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Old 2nd December 2012, 07:08 PM   #7841
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Quote:
Originally Posted by sampler View Post
Ok, here is what my simulator spitted out. Gain is 57dB and good riaa compliance with increased shunting resistor from 130k to 142k. Typical nice SE harmonic distribution for 1Vrms out with H2 dominant. There was missing bias resistor for buffer, added that.
Sampler,

I tried to simulate that with LTSpice but it doesn't seem to work.

In attachment the circut I am simulating.
Do you see anything wrong with it?
Model for the Mos are taken from the manufacturer's website.
Attached Images
File Type: jpg Simplicistic.jpg (111.1 KB, 186 views)
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Old 2nd December 2012, 07:34 PM   #7842
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I think R19 is not necessary.
You should get less gain with this circuit because the 2SK170 are less steep then the BF862
( less Gm ).
I am building the input gain cell at the moment in itīs most basic form, so lets see if it works.
Stafano, you should also raise R12 in value or the voltage over the CSS can break down.
It is better to make the CSS a little bit weaker in current supply compared to the input stage
then the other way around.
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Old 2nd December 2012, 08:27 PM   #7843
sampler is offline sampler  Lithuania
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Quote:
Originally Posted by Joachim Gerhard View Post
I am building the input gain cell at the moment in itīs most basic form, so lets see if it works.
Good, let's see what a real world throws out. Meanwhile I have done some homework, that may apply hear if DN2540 ccs misbehaves. One solution would be mosfet gyrator, that would do some self biasing. Zetex makes nice HV mosfets with very low Coss, so we get a good improvements in BW and THD, as parasitic capacitances are main source of non linearities here. Spice tends to agree with me (see attached). Don't know about noise though, it's always uncertain with mosfets. It could be a surprise in both ways. I think this could be made all smd with mosfets and bjt in sot223 and jfets in sot23. I'm starting to like it

Quote:
Originally Posted by Stefanoo View Post
I tried to simulate that with LTSpice but it doesn't seem to work.
What JG said, try to step. R12 and plot Q1 collector voltage for ~18V op point.
Attached Images
File Type: png CM_gyrator.PNG (37.0 KB, 176 views)
File Type: png gyro_fft.PNG (23.4 KB, 169 views)
File Type: png gyro_temp.PNG (19.6 KB, 159 views)
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Old 2nd December 2012, 09:17 PM   #7844
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I build the input stage and there is too much thermal drift. I ballasted the output with 100kOhm and took a 25V supply ( two 12V lead batteries in series ).
The situation is that the BD139 goes into saturation when the voltage drifts down.
The voltage over the Fetīs is stable because the Leds minus Ube force that.
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Old 2nd December 2012, 09:19 PM   #7845
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I have some Zetex MosFets but i do not know if they are usable. I will look up the types.
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Old 2nd December 2012, 09:21 PM   #7846
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The DN2540 CCS is very low in noise. I know that because i use them in my tube RIAA that is superbly low in noise for a tube solution.
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Old 2nd December 2012, 09:50 PM   #7847
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Here are the extremes, around 7V minimum and 16V maximum.
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File Type: jpg cm1.jpg (911.7 KB, 160 views)
File Type: jpg cm2.jpg (595.0 KB, 82 views)
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Old 2nd December 2012, 10:28 PM   #7848
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To find the right time to make the photo is not easy so the values you see optically are a little bit away from the extremes.
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Old 2nd December 2012, 11:14 PM   #7849
Salas is offline Salas  Greece
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Use the back light and hold button.
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Old 3rd December 2012, 12:01 AM   #7850
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Sure, sometimes i am stupid.
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