the distortion, BUT... I'm more afraid of 'current hogging' that might destroy one of the OP devices.

Regarding HEC and OPS bias, I consider it as obsolete (sorry Bob). My auto bias circuit version II not only reduces the distortion (to the same extent as HEC*), but also provides an (high speed) automatic bias control and it doesn't need an elevated front-end PSU. Please look here for a basic implementation.
Disclaimer: No one has built it yet, so I cannot guarantee it really works.

Cheers,
E.
edit; * because it uses essentially the same kind of feed forward frequency compensation.
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)

Last edited by Edmond Stuart; 5th April 2012 at 11:23 AM.
  Reply With Quote
Old 5th April 2012, 04:46 PM   #83
diyAudio Member
 
Edmond Stuart's Avatar
 
Join Date: Nov 2003
Location: Amsterdam
Default Complete Amp

Hi Andrew & Arthur,

At the bottom of this page I've put an example of a complete amp with Super-TIS, AB2 and a quadruple MOSFET output stage.
(BTW, I've no intention to redesign it for a BJT OPS, too much trouble, sorry)

Cheers,
E.
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
  Reply With Quote
Old 5th April 2012, 05:07 PM   #84
diyAudio Member
 
myhrrhleine's Avatar
 
Join Date: Jan 2006
Location: Avalon Island
Quote:
Originally Posted by Edmond Stuart View Post
Hi myhrrhleine,

Do you mean his paper about the enhanced cascode?
(i.e. "Reduction of Transistor Slope Impedane Depedent Distortion in Large-Signal Amplifiers.")

Cheers,
E.
hello,

I was thinking of this one:
Distortion Correction Circuits for Audio Amplifiers
J. Audio Eng. Soc., Vol. 29, No. 7/8, 1981 July/August
Fig. 12. Long-tail pair with error correction feedback.
__________________
Just because you can't hear it doesn't mean no one can.
  Reply With Quote
Old 5th April 2012, 05:14 PM   #85
diyAudio Member
 
myhrrhleine's Avatar
 
Join Date: Jan 2006
Location: Avalon Island
Quote:
Originally Posted by Bonsai View Post
WRT mosfets, how effective is HEC when a lot of devices are paralleled, and what about the current sharing issue in linear mode?
Hello,

I've seen four in parallel in a commercial design.
But I dont remember which brand.
The schematic was published as a discussion in EW/WW
__________________
Just because you can't hear it doesn't mean no one can.
  Reply With Quote
Old 5th April 2012, 07:42 PM   #86
diyAudio Member
 
Lazy Cat's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by Edmond Stuart View Post
At the bottom of this page I've put an example of a complete amp with Super-TIS, AB2 and a quadruple MOSFET output stage.
(BTW, I've no intention to redesign it for a BJT OPS, too much trouble, sorry)

Cheers,
E.
Wow this page really impressed me. In a so concentrated way so exact and DIY friendly explanations, very easy to follow, one can not see "every day". As a matter of fact I didn't see it ever. There's even comparison of TIS to more conventional VAS front-end and politely ruled out simply by the ppm distortion levels.
C o n g r a t u l a t i o n s.

P.S. Will the TIS project be rounded up with a PCB?
  Reply With Quote
Old 6th April 2012, 10:11 AM   #87
diyAudio Member
 
Edmond Stuart's Avatar
 
Join Date: Nov 2003
Location: Amsterdam
Default PCB

Hi Lazy Cat,

Thank you for your complements! I appreciate your feedback.

>Will the TIS project be rounded up with a PCB?
Maybe. The point is that for a project like this (THD20k ~1ppm), you will need an impeccable PCB, probably comprising four layers. Although I do have a notion of the basic principles, I consider myself not an expert in this field. So I hope someone else feels compelled to design a PCB, that adheres to the requirements for such an amp.

Cheers,
E.
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
  Reply With Quote
Old 6th April 2012, 12:23 PM   #88
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Well, to actually build and verfiy an amp like this on a non-pro DIY-level you'll need a lot of time, experience and access to the finest test equipment available.
So one would need
1) to be a seasoned expert in the field, for the experience part
2) to be retired, to afford the time
3) to have a full-blown lab at hand

Not many people seem to qualify...

Personally I'd find it more appealing to implement a minimalistic version that optimizes performance in relation to parts count and complexity instead of aiming at the ultimate in the sub-ppm realms. Of course the effort Edmond puts into all this, also the well-done documentation, is probably second to none and higly appreciated.

For a managable DIY project, I could think of a working version of the "barebone" approach plus a standard no-frills lateral output and then see how it compares to designs with similar complexity and parts count etc.
  Reply With Quote
Old 6th April 2012, 01:03 PM   #89
diyAudio Member
 
dchisholm's Avatar
 
Join Date: Mar 2011
Location: St Louis, Mo
I have a question about device selection.

Regarding Figure 2 on your site, at several places (Q2/Q5; Q9/Q11; Q7/Q8; Q16/Q17) I see medium-power driver transistors (KSC3503/KSA1381) where I expect to find small-signal devices. Was this choice driven by the need for large collector breakdown voltages, at the expense of bandwidth (Ft) and output capacitance (Cob)? Or is there another reason for using the TO-126 devices?

Conversely, the output stage uses general-purpose small-signal devices (BC550/BC560) where I expect to see medium-power drivers.

Dale
  Reply With Quote
Old 6th April 2012, 02:06 PM   #90
diyAudio Member
 
Edmond Stuart's Avatar
 
Join Date: Nov 2003
Location: Amsterdam
Hi Dale,

In fact, KSC3503 & KSA1381 are small signal transistors in a medium-power package, targeted at high definition CRT video output stages. So they do have a high ft and low Cob. Moreover, they have an exceptional high Early voltage. All properties that suit my needs.
Q19 and Q20 are pre-drivers, drawing only a few mA's and operating at a constant Vce of ca. 25V. So in this case BC560 and BC550 are more than adequate.

Cheers,
E.
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)

Last edited by Edmond Stuart; 6th April 2012 at 02:10 PM.
  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
Bogen Front End lpd Tubes / Valves 2 5th March 2008 04:12 AM
NE5534 with a new front end ...anybody? ashok Solid State 9 2nd June 2006 01:30 AM
My New Front End Pics! micb Car Audio 1 26th May 2006 02:26 PM
Noisily front end mantistube Analogue Source 10 16th January 2006 01:57 AM
Front end for sub amp mashaffer Solid State 9 22nd July 2005 03:35 AM


New To Site? Need Help?

All times are GMT. The time now is 05:19 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