Inverted phase
I am building a Pearl, and have a question for 6L6 or one of the other knowledgeable members of this thread.
I will probably want to compensate for my Pearl inverting absolute phase - just to make sure. In the DIY discussion thread the issue of inverting phase has been debated extensively, and 6L6 more or less concluded "just switch the cartridge leads", which is fine with me.
BUT, being in the building phase, wouldnt it be easier just to switch the input leads at the phono board level. That way the "problem" would be fixed permanently. Or what?
I am building a Pearl, and have a question for 6L6 or one of the other knowledgeable members of this thread.
I will probably want to compensate for my Pearl inverting absolute phase - just to make sure. In the DIY discussion thread the issue of inverting phase has been debated extensively, and 6L6 more or less concluded "just switch the cartridge leads", which is fine with me.
BUT, being in the building phase, wouldnt it be easier just to switch the input leads at the phono board level. That way the "problem" would be fixed permanently. Or what?
I have now finished my power supply and it is working fine. I have also finished stuffing the Pearl boards and would like to touch base on those before moving on.
I have measured voltages on the board and compared them to the voltages given by Algar_emi on page 627 of the Pearl discussion thread. All voltages are within +/- 1% of Algars, except the 4 around R21-R24. Here Algar gets voltages in the low fifties, but mine are in low sixties on one board and in the high sixties on the other. Bearing in mind that we are talking millivolts, my gut feeling is that the discrepancies do not matter. But is this gut feeling right or should I start a search for the reasons?
I have measured voltages on the board and compared them to the voltages given by Algar_emi on page 627 of the Pearl discussion thread. All voltages are within +/- 1% of Algars, except the 4 around R21-R24. Here Algar gets voltages in the low fifties, but mine are in low sixties on one board and in the high sixties on the other. Bearing in mind that we are talking millivolts, my gut feeling is that the discrepancies do not matter. But is this gut feeling right or should I start a search for the reasons?
Voltages around R21-R24 are depending on your JFETs. Mine are about 60mV. You may need to adjust value of R10 to make sure that voltages around Q3 are Ok.
Have a look at my voltages http://qwertyl.republika.pl/passdiy/Pearl2Vol.jpg They are different from Wayne's, especially for the first stage. There were some discussions earlier about adjusting R10 and/or R21-24 so the voltages around Q3 are Vc > Vb > Ve.
On the second stage a lot depends on what is the voltage drop on the LED. I tried quite a few different LEDs. Higher the voltage drop on LED, higher the current through Q4/Q5 and Q2.
I looked at your voltages and noted that on R21-24, your voltages for right and left channel are almost identical. Mine for left channel are 62-63 and for right channel 68-69. Does this channel difference matter?
My system is quite minimalist with a power amp and a passive preamp with just a buffer plus an attenuator, so I have no possibility of compensating for right/left channel differences.
My system is quite minimalist with a power amp and a passive preamp with just a buffer plus an attenuator, so I have no possibility of compensating for right/left channel differences.
I don't think these differences matter much, but there is a lot of clever people here so let's see what they think...
After a several month hiatus, I now have some time to focus on getting my Pearl 2 working. I'm wondering if I made a stupid mistake at the outset - for those of you who got the full kit from the Pass Labs diy store, were the JFETs "paired" in any way? I.e., pairs taped together or something? I'm wondering if I mixed things up and that's why one of my channels is so out of whack (voltage wise).
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I'm not remembering the specifics of how the jfets were packaged (I'm thinking there was just a bag of 12) but I received a set that made three groupings from: four at about 8.92, four at about 8.89, and four more at about 7.65. I used the 8mA groups for each input stage and split the 7.65 grouping for the later stage.
Thanks for all of the replies - I vaguely recall that they were all just in one bag, which I took to mean that they were all matched as one big group. I really should have measured them before I populated the boards. Lesson learned. I'm inclined to desolder them all and measure them now, but I'm worried that I'll probably end up frying them. How sensitive are these little guys?