Building a Pearl 2

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#2,781
6L6 said:
Greenwich -

1) The snubber values are not universal, but instead need to be computed for your specific transformer. Leave empty.

2) Use the 6800uF as you are planning.

3) One 10ohm 3W resistor per rail. Nothing more.

4) Either. Will both work very nicely, those are excellent mains inlets.

5) That cap, being “X2” rated, is suitable for the application. It is, however, superfluous since you are using the filtered mains inlet, so do not use.

6) As the bridge is required to carry mains faults to earth, you need one with a voltage at least that of the mains — get the 400V

7) Whatever will work. If you can get a star washer or two, to help dig into the chassis metal as well as hold everyting snug. Internal or external teeth, either will work.
Click to expand...


Many thanks, 6L6!

I will now go ahead and order the parts and report back as I make progress
 
#2,789
Hi guys I've got a small problem from an error in specifications on an ebay advert for an ultralinear bipolar power supply PCB bought from Sellarz Electronics. The ebay advert said 2x24volt secondaries on the transformer would be good for +/-30volt from the rectifier/filter board and I ordered a nice shiny shielded Toroidy transformer to match.

The PCB has arrived with paperwork that says I need 28v -30v volt secondaries and the transformer built to order is now on it's way from Poland to New Zealand. Will the Pearl 2 work from 25 volt input? I'll be using the Pearl with a music maker moving iron cartridge. For the record Sellarzs Audio have offered to help with costs etc but it's a bit messy and I'd be better off buying a new one and selling 2x24volt locally. Thoughts?
 
#2,790
Does the power supply board include regulators? Is there a schematics you can show?

If you get regulated +/- 25V out of your board you can consider bypassing the
7824/7924 regulators on the Pearl 2 pcbs and perhaps increase R1/R2/R30/R32
(the resistors directly before the regulators) to burn a bit more voltage.
 
#2,791
Hi Dennis

Supply board is this like this one which is over kill but the output is fixed so won't even produce the 25 volt on the supplied spec sheet without sending it back for some surface mount resistor swapping.

ULN-PS1 Ultra Low Noise Bipolar Power Supply | eBay

NB the advert has now been amended and only shows 25volt output max!!!


I've been offered a new Antec transformer by the PCB seller worth 12USD that would work but the Toroidy one cost me 110Euro including shipping. Looks like i'll be ordering another Toroidy if I want to use the power supply board I've got. Intended to build a supply like this one I built for my Nutube Pre-amp.

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#2,792
The Pearl 2 has it’s own regulators. Adding another regulator upstream will have little to no effect, and often series regulators work worse than just one. The outboard supply needs only to have transformer, the rectifiers, and some filter capacitors.

The beautiful Toroidy transformer will work perfectly. Remove the regulator, use in a different project,( It would be perfect for Waynes BA2018 linestage…) and replace with a pair of diode bridges and a couple of caps. Easy.

🙂
 
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#2,797
Mark Johnson said:
Anybody who wishes to contribute a Pearl 3 circuit design, + Gerbers, + BOM, is welcome to do so! Encouraged. Applauded. There's no doubt that many dozens of diyAudio members would be most grateful for your efforts. @audiostar, want to volunteer?
Click to expand...

I will give anyone who asks the Gerber files for the Mini Pearl -- it's SMT and there were two versions, one for SOT-23 devices and another for the SOIC. It is, however, a four-layer board which does a good job of eliminating some of the EMI issues.

The op-amp Pearl output stage I designed simply replaces the static sensitive MOSFET section with an OPA2604 (or similar). Must've been several years ago as I can't find it on the bench.
 
#2,798
I have a question on the Pearl2 power supply. I built a separate power supply in accordance with the build guide-which resulted in +/- 31 V going into the Pearl 2 boards. When I turn on the Pearl 2 the boards drag the power supply output down to about+/- 29 V, and the regulated +/- voltage on the boards is slightly under+/- 24V. Is that normal?

I also built a BA2018 preamp - and combined that with the Pearl 2 - tapping the BA2018 power from the regulated power of the Pearl 2 boards. When all of those are turned on, they drag the power supply down to around +/- 27 V - below ideal for the Pearl 2 boards. The regulated power on the Pearl 2 boards is still about the same.

This makes me wonder if the power supply needs more capacitance (currently 3x6800uF per rail) or lower resistance (currently 2x 10 ohms per rail). I was thinking about reworking the PSusing the universal PS board from DIYAudiostore, adding a 4th cap per rail and lowering the resistance.

I'm also wondering if the Pearl 2 boards are drawing more power than normal for some reason. The whole thing sounds great together, so maybe it's all working normally and I'm overly concerned. I would appreciate any ideas.

Thanks, bmdduck
 
#2,799
Wayne's writeup for the Pearl 2 shows 100mA current draw so your power supply with two 10 Ohm resistors would drop 0.1Ax2x10R=2.0V, which is what you measured.

You are supplying enough voltage to the regulators so your regulated supply voltage variation is probably due to tolerances in parts and possible round-off in parts values.

The additional voltage drop when you added the BA2018 preamp is of course due to the extra current drawn through the two 10 Ohm resistors. The voltage can be raised by increasing the transformer secondary voltage or by reducing the power supply resistors' resistance. The easy choice is to reduce the resistance. That will increase the power supply ripple but the regulators should not be troubled by that. Wayne's schematic shows a single 10mF capacitor after the rectifier and your supply is CRCRC with 3 x 6.8mF capacitors. So your supply even with the reduced resistors will have much less ripple than Wayne's.

To reduce the resistance, you can parallel another resistor with the existing. Try 10 Ohms. That will reduce the voltage drop by one half.

Also Wayne wrote:

"The raw power supply voltages are regulated by U1 and U2 and their associated circuitry. The unregulated 26 to 35 volt rails
are RC filtered, actively regulated down to 24 volts, and then passively filtered again before
reaching the rails of the second gain stage."

So it seems that the voltage to the regulators can be as low as 26V.

https://www.passdiy.com/pdf/PEARL%202.pdf
 
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#2,800
6L6 said:
The Pearl 2 has it’s own regulators. Adding another regulator upstream will have little to no effect, and often series regulators work worse than just one. The outboard supply needs only to have transformer, the rectifiers, and some filter capacitors.

The beautiful Toroidy transformer will work perfectly. Remove the regulator, use in a different project,( It would be perfect for Waynes BA2018 linestage…) and replace with a pair of diode bridges and a couple of caps. Easy.

🙂
Click to expand...

Many thanks would power supply boards from The store produce the +- supply needed?
 
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