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Old 19th August 2012, 07:54 AM   #251
Calvin is offline Calvin  Germany
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Hi,

just to show the differences in THD only due to different models:
The circuit simmed is described in #95 and #99 of the Zen-Cen-Sen thread A), B) is a bipolar Version.
The differences in A) and B) are the sole use of either the Philips/NXP models of the BC847C/857C or the BC847BS/857BS of Zetex/Diodes.

For both circuits the differences in THD are remarkably high, with the Zetex/Diodes models giving app. 25dB lower THD!
The spectra of THD remain similar in A), with a clean decay towards higher Ks, but the level of the Ks change. The spectra of B) differs in that K3 is higher than K2. Overall Level of THD is again much lower with Zetex/Diodes Models.
Another Sim of B) using the BC807-40/817-40 Models of Philips/NXP (807/817 are the SMD versions of BC327/337) gave similar, rather slightly worse results to the sims with the BC854C/857C Philips models. No improvement in noise figures also.

jauu
Calvin
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File Type: jpg IV complementary JFET-Satri.jpg (298.2 KB, 598 views)
File Type: jpg IV complementary JFET-Satri THD.jpg (212.9 KB, 555 views)
File Type: jpg IV complementary bipolar-Satri THD.jpg (213.3 KB, 501 views)

Last edited by Calvin; 19th August 2012 at 07:57 AM.
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Old 19th August 2012, 09:16 AM   #252
MiiB is online now MiiB  Denmark
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I really like the Bipolar version.. A little paradise in that.. I have experienced that the mirror with only one helper and both connections from the source side has higher and more even impedance. Have you tried the 337-327-40 transistors in that circuit..??
Also it would be possible to inject current via mirrors and servo the circuit so there will be no need for adjustments.. well maybe adjustment for the DAC current off set.
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Old 19th August 2012, 10:18 AM   #253
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Using discrete/unmatched bipolars, you'll need to have 100 milliVolts DC voltage
across emitter degeneration resistors. Thus at 10mA you'll need 10 ohms.
To tweak that current, inject up to 5mA (thus accomodating up to 50mv Vbe
mismatch) by hanging a high-value resistor to GND (which degrades PSRR).

If you hand-select bipolars for matching, within 10mV, you'll still need
degeneration resistors to assist in balancing the up and down behaviors, and
you'll still need say 10 ohms (and 100mv DC drop), but you can inject less
tweak-current. Using a current-source (cascoded for high Rout) as injector
will preserve PSRR.
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Old 19th August 2012, 11:25 AM   #254
EUVL is offline EUVL  Europe
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Similar (but not identical) bipolar versions as Joachim has built have been discussed and tested at the original CEN IV thread.
Here are a few links, if I may :

Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
Zen -> Cen -> Sen, evolution of a minimalistic IV Converter

We still have a few of those CEN BJT PCBs left that Davide built his with.
You are welcome to those if you would cover postage and packing.

We are definitely sticking to JFET ourselves, despite the high-ish Zin.


Patrick
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Old 19th August 2012, 01:35 PM   #255
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I am still not able to make this new input stage work. I found a mistake in my voltage divider that i use after my audio oszillator. After fixing it again i got oszillation. I hope i have not destroyed anything but the currents and voltages in the circuit look resonable.
I will now try the other channel.
Things go slow here, it is extremely hot outside so i am more in the mood to digest a cold drink. Tonight i will go to cinema with my son. Prometheus by Ridley Scott.

Last edited by Joachim Gerhard; 19th August 2012 at 01:37 PM.
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Old 20th August 2012, 11:56 AM   #256
Shinja is offline Shinja  Japan
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Old 20th August 2012, 12:58 PM   #257
EUVL is offline EUVL  Europe
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Very very clever. Love it to bits ......
Still not sure if it sounds like opamp ???????????





Patrick
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File Type: asc Opamp CEN.asc (1.4 KB, 96 views)
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Old 20th August 2012, 02:36 PM   #258
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Opamps and XEN, does that fit together ? (:
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Old 20th August 2012, 03:49 PM   #259
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by EUVL View Post
Very very clever. Love it to bits ......
Still not sure if it sounds like opamp ???????????





Patrick
shinja is a clever guy
Use a lme49600 and you will have a killer cen.
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Old 20th August 2012, 03:53 PM   #260
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Quote:
Originally Posted by smms73 View Post
shinja is a clever guy
Use a lme49600 and you will have a killer cen.
HAHAHA. Running an LME49600 backwards! I need a drink.
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