Using synth module for line levels

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

fazeka

Well-known member
Joined
Jun 3, 2004
Messages
1,186
Location
\/\//-\
Hi all,

I want to build a simple auto panner used for synths, like this:

http://musicfromouterspace.com/analogsynth_new/STEREOPANNER/STEREOPANNER.html

But I want to use it for line level, studio work instead of using it with synths. However, I understand synth levels are hotter than line levels.

Can someone help me determine what values for R47 and R48 are needed on the input to be able to use the unit with line levels?

Cheers,
Chris
 
Hi,

However, I understand synth levels are hotter than line levels.

Well, typical modular vco synth level are +/-5v hence 10v peak-peak.

In dbu this translate to +13.5dbu approximately (10v/2.828: 3.54v rms).

Depending of your line level standard and headroom you have within your system(-10dbu, +4dbu, in house standard, +12/+18/+20db headroom) you will have the opposite situation, synth module will run out of headroom before your line level signal.

The warning you see about levels are about -10db level and the fact newbie user don't really go soft about vca levels and use of EG (enveloppe generator) and the fact that this is unfiltered, so sending 30hz at+13dbu can be a disaster for non professional monitoring system.

However not being to hot with the send signal to your autopanner it should work well as is (and maybe using a bit of line amp gain if you run into s/n issue). 

From my experience with modular in the studio you may have some issues with noise (some modules treatments are noisy by nature) and balancing/debalancing but usually they interface quite well with studio gear.

By the way MFOS module are quite fun. Don't know about this one though. It could give weird/interesting results using some kind of flanger/phaser in the cv path just before entering the module.

What do you plan to use for CV? Something like Silent Way or Volta is quite handy and offer a lot of flexibility. But you lost uncertaintity of analog cv source...
 
Hi,

I'm not planning on using CV. Just want to move a monophonic ancillary track within the "stereo" field. I'm out of box, running analog tape. Very old school.  :)

Cheers,
Chris
 
KrIVIUM2323 said:
Depending of your line level standard and headroom you have within your system(-10dbu, +4dbu, in house standard, +12/+18/+20db headroom) you will have the opposite situation, synth module will run out of headroom before your line level signal.

One more question: based on the schematic, is there any way of increasing headroom within the unit so I don't have to pad down the input into it?
 
> I understand synth levels are hotter than line levels.

Typically, not much if at all.

Anyway, did you read the diagram? Am I missing something or did you?

Just do it. Unity gain is probably fine.

Do not be shy about putting a 10K potentiometer across the input. Line Input devices often want one.
 

Attachments

  • StereoPan-MFOS.gif
    StereoPan-MFOS.gif
    3.6 KB · Views: 28
Thanks Paul and Brian for your help.

OK, I can do the jumper on R48.

Are you talking about something like this for the 10k pot on the input, to replace R56?

K2Du5U7.gif


If so, I presume audio taper?
 
Yes a pot in place of R56 and yes for audio taper.

That said i won't put the pot as you have in your sketch (wiper to input) but that is more an habit that for a technical reason.

About having to pad down the input, what is your multitrack reference level?

Just pad the nescessary amount to have correct headroom (the module expect +13.5dbu max input level 10V Pk/Pk) in the whole chain and maybe add a bit more gain for U5 a/b and it should be ok ( if i'm correct you have about +4db gain as is). I wouldn't expect very clean results from the circuit, it is modular synth module after all, and part of the appeal of this kind of circuit, so as long as you don't overload the input (to much ... :) ) i won't be bothered by end results... But that is me.

If you need balanced output put a  that 1646 after r21/r37 and you'll already have 'free' +6db gain without coloration and unbalanced compatibility (without the +6db gain however).

Imho it is wise to power it with +/-15v rails.

Just want to move a monophonic ancillary track within the "stereo" field. I'm out of box, running analog tape. Very old school.  :)

Yeah makes sense. I had a quick look at schematic and haven't seen the lfo section in the schematic. Cv in is used to change rate of lfo and making some leslie start/stop simulation or varying modulation speed. Don't overlook this feature can be really fun.
 
Any decrease of input gain should be compensated with equivalent change in output gain, by reducing R6 & R28. text is clear about it.
Choice of LF411 at the input, that may have been justified at a time, considering the high source impedance of an electric guitar, should be reconsidered in view of usage at line level. TL07x or 5532 would be my choice.
 
fazeka said:
Thanks Paul and Brian for your help.

OK, I can do the jumper on R48.

Are you talking about something like this for the 10k pot on the input, to replace R56?

K2Du5U7.gif


If so, I presume audio taper?

If you use the 10K pot at the input, wire it so the signal goes into the "top" of the pot with the wiper then feeding into C4.  As you drew it, the pot will begin to short-circuit the signal source as you reduce the level.

Bri

 
KrIVIUM2323 said:
That said i won't put the pot as you have in your sketch (wiper to input) but that is more an habit that for a technical reason.

Yes, Brian said the same thing. Thank you.

KrIVIUM2323 said:
If you need balanced output put a  that 1646 after r21/r37 and you'll already have 'free' +6db gain without coloration and unbalanced compatibility (without the +6db gain however).

Do you think I could use something like this?

https://www.sparkfun.com/products/14003

And if so, do you think I would benefit to running something similar on the input?

https://www.sparkfun.com/products/14002

KrIVIUM2323 said:
Imho it is wise to power it with +/-15v rails.

Yes sir, that's what I was thinking. Slightly more headroom?

Thanks,
Chris
 
abbey road d enfer said:
Any decrease of input gain should be compensated with equivalent change in output gain, by reducing R6 & R28. text is clear about it.

I guess I am missing that in the documentation, doesn't appear to be explicitly stated?

abbey road d enfer said:
Choice of LF411 at the input, that may have been justified at a time, considering the high source impedance of an electric guitar, should be reconsidered in view of usage at line level. TL07x or 5532 would be my choice.

Can TL07x/5532 be simply swapped for the LF411 or does that whole input and related components have to change (seems that  R57 would for sure?)? Or could I use the sparkfun input PCB above? How would this affect the 10k attenuator also discussed in this thread?

Sorry for all the questions, trying to build something but also comprehend/understand/learn this stuff, too...

Thanks,
Chris
 
fazeka said:
I guess I am missing that in the documentation, doesn't appear to be explicitly stated?
You're right, I must have dreamt it. It is nevertheless true.


Can TL07x/5532 be simply swapped for the LF411 or does that whole input and related components have to change (seems that  R57 would for sure?)? 
LF411 is a single opamp; it can be replaced with a TLO71.


Or could I use the sparkfun input PCB above? How would this affect the 10k attenuator also discussed in this thread?
Yes. The 10k pot should be placed between the unbalanced output of the Sparkfun circuit and junction of R13/R26. You could then dispense with U6 and associated components (R56, C4, R57, R47, R48, C5)


 
If you do not clean off the flux after soldering it can sometimes be difficult to get a reading using a soldered joint because the flux acts as an insulating layer,

Cheers

Ian
 
ruffrecords said:
If you do not clean off the flux after soldering it can sometimes be difficult to get a reading using a soldered joint because the flux acts as an insulating layer,

Cheers

Ian

Hi Ian,

Not understanding your last post?

Cheers,
Chris
 
Slightly more headroom?

Yes. But don't expect miracles.

Your sparkfun cards can be used but you can do the same using the thru hole version of That chips, a piece  of protoboard, some resistors and capacitors. Not sure it'll be cheaper then the sparkfun cards though.

Anyway take a look at datasheet and typical application of chip even if you choose the sparkfun way: be sure the 1206/1646 are configured for -6db for line receiver and +6db for line driver. 

As stated by Abbey Road d'Enfer, you may have to compensate for gain for u5a/b, lm13700 transconductance OPA are relatively good and nice used as vca for the price but not a 2180 from a quality perspective, SN is easily compromised, they distort quite easily too (from my experience with them, but i'm not a great designer so take this with a grain of salt, other may have solution to this).

If you use a pot, as input attenuator it can be difficult to do as value will not be easily (definitely should i say) defined and you cannot easily change the ratio of R6/R7 and R28/R29 ( it could be done using a multideck pot but finding the right one will be and headache (the law and tracking) and not cheap...).

If using a stepped rotary multideck in place of the pot it could be easier to do (and you'll have one and only control for the whole circuit with a deck for input and another 2 for output compensation).

You can do it 24 step if you want (totally overkill) using this kind of rotary (for example):

http://en.uraltone.com/electronic-components/switches/rotary-switches/rotary-switch-4x24.html


As is the u5a gain in db is 20log(1+R7/R6). Just do some math for multi step of attenuation and gain and it is done.

If you use both the sparkfun cards the unit will stay unitygain (-6db in/ +6dbout) and action on the rotary stepped pot could just adapt headroom to situation.


 
abbey road d enfer said:
You're right, I must have dreamt it. It is nevertheless true.
OK. Sorry, am just trying to understand.

abbey road d enfer said:
Quote
Or could I use the sparkfun input PCB above? How would this affect the 10k attenuator also discussed in this thread?

Yes. The 10k pot should be placed between the unbalanced output of the Sparkfun circuit and junction of R13/R26. You could then dispense with U6 and associated components (R56, C4, R57, R47, R48, C5)
Great! Thank you!
 
KrIVIUM2323 said:
Yes. But don't expect miracles.
Of course.  ;D

KrIVIUM2323 said:
Your sparkfun cards can be used but you can do the same using the thru hole version of That chips, a piece  of protoboard, some resistors and capacitors. Not sure it'll be cheaper then the sparkfun cards though.
If the sparkfun is cheaper and easier, that is likely better for this situation for me.

KrIVIUM2323 said:
As stated by Abbey Road d'Enfer, you may have to compensate for gain for u5a/b
Please share an example of how I would go about this?

KrIVIUM2323 said:
If you use a pot, as input attenuator it can be difficult to do as value will not be easily (definitely should i say) defined and you cannot easily change the ratio of R6/R7 and R28/R29 ( it could be done using a multideck pot but finding the right one will be and headache (the law and tracking) and not cheap...).

If using a stepped rotary multideck in place of the pot it could be easier to do (and you'll have one and only control for the whole circuit with a deck for input and another 2 for output compensation).

You can do it 24 step if you want (totally overkill) using this kind of rotary (for example):

http://en.uraltone.com/electronic-components/switches/rotary-switches/rotary-switch-4x24.html


As is the u5a gain in db is 20log(1+R7/R6). Just do some math for multi step of attenuation and gain and it is done.

If you use both the sparkfun cards the unit will stay unitygain (-6db in/ +6dbout) and action on the rotary stepped pot could just adapt headroom to situation.
OK. I guess it's my fault having complicated this...  ::) I think I will start with what Abbey Road d'Enfer stated in his last post, using the sparkfun balanced in/outs and putting the 10k pot between the unbalanced out of the sparkfun input and the junction of R13/R26 and see how it sounds? Unless someone else thinks of another/better way?

Cheers,
Chris
 
Ugh. Sounds ugh-ly

Not at all. Maybe my explanation are not clear...  :p

Please share an example of how I would go about this?

Ok. Let's say your multitrack have max output of +23.5dbu.
The circuit max input voltage is 13.5dbu and you don't want multiple step on your attenuator, only one position.

So overall you'll need 10db attenuation. If you use the sparkfun card you'll have -6db de facto. So you need to make an attenuator of -4db. You want something like 10k impedance for the attenuator (same as pot) and an L pad (two resistors, simple):

http://www.sengpielaudio.com/calculator-Lpad.htm

As a result with something like a r1 of 3.7k and r2 of 17k ( R number referenced to the sengspielaudio calculator) it should be in ballpark.

Your input is done: -6 + -4 : -10db.

Now about your output:  you'll need +10db gain overall. As is, the circuit is at unity gain when you bypass r48/C5 for u6 and as i already stated there is +4db with value given around u5a and b.

So to have +10db the values around u5a/b have to be modified for a gain of +8db (the already present +4db + the db needed to reach +10db (minus the +6db gain in the 1646), so +4db, hence overall gain around u5a/b: +8db).

So if you keep r7 20k and make r6 13k: 20log(1+20k/13k)= +8.09db.

Done.
Repeat for the number of step you want... in case you want other step with different attenuation and compensation... ;)

Anyway, try what abbey road said.

My idea is for educational purpose and if you need multiple headroom situation. ;)

(and you'll have one and only control for the whole circuit with a deck for input and another 2 for output compensation).

...well hmmm, in fact you need 2 decks for input attenuator (r1 and r2 with value from the lpad calculator) and one deck for each for R6 and R26 (around u5a/b for compensation),... obviously!  ::)
 
KrIVIUM2323 said:
My idea is for educational purpose and if you need multiple headroom situation. ;)

I do appreciate it. I will attempt to go through what you said with a fine-toothed comb. I will probably have more questions as I slowly masticate (and digest  ;D) what you said. In which I will probably ping you individually.  ;D

Cheers,
Chris
 
Back
Top