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Old 14th September 2010, 12:33 AM   #111
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this circ can be optimized for 1541 either with dedicated 2mA CCS from positive PSU leg to I out ........ or even passively - (probably clever to use higher grade Jfets) decreasing lower Jfet current ( 2mA again ) with pot placed in source

now I'm going to sleep ....
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Old 14th September 2010, 08:38 AM   #112
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Quote:
Originally Posted by apolon34 View Post
The psrr of the circuit is almost zéro, so use a great quality psu.
Gaetan,

means you'd have to do something about the 7812/7912 regulators.
Example : 7815 reg on the left, discrete voltage regulator with -124dBV output noise on the right.
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Old 14th September 2010, 04:54 PM   #113
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Quote:
Originally Posted by Gordon McGregor View Post
Concerning the op amps - what is the difference between the discrete op amp and IC op amp, if the last one has been designed correctly?
Not much.
The problem is most of them are not designed for specific jobs.
They are jack of all trades devices, and what makes them sell or make money for the company are the thd measurements, etc.
This usually means massive amounts of gain and massive amounts of feedback.
As diyers we don't have as much opportunity to use our brain when using opamps, this eventually leads to boredom.
It might be a different story if you are a design engineer for Analog Devices or National Semiconductor. If I was offered a job by either of those two companies I would be excited, because it would be an opportunity to learn quite a lot.
I think it is all about having complete control over the design process when you use discretes, which is something I find lacking if I resort to IC's.

When I first started this hobby, my motivation was to be able to build something I couldn't afford to buy in the shop.
Now it is all about trying to understand how everything works, and building my own circuits. I think that is also true for a lot of other Pass fans.

Last edited by Melon Head; 14th September 2010 at 05:14 PM.
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Old 14th September 2010, 05:58 PM   #114
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[snip]Now it is all about trying to understand how everything works, and building my own circuits. I think that is also true for a lot of other Pass fans.
Hear! Hear! That's the best reason I know for audio diy.
I think it is true for a lot of audio diy-ers, period!

jan didden
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Old 16th September 2010, 06:20 AM   #115
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Hello

I've ad pi filters to the rails and simulated the russian bjt version of the Zen I/V amp with LTspice, but it give a bad output signal.

Anyone can check it with LTspice to see where I've done errors ?

Thank

Bye

Gaetan
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File Type: txt Zen IV amp-BJT version russian.txt (4.3 KB, 243 views)
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Old 16th September 2010, 07:00 AM   #116
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Hi Gaetan,

There is a lot of problems with this stage:
- You use a voltage source input. Should be a current source with offset=2mA, amplitude=2mA to simulate a tda1541

- the bias current is way too low. Should be around 10mA at least to correctly handle +/-2mA swing.

- the input supply should be stable if you want to use the 6k resistor as a current source. If it is not, use a current source with a jfet.

- the rails are too low to have 10mA at idle in the output resistor R1/R4.

I've made some simple modifications to make it run:
- set the source to current type
- supply with +/- 24v
- bias resistor at input 3k

it simulates ok then
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Old 16th September 2010, 08:39 AM   #117
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Quote:
Originally Posted by apolon34 View Post
....There is a lot of problems with this stage:...
Just to make sure that everyone understands clearly - there are no problems with the I/V stage from post #106 (it works nicely, with 8.5mA through input pair and PS of +/-24V instead of +/-12V, Zin=2.5 Ohms).

The only problem is the way the Gaetan simulated it (apolon34 described the errors).

Let's not hijack this thread further - guys with interest in BJT stage from post #106 can open separate thread.
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Old 16th September 2010, 08:41 AM   #118
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Hello apolon34

I've use the circuit from post 106 without mods, but I've forgot to give a sine current source.

After using your suggestions it's now working and thd spectrum simulation give a -80 db thd for the second hamonic.

Here is the new sim file in text version.

Thank you

Bye

Gaetan
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File Type: txt Zen IV amp-BJT version russian.txt (4.3 KB, 115 views)

Last edited by gaetan8888; 16th September 2010 at 08:43 AM.
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Old 16th September 2010, 08:48 AM   #119
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Quote:
Originally Posted by juma View Post
Just to make sure that everyone understands clearly - there are no problems with the I/V stage from post #106 (it works nicely, with 8.5mA through input pair and PS of +/-24V instead of +/-12V, Zin=2.5 Ohms).

The only problem is the way the Gaetan simulated it (apolon34 described the errors).

Let's not hijack this thread further - guys with interest in BJT stage from post #106 can open separate thread.
Hello

Sorry, it was not my intention to hijack this thread.

Back to the NP jfet version, the only 2SK170 here arround are a cheap chineese V version, and no 2SJ74

Does the original NP jfet version are much better than the russian bjt version ?

If yes, I will look for good jfet and built the NP Zen I/V

Thank you

Bye

Gaetan

Last edited by gaetan8888; 16th September 2010 at 08:51 AM.
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Old 16th September 2010, 09:59 AM   #120
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Quote:
Originally Posted by gaetan8888 View Post
Hello

Sorry, it was not my intention to hijack this thread.

Back to the NP jfet version, the only 2SK170 here arround are a cheap chineese V version, and no 2SJ74

Does the original NP jfet version are much better than the russian bjt version ?

If yes, I will look for good jfet and built the NP Zen I/V

Thank you

Bye

Gaetan
Sonically, the jfet version might sound better than the bjt one;
it's not the overall design that achieves this,
but mostly the nature of the devices themselves
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