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Old 3rd April 2002, 04:13 PM   #1
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Default Pearl -- does it have enough gain?

I have built a modified Pearl (Yu-hu!). It measures well, but I have not had the chance to test yet with real material.

The salient difference between my version and the original is: double the number of input and output devices, lower Rsource and more attention in the power supply.

I still only get a voltage gain of about 540 at 1KHz. The question then is whether this is really enough for a moving coil cartridge? If I read the original right, it has voltage gain of about 30*30=900 gain before RIAA meaning about 90 (about 39dB) at 1KHz. My version of course has more gain (about 54dB due to changes in circuitry) This looks really low for moving coil. Have I simply misunderstood at which frequency to compute gain and how to interpret effect on next stage?

Or is this simply a misunderstanding of the intended use of the Pearl?

Your input would be highly valued!

Petter
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Old 3rd April 2002, 07:23 PM   #2
AuroraB is offline AuroraB  Norway
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Your calcuations are totally OK....
The Pearl manual clearly states appx. 40 dB @ 1kHz.

Given the often used reference of 0 dBV, thereis indeed some dB's missing somewhere, in the case of the Pearl viewed alone, but in combination with the traditional 10-20 dB of gain in an average control or pre-amp, the output level of 0dBV should be OK , for most power amps.

As for the modified version, 54 dB seems slightly ( ??) on the low side for MC, but again adding the extra 10-20 dB from a control amp, you end up with 64-74 dB, which is quite impressive...referred to a 1V output from the control amp.
The AlephOno states 74 dB of gain ref. 0,5V output, and is concidered a very high gain unit, ( I think..?)

Erno Borbely's All-FET Phono MC pre-amp has 54 and 64 dB gain at 1 kHz, and is concidered suficcient for all but the lowest output MCs.....
As far as I know, most commercial units hovers around in this region....

Whether this is a misunderstanding of teh intended use of the Pearl---I don't think so....
Isn't this what "experimental DIY" is all about.??

Keep up the good work......
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Old 5th April 2002, 05:39 AM   #3
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Hi Petter ,
doupling the fet' is ok , but i would putting in another stage after the input - fet's.So you will have about 70 dB gain and when you will decrease the gain , you can do it with a resistor devider like in the pass ono amp.the additional stage are two fets parallel.
i similate it and it works.

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Old 5th April 2002, 05:59 AM   #4
Apogee is offline Apogee  United States
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Question I'm curious about this as well...

I use a Grado Reference 1.5 mv moving iron cartridge.

Does the standard Pearl have enough gain for this? I haven't built it yet and have been wanting to know prior to ordering the boards...

I too read the 40db gain figure. I wasn't sure how to calculate what it's output would be in volts? I assume optimum would be 0db (.775v) for the line level inputs on the preamp. Is this correct?

Any help or comments would be much appreciated!

Thanks,

Steve
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Old 5th April 2002, 06:11 AM   #5
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Hi Apogee ,
i think the Grado with 1,5 mV delivers enough Voltage.I think it is an MM System and it works fine with the Pearl and you don' t need an additional stage

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Old 5th April 2002, 06:57 PM   #6
Apogee is offline Apogee  United States
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Default Thanks Hsort!

I appreciate the reply! I will go ahead and start ordering....

Thanks again,

Steve
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Old 18th April 2002, 05:07 PM   #7
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Default It does!

Modified pearl design Empire MC1000: it does.

Unmodified: probably not.

Petter
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Old 18th April 2002, 09:04 PM   #8
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Default Pearl -- does it have enough gain?

On the suject of more gain for the Pearl Wayne (of Pass fame) has suggested to duplicate the 1st stage as a pre preamp and alter the gain.

"You could build the first gain stage of the pearl again for a pre preamp but use about 375 Ohms for a collector resistor instead of 1 K."

This is what I propose to do, or alternatively you could make a BOSOZ stage following the Pearl for balanced output with additional gain.

best regards

macka



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Old 20th April 2002, 10:21 AM   #9
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Default Yes, but ....

I actually find that there is enough gain doing what I did. If you make a pre-pre, you need to use another capacitive coupling between that stage and the first one, and this is not my cup of tea. Also, you need to figure out how many devices to use, what voltage levels to set up etc. You can see how it could be done from available Pass service manuals.

Had I done this again, I would have just used more devices

OR

Built a 2-stage balanced version a la X, again with more devices


Petter
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Old 25th April 2002, 10:58 PM   #10
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Default Pearl Gain

The gain is 40 dB at 1KHz on the Pearl.
This is best for a MM or Moving Iron (Grado) cartridge.
We at Pass did use some MC cartridges during testing.
These do work but overall system gain and speaker sensitivity count for an awful lot on if it will or not.

We used a 14 dB preamp and 30 dB amplifier feeding Klipsch LaScala horns.

An XOno or Ono is capable of 76 dB and most used at around 66 for an MC cartridge.
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