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Phono board options

How do you want the functionality split up

  • Four small boards

    Votes: 6 18.2%

  • Two boards, each a complete channel

    Votes: 13 39.4%

  • Two boards, stereo front end and stereo EQ

    Votes: 1 3.0%

  • One big board

    Votes: 11 33.3%

  • Don't care

    Votes: 2 6.1%
  • Total voters
    33
  • Poll closed .
df_genius said:
Any updates guys?
Click to expand...

I would be very interested in this too. My B4 has now been completed and includes a separate supply, wired to an 8 pin DIN socket for my 323 boards, which I am currently planning to install in my LP12 plinth. A single board would be my preference. I use an AT OC9, which I think has an output of 0.4 mV.
 
I still working on optimizing the board layout.
So watch this space!

Sharif.
 
I've now got my head around 'RS DesignSparks' PCB tools.

http://www.mediafire.com/i/?hdx1deabaahckuy

This is just to wet you appetites combined front end for MC & MM one channel only.
I need to finish the EQ stage, also I need to workout the switching between the front-end and the EQ stage.

Comments welcome!

Sharif.
 
Sharif,

The Mclaren design used ground plane style layout, so the circuits were fairly well shielded, with just a few wires run on the ground plane side of the board. Would you be able to fill in more of the spare areas on the blue side, to add extra shielding?
 
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PigletsDad said:
Should work OK, but it uses 3 op-amps stages, where 1 or at most 2 are enough.
Click to expand...

Thanks PD Ill give it a try anyway and report back if it sounds ok
I only have a CA 640P and an old PS audio MM stage to compare it against so if its better that them it must be at least resonable.
I want to try and incorporate it in my pre amp if possible.

Alan
 
PigletsDad said:
Sharif,

The Mclaren design used ground plane style layout, so the circuits were fairly well shielded, with just a few wires run on the ground plane side of the board. Would you be able to fill in more of the spare areas on the blue side, to add extra shielding?
Click to expand...

Hi PigletsDad,

Ground plane on the blue track (underside) should not be a problem.

I'm trying to sort out the type of selection switch for MC/MM?

Would it be better if it was inside the case and would need opening to access it, or have the MC/MM switch accessable on the front panel?

Sharif.
 
audioflyer said:
Would it be better if it was inside the case and would need opening to access it, or have the MC/MM switch accessable on the front panel?
Click to expand...

Only put it on the outside if it can be switched live, while music is playing. If there's any risk of a huge thump, put it inside.
 
Ill be interested to see what you decide about the switching as I was thinking about this same problem for my pre amp. I look at it as something you don’t do very often so I don’t think it would be a big deal to have to go inside the amp to do it if you did decide on a switch. But I was thinking that a switch in the signal path particularly on the MC side could be a source of noise or impedance, what about a relay switching device would that be quieter?.
I am thinking about just having 2 sets of phono inputs one for MC and one for MM.
The MC set would just route the input through the MC module to the input of the RIAA module, the MM set going directly to the RIAA input. The only thing with that is, the MC would still be powered and connected electrically to the RIAA input even if it wasn’t getting used so what effect could that have on impedance and would the unused MC phono sockets be a source of noise.

Alan
 
Guys, remember how this circuit works.

It has a front-end module, and an EQ module. There are variants for MM and MC for the front-end.

For those people who want both MC and MM in the same box, you buy two front-end boards, and build them up with values for each. You have two lots of phono inputs, wired direct to the respective front-end. The switch then goes between the front-end boards and the EQ stage, and is safe to use when live; there will be a click, but nothing too bad.

The intrinsic PSRR of the boards is good enough that a disconnected board powered up will not have any bad effects.

For most people, who only have a single turntable/tonearm/cartridge, a single front-end wired direct to the EQ board will be the right solution. If you have more TTs, you can add as many front-ends as you want, and use a multipole switch, and have whatever mixture of MM and MC you need.
 
Switching isn't ideal though is it? It makes the signal paths longer for a start which seems contrary to this design or am I missing something here? I'd suggest having plug in modules as the worst case scenario and if anyone has more than one turntable I'd suggest they have more than one phono stage.
 
I've just had the head amp transistors to find for this build, I ended up with 2SA1085 (could not find 2SA1084's anyhwere but 1085's just seem to be rated to higher voltages) and 2SC2546 off ebay. I was planning on building this with veroboard, but can wait for PCB's. A some point I plan to compare it with my Salas Jfet phono stage which I have just finished (when I have optimised the ground configuration, I am still having hum problems).

PD, with all MC phono stages being particularly sensitive to ground layouts, can you comment on a recommended ground configuration for this cct, or at lease a decent place to start from?
 
Chops54 said:
Switching isn't ideal though is it? It makes the signal paths longer for a start which seems contrary to this design or am I missing something here? I'd suggest having plug in modules as the worst case scenario and if anyone has more than one turntable I'd suggest they have more than one phono stage.
Click to expand...

Hi Si,

The switching for the MC/MM will be after the front-end and between the EQ stage so to minimise the signal path. The switching will be local using a make before break switch accessed via the front panel.

I have also another board layout which was the least popular and that is separate MC or MM front-end this will plug into the EQ stage. I personal like this option as it mean you only have to make a new front-end to plug-in thus saving on having to build a new unit.

Sharif.
 
df_genius said:
I've just had the head amp transistors to find for this build, I ended up with 2SA1085 (could not find 2SA1084's anyhwere but 1085's just seem to be rated to higher voltages) and 2SC2546 off ebay. I was planning on building this with veroboard, but can wait for PCB's. A some point I plan to compare it with my Salas Jfet phono stage which I have just finished (when I have optimised the ground configuration, I am still having hum problems).

PD, with all MC phono stages being particularly sensitive to ground layouts, can you comment on a recommended ground configuration for this cct, or at lease a decent place to start from?
Click to expand...

I planning a mix star earthing for the phono inputs and outputs ground plane for the other areas comments welcome.

Sharif.
 
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