Hi There!! First post, and new member, so Hi to everybody.
I'm having a little prob with a finished QSXM2 unit.
The build is made going with the schematic values, all resistors double checked and correct value in the correct position, all BC550/560 in the right position etc..., and the SSM's, i used DIP sockets all the way (i know it's bad :-P).
I use a Lab power supply to feed the board just for checking purpose, so +/-15V, and all seem to be ok with no IC IN, i mean no smoke or shorts or whatever.
The LED H1 lights up, not H2 tough...
Here are the probs i have so far, maybe just a stupid thing?
First the DC servo checking procedure found on "Build Instructions" don't get me to nowhere, i mean, applying a positive voltage at pin 6 of IC1 gets me a positive ( some +0.4 mV or so iirc) at TP1, and applying a negative gives me a negative (-0.55 mV iirc) at TP1, and not the contrary as you mention.
Tried to lower the values of resistors R27 and R28 and it didn't change nothing, i used a 68K in there, same same, i toought going with the schematic the basis will be just fine, a trimmer might have been easier for tweaking this actually, might try that.
Just for curiosity i tried to pass that and insert IC's since the voltage Pins seem to be just fine.
I used OP07 all the way, and the SSM's.
With all OP07 installed and no SSM's i get a 30mA load on each rails +/- , and when inserting both SSM's i have the minus rail failing at about 13V with about 100mA, and the positive voltage steady at +15V but 180mA???
Also when all IC's are in place H1 turns off, just for info.
Anyway hope i was clear enough, and any clarifications is appreciated.
Thanks a lot!
You have 1 pcs. SSM2210 and 1 pcs. SSM2220 in the prepreamp? The current is 800 uA?
R16-R17 mounted and the value 15/4 kohm? R18-R23 not mounted?
Voltage drop over R26 and R31?
Voltage drop over R12 and R13?
Thanks for the help.
QuoteYou have 1 pcs. SSM2210 and 1 pcs. SSM2220 in the prepreamp? The current is 800 uA?
Yes 1 of each, and no, positive rail goes to about 180mA, and negative to about 100mA when both are installed, take them out and all is fine, well no short and current draw is back at 30mA on both rails.
QuoteR16-R17 mounted and the value 15/4 kohm? R18-R23 not mounted?
Yes R16 and R17 mounted and beeing 15K each, that's right? EDIT: wait a minute, you wrote 15K/4, so i should have fitted about 3.7K there??? :|
R18 to R23 not mounted.
QuoteVoltage drop over R26 and R31?
Voltage drop over R12 and R13?
R26: - 0.7V
R12: - 2.7V
I had noted on my schemo (back then) and when i read the description of the pre and build that:
R13 should be 4.6V
R9 : 5.65V
R7: 0.4 to 0.5V
Thanks for the help again, appreciate.
3.3 or 3.9 k is a suitable value. Four times the current should create the same voltage drop.
Well i guess i missed that info somewhere :(, but that makes sense, hope the SSM's were ok with that...
Now here are the readings i have:
My Positive rail is at 0.2A, while my negative is at 0.1A, that's still same same, and doesn't look right, should be about 0.1A each rails no?
Oh and H2 is on, but not H1
I recommend that you identify correct current/voltages with using my measurements.
Yes that was going to be my next move anyway, now that the Emitter resistors are good.
Will keep posted.
Allright, finally got back at it, and found the current draw prob.
Along the way of the build i had used tulip pins (from DIP8) for making exchange of components easier on the input side,
but ommited to add R2 (1K)
So after that all seem to be "fine" but a couple of measures are still off compared to yours:
Pre-Amp Left Channel, MM-mode, BC550C and 560C in all positions except SSM's, OP07 as DC Servo and no input Bias Servo, Input not Shorted.
All values until here are good: Red is what i get
R28: 3.65V ------> 14V
R29: 0.8V --------> 0.8V
R30: 3.62V ------> 14V
R38: 834mV -----> 2V
R39: 834mV -----> 2V
R42 to R47 : about 325mV ----->550mV
I tried the DC Servo check again after correcting , meaning injecting a positive voltage at Pin 6 of IC1 don't get me a negative voltage but a nearly 0V positive and vice versa, while your instructions says positive gives negative and vice versa, maybe just a typo??
H1 is ON, H2 is OFF
It passes Audio but all distorted, crackling and muting audio etc...
Thanks again if you can be of any help to clarify things
Can you short the input. What is your output voltage?
2 volts over R38, R39 is normal if you have "B" type BC's
Voltage out from IC1 is +14V?
Are both channels the same?
QuoteCan you short the input. What is your output voltage?
Input shorted i have about -2mV at preamp out.
Quote2 volts over R38, R39 is normal if you have "B" type BC's
I use CG's
QuoteVoltage out from IC1 is +14V?
Well now checking back after you asking, i get 8V???? Right channel is at 10V (I lowered R27 to R30 on the Left channel, not on the right for testing purpose)
2 mV at the output looks good. J2 is not on I'll hope?
No J2 is on MM.
Audio test was passing, but the sound was bad, meaning a lot of dirt, crackling, muting etc... weird behaviour
EDIT: BTW shouldn't all LED on board be ON? I have only H1 ON, H2 is off.
Well no idea why it passes audio but so badly, crackles, distortion like, and muting signal on low levels etc....
Thanks for any clarifications if this speaks to you? I tought maybe some bad wiring, but here it's pretty light in terms of cabling, beside the power of 2x PSU feeding each channels...
For now i leave this aside, no real time unfortunatly, tought it would go smoothly, and i need to check where is the signal getting this dirty,
for now it's a failure, tried a couple of things, but nothing changes, horrible audio signal tottaly unusable as is.
I recommend you to print out the schematic in A3 if you can and start to measure all DC voltages in order to see where you have the problem.
well back to it, after all this time.
Schematic was printed and DC checking was also before, but i'll start again by redoing that, and see what's up.
But at last check all seem to be fine.
EDIT: No actually i talk too fast, after searching my files, i see that i had measured and noted all voltages corresponding to the ones you provide on your website, and some don't match at all, and here they are, i rechecked to make sure these were the latest:
Power supply +/-15V feeding board correctly
R1 at 56K
LED H1 ON
LED H2 OFF
So left channel, MM mode, BC all position, OP07, No Input Bias, input not shorted, SSM2210 and 2220:
DZ1 to DZ4 OK
R6 to R17 OK
R31 to R35 OK
Voltage check with Schematic showed that on the RIAA section some values don't match, all other transistors seem to have equal values from positive to negative rail circuit, aside of these:
pin 1 15V
While all parts seem to be "ok" on DMM test, i'd like to have your tought on that.
Thanks a lot for the help
If you short the input, what will the output voltage of IC1 be? Within normal range? Right now it's less than +- 13.5 V = DC servo is working.
What is the voltage at TP1?
If you use "B" transistors instead of "C" you will be increased base currents and by this increases voltages across som base resistors like for instance R39.
You have obviously some problem in the RIIA amp. The pre amp seems to work. Are you having the same problem in both channels?
Voltage across R58, R59, R62 and R63?
DC voltage out at the ouput?
IC2, pin 6? Less than +- 13.5 V?
So with input shorted here are the readings:
Pin 1 -15.8V
Same problem on both channels yes.
IC2 pin 6:
-5V shorted input
14.8V not shorted
DC voltage out:
0V shorted input
-12V not shorted.
Thanks again for the help
Since you have the same problem in both channels you must have some mounting error. H2, does it work? Mounted correctly? You can test this with an multimeter and diode test. It should light up some with the test current.
The input stage of the RIAA section seems to be OK.
Do you have the IC5, IC6 installed? I recommend that you short the input when you investigate the DC levels.
Can you measure the voltage across R74 and R75?
IC5 was not installed on previous DC check, but IC6 yes.
I'll have input shorted for testing OK.
R74-75 are at 0V, input shorted, all IC's in place.
H2 is not ON only H1, The LED are at 1.4V on diode check, and they were both working I tested before soldering in place.
After visual check on the RIAA section all transistors are the good ones and they test fine on dmm, and resistors too
I always dmm check before soldering, and I had already gone thru the board before for checking resistors,
So I know they are the right ones in the right place, will recheck again, but I only see a cap value error maybe,
Electro caps are all on right direction etc....
PS: on lab PSU I read 110mA current draw with all IC's In etc.... Seems it's doing good in terms of power feed, am I wrong?
I think you said about 75mA with BC550, since I use BC550C it draws a little more...
Pretty weird really, Passes Audio tough, but with distortion and lots of crackling...
R74/R75 = 0 mA
What about R72/R73?
I can't find the time to sit down
and test it all for hours these days unfortunatly, so your help
is much appreciated.
Here you have a voltage less than 0.65 V + some voltage drop over R74/75 meaning shut off V51/52.
You have to go backwards in the chain.
Voltage across R68+R70 and R69+R71?
Back again, took some time.
Going backwards in the chain we have:
Thanks again for your help.
PS: I've tried the preamp using another turntable/Amp etc... a Revox B790 mine is a Rega RP3, and funnily only one channel exhibits
the dirt in the signal using the Revox turntable and amp :-o, so i'll compare readings again from one channel to another and see what's up.
I'll keep posted if i finally find the fault in this one
Voltage across R72 is 0.2V (should be 1.3 V)
What is the voltage between base V50 and negative rail? Should be 1.3 + 0.65V
Is the transistor right type and correctly mounted?
V50 and T50 is a BC550c un the right direction.
I read 1.062 V between base and negative rail.
Here is a small Audio capture of each channel recorded with Portable Mic recorder right on front of one speaker,
just for you to hear what i'm talking about, well it seems it's more dominent at startup then after some time,
but the distorted sound is there on one channel.
Right Channel (Seem to be a good one)
Left Channel (you har the distorted sound, it's obvious on the first fade out and the middle section of the sample)
I'll need to check overall sound when this channel is hopefully up and running, and tweak things, the working channel seem to exhibit a little too much bass for my taste, but not there yet.
I'm going to vacation so I can't help you for a while but we have this:
One channel is working, that's good.
The other channel seems to have problems at the VAS stage, V52 etc. Go backwards and see why the base voltage is so low at V50. Trouble is in the input stage or the in the current generators at the emitters of the input stage.
Compare my values with your working channel, all voltages. Calculate all currents (U/R).
Check all resistor values!
No problem, have a nice one!
And yes since one channel is working then i can compare etc...
I supsect it could be some transistors that are bad, i remember encountering
same kind of problem with some other build, and it was because of the transistors.
I had checked all resistors twice, i'll do on the problematic spots, but i'll change transistors that
seem to be having wrong values in the circuit as well, might solve the problem.
Anyway, thanks for the support and i'll keep in touch.
As you know i left this one aside for some weird probs concerning the build for years;
I'm taking my time and try to give it another chance.
I've desoldered everything on one channel, and kept preamp stuffed on LEFT Channel, stuffed with BC550/560 transistors (the circuit that wasn't quit working right).
The Right Channel is stuffed with SMD BS850/860 and all BC847/857BS.
This for giving me a comparison, because i suspected that my batch of BC550/560 might be causing some problems, so tought of comparing with smd ones, might be stupid, might be a good idea, will see.....
Anyway, still didn't powered and started the test according to your build, and didn't stuff the RIAA, going step by step for now.
I just wanted to clarify some infos on the build, because circuit description on your website and the infos provided on the Schematic confuses me a little, if you can just confirm these:
From Circuit description on your website:
R1 + R97 are the values that should match the MM pickup
R3 + R97 are the values for matching MC Pickup
Info On Schematic:
R2 Resistor for MM pickup ? (circuit description gives this one in addition to C2? as EMI filtering)
C1 for MM
C52? typo prob on the Schematic?. for MC
Thanks for your help and clarifications...
Will ask questions or update on the old forum thread if this comes to an end haha.
Quote from: zayance on December 31, 2020, 10:56:08 AM
C52? typo prob on the Schematic?. for MC
Yes, type but I can't change that, I'm afraid due to an old design.
Allright, fired the thing up, and tested all points, for now with Lab PSU.
The build is a mix between SMD and TH., and using SSM for now for ease of troubleshooting, i'l try the BC847BS and 857BS tough for
Here are the values, if you have some time? I have some values low and some higher because of BC's beeing CG, but not sure of the lower ones, and i could maybe better match some points, any suggestion is welcome.
Thanks for your help, and sorry to bring this back after all this time :-)
So, i'm only able to work on this one during week-ends, so i slowly just keep at it.
Plugged your SSR03 PSU, after this one working good without any load, meaning H1 / H2 lighted up,
output voltage within specs no prob (+/-15V).
But as soon as this one is hooked up to the QSXM2 (Both channels), H1 / H2 lights up for a sec and then lights go out, since there is around
1V voltage drop, from 15V to 13.5/14V on both rails.
Didn't want to post on the PSU section, since this one seems to work as is.
I tried to the PSU to only one channel, and the PSU behaves well, no voltage drop.
Anyway, hope you can find some time to shed some light on this. Even if the T51-54 section seem to be having different behavious then yours since your tests were with 550/560's and not 850/860... (might try to match BC550/560 in this section and see if it gets better values), the circuit seem to be doing fine, and so i wanted to hear if it was passing Audio etc.. but stumbled on this with the SSR03 + QSXM2 so...
Thanks for the help and clarifications,
The SSR03 should be rock stable if you aren't in the current limitation mode. Make sure that your incoming voltage is at least 20 V. Your sense inputs are both connected, tin blob on the solder side.
QuoteMake sure that your incoming voltage is at least 20 V. Your sense inputs are both connected, tin blob on the solder side.
I'm using 15VAC Transformer, this one exhibits 17VAC wich give around 24VDC after Bridge, so.... edit: 22.5VDC To be precise at X2
Blobs are there yes.
Check that the SSR03 really regulates. Measure the voltage at pin 2 and 3 on the opamp. Those pins should have the same voltage with a millivolt or so.
Under no load attached Pin 2/3 are exact:
Under load (both channels of QSXM2) they are off:
Those this means both IC's dead? :-o
The regulators are out of the regulating range. Make sure that you have 20 V in and "in" means on pin 3 of the LM317 (IC1). Check also that your current is under the limit. Check the voltage over the current shunts (R47/R49). It should be under 600 mV
Yes Vreg is at 18VDC at pin 3
Voltage over R47/49 is at about 550mV.
hmm so i guess i should get a 2x18VAC Tranny here.
Thanks for the support Peranders, i'll keep in touch on this one, and hopefully
will be working as it should and ready for fitting in case etc....
Allright, have some days off, yippy....
Used a 2x18VAC SSR03 is doing fine now...
Audio is passing and sounds nice, all seem to be doing well, at least to me ears...
Very dynamic, had an hour listening to various stuff, mainy listening on headphones (neighbors thank me)
consisting of an Audeze LCD-X, was a nice hour of listening....
EDIT: I have the same oscillation on Preamp out, but it doesn't seem to affect the overall sound as some have mentionned,
so not sure what to think about that....
Still needs an enclosure, it was just dummy metal plate for now....
You should try to locate where you have the oscillation and try to cure it. Start with only one channel active and shorted input. If you can measure the frequency or even better having a FFT measurement you may come to the conclusion that it's a radio signal you picking up.