Pearl Two

[Mr. dB]

Originally Posted by 6L6

Ooh! Silver bumper Naim gear. Nice!

Are your cases reproductions or just something very similar?

Use 2 for the Pearl, PSU in one, both RIAA in the other.

Save the third for a linestage/selector.

Or, if you want to pursue another direction, sell the cases to me...

Exact reproductions. He even uses the same paint.

I'd have to sand the edges to get the "silver bumpers" though, they come all-black.

I've got Naim stuff now, and while I'm sort of sick of that sound, I've always been fond of the package.

Have you got a favorite connector for outboard power supplies?

[6L6]

The connector is a 4-pin microphone plug from Radio Shack.

4-Pin Female CB and HAM Radio Microphone Plug : Microphone Plugs | RadioShack.com

4-Pin Panel Mount Microphone Audio Jack : Microphone Jacks | RadioShack.com

They can also be found in a 5-pin version

[coolmaster]

Hello again.
What Red LED did you choose to use? fV of 1.7V, 1.8V, 2V? The manual says 1.7V required but Wayne uses one thats 2V fV. I'm confused here.

[6L6]

I think the basic requirement is red (visible).

The LED is acting as a reference for the constant current sources, so shouldn't be that critical.

[wayne]

The red LED is 1.7 Volts MV50640 from Fairchild or similar.

[coolmaster]

Thanks guys. Meanwhile I've got one board fired up and got going, I think its looking good so far.
Initial observation with bare board connected to DIY PSU (2X 22V 40VA transformer) dual 35VDC at output. Mains at 240V/50Hz.
1. Using ZVP3306A instead of 3310A (unobtainable from my side) ZVP3306 seems warmer on touch, normal?
2. C7 omitted.
3. C15 omitted.
4. Ordinary red LED from spares (unknown spec vF)
5. Voltage across R28/R29 is 1.12VDC. (intend to swap LED's to get closer to 1V) is closer to 1V better or leave it as is?
6. P1 adjustment looks good achieved at near zero volts.
7 Noticed it takes quite a while to go off (LED remains on for quite a while before it fades off) when powered down. I reckon this is because of large filter caps and slow discharge.
8. I read somewhere that its important and good practice to install all the transistors as lowest possible to the pcb, not exceeding 8mm to the top of transistor. Glad I did this, perhaps this is will help in performance.

[coolmaster]

Finally got some 3mm 1.8vF red LED, managed to achieve 1.03V at R29 and 1.08V at R28.
I had to swap the lot to get closest to 1V. (considering my DVM is about 1% accuracy)
All other voltages are within or close to ballpark.
I intend to reduce the gain replacing R14 to 5Kohm at a later stage. I'm going to listen to this board with designed perimeters first, also to let it be on for many hours just to ensure all ok.

[coolmaster]

Near complete build.
Pair of Cinemag SUT, Hi/low gain switch, MM/MC switch
2nd stage with gain jumper at R14 for full 55db or 40db gain to match SUT.

[jjacks4x]

Hi not much of a writer but read alot. just built Pearl II with top grade parts.
.1% res in the feedback and eq (100k\1k\6.8k\909) visay 1839 and polystyrene for eq caps. the front end seams fine both ch same gain at top of 6k8. But at the output 2db+ diff per channel. All resistor measure ok. don't know where the gain diff is coming from. offset is .05v, sounds is not quit right in low channel, but not bad bad so you could tell it is wrong. wave form looks ok on the scope. any thoughts

[Dzius]

Just read the wayne's Pearl II article and you'll find the answer. Gain regulation is described there. (Besides not every red LED have exactly the same voltage.)