Pearl phono questions, please read and answer

[Boban]

Hi there,
I would like to ask couple of questions to people who finished Pearl. I am in process of ordering all parts (received PCB’s and Qpack from Pass earlier this week).

1. What is the purpose of R1 (custom value resistor)?

2. My idea is to add Lundahl trafo for my MC cartridge (Benz LO4, output of 0.4mV) but there are some discussions here on the board about adding the third stage. Can anyone elaborate? Schematic (picture) is worth 1000 words.

3. What would be the value of custom C14/C16 for above mentioned cartridge. What is the purpose of this? Can it be by-passed?

4. What is the best C9 – coupling capacitor? How about Auricap? They are not expensive like Hovland or Jensen but much better than Solen.

5. Anyone from the list (and owner of Pearl) from greater Toronto area who is willing to share his/her building experience and/or tips? It would be great to have someone locally to ask questions via phone.

This is my first posting here and my first Pass project, so be gentle.

Regards
Boban

[wayne]

R1 sets the loading for the cartridge. MM is typically 47K Ohm.
Your cartridge is best under 1K experiment.
The caps are for MM loading and not really needed for most MC cartridges.
You can just duplicate the FET front end for extra gain.
The auri caps are quite a good value.

[Ren]

Originally posted by Boban

4. What is the best C9 – coupling capacitor? How about Auricap? They are not expensive like Hovland or Jensen but much better than Solen.

Hi Boban.

I don't recall any serious discussion on this forum regarding the best coupling cap for the Pearl. If you search on Pearl, you'll find the all the threads covering this very musical phono pre.

Browse the Electronics and Parts forum to find several lengthy threads discussing all manner of capacitative things.

BR,

Ren

[Boban]

Thanks for the answers, I will get back to you all with more questions after I receive all the parts and start working on a power supply. Can anyone recommend kit or pass power supply pcb for the pearl? Can BOSOZ pcb can be used (with modifications)?

Regards
Boban

[Ren]

There is not a PCB for the Pearl PS, but one can easily use vectorboard. There are only a couple of parts to mount:

- bridge rectifiers
- first stage of electrolytic filter caps.

AC fuse can be chassis mounted or in an IEC power inlet module.

optional RC filter for incoming AC mains can be soldered point-to-point

Xformer, of course, is chassis mounted.

The rest of the PS is on the Pearl PCB.

BR,

Ren

[Boban]

Thx Ren,
do you think that using 2 Xformers is overkill - dual mono idea?

[Ren]

Boban,

If there is one thing I've learned in past year on this diy forum is that "overkill" to one fellow is "just getting started" to another.

I built the Pearl exactly as it was described in the article because it was my first diy attempt. I can only report that it is a fine sounding phono stage as-is. Having said that, I have been thinking about fiddling a bit with the power supply:

- bypassing the initial electrolytic filter caps w\ small film-types (only the final filter caps on the Pearl PCBs are now bypassed)

- replacing the rectifier modules w\ discreet high-speed soft recovery type diodes.

...but I digress.

Would two xformers be an improvement? I don't know. If you find that it is, please post your results.

BR,

Ren

[coffin]

Hi
I remember there's a power regulator ckt on the board in PDF file.....
But of course I don't know whether the board PASSDIY offered has regulator or not.....

Pearl is an excellent phono stage IMHO. It is very quiet. very clear.

Coffin

[Saurav]

My 2 cents...

I'm using Lundahl LL9206 MC step-up transformers. I think that's a better way of doing it than adding an extra active gain stage, but that's an opinion based on reading other peoples' opinions, not on personal experience

For the load/input resistance, you need to remember that the MC transformers divides the resistance "seen" by the cartridge by the square of the turns ratio. So, if you use a standard 47K resistance and you get a transformer with 1:10 turns ratio, the cartridge will see 47,000/100 = 470 ohms. Turning it around, what this means is that you'll have to select a resistance value based on what your cartridge likes to see, and how many turns you'll have in your transformer (the number of turns will be dictated by how many dB of gain you need). So, get the cart's specs, pick the transformer, then calculate the resistance needed.

The input caps are more useful for MM carts, and apparently don't do much for MC carts.

Coupling caps - I haven't tried Auricaps in this circuit. I have them in my amps, and I'd tried North Creek Zen caps in a previous preamp and liked those too.

As Ren said, the power supply can be built quite easily on a Radio Shack board. The only problem with cheap boards is that the traces tend to lift at the slightest excuse.

[henkel]

Hi! Guys, about to start my Pearl ono build.

Now ordering parts for it, and I was told that C9 cap would influence the end result sounding of the Pearl ono.

If it's true from the experience of those who have built the Pearl ono, and care to share with me?

I like the end result to sound more dynamics and give better "omphhh" to the music so to speak, if so what brand of coupling caps should I get for thr C9?

Thanks for looking.