Hi,
I'm re-building my rack of fxs and I would like to ask you some hints on the status of the art of mixers for multiple fxs.
What I want to do is:
- stereo input
- same signal sent to fx1
- fx1 return blended to stereo input
- same signal sent to fx2 and fx3
- fx2 and fx3 blended to input&fx1
- output to power amp
The very basic idea is the following (one channel only is shown), using the low output impedance of fx as buffers to send the signal to different fxs:
In this case the power supply should be a dual +-15Vdc.
I'm open to other possibilities as well (EG I'm considering a source follower for the first stage and to "triodize" the curves of a nfet then coupled with a source follower for the second stage), I just would like to know what is the current status of the art in managing this kind of situations.
Thanks
Roberto
Mixer for multiple fxs in the loop
Moderators: pompeiisneaks, Colossal
Mixer for multiple fxs in the loop
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Re: Mixer for multiple fxs in the loop
Will these signals be sent into a tube power amp that at times will be driven into clipping?
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Re: Mixer for multiple fxs in the loop
Dunno what the current state of the art for that is, but what you've drawn should do the job, providing the input has a low source impedance.
I don't see the benefit for the 1st mixer having 6dB gain though? Its downside is that it may make the mixer more liable to clipping.
I assume all fx used can be set for 100% wet?
I don't see the benefit for the 1st mixer having 6dB gain though? Its downside is that it may make the mixer more liable to clipping.
I assume all fx used can be set for 100% wet?
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Re: Mixer for multiple fxs in the loop
100 Ohm the fx before the mixer, and 600 Ohm the other fxs. Way lower than other impedances.
That is just a memorandum to check the level at which the signal comes out from the fx before the mixer. If low, raise the gain. otherwise keep unity.
Yes, they are all set all wet.
Re: Mixer for multiple fxs in the loop
Are classic OPAMPs still used for the purpose, or maybe high voltage OPAMPs are preferred? Or (triodized) fets?
Re: Mixer for multiple fxs in the loop
This is the other option I'm evaluating, taken from Nelson Pass' B1 rev.1 and rev.2:
https://www.passdiy.com/project/preampl ... fer-preamp
REV.1
https://www.passdiy.com/project/preampl ... fer-preamp
REV.1
REV.2All of the transistors are N channel JFETs. The stock parts are 2SK170’s, LSK170’s or 2SK370’s, and you can use substitutes having Idss between than 5 and 10 milli-Amps and transconductance numbers from 5 to 30 milli- Siemens.
The buffer uses an external power supply from 18 to 24 Volts DC. You can power it with batteries, but most convenient is an external regulated supply running off the wall. The preamp typically draws fewer that 0.02 Amps, so current is not much of an issue. A regulated supply is better, but the circuit is pretty good at ignoring noise on the supply and minor fluctuations.
Re: Mixer for multiple fxs in the loop
Reading the stream of posts, I think you're overthinking this, Roberto.
My mind jumped to "Hmmmm... what exactly are you trying to do here?"
Yeah, I get that you want the "best performance" for your mixer. On the other hand, mixers are very simple things. And most mixers these days are digital.
If you're after getting something done, measure or otherwise find out the signal levels in your effects loop. Effects loops generally are at either line level (about 1vrms), effects level (about -20db to that) or wildly bigger if the amp designer didn't bother thinking about signal levels. If you have one of the "wildly bigger" type effects loop, you may have to go with discrete designs to cope with the high signal levels, or have to do a divider to drop the levels down to something approaching line levels, do the mixing, then amplify them back up for the fx loop return.
If you have either effects level or line level(ish) signals out of the send jack of the effects loop, then IMHO you would have to work really hard to justify not using stock opamps. Something like the venerable NE5532 or an LM833 or even one of the newer ones since these last two were state of the art. They will work fine, at hard-to-measure distortion levels (read that as "add no coloration or tone-sucking of their own") for signals up to about 30V pk-pk. There are remarkably small and cost effective power supply modules to make +/-15V from 120 or 240Vac these days, so not having a power supply isn't really an issue.
IMHO, go with anything discrete only if you have to. It can eat a whole lot of the time you could otherwise be playing.
If you want a mixer that adds tone of its own, I think you should reconsider your objectives.
There are active mixer schematics widely available for the cost of a new search.
Bottom line: what is it you're trying to do and what are you working with?
My mind jumped to "Hmmmm... what exactly are you trying to do here?"
Yeah, I get that you want the "best performance" for your mixer. On the other hand, mixers are very simple things. And most mixers these days are digital.
If you're after getting something done, measure or otherwise find out the signal levels in your effects loop. Effects loops generally are at either line level (about 1vrms), effects level (about -20db to that) or wildly bigger if the amp designer didn't bother thinking about signal levels. If you have one of the "wildly bigger" type effects loop, you may have to go with discrete designs to cope with the high signal levels, or have to do a divider to drop the levels down to something approaching line levels, do the mixing, then amplify them back up for the fx loop return.
If you have either effects level or line level(ish) signals out of the send jack of the effects loop, then IMHO you would have to work really hard to justify not using stock opamps. Something like the venerable NE5532 or an LM833 or even one of the newer ones since these last two were state of the art. They will work fine, at hard-to-measure distortion levels (read that as "add no coloration or tone-sucking of their own") for signals up to about 30V pk-pk. There are remarkably small and cost effective power supply modules to make +/-15V from 120 or 240Vac these days, so not having a power supply isn't really an issue.
IMHO, go with anything discrete only if you have to. It can eat a whole lot of the time you could otherwise be playing.
If you want a mixer that adds tone of its own, I think you should reconsider your objectives.
There are active mixer schematics widely available for the cost of a new search.
Bottom line: what is it you're trying to do and what are you working with?
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Re: Mixer for multiple fxs in the loop
i did many of the buffer b1 and you can put any modern smd jfet in this arangement! they need to be matched, but is easy to do.roberto wrote: ↑Wed Aug 10, 2022 2:57 pm This is the other option I'm evaluating, taken from Nelson Pass' B1 rev.1 and rev.2:
https://www.passdiy.com/project/preampl ... fer-preamp
some info about the types here
https://audioxpress.com/article/measure ... dern-jfets
i have bougt and use several from this list and use in RIAA circuits. noise doesnt exist
also +,- supply voltages you can create from single power supply, to create virtual ground with caps and resistors.. etc etc
Re: Mixer for multiple fxs in the loop
Thanks, I really appreciate your intervention. As I've never done a mixer, even if it's a simple task, I was searching what is the status of the art on this topic.
The mixer will work with line level signal. So, again, thanks for bringing me back to the roots.
I'm redesigning my rack and I would like to know if the mixer could be improved.
After the preamp I have a looper Rolls Patchwork to insert or exclude two Presonus EQ3B and a compressor Symetrix 501.
Then the signal goes to a Intellifex LTD to split the signal in stereo, used withou hush to keep the dry signal analog.
After that I enter into the first mixer, where I add the wet signal of one Lexicon MPX1 in parallel.
This signal then goes to the second mixer (that is in the same 1RU of the first mixer), where I add the wet signal of two Lexicon MPX1 in parallel.
Then I go to a VHT 2502 and two 2x12" cabs with one Fane and one Tone Tubby speakers each.
The routing is inspired by Mike Landau's old rack used in "Tales From The Bulge", but with different rack units and not chasing that sound.
Re: Mixer for multiple fxs in the loop
Thanks, may I ask you what is (if any) the sonic difference between the one with same jfets and the one with complementary jfets?
Great!! Thanks bepone!bepone wrote: ↑Thu Aug 11, 2022 7:09 amsome info about the types here
https://audioxpress.com/article/measure ... dern-jfets
Re: Mixer for multiple fxs in the loop
no problem! i didnt find any "degradation" in the sound, all are working the same.. so it is a simple impedance converter or buffer, hi input impedance , and low output. you can do mixer with it why not! small resistor in gates +sources for biasing and oscillation prevention (oscillation via Jfet source).roberto wrote: ↑Thu Aug 11, 2022 7:39 am
Thanks, may I ask you what is (if any) the sonic difference between the one with same jfets and the one with complementary jfets?
Great!! Thanks bepone!bepone wrote: ↑Thu Aug 11, 2022 7:09 amsome info about the types here
https://audioxpress.com/article/measure ... dern-jfets
also note if you willl make many those buffers, dont take the suppy from the same capacitor to avoid oscillations. make every buffer separate RC element, and local capacitor.. i'm using always local star grounding, connected between them with the buss, how the signal is travelling upstream. maybe in your case will be better total star gnd.
some pictures and schematic (oscilloscope showing input vs output, schematic will work with almost any reasonable values of resistors):
good read about Jfets is also this application doc:
Onsemi AN-6604 JFET Circuit Applications
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Re: Mixer for multiple fxs in the loop
Thank you again! Just for safety I link the document and attach it here as well.
https://www.onsemi.cn/pub/collateral/an-6604cn.pdf
Often when I read old threads, most links are dead and there's no way to understand everything.
https://www.onsemi.cn/pub/collateral/an-6604cn.pdf
Often when I read old threads, most links are dead and there's no way to understand everything.
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Re: Mixer for multiple fxs in the loop
enjoy! it is a simple build ,
i was trying to search some alternative solution to replace expensive duo 2SJ74 - 2SK170 (altough i have them too ) with modern available, low-noise Jfets, to make simple buffer . Pass B1 is excellent starting point.
If 2 the same used, matched by current, exit(0utput) is sitting at 0 volts , coupling capacitor in theory even not needed! But for protection of the next stage it is good to implement it
i was trying to search some alternative solution to replace expensive duo 2SJ74 - 2SK170 (altough i have them too ) with modern available, low-noise Jfets, to make simple buffer . Pass B1 is excellent starting point.
If 2 the same used, matched by current, exit(0utput) is sitting at 0 volts , coupling capacitor in theory even not needed! But for protection of the next stage it is good to implement it
Re: Mixer for multiple fxs in the loop
Thanks again bepone!