Hello Everyone...
I recently finished a Smoothie build, but I've run into a problem... Basically, no phase !! I've slowly turned the 250k trimmer a few times trying to dial it in, but very little if anything at all happens.
I get a small/quiet/weak amount of phase if I remove one of the transistors & the speed knob works as it should when I do this.
I've used all the correct value components other than the transistors, where I used matched 2n5952's. I flipped these 180 degrees to match the pinout of the listed 2n5457's.
I've also taken some readings...
9.29v going in
IC1
1. 3.67
2. 3.67
3. 2.48
4. 0.01
5. 3.67
6. 3.67
7. 3.67
8. 3.67
IC2
1. 3.67
2. 3.67
3. 3.67
4. 0.01
5. 4.38
6. 4.80
7. 4.80
8. 9.06
Q1
G. 3.16
S. 3.67
D. 3.67
Q2
D. 3.67
S. 3.67
G. 3.16
It seems that 3.67v is a very common reading !!
Any help would be greatly appreciated. Thanks.
Shouldn't pin 8 of the 1st opamp be equal to the V+ voltage (9.29)? Then again I have no idea what ICs are being used. The .13V difference on IC2pin8 and your V+ voltage seems to be off. Try to get a more accurate reading if possible.
You should also share the schematic for the project. That is a must. But you have my guess of where to check out.
Not a problem. Here is a link to the build PDF which includes a schematic...
http://www.madbeanpedals.com/projects/Smoothie/Smoothie_2015.pdf
Thanks.
Shorted trace between Pins 7 and 8 of IC1 ;)
Pin 8 of IC1 should be the same as Pin 8 of IC2
Quote from: 1878 on September 09, 2015, 01:56:06 PM
It seems that 3.67v is a very common reading !!
Perhaps it is in these connections that hold a clue to where the problem could lie (an obvious short)
I'm definitely not as intuitive or knowledgeable as most of the members here but my suspisions would be a short. Perhaps more than one.
Quote from: Kevin Mitchell on September 09, 2015, 02:07:06 PM
The .13V difference on IC2pin8 and your V+ voltage seems to be off.
This is due to the diode drop. Normal
Quote from: Govmnt_Lacky on September 09, 2015, 02:28:01 PM
This is due to the diode drop. Normal
Darn voltage protection diodes!
Still learning - always learning ::)
Thanks!
Thanks for the replies.
By shorted trace, do you mean 7&8 are connected ??
Quote from: 1878 on September 09, 2015, 02:35:46 PM
Thanks for the replies.
By shirted trace, do you mean 7&8 are connected ??
Yes it is very obvious by your reading if they are indeed accurate.
You can see pin 4 gets ground and pin 8 should be getting +9v (v+). Something is definitely wrong there.
Quote from: 1878 on September 09, 2015, 02:35:46 PM
Thanks for the replies.
By shirted trace, do you mean 7&8 are connected ??
Yep!
That is the first place to look. Also check IC orientation.
If there is no short, follow the V+ supply line back from IC1 Pin 8. Since IC2 has the proper V+ on pin 8 then you know it is good from there to the V+ input to the PCB.
Thanks again.
I've just reflowed all solder joints around both IC's. I'm getting slightly different readings, but I can't make too much noise at the moment due to a sleeping 3 y.o.
I'll get the audio probe onto it tomorrow.
Quote from: 1878 on September 09, 2015, 02:59:35 PM
Thanks again.
I've just reflowed all solder joints around both IC's. I'm getting slightly different readings, but I can't make too much noise at the moment due to a sleeping 3 y.o.
I'll get the audio probe onto it tomorrow.
And the voltage at IC1 Pin 8? ???
Also confirm that pin 4 of both chips is directly connected to ground. Just because they read 0v doesn't necessarily mean they are grounded.
Just had 10 minutes to have another look...
IC1 has the same readings as previous other than pin 8 which is now 9.06v. Both pin 4's go to ground.
IC1 is a TL072CP
IC2 is a TL072IP
I've tried the trimpot again to no avail. I still get the booey phase effect when I remove either of the transistors.
Thanks.
I'd keep checking for shorts seeing how you have very similar readings all over.
Sorry I'm not savvy enough to point them out. If you go off the schematic and notice the same readings on pins that are next to each other but should not be connected, those are points of suspicion. Maybe you skipped a lead while soldering, maybe it looks good but isn't. Check that all components are soldered and mounted well.
You could use an audio probe and follow as you get close to the final sound it's producing. Along the way you will find your suspects.
These two methods will keep you busy. The problem usually is a quick fix that you tend to miss. Keep at it.
Yuppity. I have a feeling it's something VERY simple. I didn't realise you had to use the smaller resistors, but I did take extra care to ensure there wasn't anything touching something it shouldn't.
I'm in work for 5 a.m tomorrow so it's an early night for me, but I'll get the audio probe onto it this weekend.
Thanks again.
If you get a chance, please repost voltages for ICs and transistors. Would like to see what the changes are now that IC1 Pin 8 is at 9V.
EDIT: Also, verify that D2 is a 4.7V Zener. You should have 4.7V on the banded side. If not, then that could be your problem.
Readings for IC1 are exactly the same as before other than pin 8. Diode is a 4.7v too. I get a 4.7v reading.
I beg your pardon. I'm getting 3.67v !!
Quote from: 1878 on September 10, 2015, 03:35:44 PM
I beg your pardon. I'm getting 3.67v !!
I was gonna catch that...
The voltage on the Zener should match the voltage on the Drain of Q2 and Q1(2N5952)
If you cannot verify the part number on that Zener, I would replace it if I were you. Maybe even try a 5.1V. Something that puts 4.7V on the banded side.
Hmm. Just swapped it out for another 4.7v zener & I got the same reading. I'm pretty sure I have a couple of 5.1v somewhere.
Just tested the voltages on the V+ rail & it's 9.06v all the way to R24 (10k). When I check the voltage at the other end of R24, I get the magical 3.67v !! Should there be such a big drop ??
Quote from: 1878 on September 11, 2015, 12:40:26 PM
Just tested the voltages on the V+ rail & it's 9.06v all the way to R24 (10k). When I check the voltage at the other end of R24, I get the magical 3.67v !! Should there be such a big drop ??
In short... YES
One side of R24 is tied directly to the V+ input rail. Hence, the 9.06V. The other side of R24 is tied to the Zener diode rail which you are showing as 3.67V
The Zener diode side 'should' be at or pretty close to 4.7V. You are losing 1 volt somewhere which could throw off the 5952 transistors and cause no phasing.
The object now if to find out why you are only getting 3.67V on that rail. According to the document, that rail is tied to D2, R24, Bias trimmer, C11, C7... well you can see from the circuit.
If changing the zener with a KNOWN GOOD 4.7 zener did not fix it then you will need to check further down the line. Start by checking values of all the components that directly touch that rail. Maybe you put in a 47K instead of 470K. Something like that.
If nothing comes from that, try a 5.1V zener or start replacing components on that rail until your voltage pops into place.
BTW... what part number zener did you use?
This one...
http://www.banzaimusic.com/4-7V-Zener-Diode-1-3W.html
I'm gonna spend some time on it tomorrow. Determined to get it sorted !!
SORTED !!
I had a bit of a brainwave moment. I bought some 750K & 3.9M resistors from Ebay. Thanks to this...
http://resistor.cherryjourney.pt/
I found out the seller had labelled them incorrectly.
Thanks to everyone for your help. I was expecting a much more subtle effect to be honest, but I have been very pleasantly surprised. I am on something of a phase quest at the moment & this is a keeper !!