EQN build thread

[briomusic]

**edited to remove wrong/misleading info**

if you are seeing DC at C53+ then the next port of call would be R35 (24V-ish on one side 22.5V-ish on the other) and also collector of TR3.
do you see/hear signal at base of TR2? did you double check pin orientation of your particular model of BC184?

 

[dandeurloo]

Ok, I'll see if I can rig up the tone probe. 

But is there also any test points I can check with my digital meter to see if any votages are out of the range they should be in?

Thanks guys.

 

[briomusic]

see my reply to holger's post.

I think in your case it's unlikely to be the voltage, but either way you will find where the level drops compared to the good board and that will take you a fair bit close to solving this.

 

[dandeurloo]

ok, I'll check now. 

Just to confirm what I am hoping to find.
Looking for voltage on c53 - 55.  No voltage on the negaitve side is good.  Also, no voltage at either side of R35 is a good thing.

I'll report back.  Thank you!

 

[dandeurloo]

ok.  I think I got problems. 

the negative legs voltages are as follows.

c53= 2.5v

c54= .34v

c55= .01v

R35 is 23v

 

[peter purpose]

Dan,
If I had one to test I'd report back..... but I don't.

As an experiment.. why not stick the smaller R29 in and report back.
If the sound is still good it might save you an awful lot of trouble.

Peter (not a good troubleshooter)

 

[dandeurloo]

Peter I can do that.  But with the voltage on the negative legs will any damage be done to parts with long term use?

Thanks

EDIT:
I just measured the EQ that I think is working properly.  Here are mu findings:

EQ 2:  the working one
R35= 23.3 on onside and 3.4 on the side closest to TR2

c53= 2.3

c54= .3

c55= .0

So maybe both are wrong here or both are right here?  Briomusic any suggestions.

I'll try swapping R29 once I get back later today.

Thanks guys.

 

[briomusic]

ok, first of all a correction I was wrong about C53-55 they are in fact part of the out-amp, not PSU bypass. I confused them with C59-60 (which are bypass). To make up for this red herring I offer up a BA283AM-PP schematic, with the components named according to PP-EQN standard and to the best of my knowledge [/disclaimer]:

The schematic (and transistor voltage table) was borrowed from the EZ1290 documentation and modified by me. If I am in breach of anyones copyrighted artwork let me know. It should help with voltage checking and signal tracing duties.

Please make sure:
1.)...you test all transistors using the hfe function of your DMM. it is not advisable to try them in the circuit with alternative orientations, you might do damage
2.)...the output transformer is connected, this circuit does not function without it.

Lastly, please do not PM me with questions - post them here. that way:
-the info is available for future builders for years to come
-anyone can have a go at helping, not just one person.

thanks.

 

[Holger]

Thank you very much...

 

[peter purpose]

Brios's retainer is paying dividends.... cough

 

[dandeurloo]

K, I just finished a session and measured these quick.  I think I'm probably with in the ballpark on both of these Eq's.  there is a small difference between the 2 eq's but probably not enough to cause 5 db level difference.  I'm gonna try and reflow the board I think.  Is there any place around the input tranny I can check?

EQ1:

TR1
B .89
C 3.64
E .34

TR2
B 3.6
C 21.4
E 3.0

TR3
B 2.4
C 21.4
E 3.1

EQ2:

TR1
B 0.89
C 3.41
E 0.35

TR2
B 3.41
C 21.6
E 2.86

TR3
B2.86
C 21.6
E 2.25

Thanks

 

[briomusic]

K, I just finished a session and measured these quick.  I think I'm probably with in the ballpark on both of these Eq's.  there is a small difference between the 2 eq's but probably not enough to cause 5 db level difference.  I'm gonna try and reflow the board I think.  Is there any place around the input tranny I can check?

EQ1:

TR1
B .89
C 3.64
E .34

TR2
B 3.6
C 21.4
E 3.0

TR3
B 2.4
C 21.4
E 3.1

EQ2:

TR1
B 0.89
C 3.41
E 0.35

TR2
B 3.41
C 21.6
E 2.86

TR3
B2.86
C 21.6
E 2.25

Thanks

@peter...felt I owed you one 

@dan I don't think DC voltages are your problem, my guess is a bad resistor (10k instead of 1k type of thing) or bad solder joint. have you already tried using the two amp-boards from the good eq?

 

[dandeurloo]

I reflowed all the solder joints last night and tested it and I think I got it.  I will use them a little and see how they work but I must have had a cold solder joint or something. 

Thanks guys, so far so good!

 

[zayance]

YEAH BABY! ;D ;D ;D, sounds great so far on quick simple vocal check, Merci monsieur Peter, second one finished also (the other two will have to wait  ;D), just one thing, Briomusic told me on PM a way of doing the clipping calibration using a comp with pushing make up gain for getting to clip the EQ (thr. all the way to no comp of course), i can do that for sure, but i wanted to be able to test that in my bench, i tried one of my pres and it clipped before going IN, and my Sound generator will not go that far in terms of voltage, any tips on doing this in Lab without much fuss ??? Thanks a lot

 

[kato]

Zayance, I like your knobs. What are you using for the small ones?
It's hard finding 4mm shaft knobs in the US. All my searches are coming up empty - at least for knobs that aren't cheap plastic.

 

[zayance]

Zayance, I like your knobs. What are you using for the small ones?
It's hard finding 4mm shaft knobs in the US. All my searches are coming up empty - at least for knobs that aren't cheap plastic.

Go Digikey, and type Kilo search field, look for 12.88cm Diameter/3.18mm Shaft (i'm using Sfernice brand Pots, they have 3.18mm shaft) Kilo Knobs don't have 4mm Shaft, view page to have a look of all the options, love these knobs, use a lot of them, nice and clean....

 

[kato]

Ahhhh! Thank you!  ;D I'm using the same pots.
I was nearing the point of 'bang my head against the wall.' You saved me from buying the wrong knobs because I read the datasheet wrong. Somehow I looked at the 61H pots, not the parv6 in the same sheet.  Whew. Those 1/8" shafts are actually very common and opens up a world of possibilities for knobs. Although I may still go with the Kilos because they look so cool.  Thank you!

 

[peter purpose]

This is what I'm up to in the knob department at present.

 

[zayance]

Hmmm looks nice in all Black, maybe next two with ed's input tranny will go all black... Anyway i need to finish calibration and test drive, it's been a while...

 

[kato]

Ooo yeah, like it. Black knobs, on black surface, with little black lights that light up black to let you know you've done it.