Carbon Comp Resistors for Certain Modules?

[inform3r]

I hope I don't get tarred and feathered for this but....
With all the talk of Jurgen's "Living VCO" that has a vintage quality to it, I've been toying with the idea of using some old Allen Beadley Carbon Comp resistors on some other modules, but only in the audio path! What do you think? Waste of time and money or will it get me closer to an "older" sound?
I don't want to debate about it. I know very well there are people that see this as complete nonsense. But I don't and it's my gear. Has anyone done this? Used carbon comp? I'm tired of certain modules sounding sterile. There has to be improvements (or lack there of to dirty some of this stuff up! So what if it adds .5 decibel more noise! I want character! We are analog obsessed after all you know!

Regards,
John

[inform3r]

OK, so how about opinions then, like "I don't think you can hear them. They just lose their value quicker, etc..." Nobody has ever thought of this before? I don't believe it.

[Uncle Krunkus]

[inform3r]

Hi Krunkus! Thanks for giving your opinion on this. Sorry if my initial post steered you away from responding. Your response definitely gave me some answers but I'm still wondering a little. It's not really about any gear sounding sterile, it was more about me seeing a lot of DIY versions of some really cool old modules. I was wondering if some Allen Bradley Carbon Comps would help add to the magic. And I might as well admit that I'm one of those guys that believes a synth is more than the sum of it's parts. Even if certain things can't be seen on a scope. I know a lot of guitar amp guys go nuts about capacitors (and sometimes resistors). Just wanted to see what the synth diy crowd thinks.

So feel free to weigh in guys. Opinions are totally cool as long as we don't have one of those "analog vs. digital-type" debates!

-John

[Uncle Krunkus]

Well,...
I'm about as skeptical as you can get on all matters mystical, spiritual, etc. etc. so I'm probably not the best person to ask.
I'm not even very sure about the whole valve thing. I haven't heard anything come out of a valve amp which isn't just another variation on skewed biasing etc. and it can all easily be simulated on a digital effects unit. (depending of course on how good the digital effects unit is )
Caps? Well, there's a smidge of truth in that I s'pose. Caps are, afterall, your little, local, current storage tanks. How fast and completely they can be emptied could have an effect on how well transients are reproduced. It's still a bit "out there" for me though. I don't think anyone over the age of 12 could hear the difference, and would they care?
Resistors?,....... Nah. I'd need a lot of convincing on that one.

[Uncle Krunkus]

Just wanted to say that I am all for messing up a nice clean signal. Experiments like that are one of my favourite pastimes.

[CJ Miller]

This is something I was just thinking about because I do still have a fair amount of 5% carbon comp resistors which I want to get rid of. I have decided to use them for prototyping, breadboarding, making perfboard circuits which I will probably screw up, and for various digital circuits.

IMO using carbon resistors would not do anything good to your audio path. The "sterility" of VCOs depends on the VCO design, and whatever you are playing it through. I'd bet that if one built an MOTM Ultra VCO and a Haible Living VCO - both with 1% metal film resistors - that the MOTM would still sound really precise, and Jürgen's would still sound lively. I'd rather use other circuits to color the sounds of my VCOs so that I am not at the mercy of building it with bad parts.

Allen Bradley resistors have such a reputation perhaps because they were the best which was available years ago. People have seen them in so many nice-sounding bits of equipment. I am all for the practice of salvaging and re-using old parts, where appropriate. It can be frugal, interesting, and reduce waste (electronics has been a dirty business). But I cannot recommend that anybody shell out extra money to buy vintage 10% AB resistors. It's like paying $10ea for LM708 op amps - why bother? I think we're better off spending the extra dollar or two instead on a waveform animator, suboctave generator, rectifier, nonlinear shaper, etc, etc.

YMMV!

[Tasmanian Alkaloid]

It's an interesting subject. I have also wondered about using carbon resistors instead of 1% 1/4 watt metal film. It seems almost all the circuits around these days ask for 1%, but i don't see why the need for precision?

It was interesting to read Ken MacBeth's thoughts about his oscillator designs- he swears that the 'vintage' sound is in 1/2 watt 5% carbon resistors. No SMT. Full stop.

[inform3r]

[Uncle Krunkus]

I too, am glad this is the kind of place where we can talk about this stuff without anyone jumping in and dropping a big arrogant clanger on either side of the fence.
There are many things which make an old analogue synth sound the way it does. Sure, alot of it is intrinsically held in the circuit designs, and possibly the number of discreet components compared to integrated circuits.
But it would also have to do with PCB layout design. Groundplane design. Interconnections and their connectors. In other words, all the design aspects which change the amount of crosstalk between components. I think crosstalk has heaps more influence than just the composition of components. And in old analogue gear, especially complete synths, all the modules are sitting inside the same space, relatively close to each other.
Decoupling is also a big contributer. A little harder to describe, and something which people usually want more of, but when you've got half a dozen separate functional circuit areas hanging off the same PSU (like you get in an analogue synth) certain compromises have to be made on the decoupling, and this would allow parts to interact with each other through the power rails.

[Tasmanian Alkaloid]

Hi John,
here's where i read Ken MacBeth's theories about using old components, particularly 1/2 Watt, 5% carbon resistors, to get the 'old' sound. You'll have to read through a few pages to hear all of his ideas.
The logic is quite simple- Want to sound like the old stuff? -Then use the same parts they used!

http://www.muffwiggler.com/forum/topic-4474.html&highlight=macbeth+oscillator

http://www.muffwiggler.com/forum/topic-5134.html&highlight=macbeth+oscillator

I also agree about the sound of old equipment. I have a few Roland string synths from the 70's, & the sound of the oscillator (with no modulation) is rich & thick. You can feel it in the air, like you can feel real instruments in the air- instruments like tubas & cellos & pianos. This is something i don't get from anything playing in the computer.
I don't know if it's to do with the ageing of the components in general, but they are full of carbon resistors.

I was suprised to see that the Living VCO's use predominantly 1% (& even 0.1%!!) metal film resistors. I'd be interested to know if Jurgen tried carbon resistors at all, & why he chose metal film. I don't see why carbon film resistors wouldn't make the VCO's even more 'living'
-Matt

[daverj]

Every type of component that you place on a circuit board, and even the board itself, has "phantom" components in it. A resistor on a board has inductance and capacitance. A capacitor has resistance and inductance. Traces on a board have all three.

The main difference between carbon comp vs carbon film or metal film resistors is that carbon comp adds more noise to a circuit. It's a very tiny amount, but it's one of the many reasons older circuits had more hiss than modern ones.

My personal belief is that the largest factor that defines the "warmth" of some older circuits is that the older circuits had a lower bandwidth and a non-linear bandwidth. The transistor designs, and early op-amp designs rolled off the frequencies at a much lower level than modern circuits, and often had hot spots in the mid-range frequencies.

Many of the old circuits were also non-linear voltage-wise. As a signal got larger they would often compress the tops and bottoms of the waveforms, turning a triangle into a semi-sine wave, or compressing high frequency spikes. They were more likely to add this type of linearity distortion, where today's circuits are more likely to clip the waveforms.

Today's designs are closer to the theoretical perfect model of whatever their function is. But they sound more sterile than the old ones because they lack the poor bandwidth, distortion, and non-linearity of the old ones.

I suspect that replacing your resistors with carbon comp ones will do little more than maybe add a tiny amount of hiss or rumble. Using lower frequency transistors and opamps would have a much larger effect, but might still not get you what you're looking for.

[frijitz]

[Tasmanian Alkaloid]

[bennethos]

Hi,

Very interesting post, I've quoted a part of Jurgen Haible's living VCO explanation. But as said, he's not using any 5% carbonfilm resistors at all for making "the sound that you feel in the air "

As he says : the situation is quite easy: Find which factors cause these random changes in a VCO

He clearly found the type of sound a vintage synth makes is not from using 5%CF resistors, or his PCB would have been loaded with them .

I have an audio electronics book, here they state (Audio electronica, elektuur, book from Holland/Belgium) :
<quote>
It's important to only use metal film resistors, these kind of resistors give less hiss/noise then carbon film resistors, for working with audio signals this can be very important. Because of the price of 1% tolerance MF resistors vs CF resistors I advise you to use them everywhere
</quote>

As someone said in this post, we need evidence... It's not always the theory that holds up .... So I think we should try it out with a VCO that sounds very clinical, replace all resistors with CF's and "hear" what happens.
I certainly wouldn't try it with the living VCO PCB as it has already too much factors in it creating the lush sound...

Comparing the result with an audio spectrum analyzer should also be done...

and another intresting thing I read once (also from Elektuur, same book) :
<quote>
Some people find LP's to have better sound than CD or remastered stuff...
He did a test where he compared an original LP vs a digital CD, he heard no audible difference.Technically speaking it is not possible an LP sounds better then a CD. If you copy the LP digitally to the CD, the CD sounds the same as the LP, therefore it has the same lush/statics sound charachter. The only thing we could find was a slight reduction in the higher frequency range (DIGITAL) comparing to LP's, people tend to find this kind of sound warmer.
Digitally remastered stuff compared to LP's also has a broader frequency spectrum, because of the remastering and literally changing the sound sometimes by adding/removing stuff when remastering.
</quote>


Jurgen Haible :
<quote>
Every few years there seems to be a heated debate how "stable" a good-sounding VCO should be, or shouldn't be.

I never quite understood how one can make an almost religious question out of this. IMO, the situation is quite easy: Find which factors cause these random changes in a VCO (there aren't many possibilities!), and then decide if you either

1. want to get rid of them, or
2. add them externally, or
3. deliberately keep them in your VCO.

VCOs with design philosophy 1 are more expensive, can be used in applications where stability is important, and you can always do Number 2.
I could have built a VCO like this, and added the linear detune feature there. But I decided to go for Number 3 in the "Living VCOs" project. Asuming those who buy them want to play animated 3-VCO-sounds in the first place, I kept everything as simple and unexpensive as possible, and I've chosen the same noisy 4-transitor exponential converter that EMS used in the VCS3. I'm not overly scientific about it - I just like the sound of it.

CS-80-Style PWM

Like the Yamaha CS-80, the Living VCOs have a limited pulse width. Even with strong pulse width modulation, you never "loose" the VCO signal, because you never get down to 0% or up to 100% pulse width. What may sound like a limitation at first, actually opens the possiblitity of "overmodulation": You can modulate the pulse width with a triangle LFO of rather slow rate, and with a depth that would normally be bigger that 100% modulation index. As a result, the modulation is clipped, becomes trapeuoid-shaped. Musically, this is like a periodic "push" of the modulated oscillator's pitch - something that sounds less detuned than ordinary PWM and allows a sonically very rich modulation.
</quote>

I hope this is usefull

grtZ
Benjamin

[bennethos]

This post can't seem to leave my mind :p

A typical component that creates a detuning factor is a germanium diode btw... if i'm not mistaken vintage stuff is full of them .

All components that do not have lineair characteristics like : transistors, diodes etc...

Overmodulation changes the waveforms as well, something JH also quotes.
You tend to have this with over-amplifying stuff.


Something about FX racks...dynamic compressors, limiters & stuff like that...They tend to have lots of special IC's & analogue multiplier circuits to amplify certain characteristics.

ie we could think of adding these kinds of circuits te multiply certain "errors", "detunes" you want vco.

We also use TL circuits as opamps, the relation between the input current and the collector current is not *lineair*. This can result in modulation. But most of the time this problem is reduced to a minnimum by adding an emitter resistor), remove this and you may find another type of sound .

I can only repeat what Jurgen Haible says... find the components/designs that create modulation/noise etc...
It's not all about parts.

[frijitz]

You people might want to at least educate yourselves on the difference between carbon film and carbon composite before going too much further with your discussion.



Ian

[Tim Servo]

I hear these sorts of debates all the time, and yet I hardly ever see any evidence presented (either for or against). It seems to me that this would be brutally simple: put together two otherwise identical VCOs, record them in identical settings, and then post the recorded files on line and let people decide for themselves.

Again, why do we never see ("hear?") any a/b data for debates like this? Build one VCO with carbon comp resistors, one with metal film. Make two SIMPLE recordings, making sure the levels are the same, and maybe even use a sequencer to remove any 'human element' in the playing style. Post the recorded files on line (maybe uncompressed WAV files?), don't tell which file is which, and then let's see ("hear?") if there's any appreciable difference. I think in a lot of debates like this, people point to their favorite recordings as examples of a sound they like. The problem with this is that there are SO many variables, especially in a group or performance recording, that it becomes almost impossible to point to a reason why "the synth here sounds better because..."

Let's be scientific about this and see if we really can nail down an element of the 'magic sound' we're all pursuing.


Tim (feeling like a "mythbuster" today) Servo

[blue hell]

[Uncle Krunkus]

[frijitz]

[frijitz]

[bennethos]

Do you guys know this link :

http://www.youtube.com/watch?v=L89eqV_BlB8

it's a comparison of vco's, vintage stuff

thx for clearing out the difference carbon film & carbon composite... read up on it .

The simple fact with carbon composite is they tend to fluctuate with temperature.. Probably a lot worse than carbon film...
They even change resistor value permanently when heated too much when soldering/desoldering...

But it doesn't change my view, I'm also convinced that these will cause more noise & stuff compared to modern ones, maybe even difficulty of keeping your VCO in tune...
All this vintage equipment tended not only to give a warmer sound but also more static/noise ...
That's somehting Jurgen Haiden DIDN'T want to incorporate in his living VCO project by the way...

cheers

[blue hell]

[frijitz]