Adding the space in pcb for the buffer will increase the PcB cost in 50%, I want this circuit to be high quality but also accessible , but I agree that including the buffer has benefits. So it will be added a modified diamond buffer that have a linearity suitable for this project (less than 0.0001% distortion) without feedback loop. buffer will be in a auxiliary PcB that can be connected in the main pcb. this way the main PcB will be more accessible and we can experiment with others buffer like the one that Joachim and MiiB present that is also a very good solution.
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I agree that the servo will always be in the audio path just as the power supply is. There is a trick to simulate the dB level of the servo vs frequency. Its not uncommon to find that an an open loop I/V design with a servo has significant feedback up to midbass . There is a model posted on this forum somehwere. May want to have the option to go sans servo and use a cap.
As far as a buffer, I guess I always think of a buffer following an I/V as an opportunity to make a nice filter in between. Its good that you are planning a separate buffer panel so folks have that option.
This is great stuff. Thanks for sharing.
you know that 2nd harmonic buffer is a very cool idea that I would love to have a lash at. why oh why did you have to come along with another IV I want to build?
qusp, I do not know any device that only produce 2° harmonic, the buffer that I was talking also product 3° harmonic but at 33 db lower level. if one has careful the third will be bellow noise floor. It is only a mosfet BS170 in single end with a ccs of 15ma and a load of 1k ohm, I have choose BS170 because it produce 10 time more distortion than a bjt.
Regal, If I understand what you are telling , you say that if a opamp has 110 DB of open loop gain for example , the filter should have at least 110db of attenuation at audio frequencies ? I will investigate this. I will see if I have time to simulate the frequency response of the servo.
I have almost finish the pcb, tomorrow I will post some 3D images of the board, the dimensions are 80mm x 90mm.
I have made some simulations to see the frequency response of the servo, and some alterations to prevent the servo from having feedback at audio frequencies.
The first image is the open loop of opa2134 , the second is the FR before the modifications, third is FR with modifications, the last is the modifications in R25 and C18.
with the modification the servo does not have excess gain to have feedback above 40hz , if we decrease R25 to 200ohms this value decrease to 20hz.
in second image in green there is th FR of the servo with only one pole, in this way the servo has excess gain to have feedback until 1000 Hz , with two pole servo this value is much lower (blue).
The first image is the open loop of opa2134 , the second is the FR before the modifications, third is FR with modifications, the last is the modifications in R25 and C18.
with the modification the servo does not have excess gain to have feedback above 40hz , if we decrease R25 to 200ohms this value decrease to 20hz.
in second image in green there is th FR of the servo with only one pole, in this way the servo has excess gain to have feedback until 1000 Hz , with two pole servo this value is much lower (blue).
Attachments
what is the purpose of the second opamp...?? phase-inversion..??
you can make a second pole by splitting the servo input-resistor in two and then have a cap to gnd in between.
you can make a second pole by splitting the servo input-resistor in two and then have a cap to gnd in between.
Yes MiiB, phase inversion. Is better to have the second pole in the output of servo to filter the noise of opamp.
I must say that is not a good idea to use this type of servo in a feedback loop of a power amplifier, but in a open loop circuit like this is oK.
I must say that is not a good idea to use this type of servo in a feedback loop of a power amplifier, but in a open loop circuit like this is oK.
PCB is for stereo channel single ended?
If you do a PCB for ESS9018 will it be balanced?
also, what is the approx power draw for this circuit (as it is right now)?
If you do a PCB for ESS9018 will it be balanced?
also, what is the approx power draw for this circuit (as it is right now)?
smms,
It seems you can route more wires on components side, not to devide ground plane.
the circuit conveys input current to output, and the current flows to ground through the IV resistor and paralleled capacitor, so it may be some benefit to separate ground return pass and ground plane.
It seems you can route more wires on components side, not to devide ground plane.
the circuit conveys input current to output, and the current flows to ground through the IV resistor and paralleled capacitor, so it may be some benefit to separate ground return pass and ground plane.
Yes Shinja, I have already changed some traces to the top side as i said in post #692.
I have take attention to the ground currents paths and the inductance of ground , important is to get the currents of the rail capacitors away from the path of the signal, there is no need to separate the ground.
I have take attention to the ground currents paths and the inductance of ground , important is to get the currents of the rail capacitors away from the path of the signal, there is no need to separate the ground.
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Im not that good to express myself, especially in English 🙂
I will separate the ground return of the rail capacitors from the rest of the ground .
This weekend will be the audioshow in Lisbon so I will not have much time left , but I hope next week to have 2 prototype board made.l am very curious to listening the final results of all of this.
I will separate the ground return of the rail capacitors from the rest of the ground .
This weekend will be the audioshow in Lisbon so I will not have much time left , but I hope next week to have 2 prototype board made.l am very curious to listening the final results of all of this.