Rich - If I were to guess, I would say that it is the connection of R7 to ground (bottom end of R7) right? If I recall correctly this pad connects to the ground plane and takes much more, repeat, much more heat and time to solder properly. There are a few others like this on the board. They are prime candidates for cold or marginal solder joints. I know because they gave me a hard time
.By the look of it, you are getting close to completing the first stage.
Pierre
Rich - try a different brand or mix of solder when you re-flow old joints. Usually the flus is a different formula , and it can help make a clean joint. Also, you should get some paste flux and put a small dab on the pads before re-soldering. Use rubbing alcohol and an old toothbrush to clean the PCB after.
Grounding Question
I've been away from this thread for a while and could use some grounding advice.
I get a buzzing sound (not sure if it's 60Hz) when using one of my tables. Touching the output jacks makes the buzz go away; touching the input jacks makes it louder.
I'm using a star ground scheme recommended here. The Pearl 2 circuit grounds, output jack grounds, power supply circuit ground, and turntable ground all come together to a central star point. Earth is connected to the star through a 10 ohm resistor. Earth is also connected to the Pearl and PS chassis.
The fact that the buzz goes away when I touch the outputs jacks me to believe I have a grounding problem somewhere. Swapping headshells/carts makes no difference.
Any ideas?
I've been away from this thread for a while and could use some grounding advice.
I get a buzzing sound (not sure if it's 60Hz) when using one of my tables. Touching the output jacks makes the buzz go away; touching the input jacks makes it louder.
I'm using a star ground scheme recommended here. The Pearl 2 circuit grounds, output jack grounds, power supply circuit ground, and turntable ground all come together to a central star point. Earth is connected to the star through a 10 ohm resistor. Earth is also connected to the Pearl and PS chassis.
The fact that the buzz goes away when I touch the outputs jacks me to believe I have a grounding problem somewhere. Swapping headshells/carts makes no difference.
Any ideas?
Start with the simple checks first, you don't need to open the case yet. Do you have a buzz with the input disconnected and shorted out? Next check that you have continuity between input and output ground using a multimeter, also check that the input and output sockets are isolated from the chassis.
What a PITFA .... !
C=9.33
B=8.53
E=7.90
things seem to have settled down .... I'll check every hour ...
Last edited:
.
My guess... Because the Pearl 2 input, output and supply grounds are already connected together on the pcb, by connecting them all through wires to another star you introduced loops that pick up stray EM fields. The worst offender would be the input ground wire because any current induced there is amplified. Not good.
The Pearl input ground goes to input jack ground. Twist that ground wire tightly with the live input wire - so that there is no gap through which a stray EM field can travel through. The Pearl output ground goes to output jack ground. The two Pearl supply grounds both go to your star ground. Connect the turntable ground to that star.
Pierre
Last edited:
What has worked in my Pearl and Pearl 2 is this -
Safety Earth - only connected to the primary side of the PSU and PSU chassis.
V+, V-, Vgnd floating in both chassis.
Input and output RCA jacks floating.
Ground lug connect to chassis.
PCB starground, (a lonely, unlabeled hole under C4 and above C12) connect to ground lug.
Just re-read your post, try connecting the turntable ground to the Pearl chassis instead.
6L6 beat me to it.
Last edited:
Rich - Yes, it would be a good idea to test the bias throughout the second stage before running a signal through it. Solder a 2.2k in lieu of Q2. Leave the gate (middle pad) of Q2 unconnected. Solder all components. Double check all the joints... Fire one channel up. Measure voltage on both sides of R28 and R29. Wayne posted what these should be. If all is good, then see if at R10 you get in the ball park of +2 volts (my guess for running with a temporary 2.2k.) If you get no crazy readings for one channel, then repeat for the other.
I find this fun and am happy to helpsorry about all the questions Sir
.Pierre
useful link :
Basic Car Audio Electronics
just look at this ..... http://www.bcae1.com/ampfail.htm
then all other pages
Basic Car Audio Electronics
just look at this ..... http://www.bcae1.com/ampfail.htm
then all other pages
Last edited:
Rich - Yes, it would be a good idea to test the bias throughout the second stage before running a signal through it. Solder a 2.2k in lieu of Q2. Leave the gate (middle pad) of Q2 unconnected. Solder all components. Double check all the joints... Fire one channel up. Measure voltage on both sides of R28 and R29. Wayne posted what these should be. If all is good, then see if at R10 you get in the ball park of +2 volts (my guess for running with a temporary 2.2k.) If you get no crazy readings for one channel, then repeat for the other.
I find this fun and am happy to help
Pierre
I'm in the ball park ... for the voltages on the schematic - with a bit of oscillation . I'm .9 VDC @ `+ output . Showing 7.56 VDC @ R10 ... which is the same as Q6 C ... BTW ,should output be shorted for this ?
Opinions please !
Rich - Ignore the + output. The one that matters now is R10.
Can you bring the voltage on R10 closer to 0 V by adjusting P1 ?
Pierre
I have 0 @ the bottom of R10
Out put
R27=-22.53
R6 = 17.50 OSC
R13 = 2.0 OSC
R28 = -23.14
R31 =-24.48
R29= -23.15
P1 = - 5 OSC