Did you try writing to Rod Elliott (the designer of your circuit) and see what he has to say?
Contacting ESP
Contacting ESP
Sometimes one responds to all the posts read from the beginning to where one has reached.Please read ALL the posts.
Thanks
Later posts get read AFTER the reply has been posted.
Flacman.
Is the amplifier single ended, or single polarity supply?
If so then the output must be given time to stabilise.
All the capacitors need time to charge to their fully operational state.
This can take more than 5 times the RC time constants and maybe for some, you may have to wait till 20 times the RC time constant has expired.
When the headphones are not connected, can the various capacitors actually charge to their final voltages?
Is the amplifier single ended, or single polarity supply?
If so then the output must be given time to stabilise.
All the capacitors need time to charge to their fully operational state.
This can take more than 5 times the RC time constants and maybe for some, you may have to wait till 20 times the RC time constant has expired.
When the headphones are not connected, can the various capacitors actually charge to their final voltages?
R5 is quite high in value.
The switching transistor (Q3) should be in saturated mode (hFE~10) when ON, i.e. base current ~ 10% of emitter current.
What current do the relays draw when ON?
Divide by 10.
That's the lowest current that should flow through the base.
You could even go to divide by 8, that would get you to an hFE of ~9
The 1k (R4) will pass 0.8mA when the Vbe is @ 0.8V (which is a typical saturated Vbe)
R5 has to pass the saturated base current PLUS that 0.8mA
If the relays draw 20mA, then the base current of Q3 would be around 2mA.
R5 current will be around 2.8mA
The voltage drop will be around 22k*2.8mA = 61.6Vdrop
What voltage is available to drive Q2 via R4 & R5?
The switching transistor (Q3) should be in saturated mode (hFE~10) when ON, i.e. base current ~ 10% of emitter current.
What current do the relays draw when ON?
Divide by 10.
That's the lowest current that should flow through the base.
You could even go to divide by 8, that would get you to an hFE of ~9
The 1k (R4) will pass 0.8mA when the Vbe is @ 0.8V (which is a typical saturated Vbe)
R5 has to pass the saturated base current PLUS that 0.8mA
If the relays draw 20mA, then the base current of Q3 would be around 2mA.
R5 current will be around 2.8mA
The voltage drop will be around 22k*2.8mA = 61.6Vdrop
What voltage is available to drive Q2 via R4 & R5?
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Thanks you.
My problem is "pop" sound when close/open relay. I have controlled relay manually (when my amplifier was stable).
(I'm testing it before connecting it to DC detection circuit and muting button)
I tried other types of relay, but the result is the same.
My amp is class A puss-pull, 130mA quiet current, dc offset about <5mV.
ps: Sorry for not mentioning from the beginning.
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are you saying that even some time after stabilising that a maual change of the isolating relays that you still hear the pop?
That would confirm that the 5mV of offset is what you are hearing.
5mV offset for a headphone amplifier is too high.
5mVac is only 36dB below 1mW into 100ohms.
a 5mV step change into 100ohms would be just as loud.
For a 95dB/mW 100ohms headphone you would hear a 5mV pop as ~ 59dB SPL.
That is too loud.
5mV offset will also pull/push the diaphragm well off centre.
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changing the 24V relays to other 24V types does not help.
You should have measured your relays before fitting to check they were compatible with the switching circuit.
What is your supply voltage?
If your 24V relays draw only 9mA, or less each, then you would find that R5 @ 22k would be suitable.
Did you measure them?
Yep. But i think 5mV dc offset is low. What is dc offset of other class AB or opamp consumer headamp?
I use 10v source with 5v Takamisawa relay (165ohm coil). I set 35mA for it's coil.
I used common source and gnd with my amplifier
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Then R5=22k is definitely not suitable.
You would need ~94V at the top of R5 to get sufficient base current to saturate Q3.
No. I do not use components like the diagram above.
I have set up from the beginning. I set 35mA for the relay's coil. I use A1013 transistor (hfe~40-100). I set base current of this transistor about 1.2mA for it's saturate mode.
What is the point in posting a schematic you did not use? Are you deliberately wasting our time?
Sorry brother!
I'm afraid to write a lot, because my English is bad.
According to your analysis, 5mV DC offset can also cause 55db "pop" sound. I think this is the cause.
I will continue this topic to find more experiences of people using other popular consumer amplifiers.
I heard people say that:
- FiioA5 (psu +-11V) has not any noise when switching relay
- TrasamHa2pro (psu +-10V) has not any noise, too. But when the user replace the opamp with the Burson V5i opamp, the "pop" sound occurred.
My guess is that this is due to the rather high bias current of the Burson op-amp. If the original circuit used an op-amp with a low bias current, e.g. with a FET input, you may get a relatively large offset when replacing it with an op-amp, which has a high bias current.
The 3 uA typical bias current of the V5i could cause an offset of 5 mV with a 1666 ohm feedback resistor (around 1k6 standard value), which sounds like a realistic resistor value.
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