MPP

[as_audio]

Have a look at the schematic in post 11309, bases are at 0V,
so emitters must be at -0.6V, collector - and reference voltage -
should be (at least slightly) positive.

Oscillation can probably be prevented by small caps between
ops output and neg input.

 

[RCruz]

Thank you. Will try that asap

 

[Joachim Gerhard]

The more gain the less Oszillation probabily

 

[RCruz]

I got rid of the oscilation (near 6MHz) with a zobel in the output of 1st stage.

Also increased IPS current to 2mA

1st stage gain is 54dB
2nd stage gain is 26dB (Not a very good distribution but it works for a final gain of 60dB @ 1khz)

Re = 800ohm might be noisy

Gain in 2nd stage can not go higher or coupling caps C12 C21 might become too large.

Below you can see the antiriaa response with and without the zobel.

If we use a DOPA for U3 we can increase headroom by using higher voltage rails for the 2nd stage

 

[Joachim Gerhard]

Right now I am building it this way passive, so a double RIAA is not necessary.
I think it is better to use circuit 2. An INA instead of the simple circuit 1.
I would raise the input idle to something like 10 mA for lowest voltage noise. I do not think that Re is playing a big roll in noise.
How high is the value of R load in your simulation ?

 

[jan.didden]

RIAA can also be setup this way :

I think this will only work if you use a series R on the opamp outputs. Otherwise the output is flat, no?

Jan

 

[Joachim Gerhard]

I think yes. This is a voltage source and not a current source like in the Paradise.

 

[RCruz]

Right now I am building it this way passive, so a double RIAA is not necessary.
I think it is better to use circuit 2. An INA instead of the simple circuit 1.
I would raise the input idle to something like 10 mA for lowest voltage noise. I do not think that Re is playing a big roll in noise.
How high is the value of R load in your simulation ?

Rload is 5k so to have 2mA idle.

Replacing Rload by 1k puts idle near 10mA. nothing else changes

 

[Joachim Gerhard]

My calculations came out with 750 Ohm so you are real close.

 

[as_audio]

Post 11307 and 11309 : the reference voltage is not required and may be even useless in this context.

 

[RCruz]

Post 11307 and 11309 : the reference voltage is not required and may be even useless in this context.

I will try that afterwards... Thank you so much.

 

[RCruz]

Here you have the arrangement with the INA.

With this new IPS current and different gain settings, the zobel seems to not be needed.

Here we have 1st stage gain = 42dB for a total gain @ 1khz of 61dB

PS: to avoid current flowing into the cartridge, the NPN bjt should be a dual monolytic item.... maybe a biss transistor.

 

[RCruz]

Here are the files....

 

[as_audio]

Diff pair without current source ?

 

[RCruz]

Diff pair without current source ?

Please explain...

 

[jan.didden]

Diff pair without current source ?

Andreas, I think U1 and U2 supply that. The feedback loop keeps the bottom of the emitter resistors at the voltage to support the right Q1, Q2 collector current versus the 5V ref.
But wasn't this supposed to be an (anti) RIAA? As I see it, it has a flat freq response.

Jan

 

[as_audio]

For me it is not completely sure that these two transistors will work as a
differential pair with full CMRR if the emitter courrent source is missing.

 

[Joachim Gerhard]

Jan, this is not an anti RIAA. It is an MC RIAA. You have quite high resistor values in the passive RIAA. Do they affect the noise ? I also think I like the current source version better.

 

[Joachim Gerhard]

The question with the resistor values goes to Ricardo.

 

[as_audio]

I do not like the idea to supply transistor currents via opamp output.
Free and independent choice of operating currents is preferred.