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Old 18th October 2021, 08:55 PM   #11531
Joachim Gerhard is offline Joachim Gerhard  Germany
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Yes. A Bit also with the drain resistors.The BJT Must Not be a Medium Power device. Only around 60mW to stand. So ist can be a smaller device with higher Hfe. This rases the Output impedance of the CCS.
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Old 18th October 2021, 09:45 PM   #11532
Joachim Gerhard is offline Joachim Gerhard  Germany
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Here we go. It is thermally stable.
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Old 18th October 2021, 10:57 PM   #11533
Hans Polak is offline Hans Polak  Netherlands
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Old 18th October 2021, 11:06 PM   #11534
Joachim Gerhard is offline Joachim Gerhard  Germany
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We got. It working. From now on it can get only worth. Or have have the new Einstein.
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Old 19th October 2021, 07:30 AM   #11535
Joachim Gerhard is offline Joachim Gerhard  Germany
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One problem remains. Matching the channels.
That makes it really hard to make a commercial product with it.
For private use it is ok. I will take the challenge and build a phono for me.
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Old 19th October 2021, 07:31 AM   #11536
Joachim Gerhard is offline Joachim Gerhard  Germany
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I was typing from my cellphone so please excuse any spelling mistake I made.
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Old 19th October 2021, 08:54 AM   #11537
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by Joachim Gerhard View Post
One problem remains. Matching the channels.
That makes it really hard to make a commercial product with it.
For private use it is ok. I will take the challenge and build a phono for me.
I came late to this thread and never realized you had a commercial goal in mind with this amp.
In that case I could give you some additional tips.

1) For a commercial product to stand off from the crowd, overload margin @20Khz should be at least 30dB or circa 158mV@20Khz for the 0.5mV@1Khz standard.
But that is easy to achieve.
The current design has the whole Riaa correction in one go, directly after the first stage, meaning that after having amplified the MC signal with the IRF3602, it will be attenuated by 40dB @20Khz, bringing it almost back to the original MC output level.
That’s why the noise performance of the second stage is now so critical.

However when you only apply the 75usec pole at this stage, the signal at 20Khz will only be attenuated by 20dB, making it possible to reduce the gain of the first stage a bit to achieve this 30dB OLM without any noise problem in the second stage.
Then between the second and the third stage the 3180usec and 318usec pole zero correction has to be placed and voila, there you are.

2) the second tip I would give to keep the product top notch, is to give it not only a SE but also a differential output. An OPA1632 instead of the OPA1652 will give you exactly that.

Then a question: what exactly do you mean with “matching the channels”.
Gain is set by resistors and not by the dual fet. Only the input capacity can vary from one fet to another, but an MC amp can easily have an input capacity of 1nF, so by adding the proper cap value up to 1nF this seems no problem.

Hans
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Old 19th October 2021, 10:08 AM   #11538
jan.didden is offline jan.didden  Europe
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@as_audio: I found a nice reference to something we discussed before:

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

So my quote was not entirely correct ;-)

Jan
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Old 19th October 2021, 10:20 AM   #11539
Joachim Gerhard is offline Joachim Gerhard  Germany
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No, i do Not Wang to make a product with the IF3602. This is for fun. The pictures Shows something that aride my curiosity besides high gain.
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Old 19th October 2021, 10:24 AM   #11540
Joachim Gerhard is offline Joachim Gerhard  Germany
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It does Not have the typical 1/F corner of a Standart JFet.
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