Pearl 3 Burning Amp 2023

[Russellc]

No, I want tried and true path that works! What do I know that would be better? KISS is hard enough.

Russellc

 

[mworthin]

The kit just works. If you ue 2SK170s, you may have cascade transistor bias issues like I did.

 

[Russellc]

Tiny bits all on. Time to sort and label resistors. Chassis on way from Italy. Time to order all the bits to finish chassis for this one.

Russellc

 

[ToreM]

A question about the value of the R27. With a resistor value of 750 ohms, I get the values 3.97 mA on one circuit board and 3.74 mA on the other. There is therefore a difference of approximately 0.23 mA between those channels. Are these values good enough or should I match them more closely?

 

[6L6]

That’s wonderfully close! Well done.

Remember, the spec is anywhere within 2-5mA. Matching doesn’t do much aside making people less worried.

 

[PierreQuiRoule]

Measurement taken off single ended output.

Jumper off (high gain)
Switch 1 ON (50 ohm input impedance)
fc 1kHz
Vin 0.328 mVrms
Vout 1.0 Vrms
Gain 69.7 dB
THD < 0.0002 percent mostly second harmonic

Repeated on other channel to be sure.

 

[PierreQuiRoule]

And.... it sounds great

 

[cubicincher]

Yes, it does!

 

[DualTriode]

Measurement taken off single ended output.

Jumper off (high gain)
Switch 1 ON (50 ohm input impedance)
fc 1kHz
Vin 0.328 mVrms
Vout 1.0 Vrms
Gain 69.7 dB
THD < 0.0002 percent mostly second harmonic

Repeated on other channel to be sure.

View attachment 1304810

View attachment 1304820

Hello,

Give us a peek at the headroom.

Turn up the input voltage until the harmonics are up out of the noise floor.

If that RTX6001 analyzer has an oscilloscope function turn up the input voltage until we see a little clipping.

Thanks DT

 

[wanders]

Probably a dumb question, but: Step 25 in the build photo guide shows how to wire an off the board LED. I get-it that there could be a reason for this on the power supply board; but I don't see the application on the phono boards.

Thanks

 

[rhthatcher]

@wanders - what chassis are you planning to use? The chassis from Gianluca at Modushop has 2 LED holes on the front panel of the RIAA box.

 

[wanders]

I haven't decided yet. I'll wait to see how it sounds and decide then how much I want to invest. In any case, I'll almost certainly keep the PSU out of sight; and only have the RIAA on display. I've been using a Salas Simplistic NJFET RIAA that I built around 2016. That's in a Hammond walnut enclosure. If the Pearl 3 is a keeper, I'd consider redoing the Salas enclosure to house the Pearl 3. I'm waiting on a few connectors then the Pearl will be ready to text.

 

[rhthatcher]

If you're building your test rig in a shoebox, cheap / spare chassis, or on a piece of plywood then you can consider the front LED (D3 & associated R26) as optional. Take it or leave it.
D1 is absolutely not optional.

 

[wanders]

Many thanks

 

[PierreQuiRoule]

Give us a peek at the headroom.

Of course headroom depends on the jumper and switches settings. I measured with jumper OFF (high gain) and all switches OFF. For these settings clipping starts at just over 3 mV rms (8.6 mV peak-peak) input. Pearl 3 output remains clean (THD < 0.004 percent) until 9.1 Vrms out. Clipping occurs (THD ~ 0.2 percent) at 9.4 Vrms i.e. when the output swing of +/- 13.3V approaches the +/-15V output stage supply rails.

Bottom line, no surprises. Nothing to see here.