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Old 1st August 2009, 04:17 PM   #721
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Join Date: Jun 2007
Well I have good news - ish!

I have moved the complete psu into its own case and now the hum and buzzing have completely gone.

However; Now it sounds like I've constructed a radio because it whistles! You know that high frequency whistle you get when they're not tuned in properly.

It actually sounds quite reasonable now, but I think I must still be picking up some interference, or I'm getting HF oscillation somewhere.

Should I be using screened cable for the inputs and outputs?
Any ideas pls?

Regards
Roy
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Old 1st August 2009, 04:40 PM   #722
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Default whistle

I've taken two separate power feeds from the PSU one to each Pearl + ONO channel but also used screened power cable with the outer screen connected at the PSU end only. Not sure how significant that is though, so maybe a few other members can pop along and comment.

You could also try a couple of ferrite bead/blocks near the end of the power cable where it enters the pearl case. I think Maplin may do them and there are some that are in two halves and can be snapped on over the cable. Often helps if there is RF pick up on the cable.

One definite source of noise is modern DECT cordless phones. Not sure how they affect high gain audio amps like the Pearl but they can certain affect DSL lines if the base station is too near them in the house. Look for things that radiate nearby, PC, TV etc. and turn everything you can off. If it disappears then turn each piece of equipment back on one at a time until the offending one makes the noise again.

Also establish if the Pearl makes that sound without a source connected. If it doesn't then suspect the source is injecting the noise.


May be none of these but it's a matter of trial and error ti find the noise if it is not within the circuit.

Just thought of another noisy source, those wonderful new Eco friendly long life bulbs that often radiate like crazy. I'm totally against them especially considering something that is supposed to save energy takes about 10 times more energy to produce than the conventional bulb
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Old 30th August 2009, 11:22 AM   #723
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I have a question here about capacitor c5 = 3300uF/35V. I'm not using a 9V battery to power the Pearl. Can I leave C5 out ? I can use the space ;-)

Thanks ! Erik.
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Old 16th September 2009, 03:25 PM   #724
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Cool Pearl PCB's

Hi.
Has anyone got a pair of Pearl PCB's they would be prepared to sell me? Thanks

Regards to all
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Old 16th September 2009, 07:35 PM   #725
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Location: UK
Quote:
Originally Posted by royville View Post
Well I have good news - ish!

......

However; Now it sounds like I've constructed a radio because it whistles! You know that high frequency whistle you get when they're not tuned in properly.

It actually sounds quite reasonable now, but I think I must still be picking up some interference, or I'm getting HF oscillation somewhere.
.....

Regards
Roy
That sounds very much like radio interference of some sort. The age old cure, fitted to many many receivers is a small (~100pF) disk ceramic on each input and ouput direct from the RCA pin to chassis.

You can just dab it on with your fingers to see if that is a sensitive area.
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Old 8th October 2009, 08:41 AM   #726
Lucas_G is offline Lucas_G  Netherlands
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I have bought a new Goldring MM 1042 cartridge and I want to use it with my Pearl phono preamp.

I found this recommendation on TNT-Audio:

"The Cartridge is very sensitive to capacitive loading. Some experimentation with it will be necessary to get the best match to your system. I ended up with 51 kOhm resistive Load and 120 pf capacitive load (plus the Tonearm cabling - probably another 50 pf or so)."

My question is:

On the Pearl the input resistance is now 47kOhm (R27). Is this close enough to the recommended 51kOhm, not to hear any difference, or should I alter these?

How do I get the recommended 120 pF? Do I have to solder two 120 pF caps on C14 and C16, or is there already a capacitive load present at the circuit?

What type a capacitors would be best, soundwise?

Thanks for your advice!
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Old 8th October 2009, 08:54 AM   #727
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Location: UK
Quote:
Originally Posted by Lucas_G View Post
I have bought a new Goldring MM 1042 cartridge and I want to use it with my Pearl phono preamp.

I found this recommendation on TNT-Audio:

"The Cartridge is very sensitive to capacitive loading. Some experimentation with it will be necessary to get the best match to your system. I ended up with 51 kOhm resistive Load and 120 pf capacitive load (plus the Tonearm cabling - probably another 50 pf or so)."

My question is:

On the Pearl the input resistance is now 47kOhm (R27). Is this close enough to the recommended 51kOhm, not to hear any difference, or should I alter these?

How do I get the recommended 120 pF? Do I have to solder two 120 pF caps on C14 and C16, or is there already a capacitive load present at the circuit?

What type a capacitors would be best, soundwise?

Thanks for your advice!
47K / 51K no difference - unless you are likely to fret about such things.

Capacitance is generally more critical and will affect the HF end of the curve. The cable capacitance can be significant.

You need a capacitance meter (a cheapo DVM is quite good enough) to measure from where you plug in the cartridge, including the cable and the Pearl card. You then need to pad this out to 120pF at C14,C16. e.g. if you measure 90pF, add a 30pF (=33pF) cap. A small silver-mica is good.

It easy to get >120pF just with the cable, so another trick is to trim the cable length to suit, if you can, physically.
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Old 23rd October 2009, 06:59 PM   #728
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Location: Irondale, AL
Default Pearl PCB's

I'm looking for a set also, PLEASE!!!
__________________
Been there, Heard that, Forgot what I was listening to!
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Old 23rd November 2009, 05:36 AM   #729
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Location: HK
Hello Cliff

According to the connection diagram of typical phono system , can you clearly show me based on what kind of condition to take the measurement of the
connection path's capacitance (that should NOT include recommended capacitance of the cartridge)

For MM Cartridge :

1) Which connection point must CLOSE ?

2) Which connection point must OPEN ?

3) DMM meter take reading of capacitance at which point and this point should be connected or disconnected ?

For MC Cartridge :

1) Which connection point must CLOSE ?

2) Which connection point must OPEN ?

3) DMM meter take reading of capacitance at which point and this point should be connected or disconnected ?

BR,
CK Wong
Attached Files
File Type: pdf Phono Capacitance.pdf (34.4 KB, 67 views)
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Old 28th November 2009, 06:00 PM   #730
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Hi all,

i am also looking for a pair of PCBs, has anyone got some left? Please PM me, thank you
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