Remove sawtooth fuzzyness on X0x (not present on 303)

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jayceefr
 
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Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

Hi,
I'm at a point where my x0xb0x sounds almost like my 303 thanks to many tweeks, transistors swaps etc...

The last difference comes from the VCO when in sawtooth, it appears to sound more creaky, fuzzy in the upper frequencies. After some FFT analysis, it seems that it has strange harmonics in high frequencies. All x0xb0x's I've heard sounded like that. I'm guessing it's a bit of noise buzzing through.

I'm wondering if running a shielded cable to provide better grounding to the VCO would help. Anyone has an idea?

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antto
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by antto »

not that i can help, but i'd like to take a look at the audio samples, if you still keep them
and, sorry for interfering :roll:

jayceefr
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

Here's a quick sample of x0xb0x saw, then square. You can here the high frequency fussyness on sawtooths, mainly on high notes. Filter and Env max, res min.
(Sorry it's a bit out of tune)
Attachments
VCO x0x1.zip
x0xb0x VCO saw then square
(527.55 KiB) Downloaded 255 times

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antto
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by antto »

thanks

well, they don't seem strange to me, the sawtooth on a 303/x0x is very sharp and when the filter is open up this is how it sounds..
btw, there is some noise on the higher notes due to the mp3 compression, don't confuse it
on an mp3, the frequency content close to the nyquist (or actually above 15-16KHz) appears as noise

jayceefr
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

Hi,
no it's not due to mp3 compression, it's also on the PCM wave before compression.
Ihave a 303 and can asure you the sawtooth is a bit smoother, in a warmer sounding way. Also these high frequency harmonics, not so disturbing without resonance make the sound of the x0x quite different when the resonance is on, making it sound more 'harsh'.


I've found a thread on gearslutz where this matter is being discussed :
http://www.gearslutz.com/board/electron ... 303-a.html

I'm quite certain this issue comes from the different PCB setup, is due to a weak grounding in this part...

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antto
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by antto »

either post samples or explain it
i pretty much hate words like: fuzzy, warm, fat, phat, thin, harsh, hollow, smooth, bright and so on.. for describing a sound
the link you showed is once again a conversation based on this kind of words
i am dealing with actuall recordings or technical descriptions..
i can tell there is nothing weird with the 303 clock (like the myths about groove)
there is a small difference in the square wave on my x0x compared to a 303, and it has something to do with a nonlinear-type component (probably a transistor)
on a 303 there is an edge at one specific spot on the square, my x0x has it too, but the edge isn't so sharp
otherwise the symmetry is the same

the sawtooth on the other hand - i haven't yet found a significant difference
btw, you are comparing the output of a 303 and x0x
don't forget that the VCO first passes thru the VCF
and any difference between the x0x and 303 VCF will take effect
not only that, but also the tuning of the envelopes (cutoff and envmod ranges, the TM3 thing)
and also the minimum feedback level which probably differe too much in the RESO=0 case between machines..

it'd be best if you can post the recordings from both the 303 and x0x you did, in .wav format or similar..

3phase
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by 3phase »

the osc of the xox most defently dont sounds like the one of the 303.. for me that applies eve stronger to the square wave..

its an interesting question why ..

grounding is an intersting point.. stray capcitys might be another..

the xox board has wider distance between the traces and better board material...

one guy tols me that in circuits with fet´s giga ohm rsitances over a board can have an influence... at least in preamp circuits...

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isak
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by isak »

I'm at a point where my x0xb0x sounds almost like my 303 thanks to many tweeks, transistors swaps etc...
can u list the tweeks that u did please?

thanks :)

jayceefr
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

I've just managed to find a solution. Now the VCO on my x0xb0x sound exactly like the one from the 303. I 've discovered the difference came from the powersupply. I added some bypass capacitors on the main board, at the arrival of J4 and the sawtooth loss it's "harshness".

I've also installed the properly rated 2291 and 1583 paired transistors ( F type as specified in the 303 service manual) and it made quite a difference, especially in the filter.


antto: yes I don't particularly like these adjectives either, it's just I didnt have a better word to explain something I clearly heard when comparing the sounds.

isak: I've installed all the properly rated transistors and all the rares parts apart from the VCA. (only 733AP, mix of 536F and 945P, 2SC2291F, 2SC1583F, 2SK30AO etc...). By doing this and by adding some bypass capacitors J4 on the main board, my x0xb0x is not recognisable from my 303. I feel like it's not a clone anymore but a replica. I can sell my 303 now :)

Brassteacher
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by Brassteacher »

BANNED wrote:Hi,
I've found a thread on gearslutz where this matter is being discussed :
http://www.gearslutz.com/board/electron ... 303-a.html

I'm quite certain this issue comes from the different PCB setup, is due to a weak grounding in this part...
I just re-read the link posted above, and I'll share my opinion on a couple things. Just my opinions of course, and I can promise you they probably are not worth much...

The EG speed issue mentioned on Gearslutz, with the x0x EG being faster than the 303, I would be willing to bet it all boils down to one thing: C62 in the TB-303 is probably close to 28 years old now, while C62 in a x0x could brand new, and still within its normal lifespan no matter what. Yes, in general electrolytic caps will eventually start drying out to the point that they don't charge as fast, the capacitance will drop, until eventually they stop working at all. Plus, electrolytic cap design has improved GREATLY in the last few years, in almost every measurable parameter. In other words, I would also bet good money that if they replaced C62 in the TB-303 they were using with a brand new cap, the EG in the 303 would be just as fast as the x0x.

Also my opinion (see above for the disclaimer :) ) - @BANNED: The bypass caps were a wise move, and most likely took care of almost all the "fuzziness" issues. Why? (again, just my opinion) The x0x has two things the 303 does not: MIDI and USB. These are two additional sources of high-frequency digital noise that the 303 just didn't have to deal with. There isn't much on the x0x i/o board to isolate, filter, or shield the noise from the digital circuitry from the power supply. Also, they just happened to park what may be the worst offender, the USB circuit, right next to the power supply. I'm sure you're aware that putting small bypass caps on the larger electrolytics filters out a lot of the high frequency noise, but not many other people know this. Large caps (well, all of them really) have a "drop-out" frequency, which is basically the frequency where the cap can no longer respond fast enough to filter that frequency and above. The smaller cap in parallel basically "takes over" when the bigger one gives up. Yes, this description is a bit simplified.

Hmm, I wonder if a few strategically placed ferrite beads would help the situation also...

As far as the difference in board layout between the x0x and the 303 goes, I would imagine any stray capacitance is a non-issue. We simply are not dealing with frequencies high enough to it to be a factor. Not much on the board gets into the GHz range 8) . The difference in board material could have been a factor IF the audio path in either version was really clean, but it's not.

jayceefr
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

Yes I've bypassed the two power rails with an electrolytic and a small propylene cap each. I suspected the power lines to be noisy as I noticed there was a slight wobble on the low pitches and the 'fuzzness' sounded like high frequency noise. With the caps intalled on the main board the difference is not subtle, the vco is a lot smoother. I would recommend this 'mod' to every x0x owner.

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altitude
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by altitude »

can you post some detailed info on where exactly these were dropped in?

jayceefr
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by jayceefr »

I soldered them right at the arrival of J4 on the main board, there's the 2 power lines 5.33 and 12 on each side, and the ground in the middle.

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isak
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by isak »

BANNED,

thank you for sharing this :)
as i understand u put 2 capacitors on each side? 1 electrolytic and 1 propylene?
u did in on the j4 jumper wire it self? i mean before reaching the mainboard?
can u say please what values the caps are?

thanks you again BANNED
cheers
isak E.

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altitude
 
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Re: Remove sawtooth fuzzyness on X0x (not present on 303)

Post by altitude »

I just tried this on mine with a switch and I cant hear any difference at all.. C11, C31 and C32 already perform that function and are more than enough, I suspect Jay has something else going on where more filtering is making a difference..

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