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Possible 2SC2291 Replacement
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Please be positive and constructive with your questions and comments.

Possible 2SC2291 Replacement

by pulsar256 on Sun Apr 21, 2013 9:00 am

Hey Guys,

during my buildup of the x0xb0x I ran into a fake 2291 transistor and hacked a rude replacement from 2*BC337A together in order to continue soldering while waiting for the replacement to arrive. Now the x0x is complete and I have compared both solutions. Without going into frequency spectrum analysis and in detail comparison - they do sound pretty much the same to me. Perhaps I am not very picky about that, but I thought this might be something worth sharing here with you.

I have uploaded a short test-sequence over at Soundcloud using both variations if you want to check it out yourself:

https://soundcloud.com/pulsar/x0xb0x-2xbc337a
https://soundcloud.com/pulsar/x0xb0x-2sc2291

Original 96kHz WAV files should be downloadable as well.

Cheers!

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Re: Possible 2SC2291 Replacement

by Arnoid on Tue Sep 17, 2013 10:36 am

Would this trick also work with 2* BC547 ?
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Re: Possible 2SC2291 Replacement

by pulsar256 on Tue Sep 17, 2013 11:47 am

The BC547 have a lower ß, no Idea how this would affect the sound. Just give it a try.

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Re: Possible 2SC2291 Replacement

by Arnoid on Wed Sep 18, 2013 2:38 am

Okay can't I harm anything else ? Because I'm working on a a tb303 with the same problem as described in these topics:
viewtopic.php?f=12&t=34353&p=169937
viewtopic.php?f=12&t=30490

I just want to test if it's the 2SC2291 that's broken with some transistors I have in stock (BC547 in this case) before ordering a 2SC2291.
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Re: Possible 2SC2291 Replacement

by mario1089 on Wed Sep 18, 2013 3:10 am

Just from a quick listening I`d say it sounds like the filter slope is less steep with the replacement. At least it`s obvious there is more high frequencies left over for a given center freq. The point now is, for me personally it sounds BETTER like this. I mean I`m constantly trying to add brights to the signal using distortion, bitcrushing and all of that, so this mod sounds pretty much like useful for me. I think I`ll also make this optional in my xox. Thanx for sharing!
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Re: Possible 2SC2291 Replacement

by pulsar256 on Wed Sep 18, 2013 4:40 am

Arnoid wrote:Okay can't I harm anything else ? Because I'm working on a a tb303 with the same problem as described in these topics:
viewtopic.php?f=12&t=34353&p=169937
viewtopic.php?f=12&t=30490

I just want to test if it's the 2SC2291 that's broken with some transistors I have in stock (BC547 in this case) before ordering a 2SC2291.


if you do not mess up the polarity or introduce shorts - I don't see how you could break anything. Did you test your 2291 with a transistor- or a diode-tester? At least you can test the PN junctions with a multimeter in the diode-mode. Chances are this is a knockoff and has a completly different pinout. I did also have this pleasure: http://www.adafruit.com/forums/viewtopi ... 12&t=38575

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Re: Possible 2SC2291 Replacement

by Arnoid on Wed Sep 18, 2013 7:55 am

pulsar256 wrote:
Arnoid wrote:Okay can't I harm anything else ? Because I'm working on a a tb303 with the same problem as described in these topics:
viewtopic.php?f=12&t=34353&p=169937
viewtopic.php?f=12&t=30490

I just want to test if it's the 2SC2291 that's broken with some transistors I have in stock (BC547 in this case) before ordering a 2SC2291.


if you do not mess up the polarity or introduce shorts - I don't see how you could break anything. Did you test your 2291 with a transistor- or a diode-tester? At least you can test the PN junctions with a multimeter in the diode-mode. Chances are this is a knockoff and has a completly different pinout. I did also have this pleasure: http://www.adafruit.com/forums/viewtopi ... 12&t=38575


Nope I didn't gonna solder it out tonight and I'll test it with a diode tester I don't have a transistor tester.
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by mario1089 on Wed Sep 18, 2013 2:29 pm

@ pulsar: Do you think you could give us another comparing audio file example, with looooong straight notes (0%, 50%, 75%, 100% reso), so we can check whats actually happening in freq domain? Talked to another guy and he agreed on that it actually sounds better, he thinks the same about the need to have brightness added for contemporary mixes. Thanx!
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Re: Possible 2SC2291 Replacement

by pulsar256 on Wed Sep 18, 2013 2:32 pm

sure, give me a minute so set it up.

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Re:

by pulsar256 on Wed Sep 18, 2013 3:10 pm

mario1089 wrote:@ pulsar: Do you think you could give us another comparing audio file example, with looooong straight notes (0%, 50%, 75%, 100% reso), so we can check whats actually happening in freq domain? Talked to another guy and he agreed on that it actually sounds better, he thinks the same about the need to have brightness added for contemporary mixes. Thanx!



http://machschnellgeld.de/2sc2291-vs-2b ... 0xb0x.xrns

If you do not use renoise (http://renoise.com) open the xrns with 7zip/winzip/<whatever>zip, you will see what is going on. The samples are flac/96khz/32bit. Audacity fu**** it up when opening these. Foobar doesnt.


setup:

- tm3 tuned for maximum, so the filter opens as much as possible. I am using a cuttoff-range mod to compensate for this. all mods are disabled!
- altering non accented and accented notes with same settings before lowering the resonance to the next step.
- tune: 50%
- cuttoff: See sample-name (c100,c75,c50)
- resonance: [100, 75, 50, 25, 0]
- env mod: 50%
- decay: 50%
- accent 50%

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Re: Possible 2SC2291 Replacement

by pulsar256 on Wed Sep 18, 2013 4:01 pm

... and made another one with much better audible filter sweeps:

http://machschnellgeld.de/2sc2291-vs-2b ... x_2nd.xrns


This time with:

- tune: 100%
- cuttoff: See sample-name (c100,c75,c50,c25,c0)
- resonance: [100, 75, 50, 25, 0]
- env mod: 100%
- decay: 100%
- accent 0%
- non-accented notes
- no EQing (sorry, forgot to zero the EQ in the last take)

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Re: Possible 2SC2291 Replacement

by mario1089 on Thu Sep 19, 2013 2:55 am

Thanx!

I took one of the files (after having a hard time with those flacs) with no reso and analyzed one waveform.
With the mod, the filter slope is 12db/Oct (see pic). I dont have my xox at hand to compare, but I would be surprised if the original filter is not of that -18db/Oct kind that it`s told to be.

I only have a rough understanding of analogue electronics, so what does this mean? Obviously the last stage of the filter now isnt actually filtering, or what? Shouldnt there be an easier way to get the 12 db signal, maybe by picking up the signal before 2291? Or what? Opinions, anyone?
Attachments
XOX.png
XOX.png (43.86 KiB) Viewed 2233 times
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Re: Possible 2SC2291 Replacement

by antto on Thu Sep 19, 2013 3:10 am

i haven't listened to anything (why flac.. :cry: )

Mario: skip that thing with the slope
if you hear a 4-pole filter with a 24dB slope, and then the same 4-pole filter with a 18dB slope - the difference is slim

as for trying to measure the said slope from the output like with that spectrum scope - that's.. not the right way
how did you calculate that it's 12dB from that image?
EDIT: i see, you've indicated that if at that given frequency the amplitude is -20dB, 3 octaves up it's roughly -56dB
and (-56--20) = -36, divided by 3 = -12
except that this is wrong, because the original input is not flat in the frequency domain.. it's a sawtooth (or worse, an irregular square)
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)

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Re: Possible 2SC2291 Replacement

by pulsar256 on Thu Sep 19, 2013 3:20 am

First time I come across ppl having problems with flac in a audio forum ;) So, how about a ARJ File with all the samples as WAV? Ok, just kidding. It's a ZIP File:

http://machschnellgeld.de/x0xb0x-2sc229 ... bc337a.zip

as a bonus I've also added audio samples of an modified filter section (devilfish-ish filter overload, resonance boost, cuttoff boost)

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Re: Possible 2SC2291 Replacement

by mario1089 on Thu Sep 19, 2013 3:45 am

Yeah, stupid me. Should have started to think before doing that calculation.
Anyway, any opinion what actually is going on with that mod? I think it`s obvious that for the comparing files, that mod has the same resonance peak, but there is more high frequencies left over "right" of the reso peak. And this does sound like a lower steepness of the filter, or not?
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Please be positive and constructive with your questions and comments.