Phono Transfer System Construction Information

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Fri May 17, 2019 4:48 pm

Yeah its a funny one, which is why I shipped all my carts to Hans for him to measure and try and come up with a workable model for the generator. The challenge now if mapping that to the complete system. There are bits of the puzzle still missing and experiments to be done to try and polish the vinyl t**d a little more. And keeps me out the pub!

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Thu Jun 13, 2019 5:27 pm

Planning phase starting for 2 phono stages I am building. One for myself which will be uneccessarily complex cos I can and one for a friend which is simpler and the one I'm working out now. It'll have balanced MM and Balanced MC inputs and then the option of using analog RIAA using the monitor switcher or digital using a Behringer DCS2496. He also wants an output volume control to set the level going into his main amplifier. Not sure I see why, but I did tell him he could have whatever he wanted as long as he pays for the bits!

So I have a few decisions to make.

Firstly where to do the switching. As laid out the RIAA switching board expects one input to be from phono and the other as a return from the DAW. Temptation 1 is to put the two phonos into those inputs (as he will never use the inverse RIAA and if using the Behringer will always do RIAA in that). Then have a selector between EQ return and 'all analog' afterwards, which can feed the additional preamp stage he wants. This way the MM and MC is hardwired until after the main gain is added.

More tricky will be the input loading. He wants to be able to change MC R and MM R and C from the front panel. Without testing it I'm a little wary of the extra wiring so need to test that before I commit.

As it has the output gain stage It's tempting not to bother with gain selection on either MM or MC but I'll probably put a 12dB high/low step in to prevent overdrive of the Behringer. Again twitchy about running wiring for that inside the case without experimenting.

This friend has a bit of a collecting habit and has some 35 cartridges that he uses in rotation, which is why the front panel settings are important to him. I am trying to curb his buying habits!

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Thu Jun 13, 2019 6:10 pm

billshurv wrote:
Thu Jun 13, 2019 5:27 pm
Firstly where to do the switching. As laid out the RIAA switching board expects one input to be from phono and the other as a return from the DAW. Temptation 1 is to put the two phonos into those inputs (as he will never use the inverse RIAA and if using the Behringer will always do RIAA in that). Then have a selector between EQ return and 'all analog' afterwards, which can feed the additional preamp stage he wants. This way the MM and MC is hardwired until after the main gain is added.
Several people have used the "line" input as Phono 2.

The MM board has driven shields for controlling Rgain with either a DPDT toggle or pot.
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billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Fri Jun 14, 2019 6:46 am

Hadn't spotted the driven shield. That's one to tick off the worry list :D

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Fri Jun 14, 2019 7:08 am

I need to document how to use the shield drive.
It's different depending on whether a pot or A/B gain switch is used.

I would put the MC preamp on the RIAA EQ "Phono" (Input 1) since it has a gain trim stage in the flat pre-EQ path to adjust channel balance.
(Though the MC preamp board does have a trim I don't recommend using it for high gain where setting it below 5Ω is required.)

The MM preamp has an on-board trim so feeding it into the "Line" (Phono 2) input is a better option.

Phono 1 or Phono 2 can feed the RIAA EQ input and be routed to the monitor output.

Phono 1 can feed either the Monitor or Record outputs flat or with EQ.
IIRC Phono 2 can only feed the record output through the EQ though it can feed the Monitor output either Flat or with EQ.

Depending on how you anticipate using it you might reverse the roles of the Record and Monitor outputs.

Switchable loading might best be done at the input connectors using relays.
I'm not crazy about it if there are long lead lengths.
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billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Fri Jun 14, 2019 4:14 pm

I do have a packet of reed relays I was given that would work for this. Worth a try using them. Not keen on normal relays for signals to low to guarantee conduction. Will mull on that.

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Fri Jun 14, 2019 5:10 pm

What termination values would your friend need for the MC input?

One of the tests I want to run on the DL-103 are the square wave response versus Rterm.
I'm currently using 100Ω.
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billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Jun 18, 2019 2:58 am

Sorry missed this. 47k definately then a couple of lower values. probably 100R 1k, 10k

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Wed Jun 19, 2019 4:51 pm

mediatechnology wrote:
Fri Jun 14, 2019 7:08 am

Phono 1 can feed either the Monitor or Record outputs flat or with EQ.
IIRC Phono 2 can only feed the record output through the EQ though it can feed the Monitor output either Flat or with EQ.

Depending on how you anticipate using it you might reverse the roles of the Record and Monitor outputs.

I had a quiet spell this afternoon in the office so printed the schematics and had a look. I see what you mean. That would work fine. Load selection via relays also looks good as soon as I've worked out best way to hook a daughter board up. I think we have a plan :)

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Wed Jun 19, 2019 5:35 pm

Cool.

I think 10KΩ for the MC input is probably too high a target.
The bias resistors are 499Ω which makes the maximum differential load 1K.

MC carts outputting 1-2 mV are likely a better match for the MM preamp.
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