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Hi all, first post but a long time lurker/builder.
I picked up a 69 Stones Drive, along with the necessary components during the last sale – and this weekend I set out to put it together.
Note: I’m pretty fanatical about measuring/testing components before soldering, as I hate desoldering…Anyway, after following the build doc, testing/measuring/verifying FET Pinouts, and soldering components, I cleaned the board with iso and scraped around my solder joints to eliminate any potential solder bridges. Once done, I hooked it up to my test rig/power (One Spot 9V adapter) to set the bias – and there’s where the problem occurred.
For all my previous builds, before I set the bias I try to find the ‘middle’ of the trimmer, as it always seems to be easier to adjust minutely rather than dial up, then back, etc. So – I checked the drain of Q5, and the voltage registered 9.39VDC. Dialed the trimmer up, then back – no change in voltage.
I went back and reflowed all my solder joints, just to be sure, and tried again: 9.39 VDC. I measured the other FETs, and the voltages are below. I hooked it up to the test box, and nothing but hiss when I turn up the volume (as if there’s not even input signal getting in).
I just got the FETS from Small Bear (as in they were delivered the same day as the Stones Drive PCB) so I’m confident they’re legit. All the other components are from reputable sellers and all tested to spec prior to soldering.
I’ll be testing it later/tomorrow with the audio probe to see if I can determine where the signal is dying, but any help or suggestions would be greatly appreciated
D | S | G
Q1 9.39 | .827 | 0
Q2 9.39 | 9.3 | 8.89
Q3 9.39 | 9.3 | 8.25
Q4 9.39 | 9.3 | 8.89
Q5 9.39 | 9.3 | 8.41
Craig – Dbl-check that there is +4.5v at the junction of C21 (22µF), R18 (10K) & R19 (10K)
If there is not +4.5v at that junction, dbl-check the values of R18 & R19 and ensure C21 is not shorted or open.
Are the JFETs J113s? (Cannot see from the photos.)
The JFETS are J113 from Small Bear – verified the pinout before installing. I double-checked the voltages at the junction – 9v (+) at all. Swapped out C21 for a brand new 22u, cleaned between the solder pads, and pulled R18/19 – measured at 10k spot on. Cleaned the junctions there, resolder, and no difference.
Are you using protection on the back of your pots so as not to short out against the board solder joints?
Also is that a Tantalum cap at C10, the yellow one or is it MLCC?
I have a piece of closed-cell adhesive back foam that I slide in between the pots and board during build/testing so there’s no shorting. Once I’ve tested and verified a build, I’ll pull the adhesive covering and stick it to the back of the pots. And the cap at C10 is an MLCC 220n.
So, I was never able to get the original build working, so I ordered another board to start again. I’ve populated the board with all the components (all verified for value) except the FETs – and after comparing the board to the schematic, I want to be sure I am installing the J113s correctly.
The J113s I have are from Small Bear, and they have the pinout as shown in the attached image. Should they be oriented according to the silkscreen on the pcb?
So I attempted build #2 tonight: measured and tested all components prior to installing. I used all new components – new J113s (purchased from Small Bear), confirmed the pinout on my Atlas DCA55 (matches the image in my post above) and installed per the pcb silkscreen. Once soldering was complete, scraped between all solder pads with my Xacto knife, then cleaned the board with iso. Hooked it up to power, and I get the same results as board #1: voltages across the FETs are almost identical to the first build voltages I posted above, the voltage at the junction of C21 / R18 / R19 is 9v. and turning the trimpot has no effect. I’ve got plastic covers on the back of the pots, my test rig is working properly (I had just finished and tested a couple of stripboard builds with it before diving into this one) – so I am completely lost.
R2 in both builds look like 430K resistors ( yellow, orange, black, orange, brown) not 47K (yellow, purple, black, red, brown) that would have a knock on effect and stop audio at Q1
Well, that’s frustrating. I’ve replaced the resistor with the “correct” value (verified by color code and meter) – dunno how that happened but I think it was a combo platter of ‘not paying attention when grabbing resistors’ and my meter flaking out.
After replacing the resistor, I checked the other components by color code, as well as using my old Analog Triplett meter, and they all seem to be correct. I have a new digital meter on the way (go Amazon) so I can verify once I receive it.
HOWEVER….still no output, and with the trimmer at max I can now only get the voltage on the drain of Q5 down to 7.5 v.
The pot on the left drive I think it is looks like it’s lacking solder
Did you try changing R2 on your first build
Heres a close up of the drive pot. Solder looks good, and I checked the pad and leg for continuity.
Build #1 landed in the ‘circular file’,,,,
Is it correct that you don’t get VB at the junction of R18 and 19 ?
Also check the pads you’ve scraped between with your exacto it’s ok doing this on vero but not pcb some pcb traces are not that deep and fairly easy to cut through
I’d perhaps continuity check the circuit placing your leads on the component leg / pin and not the solder pads
Concentrate particularly on the area where audio stops
So, I actually ‘found’ that I had ordered two boards, last time. And I can’t seem to locate my audio probe right now…so because my blood pressure is starting to rise, I decided to try build #3…
Measured all components. TWICE, to make sure. Soldered carefully and thoroughly. Cleaned the flux off the board with iso after soldering. Hooked up to my test rig to set the drain voltage for Q5, and the trimmer (once again) has no effect on the voltage. I’m going to dig for the audio probe and see what that turns up…Apologies for the semi-blurry pics. WIll try to get better ones later, after a nice long walk.
Haven’t located the audio probe yet, but I went back to check the voltages across all the J113s and it’s almost identical to the voltages in my first post – Q5 is exactly the same, and the trimmer has no effect. I am using a horizontal 10k trimmer (verified working prior to soldering) from Tayda, oriented according to the silkscreen on the pcb.
Also: using the analog Triplett meter I get ~9vdc anywhere I touch on the board: solder pad, component, the board itself…
I am not sure why this is getting overlooked twice but Cybercow and Billy have asked:
Is it correct that you don’t get VB at the junction of R18 and 19 ?
I think that needs to be clarified unless I missed it somewhere.
All you need to do is use your DMM and put the black probe on ground and the red probe on the + positive pad of C21. Then report your voltage.
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