(Another) Pearl 2 Buiild

[jetlag]

Hi
Didn't want to start another thread. So here goes my Pearl build.

Yet to power it up.

Later
Peace
Jetlag

 

[jls001]

Wow!!! Nice and clean build.

Please show PS too.

 

[omishra]

Nice one! Clean build.
At right side input wire is crossing both outputs paralleled path. Its too near to each other. May cause trouble for you, oscillation or feedback in phono stage.

 

[jetlag]

Thanks Joshua and Om.
Will post PS pics also.
Re connections, I have used shielded twisted pairs. I hope there would be no oscillation...still will check-up while setting offset.

Peace
Jetlag

 

[jls001]

I can't see the grounding terminal. Is it hidden away somewhere?

 

[omishra]

Also I can see values of C10, 11 and 20 little different. Please refer first post in this same thread which has close up. Those are RIAA filter caps. Must be accurate.

 

[jetlag]

Om
Yes, they look different, but I have measured and match the Wima's to the 5th decimal.

Peace

 

[jetlag]

Re: Help!

Hi Om
Had an opportunity to power-up the Pearl and Oops...the R29 went up in smoke:sad:.
Initial troubleshooting revealed that the LED's are bad. Now why would 2 defective LED's allow more current to be drawn across R29. What am I doing wrong?
Have replacement resistors and LED's, but I am holding back myself.

BTW, the DC rail is + & - 33 V regulated ( I am using a different board than what u designed). Can this be a problem?. Wayne's write-up doesn't stop us from using regulated DC.

Please help.

Later
Jetlag

 

[omishra]

No harm in using pre regulated +- 33V. Please install those red LEDs correctly on PCB and for display purpose add extra LEDs from 24V power supply rail with 18k resistance in series. Those red LEDs are crucial for voltage reference. Please refrain long wires for them. Also check P1, Q2, and Q11. Values of resistances must be correct. Start 5K across P1 max value.

 

[jetlag]

Thanks Om
Will try and post again. Any references for Q2 & Q11?

Peace
Jet lag

 

[omishra]

Thanks Om
Will try and post again. Any references for Q2 & Q11?

Peace
Jet lag

I will attach voltage reference diagram for you. Actually it's there on DIYA but now I am not getting it, last time I sent it to couple of FMs.

It's here , voltage reference.

 

[jls001]

I will attach voltage reference diagram for you. Actually it's there on DIYA but now I am not getting it, last time I sent it to couple of FMs.

It's here , voltage reference.

Thanks, Om. Voltage reference will be really useful for troubleshooting.

Jetlag: a dumb suggestion here - do re-check the terminal of the LEDs - refer page 1 of this thread for diagram. Though I admit that even if you reverse the terminals by mistake, it will only present a open circuit and shouldn't lead to R29 blowing up. You should check all the components which are near R29, namely, Q11, LED1, R27, C21, and may be even Q10 and R28.

 

[jetlag]

Thanks Om
Will check.
@Joshua
Q11 Kaput!:sad:

Will update after replacement.

Peace
Jetlag

 

[jls001]

All the best. Where are you sourcing the replacement transistor?

This may sound stupid but do ensure that the correct terminals of transistors goes into the right holes. See pictures on post # 4 which shows Q11. I was confused enough by the correct terminals of the transistors so I had proceeded only after clarifying it from Om.

 

[jetlag]

>Where are you sourcing the replacement transistor?
One and only Sachin!!

Peace
Jetlag

 

[omishra]

One more unusual but important thing about this transistor ZTX450 - normally any transistors number is printed on its flat side. But this transistor has its name printed on curved side. Be aware of this while mounting on PCB.

 

[jls001]

@Jetlag: any updates on your build?

 

[jls001]

If you don't want to use SUT then you have to raise gain of second stage (either R15=jumper -> extra gain R15=1K ..so on, or R14=1K? -> 301 ? For extra gain) Then you can add switch as above. But this adds residual hiss into phono stage and widely needs more internal separation in enclosure to separate switches and gain stages.

@omishra: Hi Om, after I completed and started using the B1, described here, I am facing inadequate gain on the Pearl II with my primary cartridge which has output of 0.23 mV. I need to put the volume knob really, really high to get adequate SPL.

As per KAB USA's description here (please scroll down to the bottom of the page), I need a gain of 62.63 dB on the Pearl II to get adequate line level voltage (of 325 mV) from the Pearl II's output. [G = 20 log (V/Vref), where V = 325 mV and Vref = 0.23 mV, this assumption being for 5 cm/sec]

How do I play around with the values of R15 and R14 on Pearl II to get about 62 dB gain? Please advice. Thanks in advance.

FWIW, the Hypnotoad AD797 is producing excellent SPL (with a Denon DL 103 which has output of about 0.3 mV) when connected to the B1. No need to turn the volume knob very high.

 

[sachu888]

You will need to replace 1k resisters(R14) on Pearl to lower values like 330R to get 62db(approx)gain.

Regards,
Sachin

 

[jls001]

You will need to replace 1k resisters(R14) on Pearl to lower values like 330R to get 62db(approx)gain.

Regards,
Sachin

I temporarily paralleled 470 Ohms to R14 (1000 Ohms) to get about 320 Ohms. The gain has gone up but it is still less than the Hypnotoad AD797 at the same volume position. So I guess I will try and reduce R14 further.

Any idea if there is a danger of going too low with R14 value leading to oscillation?

I was thinking 270 Ohms may be a good target.