Phono Transfer System

Construction information for DIY projects, including the MS Mid Side Matrix, Width Controller, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
quattro64
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Re: Phono Transfer System

Post by quattro64 » Sun Jul 16, 2017 10:18 pm

Thanks!, I'm glad you are familiar with these EVMs. I looked at the pcm4204evm guide and the schematic shows the currently blank spots for the possible caps. It looks like it wants electrolytics. Could film caps work? This is for dc blocking, correct? Schema also shows an R in parallel with the cap. Both have undetermined values?? What vdc and uF should I go for? I would prefer to use caps on the evm and then jump the connections on the MM phono. Thanks again.

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mediatechnology
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Re: Phono Transfer System

Post by mediatechnology » Mon Jul 17, 2017 4:16 am

The PCN4202 EVM does want electrolytics for DC blocking.
I agree that it would be best to add the caps to the EVM.

The input impedance is low - around 1K - so you would need at least 47 uF.
The parallel resistors jumper the caps when they are not installed so you will need to remove them.
A 25V cap should be sufficient.

quattro64
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Re: Phono Transfer System

Post by quattro64 » Mon Jul 17, 2017 11:22 am

Thanks, 1k is low so yes I will start with 47uf, impedance mismatch shows up in either rolled off highs or no bass, I'll experiment if 47uf doesn't work. I have a bunch of 47uf 16v, will those work? So the plan is to jump the c4-c5, c24-c25 on the MM then remove any jumpers or Rs on the evm and replace with polar lytics, correct?

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mediatechnology
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Re: Phono Transfer System

Post by mediatechnology » Mon Jul 17, 2017 12:44 pm

quattro64 wrote:
Mon Jul 17, 2017 11:22 am
Thanks, 1k is low so yes I will start with 47uf, impedance mismatch shows up in either rolled off highs or no bass, I'll experiment if 47uf doesn't work. I have a bunch of 47uf 16v, will those work? So the plan is to jump the c4-c5, c24-c25 on the MM then remove any jumpers or Rs on the evm and replace with polar lytics, correct?
47 uF is probably the minimum you would want to use. Yes, jump C4, C5 et al and remove jumper resistors on the EVM. Replace with polar caps having plus terminals pointing to the OPA1632.

quattro64
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Re: Phono Transfer System

Post by quattro64 » Mon Jul 17, 2017 2:54 pm

Cool, I'll start with these and then let you know how it goes. Thanks again! :D

quattro64
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Joined: Sat Jul 15, 2017 5:37 pm

Re: Phono Transfer System

Post by quattro64 » Tue Jul 18, 2017 5:09 pm

After reading through the pcm4222evm thread I see that without the caps the opamps are forced to run in class A bias. Due to the dc they're required to sink? Anyway I might like that, at least to try it out. Maybe set it up on a switch. Seems there is more input R on the pcm4204evm compared to the pcm4222 so 47uf is probably fine. Also, it seems since it is 4 channel it requires more continuous current to run, 0.5mV versus the 0.2mV of the 4222. So I wonder if my regulated 1.5 amp supply will be able to run both the flat mm phono and the 4204 at +-15V?

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mediatechnology
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Re: Phono Transfer System

Post by mediatechnology » Thu Jul 20, 2017 1:18 pm

quattro64 wrote:
Tue Jul 18, 2017 5:09 pm
After reading through the pcm4222evm thread I see that without the caps the opamps are forced to run in class A bias. Due to the dc they're required to sink? Anyway I might like that, at least to try it out. Maybe set it up on a switch. Seems there is more input R on the pcm4204evm compared to the pcm4222 so 47uf is probably fine. Also, it seems since it is 4 channel it requires more continuous current to run, 0.5mV versus the 0.2mV of the 4222. So I wonder if my regulated 1.5 amp supply will be able to run both the flat mm phono and the 4204 at +-15V?
I haven't found that there is any distortion penalty for not having coupling caps with the op amps in class-A having to sink current from the EVM. You'll lose a little headroom since about 2 mA of THAT1240 output current can't be used for signal. The 1240s Isc is 25 mA typical.

I wouldn't recommend any kind of switching since it is guaranteed to click.

47uF/1K, which is really 23.5uF/2K differentially with the PCM4202EVM, works out to be 3.4 Hz.

The flat preamp pulls very little current usually about 8 mA per channel. The maximum should be no more than 20 mA/per channel.

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