ours sound like the 2*5*2*0?

[clintrubber]

omeiko wrote:
...Is anyone interested in sound clips?
Yes!

Another yes here.

Thanks

 

[Sleeper]

yeah, excellent guys thanks for the pics, I'm glad I brought it up.
just have to go through my list, I still need a few parts... order em this weekend, I won't be getting to em right away though. at least a week or so for the parts.

about the transistor matching here, in the notes it says to match q1-q2 w. hfe > 400
that's it? my dmm has an hfe tester so this seems good n easy.
did you do it that way or use a jig?

I have a jig I used when I built some hamptones, I'd have to check, but I think I was measuring output voltage on those...




Going to use the first pair of a*p*i s as the summing amps on a passive mix bus, that's partly why I'm going with the 2520's as opposed to the 1731. I want something fairly bright for this, so I'm starting here. :idea:
I have some input trafo questions about this, but i'll research a bit more first.

Sleeper

 

[Bauman]

From left: JE990 (with bc550/560 and bd139/140 transistors),

Layout available? What are you using for input pair?

And yes, pls, post some soundclips!

:guinness:
Fabio

 

[omeiko]

about the transistor matching here, in the notes it says to match q1-q2 w. hfe > 400
that's it? my dmm has an hfe tester so this seems good n easy.
did you do it that way or use a jig?

I didn't worry too much about matching.
I think it affects mostly the noise performance (correct me if I'm wrong).
My home studios ambient noise is so high anyway that it outweights any noise in my preamp. Don't have any ribbons either.
I know this isn't ideal approach but I'll use these op-amps the way they are now and see if I run into any problems.
They really aren't that noisy anyway.

Quote:
From left: JE990 (with bc550/560 and bd139/140 transistors),

Layout available? What are you using for input pair?

Look here. Dale has made a 990 in a 2520 pinout. I'm using just pair of bc550's. http://www.groupdiy.com/index.php?topic=1401&start=0

It might take a while with the soundclips but I'll post them when I'm done.

Cheers.

-Okko

 

[Flatpicker]

[quote author="omeiko"]It might take a while with the soundclips but I'll post them when I'm done...[/quote]Take your time, Okko. No hurry. We appriciate the effort!

 

[robomatique]

[quote author="Sleeper"]
about the transistor matching here, in the notes it says to match q1-q2 w. hfe > 400
that's it? my dmm has an hfe tester so this seems good n easy.
did you do it that way or use a jig?

Sleeper[/quote]

I am thinking of this as well. Is it ok to just find transistors with matching hfe over 400 or is there anything else to think about? I also have a multimeter with hfe testing built in.

What is jig?

RObert

 

[Sleeper]

http://www.groupdiy.com/index.php?topic=1766&start=0&postdays=0&postorder=asc&highlight=hamptone

This should give you info you need about jigs-aka test fixtures.
I was looking at the bc550 and bc560 datasheets(i don't have it in front of me right now ...i forget which we are talking about), but if you can find
bc550c they are all from 450 to 800 hfe
don't get bc550a or bc550b- these are presorted and they will be too low.
straight bc550 will just be a crapshoot, so buy a lot of them.

sleeper

 

[deveng]

omeiko wrote: I used a 47pf np0 ceramic.
I have done only a quick test and it seems to be working. I haven't made any measurements yet.

I've done more simulations for 3 circuits: the 1731, a 2*5*2*0 without a current source (2520r268) and finally a 2*5*2*0 with a current source. First I strongly suggest using a 10pf value for the capacitor that feeds back from the base of the output transisor to the base/collector junction between the input pair and second stage (C2 on the 1731, C5 on the 2*5*2*0). When using the 47pf cap there is not enough high frequency feedback for this Miller loop and simulations show a tendancy to oscillate. I believe Peter can confirm this one with a real unit! It would be interesting to do some tests on your newly assembled board with the 47pf value and see if this happening, then change the value to a 10pf value and test again. Check the gain range from min to max. Some of schematic versions have local feedback around the 2nd to the last stage but this does not seem to be effective. Even after changing from a 47pf to a 10pf value there is still a bump in the high end. This can be corrected by increasing the resistor value between the input differential pair collectors from the original schematic values of 91 or 100 up to 1k. It appears that as the C5 value was changed to a smaller value the local feedback around the 2nd to last stage transistors became unnecessary and this was removed.

regards,
Jeff

 

[Bauman]

It appears that as the C5 value was changed to a smaller value the local feedback around the 2nd to last stage transistors became unnecessary and this was removed.

Are you talking about R10/C2 on 2.5.2.0 (marked as GONE on the schemos...). :!: :?:

So even in Melcor do you think the 47pF can be 10pF? This one works with 47pF, but 2.5.2.0BC oscilates a lot in several gain positions with 47pF...

 

[deveng]

Are you talking about R10/C2

Yes those are the ones.

I found the 1731 has a mild oscillation at many gain settings (simulations) and it was completely eliminated by changing to the 10pf value.

On the 2*5*2*0 simulations the oscillations were awful and this did the trick there as well. Even if that's all you do it should show a significant improvement. Please let us know how it goes!

Regards,
Jeff

 

[Bauman]

Cool Jeff, thanks for all this inputs! Gonna test and report back.

cheers!
Fabio

 

[jrmintz]

Is there a 2*5*2*0 schematic around somewhere? I've been lookin and I don't see one.

Thanks

 

[hodad]

re Bc550 & hfe: I bought a bunch of plain BC550's from mouser & almost all have been in the 400-450 range, so finding a decent matching pair might not be as hard as all that.

Tom

 

[CJ]

Seth:

http://www.danalexanderaudio.com/api.html

Wait, no opamp schemo there.

:roll:

 

[Bauman]

Seth, CJ,

http://www.thediypill.phx.com.br/forumfiles/sch2520BC_r1.gif
http://www.thediypill.phx.com.br/forumfiles/sch2520_r1.gif
http://www.thediypill.phx.com.br/forumfiles/schPP2520_R268.gif

:guinness:
Fabio

 

[jrmintz]

Thanks Fabio.

:grin:

 

[pmroz]

... great thread, thanks to everyone.

Fabio, could you link this to your meta ? important info here for builder/ testers...

 

[Bauman]

Fabio, could you link this to your meta ? important info here for builder/ testers...

SURE! It's done!

:guinness:

 

[pmroz]

Hi all....

any updates on the R10/C2 discussion... testing, clips etc?

 

[Gus]

Come on people try tip 29s and 30s 2n5088s 2n4401 etc.