Love Squeeze problem with 0v at some components

[nonost]

 Hi everyone! Months ago I built one Lovely Squeezer kit from FuzzDogs. That's a Love Squeeze clone based on the same layout that I've seen around the internet.

The pedal is working very good but now I think maybe something is not going totally ok. These are my voltages with a new battery at 9.15v:

*=*=*=*
     IC
*=*=*=*

1 --> 4.80v
2 --> 4.80v
3 --> 2.40v
4 --> 0v
5 --> 2.40v
6 --> 4.80v
7 --> 4.80v
8 --> 8.65v

After seing in a couple of topics that voltages at pins 1,2,3,5,6,7 should be the same I started to worry a little bit. As you can see my voltages at pins 1,2,6,7 are ok, but not the ones at pins 3 and 5, they are exactly half the value they should be.

So then I meassured the transistor voltages and...

*=*=*
  Q1
*=*=*

D --> 0v
S --> 0v
G --> 0v

After that I thought it would be a good idea to test every capacitor (I'm going to do this in all my next buildings even if they look to sound ok) and I found that C6 was 0v. Looking at the schematic I checked near components and I got a few more 0v at R11, R12, R6 and the two 1N5817 diodes (D3 and D4).

I'm not and expert...so the first thing that comes to my mind it's that maybe I could have fried the diodes.

Any hint about what's happening here? It's weird because the pedal is sounding good 

I would really appreciate your help!

[GibsonGM]

Hi Nonost...

Capacitors block DC voltage, buddy!  So on one side of a cap, you may have a DC voltage...and should not have it on the other side of it.    At C5, you can expect a DC voltage at the top of the cap, by where it says "OK" - and you would expect there to be no DC voltage below it.   You do not need to "test every capacitor" - they are usually quite reliable and the problem is with US, not them!     

C9 is blocking any DC from reaching Q1, so no DC reading there, either -  at quiessence (at rest).     

Can you try to see if you can measure DC on the gate of Q1, WHILE YOU PLAY or input an AC signal to the circuit?   This looks 'dynamic'...it seems that the zeners may rectify some AC after a certain threshold and apply it to Q1.   You would not see this at rest.    You could measure this at R12. 


Yes, pin3 and pin5 seem a little low, but perhaps this circuit is intended to operate with that voltage on the inputs?  What does your VB measure?
If it is "working very good", then maybe it is ok?

[Kipper4]

D3 D4 are most likely Schottky in the rectifier No?

[nonost]

  Hi GibsonGM, thanks for your help! I will burn in my mind that capacitors block DC current, I swear  . I'm still kind of beginner. But some questions come to my mind...If there isn't voltage at diodes and transistor, how can they work? I thought that since they are active components the would need some power.

At VB I get 4.7v. With VB there's a 1M resistor in series and after that resistor the voltage drops to 2.35v (exactly half), which is actually the voltage that pins 3 and 5 take. That resistor is present in every layout so I can't understand why you should get the same meassure at pins 1,2,3,5,6 and 7 

In this topic http://www.diystompboxes.com/smfforum/index.php?topic=117237.msg1088269#msg1088269 the user Kipper4 (who has answered in this topic as well, thanks!) said:

pins 1,2,3,5,6,7 of the Ic should all be around 4v6 seen at VB.

and here http://www.sabrotone.com/?p=1331 the user Metev Obelek says:

Maybe we could compare our voltage loadings at the IC pins (i.e. 4.85V at pin 1 & 2; 4.35V at pin 3 & 5 ; 0V at pin 4; 4.86V at pin 6 & 7; and 8.87V at pin which I measured with effect on bypass, both knobs at zero and a healthy 9V battery (showing 9.11V).

Maybe I did something wrong even though the pedal is working. Tomorrow I will do the meassure that GibsonGM suggested playing the guitar.

About the D3 D4 diodes, yes they are Schottky. I've used a couple of 1N5817.

[PRR]

> pins 3 and 5, they are exactly half the value they should be.

I bet those pins are biased with 1Meg resistors, and your meter is 1Meg loading.

If you had a second meter, and watched that stage's output, you would see it fall from 4.8V to 2.4V when you poked the input with the first meter.

The FET in that circuit is not an amplifier but a voltage variable resistor. At rest, yes, all three pins will show zero. With signal, (as Mike says) D3 will rectify a negative voltage to the FET Gate, turning it off and reducing gain by adding resistance in the R4 leg of the gain-setting feedback around IC1A. This is also a very high resistance point: poking it with your meter may spoil the compression, but you should see some negative kicks on hard strums.

[nonost]

 Hi PRR! Pins 3 and 5 are in series with an 1M resistor that comes directly from VB. Sadly I don't have a second multimeter to do the test.

I've done the meassurements while playing and got nothing...I'm doing something wrong because the compression is working, as I turn the knob clockwise the volume is raised so...I may be doing the test wrong. I do as usual:

• set volts on the tester
• black led to ground
• red led touching the component

[antonis]

I'm doing something wrong because the compression is working, as I turn the knob clockwise the volume is raised so...

Do you mean Compression knob or Volume knob..??

[nonost]

 Ey Antonis! I meant the Compression knob. As I turn the Compression knob clockwise the volume increases, which is the expected behavior in a compressor, isn't? Needless to say that with the Volume knob I can adjust the volume with any problems: below unity, at unity or even boost the signal.

[antonis]

As I turn the Compression knob clockwise the volume increases, which is the expected behavior in a compressor, isn't?

Maybe yes, maybe no..

Compression pot setting (in parallel with R4) set the feedback resistor value and consequently the Gain with R5 in series with Q1 channel resistance..
(Ok it's not that simple but let's ingnore IC1A OUT loading by Vol pot+R13+OUT load..)

If the signal is enough amplified (hitting the PS rails) at some Comp pot setting, Volume will NOT further increase..
(actually, signal "headroom" is set by D1/D2 forward voltage drop - any higher voltage is by-passed out of NFB loop..)

So your Compression pot should mainly set Compression level and incidentally Volume..

[nonost]

So your Compression pot should mainly set Compression level and incidentally Volume..

Actually that's how I would explain the way that the Compression pot works in this pedal. Since it's working fine I can't see why I don't get any voltage different than zero when I do the meassurements with an input signal (playing the guitar at the same time).

[PRR]

> set volts on the tester

AC? Or DC?

[nonost]

I tried both, got nothing... I've meassured resistance and got 1.63k at transistor drain, 1R at gate and no reading at source. Also it reads 2.73k at diode D3. But the values don't change when I hit the strings.

[antonis]

One of us MUST be confused.. 

Resistance measurement is always obtained between two points..

When you say you've measured 1k63 AT transistor Drain, do I have to presume that one of test leads was placed on Drain and the other on GND..??
(probably not, of course, 'cause your readings don't make sense in that way.. - i.e. you should read very high resistance between Gate and GND..)

I'm pretty sure you took measurements in the wrong way, so to start with:

Turn your multimeter on DC Voltage and measure DC bias voltage on pins 3 & 5, taking in mind your meter internal resistance..
(e.g. if R3 & R7 are 1M resistors and your meter resistance is also rated at 1M, you'll read exactly the half of expected V_B at pins 3 & 5.. if it's 10M you'll read 0.9 of expected V_B and so on..)

After correct bias verification, we can proceed with AC signal measurents.. 

[GibsonGM]

To clarify...DC measurements are taken with the circuit "on"....resistance measurements, with no power applied to the circuit....

[nonost]

 Firstly, thanks for you patience Antonis, thanks to all of you.

When you say you've measured 1k63 AT transistor Drain, do I have to presume that one of test leads was placed on Drain and the other on GND..??
(probably not, of course, 'cause your readings don't make sense in that way.. - i.e. you should read very high resistance between Gate and GND..)

Yes, with the black lead to ground and the red one placed at transistor Drain I get 1k63...

Turn your multimeter on DC Voltage and measure DC bias voltage on pins 3 & 5, taking in mind your meter internal resistance..
(e.g. if R3 & R7 are 1M resistors and your meter resistance is also rated at 1M, you'll read exactly the half of expected V_B at pins 3 & 5.. if it's 10M you'll read 0.9 of expected V_B and so on..)

Then again with the black lead to ground (and DC volts set on the tester), on pins 3 & 5 I get exactly half the expected value. On pins 1,2,6 & 7 I get 4.7v and on pins 3 & 5 I get 2.35v. So I think we could assume that my meter internal resistance is 1M. But to be honest, I don't know why is this happening, I mean... I don't understand why/when do we have to take into account the meter internal resistance. But this is another topic I guess 

To clarify...DC measurements are taken with the circuit "on"....resistance measurements, with no power applied to the circuit....

Yes, I'm aware of that!

[PRR]

> 1R at gate

That can't be right. Suspect a short.

> no reading at source.

There really should be a reading. It may be zero, or overload, or "INF", or "--ACK!--", but it should say something. Report just what it says, "nothing" is not clear.

[antonis]

But to be honest, I don't know why is this happening, I mean... I don't understand why/when do we have to take into account the meter internal resistance.

You can call it "loading effect" or whatever else you like... 

When you measure voltage, you actually place meter's resistance in parallel to resistance on which you want to measure voltage drop..
(without resistance there isn't any voltage drop..)

So, meter actually reads voltage drop on its own resistor, placed in parallel with the one of interest..

The bigger the meter's resistor value the lower the deviation of actual value.. 
(a safe analogy is 10:1 or greater..)

P.S.
Beware of what PRR told you about FET measurements..

[nonost]

 Sorry guys I switched the gate/source values before...here the good and new ones:

• Drain ----> 1k6
• Source -->  1R
• Gate ---->  113k

Now I'm getting resistance at transistor Gate...maybe before I forgot to disconnect the battery when I got nothing. With nothing I meant that the tester wasn't displaying anything else than the "1" that is always showing up waiting for you to do something. But that it's not happening anymore, as you can see there's a high resistance at transistor Gate.

I've attached a picture with some resistance readings:



Does it look good?

I'm getting AC volts at C5 and C9 (boundaries of the problematic area) but the tester shows 00.0 for D3, D4, R11, R12, R6, C6 and Q1.

P.S.
Beware of what PRR told you about FET measurements..

What do you mean exactly? Sorry

[antonis]

Your measurements don't make sense..
(in case of faithful circuit reproduction..)

2k75 (on blue square) should be O (zero).. - (or less than an Ohm - depending on your test leads resistance..)
(unless you mean you take the same measurent on R12/C6 and on R11/D3 .).

1k47 on D3/D4/C5 should lie in MegaOhm region..

Can't say anything about 113k on Q1 Gate w/o R12+R11 values..

1k47 on Q1 Drain doesn't indicate a healthy Fet..

There are lot of dicrepancies in your measurements..
(e.g. you can't take 1k28 resistance across D3..)

P.S. Are you sure C5/C9 aren't shorted..??

[nonost]

2k75 (on blue square) should be O (zero).. - (or less than an Ohm - depending on your test leads resistance..)
(unless you mean you take the same measurent on R12/C6 and on R11/D3 .). :icon_wink

I meant that D3 anode, R11 positive, C6 negative & R12 positive all of them read the same --> 2k75. Sorry if it wasn't very clear.

All resistance tests done with black lead to groung.

At C5+ I get around 105k (which is basically the same resistance that I get at IC pin 7) and then it drops to 1k45 at the negative lug.

Since the pedal/compression it's working I should assume that I am doing the meassurements very wrong. That or my shitty tester is trolling me...

Thanks for all the feedback Antonis 

P.S.

P.S. Are you sure C5/C9 aren't shorted..??

I've checked continuity among the components and everything is fine