ROG EA Tremolo problem

[ezanker]

I've breadboarded the ROG EA Tremolo and I'm gettin no sound.

Substitutions (using parts I have):
1M resistor on input changed to 1.2M
180 Ohm on Q1 Source is 200 Ohm
250K-L Depth pot is 500K-L
100K-RA Rate pot is 100K-L

I checked the pinouts and have used all 3 of these before with success.  I tried switching out the BS170 and the J201 separately, but it made no difference.  The LED is a 5mm red which is blinking, and the rate of blinking does change with the rate pot.

Voltages are as follows (Measured at max rate):
Q1 BS170              
D = 2V                  
G = 4.6V                
s = 2V                    

Q2 J201                
D = 0.002V          
G = 0.3-0.4            
S = 0V                

Q3 2N5088
C = 3.5V (varies with blinking)
B = 0.58V
E = 0V

The voltage on the positive side of the 22uF Electro is 1.7V.

In probing the circuit, I get sound at the input and after the .1uF input cap only.

Any ideas or suggestions would be greatly appreciated.

Thanks,
Erik

[gez]

Voltages are as follows (Measured at max rate):
Q1 BS170              
D = 2V                  
G = 4.6V                
s = 2V                    

Drain and Source can't be at same voltage.  Either you've shorted the channel or the pinout is wrong/damaged the MOSFET.

[ezanker]

The pin out I'm using is with flat side up and pins pointing down:
Left to right = D, G, S

I used the BS170 in the Blue Magic this way successfully, and this one is from the same batch/manufacturer.  I have also switched it out once.

With the power off, I measure 100K resistance between source and drain points in the circuit.  With power on, there is 10 Ohms resistance between the 2 points.

Erik

[gez]

The pin out I'm using is with flat side up and pins pointing down:
Left to right = D, G, S

I used the BS170 in the Blue Magic this way successfully, and this one is from the same batch/manufacturer.  I have also switched it out once.

With the power off, I measure 100K resistance between source and drain points in the circuit.  With power on, there is 10 Ohms resistance between the 2 points.

Can't remember the pinout and don't have data sheet handy.  Possibly a short between source and drain...

[ezanker]

Thanks for the responses Gez.

I'm not measuring a short resistance-wise, nothing on the breadboard is obviously connecting these 2 points.

When I pull the BS170 out and measure resistance between source and drain it is open circuit.

Is the 0V at Q2 drain reasonable?

[gez]

When I pull the BS170 out and measure resistance between source and drain it is open circuit.

Is the 0V at Q2 drain reasonable?

Edit:  Didn't see the Q2 bit.  Yeah, that's reasonable, it's AC coupled.

RG posted something about BS170s not all having the same pinout if I recall (might have dreamt that though).  Probably fried.

[ezanker]

I pulled the BS170 and measured resistance between source and drain points on the breadboard.  There is 100K resistance and no obvious short.

I put in a third BS170 and still no sound and the same voltages.  

Anyone else have any ideas :?:

If not, I guess I'll dissassemble it and start over (the beauty of breadboarding, right?)

[gez]

I pulled the BS170 and measured resistance between source and drain points on the breadboard.  There is 100K resistance and no obvious short.

A fellow forumite noted that with a certain type of breadboard sold in the US (I don't have this problem with the ones I use) there's a sticky backing which collects bits of component wire 'dust' - tiny particles scratch off when you stick the leads in to the holes -  which over time can create bridges.  See if you can take your board apart and give it a clean (that's what he does).

[gez]

PS  Nothing stopping you from shifting that part of the circuit to another area of the board.  :wink:

[nightingale]

hello ezanker, and Gez!!
I have built probably 5 or so ROG ea trems for freinds.. and i have never had one that did not need some type of debugging. The last one I built I had to increase the value of the 22uf cap between the mosfet, and the jfet?

and just for the record.. every one that I built had completely different voltages on the jfet to find the sweet sounding spot on the trimmer?
My guess would be that this circuit is really sensitive to the gain of the mosfet?

I sort of have a love hate with this circuit.. It sounds sooo good, but the circuit takes a little extra tweaking to get it work.

As a matter of fact.. I just finished populating one of torchy's vero board layouts fo the EA trem.. I might be able to get you some voltages if i can get it up and running tonight.. i might have just cursed myself tho..

[ezanker]

Thanks for all the replies and help.  It turns out my problem is really embarassing  :oops:  :oops:  :oops:

I had biased the MOSFET for 4.5V at the gate instead of the drain.  As soon as I rebiased, it started working and it does sound really good.  

Sometimes the most obvious problems take the longest to find.  I recently boxed up a Tube Reamer and it worked fine on the perf but did not work after putting it in the box.  I measured voltages and resistance for 15 minutes until I measured that the output was shorted to ground...(you guessed it, the Volume pot was all the way down  :oops: ).

Anyway, again thanks for all the help and I'll check extra carefully before I ask this kind of question again.

Erik

[Danny G]

Don't sweat the idiot de-bugging.  

It took me 2 weeks to realize that my TS-808 was dead because one of the volume lugs was touching the side of the box...  :oops: