Pearl Two

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nar

nar

Member
Joined 2002
richluvsound said:
Nar , thank looks straight forward enough .... are there PCB's for this ?

Rich
Click to expand...

You mean, pics I posted ? :)

Yes, there are PCBs, I myself own a very pair, the other one is reserved for a gentleman, but otherwise .pdf is available + even Gerbers if one wants :cool:

Those are not my work (PSU). All credits go to ChefDeGaar alias Flat of Francois :) There is a small error in it though; the traces near the tension reference LM336.5, but it can be corrected easily by offset a component to the left.

Conveniently .pdf can be printed to transparent on today's personal printers, so you can etch them yourself or make them done by a local shop @ low cost; if you know a professional that likes Gerber input, you can have it done with silk screen on top and metalized pads + solder mask.

I don't want to post any links if no one feels the need, but in case PM or reply here, I'll post links then :)

Best,

nAr
 
M

milosz

Member
Joined 2006
K170BL

Spencer over at FETAudio sold me two matched quads of K170BL, $12.00 incl shipping

Easiest way to make sure I've got matched FETs in there is to buy this pair of matched quads, desolder or snip the old ones out / clean up the holes and pop the new ones in.


This Pearl seems to be a VERY VERY quiet phono stage, what I've heard of it so far.

Got a VPI Scout coming to replace the Rega Planar 3, looking forward to a new level of phonography....
 
nar

nar

Member
Joined 2002
richluvsound said:
So its correct for a symmetrical PS .... + rail , - rail and ground x 2 ?
Click to expand...

Yes, even if I suggest having one Ground, distributed to the 2 channels into the Pearl II box, considering you use a single PSU; the other conductor would be for Earth, to phono preamp chassis directly, and different from audio GND (because Audio GND isolated from chassis) :)

Best,

nAr
 
nar

nar

Member
Joined 2002
Dzius said:
Is there any point in turning Pearl phono stage into standard preamp? Which part of it would be better for that. First before RIAA crossover or second after with ZVP3310?
Click to expand...

Depends of what you want to do :cool:

First stage would have higher output impedance, and you would have to experiment to find its saturation level.

2nd stage could do it, but the biasing of the diff. pair would have to be increased, and overall closed loop adjusted to lower gain setting, since we would deal with higher levels :)
20 dB would be plenty I guess

Cheers,

nAr
 
Last edited:
nar

nar

Member
Joined 2002
Dzius said:
Just came to conclusion that whole or at least part of Pearl cirquit without RIAA filter can be used as very silent line stage preamp for First Watt F4. Are there any objectives against ? In whole 55dB of gain is probably much more we need for that.
Click to expand...

I would perfectly agree; except for those points :

- Input sensivity is about 1 mV or less on Pearl II, compared to the 2V or so from modern sources; you'll have to attenuate at the input
- Because : Pearl II is designed to deal with tiny loooow levels, and good thd and overall performance are seen for an output of about 1V or so, even if the last stage can swing a lot more, but with distortion increased.
- Remove passive RIAA filter between stages, and you can start tweaking the design to your needs :cool:

So, in order to conveniently drive a F4, it is possible, but revising parts of the circuit; diff pair bias increased, and so on for the output stage, and scale up rails in order to be able to get good output swing with low noise and distortion.
You should consider what does the F4 needs as input swing to feed your current speakers with the correct SPL. Then as a safety rule, get rails of about x 2 times the output swing needed. If you need 24V swing, use 48V rails.

At least this is how I would try it for a start :)

Best,

nAr
 
M

McQuaide

Member
Joined 2011
Finished a Pearl 2 build

I just finished my Pearl 2 builds, set the voltages to zero, and both boards worked on the first try:D

The only issue I have is a buzzing sound that goes away when I touch the ground post. Here's how it's configured:

I used this linear PS: Power Supplies, Power Supply, Bench Supplies, Transformers

Data sheet here: http://www.mpja.com/download/ip.pdf

I didn't use the "sense" connections on the PS. The PS chassis is grounded to earth. Both Pearl circuit boards are grounded to the Pearl's chassis and to the turntable.

Connecting the PS chassis ground to the Pearl chassis doesn't make any difference in the buzzing sound. As I said, touching the Pearl ground post makes the buzz go away.

Any ideas? I want to do some listening tests, but my wife refuses to stand there with her finger on the ground post:confused:

Mark
 
M

McQuaide

Member
Joined 2011
OK, I'm back again with more problems. Here's the PS I'm using. It doesn't have a ground connection on the CB. I get 28v across +out and -S, and -28v across -out and +S. I'm connecting to the Pearl 2 boards using +out and -out only.

An externally hosted image should be here but it was not working when we last tested it.


I'm seeing about 6v coming out of U1 and -16v coming out of U2. Both boards make sound when connected to a TT, but are weak. I tried connecting 3 9v batteries in series and got approximately the same voltages.

I'm trying to figure out the next steps for troubleshooting. Any ideas would be greatly appreciated.:)

Here are photos of the build:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
nar

nar

Member
Joined 2002
I get 28v across +out and -S, and -28v across -out and +S
Click to expand...

What is the purpose of - S and +S then ?

It seems to me you should perhaps try to tie -S and +S at PSU level, and then it would become a ground ref., between when +28 and -28V can articulate :)

Then ideally you route 3 wires to the board +28 GND -28

Should help achieving 24V out of U1 and U2

A schematic of your PSU would help too

Try at own risks :eek:

Best,

nAr
 
M

McQuaide

Member
Joined 2011
The S+ and S- are sense terminals. The PS uses these to sense voltage at the load to compensate for line losses.

There's no schematic for the PS and none that I can see on the website.

Regardless of the PS, shouldn't I be able to test the Pearl boards with batteries? I'm seeing the same symptoms with multiple 9v batts in series.

Thanks for your help.
 
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