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Questions about quality in the audio path
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Questions about quality in the audio path
discomicke
So, i really want to start caring more about what components are in the audio path of my modules.

"audio grade"-coax: What cables do you guys use for this ? would appriciate mouser part#, there's so many options out there.

Caps in the audio path: when looking at diy hi-fi there seems to be alot of mysticism around the use of different caps. Is this crucial to synth diy? have you noticed differences between lower and higher quality caps ?

Low noise transistors: according to datasheets they seem to be around 1dB better than their "normal" counterparts, so this would be a good idea, right ?

Not out to make the best audiopath possible in a synthmodule, just want to be informed about the benefits/drawbacks of component selection.
Neutron7
Most of your audio path between modules will not be much of a problem because it is running at i nice healthy +- 5v, a lot more than what you see in most audiophile components, so any noise or distortion will be comparatively small, unless there is actually a problem with a circuit or grounding.

It is inside modules where sometimes voltages are greatly reduced, however most modules are pretty carefully designed to work with the components they have.

as for "audio grade" cables that usually means "pretty to look at and more expensive" electrons do not care what the cable looks like as long as it conducts electricity properly smile just watch some cheapo patch cables, they can actually make noise when they get moved.
discomicke
Since this is the music tech DIY section the question was regarding building my own synth modules, choosing components and cables within the module smile
Neutron7
For internal cables, decent coax is good, but it does not have to be fancy,
"audiophile" stuff.
as for the transistors, it might take a bit of experimentation to make sure they work and do not change the sound for the worse.

op amps? well there are lots of ones which are measurably better than 07x/08x and not even that much more money, they would be good in mixers and so on.

capacitors, ceramic ones are supposed to be bad, i replace them with film ones if it is feasible. sometimes there is a Electrolytic input/output capacitor, which are supposed to be bad as well, In that case i will actually use an "audio grade" panasonic capacitor, not that i could even hear any difference smile
daverj
For really short runs within a module I'm not sure you would notice the difference between different types of coax, but the better coax for audio is one with a full braid shield instead of a simple foil shield.
Big G
discomicke wrote:
"audio grade"-coax: What cables do you guys use for this ? would appriciate mouser part#, there's so many options out there.


No such thing. Coaxial cable is used for radio frequency circuits. Professional audio uses screened twisted pair cable and is balanced. Most synthesizers are unbalanced, high impedance with consumer connectors so the cable is not going to make an improvement.

Quote:
Caps in the audio path: when looking at diy hi-fi there seems to be alot of mysticism around the use of different caps. Is this crucial to synth diy? have you noticed differences between lower and higher quality caps ?


Most synthesizer circuitry is DC coupled i.e. no capacitors. Where they are used in VCOs and VCFs there is no mysticism. Parameters like temperature stability would be more important and dictate the type used e.g. polystyrene.

Quote:
Low noise transistors: according to datasheets they seem to be around 1dB better than their "normal" counterparts, so this would be a good idea, right ?


I don't think you are reading the data sheet correctly. dBs are relative to something and 1dB is not a lot of difference. Noise of low noise transistors would be quoted in nV/rootHz (where root is a squareroot symbol) and less than 4 would be a good figure. Not many synthesizers have transistors passing audio, they are either used for exponential converters or as switches in logic functions, the audio is mainly op amps.
discomicke
the more you learn, the more you realize how little you know
emdot_ambient
Neutron7 wrote:
capacitors, ceramic ones are supposed to be bad, i replace them with film ones if it is feasible.

Not in all cases. Ceramics are fine when they're used for things like decoupling.
Neutron7
emdot_ambient wrote:
Neutron7 wrote:
capacitors, ceramic ones are supposed to be bad, i replace them with film ones if it is feasible.

Not in all cases. Ceramics are fine when they're used for things like decoupling.


sure, i meant in the signal path, and in feedback of op amps, which sort of counts as being in the signal path, but i think the really small ceramics like the 33 or 17 pf you sometimes see for op amp stability can be left ceramic, because they are working at much higher frequency to stop oscillation.

(if you have an audiophile dog/cat/ferret/bat, s/he may beg to differ)
discomicke
audiophile dogs are the worst

CLee
I have just started buying 1% for all my resistors. For the amount of work I'm doing it's easier than stocking 2 sets, one 1% and one 5%. What ever you do don't use old style carbon resistors, they contribute a lot of noise, especially in high gain circuits.

For caps the designer will usually spec a specific type of cap if its needed, like a polystyrene cap in a VCO. For others, do like has been said already: Ceramic for bypass, polyester for others, and I have started using caps specified for audio for AC coupling electrolytics.

Stay away from Tantalum capacitors. When I first started in DIY they were considered high end, but now have a deserved reputation for going bad over time.

Craig
megaohm
discomicke wrote:
So, i really want to start caring more about what components are in the audio path of my modules.


Why? Are you experiencing problems with noise, distortion, etc.?
Perhaps just curious? It's a perfectly respectable reason.

If you want to improve your audio path the best components to start upgrading are whatever is in your mixer, amp, soundcard, speakers, etc.

The return on upgrading the audio signal path of a module will probably insignificant. In fact, I challenge anyone to point me to a synth circuit that exhibits significant differences between say a TL072 and whatever the greatest op amp in the world, or between the cheapest Xicon electro and a Nichicon Muse, metal film or carbon resistors, etc.

I'm a pretty objective guy and I'm happy to be proven wrong.
I have heard improvement when upgrading electro caps in pro audio equipment (pre amps and channel strips for example) and other rack gear. Most of these things are dealing with different signal levels, impedances, etc. and are processing external sounds, guitars, mics, and need heavy boosting where some slight differences will be jacked up and easier to hear.

OK that's out of the way.
I'll do my best to answer your questions AND give you mouser part#. hihi

Quote:


"audio grade"-coax: What cables do you guys use for this ? would appriciate mouser part#, there's so many options out there.


Belden RG174/U 26AWG Co-Axial cable.
Mouser # 566-8216-100


Quote:
Caps in the audio path: when looking at diy hi-fi there seems to be alot of mysticism around the use of different caps. Is this crucial to synth diy? have you noticed differences between lower and higher quality caps ?


IMO, it makes little to no difference and is not crucial.
I don't have a part number but my friend who replaces caps in his recording gear tells me that Nichicon Muse are really good.
I don't know what Panasonic caps are supposed to be great so no part # there either. By the way, Mouser has quite a selection of Panasonic caps that are not in the catalog. It's a good idea to use search and narrow it down from there.

For small values (pF) ceramic COG and NPO types can be better than polyester varieties.
couple axial lead 100pF:
Kemet - mouser - 80-C410C101J1G
AVX - mouser - 581-SA102A101JAR

radial 5mm lead spacing:
Kemet - mouser - 80-C315C101J1G


Quote:
Low noise transistors: according to datasheets they seem to be around 1dB better than their "normal" counterparts, so this would be a good idea, right ?


Never noticed any difference between transistors in a synth circuit.
I use (read off the bags they came in):
2N3904 - mouser # 512-2N3904TFR
BC550 - mouser # 512-BC550CBU


Quote:
Not out to make the best audiopath possible in a synthmodule, just want to be informed about the benefits/drawbacks of component selection.


That is an honorable goal, sir. Please post any discoveries you make.

Take everyone's advice on this subject with a heaping spoon of salt (my own included!).
A good way to compare parts is to build up two of the same circuit and simply listen. In fact, build one with the cheapest parts you can get and see if there is a big difference even then.
Keep in mind that small differences can, and do, add up. Maybe a VCF has a bit of noise. Run your signal through three of these and you will end up with more noise. Also, remember that changing things...well...changes things! If you have a module you love to death leave it be.
For my purposes a synth is a musical instrument.
If it sounds good it is good.

Best of luck,
p.
cbm
discomicke wrote:
audiophile dogs are the worst

Wouldn't those phones be Grados, is the dog was a true audiophile?
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