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 16th September 2012, 08:51 AM   #961
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by keantoken View Post
Ho much matching do you think is necessary for this frontend? I just measured 10 Fairchild BC550C's. They ere mostly ithin .3mV of each other, but never larger than .8mV apart. In the simulator I find a 2.7mV mismatch causes a 10% current difference in an LTP and a .3mV difference causes a 1.1% current difference.
I think matching by measuring individuals is worthless for us amateurs who cannot control Tj.

I repeatedly recommend REF&DUT matching to make some attempt at holding similar Tj between DUT and REF.

If Tj is uncontrolled then one cannot possibly rely on any measurements.

Ref your 0.3mV or sim at 2.7mV This would almost certainly have been revealed had you clamped the two devices together and applied the Test & Measurement jig to the pair. Matching of the collector currents to <1% is not easy. Most importantly the resistors must be selected to be <<1%. The base resistors must also be allowed for, or shorted out, otherwise a small difference in hFE will draw different base currents and the base resistor then applies a Vbe diff due to the different Base resistor Vdrop.

By the Way, I don't match Vbe. I send the same voltage to both bases. I measure the absolute collector currents and the differential collector voltages. If the REF & DUT has a small Vbe mismatch then the jig throws this out as a severe Ic mismatch. Try the next pair.

I swing the test Ic either side of operating bias current by adjusting the applied base voltage. If the REF & DUT track (near zero differential collector voltage) over a decent range of Ic, then I have a matched pair.
__________________
regards Andrew T.

Last edited by AndrewT; 16th September 2012 at 09:08 AM.
  Reply With Quote
Old 16th September 2012, 09:04 AM   #962
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by Dave Zan View Post
I already satisfy Self, Cordell and ..............and now Edmond will like it too
Don't include me in that company. I only read, assess, choose/bin and then test. I don't "design" anything. I copy what I think are the "good enough" proposals and try to implement in a useful way.
__________________
regards Andrew T.
  Reply With Quote
Old 16th September 2012, 09:18 AM   #963
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
[QUOTE=HarryDymond;3165854]Ah, ok. What I see in that post is what I meant by a diamond buffer + EF triple (as what I mean is [diamond buffer + EF] triple, rather than [diamond buffer] + [EF triple]). Arthur, where did your transistor models come from? Many are really poor. If the models for the drivers aren't great, how about trying my 2SC5171/2SA1930 models? And for the final output devices, I wonder if using 1302/3281 output transistors would make much difference as these have flatter beta vs. Ic, and higher Vceo with possibly correspondingly lower early effect (although this doesn't always go hand-in-hand).

Hello Harry,

My previous sims where with Fairchild models predrivers KSC2690 and KSA1220, and Sanken supplied models of the 2SA1216 and 2SC2922, all other models are Cordell derived types.

Thank you for your work on the 2SC5171/2SA1930 models attached are some sims using them with (Cordell models) MJL1302C/MJL1302C. I also included simulations showing an additional ideal buffer between the TIS input stage and diamond EF output stage which provides perfect loading of the TIS stage and I think the results speak for themselves.

Arthur
Attached Images
File Type: png TIS_BUFFER + DIAMOND EF OUTPUT.png (59.2 KB, 117 views)
File Type: png TIS_BUFFER + DIAMOND EF OUTPUT_THD.png (72.9 KB, 118 views)
File Type: png TIS_DIAMOND EF OUTPUT.png (60.7 KB, 113 views)
File Type: png TIS_DIAMOND EF OUTPUT THD.png (42.1 KB, 89 views)
  Reply With Quote
Old 16th September 2012, 09:48 AM   #964
diyAudio Member
 
Join Date: May 2005
Location: Bristol, UK
Thanks for your efforts Arthur; most intriguing! Looks like different transistors make near-as-damn-it no difference, and the addition of an ideal buffer also makes no difference. Presumably this means the triple isn't upsetting the performance of the front-end but we're merely seeing a limit on the performance of this type of output stage? If this is the case I'm surprised that this is nearly 0.003%; I would have expected somewhere between 1 and 10 ppm (although I haven't seen a loop-gain plot so is loop gain from 20 - 100 kHz just not that high?). What happens if you add a second pair of output devices?

Could you also probe the output of the front end (i.e. the node joining Q8 and Q12 collectors) and calculate distortion at this point?
  Reply With Quote
Old 16th September 2012, 11:05 AM   #965
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Default TIS VOUT THD

Hello Harry,

See attached schematic and THD plot.

Regards
Arthur
Attached Images
File Type: png TIS_VOUT THD.png (58.0 KB, 84 views)
File Type: png TIS_VOUT THD GRAPH.png (60.4 KB, 48 views)
  Reply With Quote
Old 16th September 2012, 11:15 AM   #966
diyAudio Member
 
Join Date: May 2005
Location: Bristol, UK
Quote:
Originally Posted by PHEONIX View Post
Hello Harry,

See attached schematic and THD plot.

Regards
Arthur
oops! I wasn't thinking was I? To linearise the output stage, a pre-distorted signal must be applied at its input. So when negative feedback is working, we would expect the front end to have a distorted output!
  Reply With Quote
Old 16th September 2012, 11:19 AM   #967
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Default THD with 2 pairs.

Hello Harry,

Even when I load the TIS_VOUT node with 100k it has very little effect on the THD at the output across the 8R load.

Attached is the THD simulation with 2 output pairs.

Regards
Arthur
Attached Images
File Type: png TIS_BUFFER + DIAMOND EF 2 pairs.png (61.4 KB, 38 views)
File Type: png TIS_BUFFER + DIAMOND EF 2 pairs_THD.png (53.2 KB, 30 views)
  Reply With Quote
Old 16th September 2012, 11:24 AM   #968
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Hello Harry,

My understanding is also that the THD output of the TIS should be higher.

Arthur
  Reply With Quote
Old 16th September 2012, 11:24 AM   #969
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by HarryDymond View Post
oops! I wasn't thinking was I?
I had to rethink too.
To see the distortion of the superTIS we need to take the feedback from the superTIS output.
Will need to be buffered but that is easy, can we see that, Arthur?

Best wishes
David

PS
Quote:
Originally Posted by Pheonix
Even when I load the TIS_VOUT node with 100k it has very little effect on the THD at the output
Perhaps my concern about the load on the superTIS has been based on a faulty assumption all the time.

Last edited by Dave Zan; 16th September 2012 at 11:35 AM. Reason: Added PS and buffer requirement
  Reply With Quote
Old 16th September 2012, 11:40 AM   #970
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Default TIS THD with ideal ouput stage

Hello Dave and Harry,

The TIS stage by itself has very low THD its fair to say that the main source of distortion is the conventional diamond EF output stage. Even the simulation with the addition of the ideal buffer between the TIS output and conventional output made a very small difference and I don't think its worth the effort.

Regards
Arthur
Attached Images
File Type: png TIS_THD.png (40.8 KB, 46 views)
File Type: png TIS_THD_graph.png (66.3 KB, 47 views)
  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 02:19 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