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Old 21st July 2008, 06:06 PM   #21
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RIAA + Inverse RIAA...
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Old 21st July 2008, 08:36 PM   #22
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you have such a nice instrument.
I wish i could have one.

Anyways out of my PSpice Analyzer (ehehe sounds just like your Agilent analyzer) i get this frequency response...as the total freq resp MM + MC.

The two curves totally look the same to me...look at the file.

Ad far as this is concern it would look like the inverse RIAA i am using is not correct.
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Old 21st July 2008, 08:46 PM   #23
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Quote:
Originally posted by analog_sa




There is a -40db attenuation from the inverse riaa.



Stefano

Not sure what driving impedance the inverse riaa expects but it's unlikely to be 150ohm. You may need to modify the 1.91k resistor respectively.
thanks a lot for your adive.
I tried to change the output resistor from 150ohm to 1.9K with no effect and tried to change the 1.91K in series at the capacitor on the inverse RIAA block but the odd point on the middle band was just magnified.

Did i miss something?
Did you mean to change something else?


Thank you
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Old 21st July 2008, 09:28 PM   #24
drdagor is offline drdagor  United States
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Default Thermistor causing grief

I think there is a good explanation about why thermistors may be causing you grief.

Remember from the early notes that what the thermistors do is change the bias point. As soon as the thermistors start to do their thing they will increase distortion.

The distortion plots from Pasos today show thatthe distortion is really low. But if the device is running hot, the thermistor action won't lower the distortion. If the thermistor is doing its thing, increasing bias will cause increasing heat which will cause the thermistor to operate, which will increase distortion.

I'll bet the transistors are running hotter than folks think. Remember Papa's note saying that he sets bias with a thermometer. He gradually turns up bias until the MOSFET temp is 25degrees C above ambient. Check that before you give up on thermistors.

Anybody got a candy thermometer? Anybody want to make s'mores over their class A amp? I'll bring the graham crackers.
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Old 21st July 2008, 10:43 PM   #25
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emm emmm.....i am nooottt quite sure.....but i think you reply to the wrong post.

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Old 21st July 2008, 11:29 PM   #26
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The question of whether to use a balanced or single-ended RIAA stage is an old one. There are arguments for both sides of the issue but, lacking a center tap on the coils in the phono cartridge, you're left creating a virtual ground between the two existing pins. Whether this is truly a balanced signal is in the eye of the beholder.
Note that you can't just build a balanced phono stage and hot-wire the two existing signal pins to the + and - inputs of the balanced circuit--if you do, you'll get a ferocious hum. You have to supply a new wiring harness from the phono stage to the arm and shield both the signal leads.
Most people don't even try. The vast majority of phono circuits on the market are single-ended. Not surprisingly, turntables are wired to mate with those phono stages. Those who wish to try balanced phono stages are left having to create their own wiring harness or buy one of the few on the market. There are a few commercial products that allow balanced phono inputs, but you'll see instructions on how to roll your own interconnects in the owner's manuals.
I've seen posts wherein people claimed they were learning things from simulation programs. I've also seen posts where it was painfully clear that the poster hadn't learned anything at all. I suppose it depends on how you define the word 'learn.' I've yet to see a program that actually teaches things like Norton's Law and Thevenin equivalents and such. About the most you can hope for is to enter a circuit and see if it works. But--and this seems to be the case here--there are circuits that work and simulations claim they don't (see the first part of the Aleph-X thread for more of same). Is it the simulation program? Is it the device models? Is it the operator? Or perhaps it was just cosmic rays hitting the processor chip in your computer at the wrong moment, causing odd results.
If you want to build a circuit, then build the circuit. That way you can actually listen to music.

Grey
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Old 22nd July 2008, 06:59 AM   #27
h_a is offline h_a  Europe
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Grey, long time no see!

Glad to see you having again time to post! Have fun, Hannes
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Old 22nd July 2008, 02:24 PM   #28
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Quote:
Originally posted by GRollins
The question of whether to use a balanced or single-ended RIAA stage is an old one. There are arguments for both sides of the issue but, lacking a center tap on the coils in the phono cartridge, you're left creating a virtual ground between the two existing pins. Whether this is truly a balanced signal is in the eye of the beholder.
Note that you can't just build a balanced phono stage and hot-wire the two existing signal pins to the + and - inputs of the balanced circuit--if you do, you'll get a ferocious hum. You have to supply a new wiring harness from the phono stage to the arm and shield both the signal leads.
Most people don't even try. The vast majority of phono circuits on the market are single-ended. Not surprisingly, turntables are wired to mate with those phono stages. Those who wish to try balanced phono stages are left having to create their own wiring harness or buy one of the few on the market. There are a few commercial products that allow balanced phono inputs, but you'll see instructions on how to roll your own interconnects in the owner's manuals.
I've seen posts wherein people claimed they were learning things from simulation programs. I've also seen posts where it was painfully clear that the poster hadn't learned anything at all. I suppose it depends on how you define the word 'learn.' I've yet to see a program that actually teaches things like Norton's Law and Thevenin equivalents and such. About the most you can hope for is to enter a circuit and see if it works. But--and this seems to be the case here--there are circuits that work and simulations claim they don't (see the first part of the Aleph-X thread for more of same). Is it the simulation program? Is it the device models? Is it the operator? Or perhaps it was just cosmic rays hitting the processor chip in your computer at the wrong moment, causing odd results.
If you want to build a circuit, then build the circuit. That way you can actually listen to music.

Grey
Grey, besides the fact you don't like simulators which i still think are useful for the purpose they are made for,nothing more nothing less and, as you can see...in this fortunated case....frequency response obtained by Spice looks the same as the one obtained by direct measuring of the circuit.
Surprisingly in this case simulator is not so horrible, isn't it?

It is also not always possible to own an agilent analyzer...for poor guy as i am..

Said that, since your experience goes far beyond mine plus the simulator together for sure, don't you wanna comment the graphs posted here on the 3d?
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Old 22nd July 2008, 02:59 PM   #29
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Hi Stefano


Two possible issues:

1. The Hagerman inverse riaa expects 50ohm of source and you have 150ohm. Reduce 1k91 to 1k8

2. Not sure what is the capacitance in parallel to 88.7k in your circuit. Not enough resolution for my ageing eyes. Should be 2n7 in parallel with 33n and it looks like 27n.


In fact you can check this riaa in the feedback of any opamp, no need to be this complicated discrete circuit and results will be the same.
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Old 22nd July 2008, 05:15 PM   #30
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Thank you very much analog.
Your eyes are in a perfect shape

I just changed the value and now the inverse curve response show a deviation from the ideal response of 0.08dB which is in accordance with the original specification.

Now the cure response at the output of the inverse RIAA filter is exacly like the response tortello kindly posted on a previous 3d....not too bad for such a stupid tool (i mean spice...eheheh not the agilent...magaaarriiii!!)

thank you again you were very nice to help me out.
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