The bottom trace above is correct.
It looks like one of the EQ components is wrong or there is a bad solder joint (I often forget to solder one side of a resistor or cap down🙂 )
Just to make sure we don't have a JFET issue, can you measure the voltage drop across R82 and R61 and then across R75 and across R66.
It looks like one of the EQ components is wrong or there is a bad solder joint (I often forget to solder one side of a resistor or cap down🙂 )
Just to make sure we don't have a JFET issue, can you measure the voltage drop across R82 and R61 and then across R75 and across R66.
2.443\2.444
.265\.265
Guess I am measuring caps and resistors around the LSK in the bad channel?
.265\.265
Guess I am measuring caps and resistors around the LSK in the bad channel?
I did find bad solder on C81. That made both curves nearly the same. There is still a slight level difference, and they both look like the one you pointed out as incorrect. L .404 vpp, R .393vpp. Superimposed trace attached note the slight level difference. I am finding 66 year old eyes are not suitable for SMD....
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Ok. The levels are now 1.1% apart - within component tolerances and acceptable (This difference will be inaudible and is about .26 dB).
I’ll inject a square wave into mine later today - I may have gotten the shape comment wrong - I’m trying to remember a while back 🙂
I’ll inject a square wave into mine later today - I may have gotten the shape comment wrong - I’m trying to remember a while back 🙂
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Yes - you are measuring the drain and source currents of the JFET’s. Those values are correct so the JFET stage is fine.
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PCB sets are available again. The lead time from my PCB supplier is about 10 days. Apologies for those of you that have had to wait - your boards will be dispatched on Monday.
A few builders have had problems sourcing the OPA2188/9 for the MC input stage offset servo.
A builder (Phil) has suggested this part which I think should do the job- OPA2182
https://www.ti.com/lit/ds/symlink/o...mCh0h5gDOEAAYAiAAEgJmG_D_BwE%26gclsrc%3Daw.ds
A builder (Phil) has suggested this part which I think should do the job- OPA2182
https://www.ti.com/lit/ds/symlink/o...mCh0h5gDOEAAYAiAAEgJmG_D_BwE%26gclsrc%3Daw.ds
Just received the OPA2182 and other parts,will let you know how it turns out too. Thanks for the design and pcbs.
I’ll have to look that one up - sorry not familiar with it. The demands for the MC input offset are quite high - no more than a few uV offset.
For power amps a TL 071/2 or equivalent is ok.
For power amps a TL 071/2 or equivalent is ok.
Hi Bonsai,
I finally collected all the parts and am testing the PSU section before installing the remaining IC's. Everything looks good except for the +10V Raw Supply for -15V Reg. Here are my measurements:
+15V = 15.06 V
-15V = -15.08 V
+25 Raw = 27.42 V
+10 Raw = 12.03 V
Would this concern you before I move forward? Solder joints look good to me--I can post pictures if needed. Thanks!
I finally collected all the parts and am testing the PSU section before installing the remaining IC's. Everything looks good except for the +10V Raw Supply for -15V Reg. Here are my measurements:
+15V = 15.06 V
-15V = -15.08 V
+25 Raw = 27.42 V
+10 Raw = 12.03 V
Would this concern you before I move forward? Solder joints look good to me--I can post pictures if needed. Thanks!
That looks excellent Chris!
Please can you give the exact readings for the +-5 volt rails and the +10V rail.
Please can you give the exact readings for the +-5 volt rails and the +10V rail.
Thanks, Andrew. I placed the remaining IC's and have the following readings:
+10V Sys Ref = 10.05 V
+10V RC = 9.93 V
+10V LC = 9.94 V
-5V LC = -5.038 V
+5V LC = 5.025 V
-5V RC = -5.039 V
+5V RC = 5.026 V
R82 = 2.518 V
R61 = 2.585 V
U26 PIN 7 = -7.3 mV
U19 PIN 7 = -16.0 mV
Q1 & Q2 = 13.4 mV (collector)
Q3 = -14.9 mV
Q4 = -14.8 mV
U7 = 1.0 mV (PIN 6)
U17 = 0.3 mV
U18 = 1.7 mV
U27 = -1.2 mV
I do not have any voltage between the input and ground of the MC input connector. The reading was a bit jittery as I steadied my hand but seemed to be zero once I stopped moving. It's a cheap multimeter.
Everything appears to be within range at this point, huh? I can't wait to listen to it!
+10V Sys Ref = 10.05 V
+10V RC = 9.93 V
+10V LC = 9.94 V
-5V LC = -5.038 V
+5V LC = 5.025 V
-5V RC = -5.039 V
+5V RC = 5.026 V
R82 = 2.518 V
R61 = 2.585 V
U26 PIN 7 = -7.3 mV
U19 PIN 7 = -16.0 mV
Q1 & Q2 = 13.4 mV (collector)
Q3 = -14.9 mV
Q4 = -14.8 mV
U7 = 1.0 mV (PIN 6)
U17 = 0.3 mV
U18 = 1.7 mV
U27 = -1.2 mV
I do not have any voltage between the input and ground of the MC input connector. The reading was a bit jittery as I steadied my hand but seemed to be zero once I stopped moving. It's a cheap multimeter.
Everything appears to be within range at this point, huh? I can't wait to listen to it!
Chris, the collector voltages on Q1-Q4 (this the left and right MC input stage) look very low. Wrt 0V, you should be reading c. 2 volts nominal.
Your other voltages all look good.
Your other voltages all look good.