Building a Pearl 2

[6L6]

Have had a Pearl 2 for almost a decade. No power up issues at all.

 

[mattking52]

Is there any voltage references for this phono? My mate has it, but it doesn't work, it distorts and speaker cones are going in-out 'like crazy', without any input signal. JFETs are 2SK170 with 77mV through 10R source resistors.

Thanks

See post #1002 in this thread for a schematic annotated with expected node voltages throughout the circuit.

 

[itsikhefez]

Hey all. I'm starting a second Pearl build and sourced JFET's elsewhere.
They are 2SK170BL, with an 11mA Idss.

Should I make any changes to the resistor values?

 

[esprit]

Hello
When I ordered 2SK370's, I received 2SK3703-1e in TO2 format.
can I use the 2SK3703-1e.

 

[Dennis Hui]

2SK3703-1e seems to be a mosfet and cannot be used in place of 2sk370/2sk170.

 

[esprit]

Understood
any idea where I can buy 2sk370.

 

[Wellerman]

Hey all. I'm starting a second Pearl build and sourced JFET's elsewhere.
They are 2SK170BL, with an 11mA Idss.

Should I make any changes to the resistor values?

Maybe increase R21-R24 to 20R. I'm afraid voltages around Q3 will not be what they should be with high Idss parts (also the case in an earlier build of mine with 8-9 mA Idss parts)

 

[jackinnj]

Understood
any idea where I can buy 2sk370.

Use LSK170B -- now carried by a major semi distributor NacSemi Your Global Partner For Electronic Design and Fulfillment Services - NAC Semi

some of the smaller distributors like Allegro and Trendsetter carry low noise JFETs.

you can also get an SOT adapter and use CPH3910 which is in current production from ONSemi -- SYN08 has tested them and found their noise to be only slightly worse than BF862. gfs of 20 to 40 mS
https://www.onsemi.com/pub/Collateral/ENA1965-D.PDF

 

[Flikoman]

I had Pearl 2 with some problems, buzzing, humming and distorsions. Since I had no ZVP3310A at hand I decided to try to adapt to BJT.

After this mod, I works and sounds excellent. I still isn't finished, need to adjust offset a bit, but it works.

P.S.
Sorry if this isn't OK, since it isn't original design anymore. Just trying to help.

Regards

 

[6L6]

That is great!

Have you got the offset adjusted properly?

 

[Flikoman]

Output offset isn't a problem, it has 3mV at the output.

I'm talking about offset at collector of output BJT, it has 4V there. There is P1 trimer to adjust this offset. I have about 4V at the collector of BJT.

 

[Flikoman]

Listening to some vinyl.

It sounds very good!

 

[Wellerman]

that's a lot of capacitors!

 

[AnthonyA]

Flikoman,

Can I ask for the Gerber of your pcb please?

Thanks in advanced.

 

[Flikoman]

I'll share it if my friend finds it. His HDD is broken and this Pearl 2 wasn't working good so it was off shelf for a few years until it got to me for a repair.

So, this Pearl 2 isn't mine.

 

[AnthonyA]

Okay thanks

 

[timlein]

External or Internal power transformer?

Re building a Pearl2 phono preamp. Does one really get lower noise (hum?) if the power transformer is in a separately located box? Has this been documented with measurements? Reason I ask is because I see many phono preamps that have internal power transformers and they claim to have low noise. Does using a toroidal power transformer allow one to have the transformer in the same box without any hum problems?

 

[6L6]

The Pearl 2 will not be quiet if it’s transformer is within 3’ of it.

This is true of every phono I’ve ever built.

 

[timlein]

Thanks for info (and confirmation)!

So all the commercial (not DIY) phono preamps I see with built in power transformers have a bit more noise/hum due to the built in transformer? Or perhaps they have shields inside the box?

 

[Eric]

Maybe I got lucky, but my Pearl II is a single chassis build with the transformer and PCBs all in one place. It used to be in two boxes and I put it all together into one as an experiment. I can't tell the difference. Link is in my signature.