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Richard Lee's Ultra low Noise MC Head Amp
Richard Lee's Ultra low Noise MC Head Amp
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Old 16th August 2019, 11:57 AM   #1311
aboos is offline aboos  Germany
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Quote:
Originally Posted by herve00fr View Post
I'm glad to see that doing some math decrease the input current noise from 58nV/rtHz to 20pA/rtHz.
I have not the time to make simulation and calculation right now but I think this behaviour is only due to the current mirror noise into the output impedance of the amplifier.
This can be lowered by increasing the degeneration resistors and the power supply.
The 58nV were my error, I made pV to nV
Just could also confirm with a couple of sims that it is indeed the current mirror noise current flowing through the output resistor creating an output noise voltage. The relative change to amplified input noise was simply the fact that gain changes with these amps with changing source resistor.
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Old 17th August 2019, 02:39 AM   #1312
kgrlee is offline kgrlee
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Quote:
Originally Posted by herve00fr View Post
I think this behaviour is only due to the current mirror noise into the output impedance of the amplifier.
This can be lowered by increasing the degeneration resistors and the power supply.
What is the purpose of the current mirror? What benefits does it bring compared to syn08's #375 or true Duraglit?

In particular, what extra benefits does it give to a user or builder?
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Old 18th August 2019, 12:06 PM   #1313
Hans Polak is offline Hans Polak  Netherlands
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@syn08
That suggestion to have my PCBs made by JLCPCB was very welcome, thanks.
They charge a fraction of what I used to pay locally and their return time is second to none.
Anxious looking forward to publish noise figures on my Inverting and Non Inverting universal Head Amp based on these ZTX trannies.

Hans
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Old 18th August 2019, 10:49 PM   #1314
herve00fr is offline herve00fr  France
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Quote:
Originally Posted by aboos View Post
The 58nV were my error, I made pV to nV
Just could also confirm with a couple of sims that it is indeed the current mirror noise current flowing through the output resistor creating an output noise voltage. The relative change to amplified input noise was simply the fact that gain changes with these amps with changing source resistor.
That's correct.
Increasing the power supply to 6V and the degeneration resistors to 400 ohm, give an input current noise density of ~10.5 pA/rtHz and an input voltage noise density of ~220pV/rtHz.

Quote:
Originally Posted by kgrlee View Post
What is the purpose of the current mirror? What benefits does it bring compared to syn08's #375 or true Duraglit?

In particular, what extra benefits does it give to a user or builder?
The purpose to the current mirror was to increase the gain of #375 schematic with ~same noise.
The gain is increased but at the expense of an input current noise density penalty caused by the current mirror noise.
So the schematic could be competitive for very low resistive cart, but have absolutly no interest for the others.
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Old 18th August 2019, 11:29 PM   #1315
gerhard is offline gerhard  Germany
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Quote:
Originally Posted by Hans Polak View Post
@syn08
That suggestion to have my PCB’s made by JLCPCB was very welcome, thanks.
They charge a fraction of what I used to pay locally and their return time is second to none.
Anxious looking forward to publish noise figures on my Inverting and Non Inverting universal Head Amp based on these ZTX trannies.
Hans
Just uploaded today, really yesterday, 2 boards to PCBway.
One of my boards was bigger than 100*100 mm by 6 mm, that exploded it's price by *5.5.
Still OK. First time they get a little more than DHL for the transport.
It was Sunday, also in China, but they reviewed my boards immediately.
Next time I'll watch the form factor more closely.

I also ordered some stuff from DK, amongst it the npn and pnp ZTX trannies.
Somehow I always find interesting stuff until it hurts in the wallet.
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Old 18th August 2019, 11:41 PM   #1316
syn08 is offline syn08  Canada
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And they do 4 layers for a very reasonable price, with controlled impedance for free!
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Old Yesterday, 01:52 AM   #1317
gerhard is offline gerhard  Germany
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Nevertheless I included some test structures, a "50 Ohm" line for the TDR,
Some test-SMAs for the VNA and some GaN transistors. That will stress their solder mask, and maybe more.
That are just nekkid chips with 4 bumps for reflow solder.

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The bottom 2/3 are just another FET preamp.
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Last edited by gerhard; Yesterday at 01:59 AM.
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Old Yesterday, 08:42 AM   #1318
billshurv is offline billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
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Originally Posted by gerhard View Post
Somehow I always find interesting stuff until it hurts in the wallet.

I reckon you have enough to write a book on low noise designs now!
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Old Yesterday, 11:20 AM   #1319
kgrlee is offline kgrlee
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Quote:
Originally Posted by herve00fr View Post
The purpose to the current mirror was to increase the gain of #375 schematic with ~same noise.
If you are using your circuit for a MC head amp, your maximum gain is going to be limited by the 47K i/p of your MM RIAA amp.

#375's gain is limited by R4 & 5, which feed the current mirror and appear in parallel with the output resistor R7.

True Duraglit uses much larger resistors so can be matched to much higher gain. It also has slightly less noise & THD than #375 at half the current bla bla ..

If this isn't just a SPICE world exercise but you are building a real life device, pay attention to Bonsai & syn08's caveats about power supplies & solar cells or use batteries.
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Old Yesterday, 01:16 PM   #1320
syn08 is offline syn08  Canada
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Quote:
Originally Posted by kgrlee View Post
#375's gain is limited by R4 & 5, which feed the current mirror and appear in parallel with the output resistor R7.
Nope. #375 gain is limited by the power supply voltage. It is independent on R4/R5.
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