525 build thread

[Sredna]

Page 10, Reply #195. 

 

[user 10827]

my brain honestly!

thank you!

Now i have spotted my mistake! lets see if we can get this thing working....

 

[bdubya]

Another Ben, here.  In the same boat, sort of.  I've completely built up one of my two units.  I can trace a tone into the opamp at 1.1V(started out with 3.9V at the input jack), then out of the upright opamp, i get 3.4V.  My symptoms are very low signal once the comp is engaged, but once I tweaked R7 a bit, i started to get normal levels of audio, but the signal is distorted and coming in bursts, not unlike something thats been gated and sent through a distortion box.  Which is cool, I ran some samples through and will use them, they sound F'd up.  But obviously, not the end result I'm going for.  

I'm thinking I need to crank more juice into this thing than my soundcard can push, either that or get a more sensitive meter to look at the AC.  There are other test points on the PCB, little spots for your probes, where I can tell there's SOME signal, but its too low for me to see with my meter, except for the one between T1/A2, which reads something crazily high, like 34VAC.  Anyone have a notion as to what "good" readings might be at these points?  I'm going to remove my rotary switch and replace it with some resistors temporarily to troubleshoot, as I may have screwed that up; at the very least it seems the most likely problem at this point. 

Also, I had C21(the tantalum) flipped around.  Didn't blow up or make anything smoke, but I replaced it with a new one in the correct orientation.  No noticeable change.  Could anything have been harmed elsewhere in the circuit from this mis-orientation?  I know enough to be dangerous to myself and my projects, but not enough to know the function of C21. 

Anyhow, I'll post my findings as I fix things, but I'm sloooooowww.  Thanks for all the great information!

bw

 

[user 10827]

Hi Ben,

Im not an expert at all but ill try and help,

when you mention bursts, are you using test tone or music whilst testing? tone im assuming...sounds like your input amp is fine so that's good, C21 should have not caused any thing else to go wrong looking at the drawing so that should be good, is it possible you have other components in backwards, maybe a diode somewhere? im trying to think what would be causing these bursts, obviously some sort of oscillation some where,

What are the meters doing whilst its bursting? when you turn the input control up do you get any GR shown on the meter?

Pete

 

[bdubya]

Thanks for the response, I'll double check all diodes for proper orientation.  I haven't stuffed the meter portion of the circuit yet, basically just using that board for the In and Out Pots, I left off the attack pot, as it doesn't seem to do anything, by all accounts.  I've jumped both ATT pads and the "grnd" pad next to them together, in order to simulate one extremity of the attack pot.  I figured that since the 10k attack pot is close to zero ohms at the one end, a short would be okay.  I may have done this improperly.  I don't really have a permanent setup, so after thanksgiving I'll bust it back out and try everything I can think of.  I have most all of the parts in spare, so it'll get there.  Thanks again for your insight.

bw

 

[peter purpose]

I've jumped both ATT pads and the "grnd" pad next to them together, in order to simulate one extremity of the attack pot.
bw

Wrong. Grounding the ATT pads will take the control signal to ground. NFG

 

[bdubya]

I've jumped both ATT pads and the "grnd" pad next to them together, in order to simulate one extremity of the attack pot.
bw

Wrong. Grounding the ATT pads will take the control signal to ground. NFG

Yep, i now see what you mean.  I tried messing around with it a variety of ways, as I knew I wasn't making a very informed decision with that move, but in retrospect, all of them involved shorting one of the ATT pads to grnd, which is wrong.  Would jumping the two ATT pads together then be the correct approach, do i need SOME resistance between the two or am I barking up the wrong tree in thinking that I don't need to connect the ATT pads to the potentiometer/meter board if i'm leaving off the attack pot itself . . .  I have the correct pot on hand, I'm just a cheap unemployed bastard and want to save it for something where it does something.  Hell, I should give it away on the giveaway thread.  It's an Omeg, nice pot.  Thanks for the heads up peter.  cheers!

bw

 

[user 10827]

HI Ben,

The easiest thing to do is wire up the meter board normally, then, where the Attack pot lives, it has 3 connections to the PCB, correct? to emulate the pot hard left or hard right just fit a 10k resistor between the middle and one of the outer pins, and short the one pin remaining to the middle pin again.

ok?

 

[peter purpose]

Jump the two att pads on the main board together. This will give you standard a 525. Wireing the meter board normally will get you nothing without modifying it. And only very little attack when modified.

 

[bdubya]

Gotcha.  To the rotary switch, then, and triple-checking the diodes.  I wired it up a year and a half ago, when i knew even less than I do now about this stuff (I dove into the shallow end with this one).  It's been a huge learning experience, though, and will be that much cooler once it works.  I'll take some readings at those test points once it works, as it seems like that would help out a bit with the trouble-shooting, at least in narrowing down the section of the circuit that's not performing, if we knew what "good" readings would be at those points. thanks again

bw 

 

[user 10827]

Hi Peter,

Just to say i got both working, I misread the input op amp components, I missed the BC550c, i had all 560's in there, either my dyslexia or stupidity! If i had of got that right it would of worked on first power up.

So thanks for a great project.

Best
Pete

 

[Jim50hertz]

Just to say i got both working

8) 8) 8) 8)

 

[user 10827]

You can buy em back if you need em! 

hope all is well Jim,

Pete

 

[bdubya]

So the main part of my problem ended up being a shoddy solder joint at the (-) input of A2.  Now the sound is nice and clean, but I have to reassemble the rotary switch that got sacrificed in the hunt in order to verify the rest of it.  What made me realize that it was a power issue was when I was listening through an equalizer that wasn't powered on.  I noticed that I could hear the signal, just very low and distorted.  Sounded a whole lot like what was happening with the 525, so I checked for continuity between the + and - inputs on each DOA to their corresponding power inputs on the edge connector (13,14,15) as well as verifying ground in the same manner,  I got thrown for a moment because I didn't have the red and black leads on my meter oriented in the right polarity (because of polar capacitors blocking the DC in one direction?).  After I got that brain-fart out, I found the lack of continuity on the (-) input of A2.  I'm checking all my builds in this manner from now on, which I'm sure for some of you is an obvious step, but revelations are relative.  Pretty rewarding, when things don't work.  Better education than college.  I was psyched and felt the need to share . . .take care, have fun in the snow, if it applies to you.

 

[substitute]

Finally getting ready to push these towards the finish line, a little confused about calibration though.

step 4. c adjusting r7 for output from A1.  I don't understand what is meant by monitor from pin 8.  Does that mean the - input pin on the edge or something else? 

and just to be clear, I'm measuring 0db (0.774v) across + & - of the input xlr, then I should be adjusting R7 for the same measuring from pin 8 to ground?

 

[peter purpose]

Pin designation in the calibration notes refer to the standard schematic.
You'll have to compare the two to find test points.

 

[substitute]

Thanks, that would make sense, looking at the schem I can trace pin 8 back to the output of A1.  I'm sure when I sit down with the pcb I'll be able to trace around and find that location on the actual boards, but I'm still a little foggy on what and how I'm measuring.

Am I right in thinking I should be measuring from "pin 8" to ground and setting R7 to -5dbu (0.435v)?

How are other folks setting their quiescent current?

 

[peter purpose]

Am I right in thinking I should be measuring from "pin 8" to ground and setting R7 to -5dbu (0.435v)?

Jess

 

[substitute]

thank you my freng

 

[magruith]

Hi everyone!

I have a problem I can't find out how to solder the switch. What do sw5a p20, sw5b p20, sw5b pole, sw5a po/r64 and sw5a pole mean please?
where are the pins on the switch please?

Thanks in advance guys!

Magruith