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Old 17th September 2006, 01:34 AM   #41
spencer is offline spencer  Hong Kong
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Hi Cheff,

Very nice work and I am interested to build your current mirror UGS. Few questions:

1. The Idss of K389 and J109 BL grade is from about 6mA and up to 12mA, since the bias is at about 3.5mA, can I use fet of about 6.5mA Idss? What is the performance difference (gain, distortion, sound etc.) for 6.5mA and 10mA Idss parts?

2. Must I match the Idss of K389 to J109, or within what % will not deteriate the distortion/gain too much?

The reason I ask is that I have about 20pcs K389 but no J109 and if I am to get J109 to match them, I have to know how many expensive J109 I should buy.

Where do you think J109 is still available?

Thanks,
Spencer
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Old 17th September 2006, 07:13 AM   #42
EUVL is offline EUVL  Europe
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Cheff,

Very impressive.

Could you tell us a bit about your control board ?
Is it your own design (as a see a different PCB colour to the rest) ?
I guess it is uP based, with remote control ?
What uP are you using ?

Thanks,
Patrick
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Old 17th September 2006, 06:05 PM   #43
Manu is offline Manu  Europe
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Formidable!
Would you share the design of the control board too? Is there a PCB availlable ?
Le botier aussi est "fait main"? J'aime beaucoup aussi
Bravo encore.
Manu
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Old 17th September 2006, 06:30 PM   #44
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Cheff,

Nice pre.

It's the UGS that puzzles me a little bit.
You mentioned a biascurrent through the jfets of 3,5mA.

The current mirror would mirror this bias current to the output bjt.
But it looks like the current through the output (being part of the
mirror) is much higher?
Is the mirror not functioning as a mirror?

Also OL gain looks like 25-26 dB. CL gain 14dB
That's awfull liitle feedback
But then you mention 35dB as OL Gain.

Just to verify: Could you post the bias voltages for the jfets.

The results I get (in sim using simetrix) are very similar to one of
the previous posters. Notice the crossover distortion?

Hope you can shed a light or two...

Regards
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Old 18th September 2006, 10:23 AM   #45
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Hi rtirion

If you look at the current mirror the emitter resistors are not the same.
So the current in the output is double the current of the jfet.

Rob
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Old 18th September 2006, 10:39 AM   #46
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Hi all,
Thanks for the questions

Quote:
Originally posted by spencer
1. The Idss of K389 and J109 BL grade is from about 6mA and up to 12mA, since the bias is at about 3.5mA, can I use fet of about 6.5mA Idss? What is the performance difference (gain, distortion, sound etc.) for 6.5mA and 10mA Idss parts?
Bias will depend on the Idss ratings, since it impacts on the Id=f(vgs) curve.
I quickly simulated using GR parts, with an Idss of about 4mA, and
as awaited the bias is lower (2.3mA). The whole pre will work, but
expect lower gain, both open loop and with CR. So, to answer your
question, it will work for a 6.5mA part, but the input range before
clipping will be reduced, and hence the output swing. But in
"normal" applications, the clipping levels will seldom be reached...
So if you find BL parts, just try them, listen carefully on your setup,
and try to go ahead by matching Idss, pinchoff, transconductance,
Vbe, Hfe, etc... and tell us what you find. That's what this forum is
about

Quote:
Originally posted by spencer
2. Must I match the Idss of K389 to J109, or within what % will not deteriate the distortion/gain too much?

The reason I ask is that I have about 20pcs K389 but no J109 and if I am to get J109 to match them, I have to know how many expensive J109 I should buy.
The fets I used are not matched (N & P wise) but their Idss is between
8 and 10mA each, for those I measured. And I didn't tried to match
them, but your point is an interesting issue. I don't have the
proper measurement facilities, so it's very hard for me to tell you
about real distorsion figures... But sure, this has to be investigated.
Again, buy 2 to 4 2SJ109BL, and try them the design before going
further... In the case you don't like it...

Quote:
Originally posted by spencer
Where do you think J109 is still available?
I really don't know. Got mine in France. But in your part of the world,
this should be easier. Had a look at http://www.hkinventory.com/public/Home.asp ?

Quote:
Originally posted by EUVL
Cheff,

Very impressive.

Could you tell us a bit about your control board ?
Is it your own design (as a see a different PCB colour to the rest) ?
I guess it is uP based, with remote control ?
What uP are you using ?

Thanks,
Patrick
Thanks Patrick.
The control board is also my design, but the final pcb was a bit
beyond my local shop possibilities, so I had it made by a pro shop,
which explains the different color
The C is an Atmel AVR ATmega64. It's remote controlled (Philips
RC5 code), with a learn function. It is specifically designed to meet
my needs, but if needed, I will post the schematics, Gerber files and
software.

A view of the whole board :

Click the image to open in full size.


Quote:
Originally posted by rtirion
It's the UGS that puzzles me a little bit.
You mentioned a biascurrent through the jfets of 3,5mA.

The current mirror would mirror this bias current to the output bjt.
But it looks like the current through the output (being part of the
mirror) is much higher?
Is the mirror not functioning as a mirror?
Well, it's an "amplifying" mirror
Just a crumb from the master :
http://www.diyaudio.com/forums/showt...295#post720295

Quote:
Originally posted by rtirion
Also OL gain looks like 25-26 dB. CL gain 14dB
That's awfull liitle feedback
But then you mention 35dB as OL Gain.
It depends on which gain you're talking about, and I generally
consider the differential gain (Vout+ - Vout-)/(Vin+ - Vin-). My sims
give an OL Diff Gain of 33dB (sorry for the 35dB, it was from memory....),
and a CL Gain of 10.5dB. Substract 6dB to get the unbalanced gain.

Besides, it seems to me that NP mentionned that SuSy was more
effective when the amount of feedback was not too high, but
I can't find the post...

Quote:
Originally posted by rtirion
Just to verify: Could you post the bias voltages for the jfets.
Here you are (bias conditions):

Click the image to open in full size.


Quote:
Originally posted by rtirion
The results I get (in sim using simetrix) are very similar to one of
the previous posters. Notice the crossover distortion?
I'm a bit puzzled about your crossover distortion, as both branches
(positive and negative) are always working and never cutting off..
Do we speak about the same thing ?

Regards,
__________________
/Cheff - Falling feels like flying, until you hit the ground
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Old 18th September 2006, 12:16 PM   #47
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For people having downloaded the PCBs' PDF, there's a little error on the actual
size of the boards. The correct size is 55.12mm x 38.34 mm. You can use the pdf
you already have "as is", but don't try to scale it to get the size mentionned in the
file

The pdf has been corrected, and is still available here

Sorry for inconvenience

Regards
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Old 18th September 2006, 08:27 PM   #48
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Default Problem solved.

Cheff,

You're a live safer.
The schematic with the bias voltages was very, very helpfull.

Showed I made a terrible mistake. Used a j175 model instead
of 2sj109 model.
That tipped things a little out of balance.
Checked the schematic more than 10 times, still didn't see my
mistake. I am probably a seeing blind bat or something.
Unfortunatly I do no longer own a huge CRT monitor.
Otherwise I would show you the big dents in the screen from
banging my head against it.

But, I changed the j175 to 2sj109 and everything (bias wise and
looking at the wavevorm 1K sine, no more crossover) looks perfectly normal.
Bias voltages/currents are a little different but nothing alarming.

Will look at OL and CL gain, and report back later.

Thanks again
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Old 19th September 2006, 08:38 PM   #49
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Hi Cheff

Quote:
The C is an Atmel AVR ATmega64. It's remote controlled (Philips
RC5 code), with a learn function. It is specifically designed to meet
my needs, but if needed, I will post the schematics, Gerber files and
software.
I'm very intrested would you post it.
Looks very nice.

Thanks
Rob
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Old 19th September 2006, 09:33 PM   #50
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Hello Cheff,

Nice work, very impressive. Hats off.

Simulation figures look good. To what extend do they correlate with real measured figures?

Regards.
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