I finished the shunty some time ago now, and have been trying to get it working properly. I did it all p2p, so it's possible some of the problems are due to incorrect wiring, but I don't think so - I have checked things pretty carefully.
First problem was odd: Turning the shunty on, I had AC where I should, but the DC voltages on the capacitors C2 and C2A came up really slooooowwwwlllllyyy... like, about six minutes to get up to +/- 15 volts or so... and next to nothing on the outputs J3 and J3A. (+/- 2 V with no load... +/- 0 V with a load...) Since things didnt' work properly even disconnecting the whole circuit after the fuses OS1 and OS1A, I decided the problem was likely the capacitors: either they were old stock (I thought they were nice and cheap - maybe this is why) or they were operating too close to or at their DC voltage limit. (Is this likely to be the problem? 63VDC limit, and about 90VAC coming out of the transformer - this would give 90*1.414 or about 127 VDC total across them... that's 63.5 V each...) In any event I bought new capacitors with a 100VDC limit and rebuilt everything before the fuses. (I confess I just used a rectifier bridge I had hanging around and didn't bother with R21 and R22. What are these for, anyway?) Fired it up, and the upper half works fine; I can use WR1 to adjust output voltage and things are AOK.
The lower half only partly works, though. Adjusting WR1A makes no difference to the output voltage. Checking, I found that U1A was duff, so I switched it out, and that is now fine, but still no go.
SO here's my main question. If I understand the cookbook correctly, Q4 and Q4A *should* work to make the voltage on their bases equal to the voltage on the bases of Q5 and Q5A, which is 5V, fixed by U1 and U1A. This can be measured for Q4 and Q5, but the voltage on the base of Q4A can be altered by WR1A, and is definitely different from the 5V we have on Q5A. So it seems this part of the circuit is the problem, right? I can't seem to find anything wrong with the Darlington Q11A, which seems a likely culprit - in operation there is no voltage across base and emitter as there is for Q11, but maybe something else is wrong. Anyone have any ideas? Did I understand this correctly?
Pumpkin boards are well advanced, but obviously no use without a working shunty....
Thanks for any help
Cheers
Nigel
First problem was odd: Turning the shunty on, I had AC where I should, but the DC voltages on the capacitors C2 and C2A came up really slooooowwwwlllllyyy... like, about six minutes to get up to +/- 15 volts or so... and next to nothing on the outputs J3 and J3A. (+/- 2 V with no load... +/- 0 V with a load...) Since things didnt' work properly even disconnecting the whole circuit after the fuses OS1 and OS1A, I decided the problem was likely the capacitors: either they were old stock (I thought they were nice and cheap - maybe this is why) or they were operating too close to or at their DC voltage limit. (Is this likely to be the problem? 63VDC limit, and about 90VAC coming out of the transformer - this would give 90*1.414 or about 127 VDC total across them... that's 63.5 V each...) In any event I bought new capacitors with a 100VDC limit and rebuilt everything before the fuses. (I confess I just used a rectifier bridge I had hanging around and didn't bother with R21 and R22. What are these for, anyway?) Fired it up, and the upper half works fine; I can use WR1 to adjust output voltage and things are AOK.
The lower half only partly works, though. Adjusting WR1A makes no difference to the output voltage. Checking, I found that U1A was duff, so I switched it out, and that is now fine, but still no go.
SO here's my main question. If I understand the cookbook correctly, Q4 and Q4A *should* work to make the voltage on their bases equal to the voltage on the bases of Q5 and Q5A, which is 5V, fixed by U1 and U1A. This can be measured for Q4 and Q5, but the voltage on the base of Q4A can be altered by WR1A, and is definitely different from the 5V we have on Q5A. So it seems this part of the circuit is the problem, right? I can't seem to find anything wrong with the Darlington Q11A, which seems a likely culprit - in operation there is no voltage across base and emitter as there is for Q11, but maybe something else is wrong. Anyone have any ideas? Did I understand this correctly?
Pumpkin boards are well advanced, but obviously no use without a working shunty....
Thanks for any help
Cheers
Nigel
njepitt said:
nope ;
you'll always have same voltage on bases of Qs in diff amp ; that's intrinsic characteristic of stage itself ;
so - you have fixed potential on one side ( via little 5V chip)
on other side you have voltage potential divider ; with that divider you are able to adjust ratio of voltage above base and at base , so - in fact you are adjusting output voltage as multiple of reference 5V
re-read CookBook ; I think I can't explain better , at least not with my Weissmueller Engrish ...
😀
OK ZM, thanks. I have taken a look at the cookbook again, and although I am not sure I have understood things correctly, I think the problem must be in this part of the circuit.
In your post you say "...you'll always have same voltage on bases of Qs in diff amp ; that's intrinsic characteristic of stage itself...". Well, the bases of Q4 and Q5 are at the same voltage (in the upper half that's working properly), but the bases of Q4A and Q5A are not.
Further evidence that something is wrong with this part comes from looking at R12 and R20 in the upper half, which have voltages across them so current is flowing, but when I look at R12A and R20A in the lwoer half there is no voltage, so (I guess) there is no current flowing in the loop they form with the Darlington Q11A. In the cookbook it says "Yoyoing current through Q5 is routed through R12, and that current is resulting in adequate amount for gentle opening and closing Q11". Apparently this is happening with Q11 but not Q11A....
I can't find anything else wrong, so I suppose I'll try replacing the darlington. (Even though I can't find anything obviously wrong with it...)
Thanks again
Cheers
Nigel
In your post you say "...you'll always have same voltage on bases of Qs in diff amp ; that's intrinsic characteristic of stage itself...". Well, the bases of Q4 and Q5 are at the same voltage (in the upper half that's working properly), but the bases of Q4A and Q5A are not.
Further evidence that something is wrong with this part comes from looking at R12 and R20 in the upper half, which have voltages across them so current is flowing, but when I look at R12A and R20A in the lwoer half there is no voltage, so (I guess) there is no current flowing in the loop they form with the Darlington Q11A. In the cookbook it says "Yoyoing current through Q5 is routed through R12, and that current is resulting in adequate amount for gentle opening and closing Q11". Apparently this is happening with Q11 but not Q11A....
I can't find anything else wrong, so I suppose I'll try replacing the darlington. (Even though I can't find anything obviously wrong with it...)
Thanks again
Cheers
Nigel
njepitt said:
well , fact is that few Shunty's are already made .... functional 😉
without any pic I can't say what's wrong in your actual piece .
darlingtons are usually tough little buggers ....
anyway- catch with them is that you must use something different way of testing them than just plain diode test on your DMM
use 12V (for instance) supply and adequate resistor - make small ccs and measure it ;
off course - first desolder it from Shunty
Thanks again, ZM. I don't doubt that there are loads of working shunties - whatever the problem is it is surely the result of (my) human error... Of course, this would happen less often if I did pcbs, but I find doing p2p such fun....
I really didn't expect you to find the fault (I was just hoping for the kind of help you gave in the above couple of posts) - and I don't think a pic will help, since the p2p wiring is a bit messy looking. But given the measurements above, do you agree that it is likely to be in this part of the circuit?
If I am going to desolder the darlington to test it I might as well put a new one in and see what happens... As soon as I can go by the shop, that is...
Cheers
Nigel
I really didn't expect you to find the fault (I was just hoping for the kind of help you gave in the above couple of posts) - and I don't think a pic will help, since the p2p wiring is a bit messy looking. But given the measurements above, do you agree that it is likely to be in this part of the circuit?
If I am going to desolder the darlington to test it I might as well put a new one in and see what happens... As soon as I can go by the shop, that is...
Cheers
Nigel
Zen Mod said:
Switched out the darlington - no change 🙁
Well, I suppose in light of ZM's remarks above it was not so likely to be the problem... Now I'm checking things again, but no luck so far....
yup ;
being in repair biz for years , I know how frustrating things can be .....
but - often I'm laughing at end , after finding silly mistake or malfunction ...
good luck 🙂
being in repair biz for years , I know how frustrating things can be .....
but - often I'm laughing at end , after finding silly mistake or malfunction ...
good luck 🙂
Found it!!!
And of course, as could have been guessed, it turns out to be a stupid little mistake...
I am using the kind of prototype board that has the little copper islands around each hole. I quite like this (usually) and in any event it's the only kind I can get around here. Well, the connection between R10A, R11A and C10A was made with the (bare) lead of R10A, which was bent around a totally different component lead - I think the earthed end of R9A. No solder on this island, hence no obvious problem, but just the same, the lead of R10A had been pressed down somehow, and was touching the copper island, making a short to earth.... I bent the lead up carefully to break the connection and everything is working just fine....
So there is something to be said for PCBs after all... 🙂
On a different topic, I mentioned above that I am not using R21 and R22 on the AC inputs. I'd like to understand what they're for, though....
Thanks
Nigel
And of course, as could have been guessed, it turns out to be a stupid little mistake...
I am using the kind of prototype board that has the little copper islands around each hole. I quite like this (usually) and in any event it's the only kind I can get around here. Well, the connection between R10A, R11A and C10A was made with the (bare) lead of R10A, which was bent around a totally different component lead - I think the earthed end of R9A. No solder on this island, hence no obvious problem, but just the same, the lead of R10A had been pressed down somehow, and was touching the copper island, making a short to earth.... I bent the lead up carefully to break the connection and everything is working just fine....
So there is something to be said for PCBs after all... 🙂
On a different topic, I mentioned above that I am not using R21 and R22 on the AC inputs. I'd like to understand what they're for, though....
Thanks
Nigel
glad you found it 😉
these resistors are for surge/inrush protection .....
naah ..... fancy little bits (often unnecessary , but sometimes contributing in overall scheme of things )
these resistors are for surge/inrush protection .....
naah ..... fancy little bits (often unnecessary , but sometimes contributing in overall scheme of things )
Hi,
I got a question about altering gain?
Has anybody any experiences about maximum gain and how do you change the values of: R5/R1/R6/R3/C1/C2?? 🙂
Best regards
Felix
I got a question about altering gain?
Has anybody any experiences about maximum gain and how do you change the values of: R5/R1/R6/R3/C1/C2?? 🙂
Best regards
Felix
Kamel said:
in what gain you are interested ?
anyway - ratio of R5/R1 (and R6/R3) is gain defining .
for most cases is logical to leave R1 and R3 at 10K
increasing both R5 and R6 will increase gain.
while increasing them , you mast decrease both C1 and C2 , to maintain same RC multiple as in case with 100k/5p
example - if resistors are 150K (for gain of 15x or 23,5db) you must decrease caps to 3p3
maybe you can completely toss them , but you must confirm forst with CRO (scope) that you don't have oscillations on output .
did you receive my email ?
Hi,
yes I was interested in alternating gain to 15x!
Thanks a lot!
Yes I recieved your Email 🙂 🙂
On Friday I'll pay via Paypal!
Best regards
Felix
yes I was interested in alternating gain to 15x!
Thanks a lot!
Yes I recieved your Email 🙂 🙂
On Friday I'll pay via Paypal!
Best regards
Felix
Hi Chocky, hit all (and hi Felix 😉),
Today was the big day - I fired up my Shuntys the first time. I didn't really expect it to work and guess what - it didn't 😉.
Big Picture Here
On both shuntys I have the same problem. The "upper" channel kind of swings, the LED is blinking and the DC on the outputs is just 13V.
The "lower" channel delivers a stable DC of 39V but can not be adjusted, if I turn the trimmer nothing happens.
I already checked all Qs (well the Qs that are not glued together 🙄 ) and the rest of the boards for but coudn't find any error.
Exactly the same happens on both shuntys with DC in as well as AC in. So wathever I did, i did it twice 😉.
Any ideas where to start?
Thanks
Sven
Today was the big day - I fired up my Shuntys the first time. I didn't really expect it to work and guess what - it didn't 😉.
Big Picture Here
On both shuntys I have the same problem. The "upper" channel kind of swings, the LED is blinking and the DC on the outputs is just 13V.
The "lower" channel delivers a stable DC of 39V but can not be adjusted, if I turn the trimmer nothing happens.
I already checked all Qs (well the Qs that are not glued together 🙄 ) and the rest of the boards for but coudn't find any error.
Exactly the same happens on both shuntys with DC in as well as AC in. So wathever I did, i did it twice 😉.
Any ideas where to start?
Thanks
Sven
Abraxas336 said:
first - Q1 and Q1a aren't isolated from heatsinks , so be sure that heatsink aren't in contact with upper groundplane .
second - did you read last few notes in Cook Book ?
this one :
besides that - desolder JP2 for test , in case that you have somewhere short of any part or trace with upper groundplane ;
with JP2 desoldering , upper plane isn't connected to gnd anymore .
try these few things , then let me know .
Hi Choky,
Did that of course, not in contact with anything. All heatsinks are taped to make sure. All Qs have been testet for contact with heatsinks.
Yes Sir! 😀 Rs are 2.2 and good working condition 😉.
Testet on one Shunty, no connection after desoldering JP2. It was kind of messy so I left the other one since the error has to be on both...
Thanks for your help!
Sven
Did that of course, not in contact with anything. All heatsinks are taped to make sure. All Qs have been testet for contact with heatsinks.
Yes Sir! 😀 Rs are 2.2 and good working condition 😉.
Testet on one Shunty, no connection after desoldering JP2. It was kind of messy so I left the other one since the error has to be on both...
Thanks for your help!
Sven
Mhh. I thought about this while I was waiting for my post to be released by a mod. The error is exactly the same on both Shuntys. Its likely I placed a part wrong. I recalled my last steps and altough I'm not sure there is a possibility I mixed up Q4/Q5 Q6/Q7 Q4A/Q5A Q6A/Q7A pairs. I prepared the Q4/Q5 Q6/Q7 pairs first and may have placed them in Q4/Q5 Q4A/Q5A. Unfortunateley this means unsoldering 8x6 legs, break up pairs and check. 🙁 🙁 🙁
