Here's a SALUTE to CarlosFM for his thumb-rule formula of approx. 8.0 - 8.5mA biasing.
I am using the cousin of 627, the OPA2107(dual) and
1st I biased it lightly at 5.5mA - it started to sing.....
Next, I pushed this to 6.0mA - it was definitely singing.....
Then again, I said last try at 7.0mA - the singing became so much better
And Finally I told myself, what the heck, push it to 8.0mA - it has now seduced me.....
I did a lot of R&D but CarlosFM did much more or else he confidently wont keep saying to bias at 8.0 - 8.5mA.
Hats off to you Carlos!! I love this romance!
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Arup
I am using the cousin of 627, the OPA2107(dual) and
1st I biased it lightly at 5.5mA - it started to sing.....
Next, I pushed this to 6.0mA - it was definitely singing.....
Then again, I said last try at 7.0mA - the singing became so much better
And Finally I told myself, what the heck, push it to 8.0mA - it has now seduced me.....
I did a lot of R&D but CarlosFM did much more or else he confidently wont keep saying to bias at 8.0 - 8.5mA.
Hats off to you Carlos!! I love this romance!
---------------------
Arup
Hi Keith:
I checked the supply on the pins, i.e. 4 & 8 as its a dual opamp in my case. Divide the number & I got 12.14V. So, its a +/- 12V PS.
Using V = I x R; for 5.5mA bias, I used (12/0.0055=2181) a 2.2k resistor. For 6mA, it was 2k. For 7mA I used 1.8k and finally for 8mA it was 1.5k.
Arup
I checked the supply on the pins, i.e. 4 & 8 as its a dual opamp in my case. Divide the number & I got 12.14V. So, its a +/- 12V PS.
Using V = I x R; for 5.5mA bias, I used (12/0.0055=2181) a 2.2k resistor. For 6mA, it was 2k. For 7mA I used 1.8k and finally for 8mA it was 1.5k.
Arup
So it was by using the formula and not something you measured!
I guessed the formula helped..... Thank matjans!
I was thinkiing you could measure it with a DMM or something!
My CDP has +/- 15 volts and I figured 1.8K resistor between the V- and output would do it then I was intrigued by the JFET Cascode. I have already made them and need some time to install them and other mods while the PCB is out.
I am still deciding which output caps to replace the stock ones.
Thanks!
Regards//Keith
I guessed the formula helped..... Thank matjans!
I was thinkiing you could measure it with a DMM or something!
My CDP has +/- 15 volts and I figured 1.8K resistor between the V- and output would do it then I was intrigued by the JFET Cascode. I have already made them and need some time to install them and other mods while the PCB is out.
I am still deciding which output caps to replace the stock ones.
Thanks!
Regards//Keith
Hey analog_sa
In mid April, I decided to start learning about DIY AND electronics. I think I have moved along OK in four months. I guess the statement about the DMM or something really got to you. So it was stupid (I do that every now and then). Now I'll bet if I search every thread you ever posted, I'll bet you have done that too (with probably more than four months experience when you posted to the thread, and I have to laugh when I say experience on my part, it's more like I was groping).
Yes you can measure it with a DMM and not something. Although knowing Ohm's law helps, it doesn't help with the actual placing of the probes in a series with an op amp in the pcb. That I am a little reluctant about doing, in my groping I already fried one OPA627 somewhere close to month number 3 in my four months of groping along!
I know you said you don't like Class A Biased op amps in the output stage. I see so much conflicting stuff about it, I am choosing to learn it myself. Don't be insulted that I am still looking for answers. I really do want to understand this completely! Everytime I learn something at least some of it applies to the next thing I have to learn. This is the best way and the more I learn, the less stupid things I will write!
Regards//Keith
In mid April, I decided to start learning about DIY AND electronics. I think I have moved along OK in four months. I guess the statement about the DMM or something really got to you. So it was stupid (I do that every now and then). Now I'll bet if I search every thread you ever posted, I'll bet you have done that too (with probably more than four months experience when you posted to the thread, and I have to laugh when I say experience on my part, it's more like I was groping).
Yes you can measure it with a DMM and not something. Although knowing Ohm's law helps, it doesn't help with the actual placing of the probes in a series with an op amp in the pcb. That I am a little reluctant about doing, in my groping I already fried one OPA627 somewhere close to month number 3 in my four months of groping along!
I know you said you don't like Class A Biased op amps in the output stage. I see so much conflicting stuff about it, I am choosing to learn it myself. Don't be insulted that I am still looking for answers. I really do want to understand this completely! Everytime I learn something at least some of it applies to the next thing I have to learn. This is the best way and the more I learn, the less stupid things I will write!
Regards//Keith
Keith
I have no problem with the class A biasing. As any other contentious topic in audio the best approach is to build and listen.
So, what's taking you so long? Building cascodes, conducting opinion surveys... For something which takes 5 minutes.
How to measure the current? Connect an ammeter in series with the current setting resistor (or CCS) just to make sure the correct current is running through the output and sit down for a listen.
The best place to learn basic electronics is not a diy forum. You really need a few textbooks and sufficient motivation to read them.
I have no problem with the class A biasing. As any other contentious topic in audio the best approach is to build and listen.
So, what's taking you so long? Building cascodes, conducting opinion surveys... For something which takes 5 minutes.
How to measure the current? Connect an ammeter in series with the current setting resistor (or CCS) just to make sure the correct current is running through the output and sit down for a listen.
The best place to learn basic electronics is not a diy forum. You really need a few textbooks and sufficient motivation to read them.
Very true Andrew & appreciate you pointing towards it. The transition from +/- 12V to 15V to 18V PS is NOT a linear curve.
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KP11520:
15V / 0.008A = 1875ohms
So a 1.8k will actually bias it higher than 8mA. I'd say you take a shot with a 2k (1% Tol) metal-film resistor which would bias to 7.5mA. If this is working in that circuit the results would already be there and you should be able to hear/feel it. At the same time, its safe-playing.
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Arup
--------------------
KP11520:
15V / 0.008A = 1875ohms
So a 1.8k will actually bias it higher than 8mA. I'd say you take a shot with a 2k (1% Tol) metal-film resistor which would bias to 7.5mA. If this is working in that circuit the results would already be there and you should be able to hear/feel it. At the same time, its safe-playing.
--------------------
Arup
That 120mW is the dissipation from the resistor. A 'nornal' one is rated at 600mW at 70°C.
Does it mean that the chip is dissipating the same mW? A chip has a much larger surface area than the 0.6W resistor and semiconductors seem to work just fine at higher temps just their life span is shortened.
I used the finger test to feel how warm the chip was. A surface mount non-dual OpAmp (AD825) seemed OK with a 2K and ± 15V supplies. Maybe it was at 40°C.
Does it mean that the chip is dissipating the same mW? A chip has a much larger surface area than the 0.6W resistor and semiconductors seem to work just fine at higher temps just their life span is shortened.
I used the finger test to feel how warm the chip was. A surface mount non-dual OpAmp (AD825) seemed OK with a 2K and ± 15V supplies. Maybe it was at 40°C.
I use the opamp before a discrete buffer stage in my headphone amp,and I have a switch on the bias,wich use jfets.
I can´t say that I here any difference with or without bias...
Maybee there would be a difference if the buffert where not there..
Maybee you here diference in your preamp,if you only have the opams,not a buffer.
Try it and report..
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