Most unusual Mixer project...

I am planning an unusual mixer project..(It's one hell of a learning curve, but that's the way I prefer to learn..) Part of which will consist of a 4-way crossover section (sallen key filters), each channel fed independantly from a virtual earth summing section. The sources (line input pre's) will be split and connected in parallel to all 4 mix sections. This configuration will allow me to mute each source off the mixbuss for each filter section, to control which frequency band of each source comes out of the other end. I guess I need to keep the parallel input impedance of the 4 mix sections high enough to avoid loading the source...any suggestions..?,
At the output end, the signals from the four filter sections will be summed once more, and I need level control at some point between the filter outs and the final mixers inputs. I have been looking at the formulae for input impedance into a virtual earth summer, and I'm a bit confused about how placing a level pot infront of each channels mix resistor effects my calculations for source/input impedance (and therefore the feedback/gain resistor and the mix resistors themselves).. If this would complicate design too much I could buffer the volume pot before each mix channel, but I'd rather avoid the extra op-amp stage if I can. I'd also like to really understand the calculations! If anyone can give me, or point me towards a more detailed description of these design factors for a virtual earth sum stage I'd be grateful. I've searched hard but not found anything more than the basics. It can be difficult moving on from simply reproducing standard circuit blocks to creating something a bit different, sometimes I just find my searches for the relevant info at a dead end....Any thoughts I'd be very happy to hear them..Thanks folks..Jeth

Hi & welcome,

I understand you want to have separate blends for frequency ranges ?

Might give exciting results. Dunno why the QuadraFuzz unit (PAiA or VST) from Craig A. comes to mind :wink: You want to be able to process the various bands independently as well ?

Just to be sure please draw us a block-digram for your intended system. After that the circuit details will be more easy to discuss.

Bye,

Peter

Thanks for a lightning fast reply. I'll get a diagram together and post it asap. I'll have to sketch and scan it as this is not my computer and the drawing program is rubbish. ..Till then..

Clint, finally got a diagram together for you (or anyone else who cares to) to look at...Wasn't so easy as i'm on a borrowed computer with less than ideal facilities..Hope it works and look forward to your comments/advice, thanks,Jeth

Still no interest here, but I have a particular query so I thought I'd add it just in case.

My sources are feeding the four filter stages. I'm unsure where to put level control. I can put it after the filter channel mix input before the filter, but this would effect the level of the entire frequency range for each channel...I'm thinking possible wasted headroom, the pot would also require buffering.
I could also put the pots on the filter outs, giving control of the respective frequency bands but not allowing me to do anything about differences in the frequency content of the sources. (for example, if one source is bass heavy I have to reduce it's gain giving a lower level to all filter sections)
Final option is variable gain to trim the mix input sections AND level on the outputs.
Any thoughts, I'd like to save on pots and avoid two level controls for each band, but I also want the filters running at optimum level.

sorry
I can't follow your diagram and some of the references don't quite add up
... the others may be having the same problem

the switches to the mix bus ABCD seem screwy ... or is that a ground/mute position ?

your mix buss amps seem to all join ... to the Mic out amp ... that makes it the mix buss
and the other amps the input buffers
or are there two mix stages here ???

individual channel out buffers are all feed from the same source ?

Kev, sorry about that...Here is an edited version of my project description, hopefully it will make more sense to you...
------------------------------------------------------------------------
a 4-way crossover section (sallen key filters), each channel fed independantly from a virtual earth summing section. The 5 or 6 sources (line input pre's) will be split and connected in parallel to all 4 mix sections. This configuration will allow me to mute some of the sources off the mixbus for each filter section, to control which frequency bands of each source come out of the other end. The filter outputs will be sent individually to balanced out sections (basically crossover outs) and also summed to provide a mixed output of all 4 bands.

Yes, the switch arrangement is a mute to ground for the input of the source to each of the filter sections summing stage inputs.

Let me know if there's anything else I didn't make clear! Thanks, Jeth

Just to add...my main query is regarding the gain structure for this set up..Or obviously, do tell me if you think it just won't work!

[quote author="jeth"]... The filter outputs will be sent individually to balanced out sections (basically crossover outs) and also summed to provide a mixed output of all 4 bands. [/quote]
:shock:

so active cross-overs work well for PA
and
active frequency spliting works well for multiband compression

so
therefore
active frequency spliting could work well for the summing junction

??

is this the basic pretence of the idea ?

if not
explain WHY we are going in this direction ... it may help to work the topology if we know why you are heading this way.

Hey Kev, Sorry but I kind of assumed that folks here were more interested in the technical details than the obscure use of my project! Apologies also if my description of the layout left you none the wiser...

Basically, I want to build a mixer for reggae sound system use. (I did say obscure) ... It's possible to buy such a piece of kit from one of a few specialist builders, but they generally use the cheapest chips and components, and techniques passed on from the soundmen of generations past. I've spent a long while thinking about how I could build something to a better standard. Building my own is also an incentive to learn more (more of a spiral than a curve :shock: ) and an opportunity to tailor the functionality exactly to my needs.

So, now you know why, I'll try to make the layout make some sense for you...

6 line level inputs. Each fed in parallel to Summing amps A/B/C/D, so each sum section has an input from all 6 sources. The summing amps then drive sallen key bandpass sections. We now have four seperate frequency bands all fed with the same mix of signals. This is to allow selective muting of a chosen source into a particular freq' band.
Example.. Input 2 is from a CD player, Input 1 is from an external mic pre-strip. I want to "kill" the bass frequency from CD input 2, whilst leaving the mic unaffected. I mute (to ground) the signal from CD in to the bass filter section mixing input stage.
Why not use a filter switched into the signal path as in a standard DJ kill switch? Because my unit also needs to have seperate outputs to feed the amps for each frequency band. (Why have two sets of filters?-seen this done and it didn't sound good) So each bands output feeds a balanced output driver. The bandpass sections outputs are also summed once more to provide a record/aux output of the entire mixer output.

Other features will include 2x aux send/return loops, with the returns also fed to the mix stages at each bandpass section input, to allow frequency selection on fx return signal. Possibly some eq facilities at a later date..gonna get the main structure sorted first. My previous unit had Graphic, parametric and baxandall tone control sections :roll: ..another reason to DIY..cut out the unnecessary and the noise that goes with it..

Thanks for your persistent efforts to understand what I'm up to, Hope you got it now..and that you may have some thoughts..Jeth

Look let me know if you've given up trying to decipher my descriptions and I'll get a full block diagram together thats actually readable and post it!! I'd really like to get some feedback on this.

Sort of like having 4 sub groups with band pass filters on them?

You might be able to do something with a regular mixer by routing subgroups or auxes back into spare channels and EQ-ing them. E.g.

1. Route 6 channels to 4 subgroups as required
2. Route the 4 subgroup outs back into another 4 channels
3. EQ the 4 channels to pass the 4 frequency ranges you want. If the channel EQ wasn't up to the job you could build just your bandpass filters and patch them in using the channel insersts.
4. Route the four channels to the main mix bus. Make sure not to route them to the subgroups or you could be in for some feedback!

This also gives you the option of feeding your aux sends from either the original channels or the band limited subgroups. You can also patch the auxes into regular channels and EQ the returns.

Hey Mark..thought this thread was long dead so thanks for your input. Unfortunately I do really want to build a stand alone unit for this purpose (as a learning experience as much as anything)... There are already such units available from a few custom builders but as they are all limited by commercial concerns the designs tend to be fairly standard and in my opinion lack many features that I would like to have available.
Why a dedicated unit rather than configuring the mixer..mainly for playability as this is used for live manipulation of recorded music. It's good to have all the controls you need, and only those you need, all there in reach. Also a dedicated unit means less external cabling between kit, important with sources amplified to high levels..also altogether less excess circuitry in the signal path. On top of this, i want to play with the design and see what happens, from both a sound and function point of view.
One feature i would like is to be able to send seperate bands individually to fx units, unfortunately this would mean all the sources feeding the given band being passed to the fx at once...I need to effect some sources but not others so I would have to achieve this with some sort of switchable filtering on the sends themselves.
Thanks for your comments though..Easy now, Jeth

Jeth…. If you still out there….. new member and only just working out the whole forum thing….

This thread is amazing! Sadly I have no skills or knowledge to offer…..but I’d love to know how you got on with this project.

I’m also a reggae sound system fan…. I’d love to build my own custom pre amp mixer….

I’m currently (very slowly, but inevitably) restoring my good friends sound system, which he left in my care when he passed away, aside from general maintenance and a bit of tlc to the boxes and custom jah tubby amps (original bullet proof 80’s builds) , the missing piece of the puzzle for me is the pre amp mixer…….I’m trying to raise funds (very slowly, but inevitably!) to buy a custom pre from one of the few builders out there - all the usual suspects considered…..(quite like the look of Sound and pressure phil bush builds)

Anyway like I say really interested in how your project came along - hopefully you’ll pick this up!

MidnightArrakis said:

PLEASE ENLIGHTEN ME!!! -- What makes a "reggae sound system" --

Click to expand...

A good reggae system is constituted of heterogenous gear randomly assembled, without any consideration for directivity patterns, polarity and frequency response; it must be huge and flashy (chrome speaker surrounds and horns are a bonus).
Scooped bass bins are are appreciated by ganja smokers who can lie down on them.
Mid and high cabinets do not need to be connected since reggae is only bass and kick drum.


P.S: I love reggae (Toots, Cliff, Melodians, Boothe, Dekker...)

abbey road d enfer said:

A good reggae system is constituted of heterogenous gear randomly assembled, without any consideration for directivity patterns, polarity and frequency response; it must be huge and flashy (chrome speaker surrounds and horns are a bonus).
Scooped bass bins are are appreciated by ganja smokers who can lie down on them.
Mid and high cabinets do not need to be connected since reggae is only bass and kick drum.


P.S: I love reggae (Toots, Cliff, Melodians, Boothe, Dekker...)

Click to expand...

nothing like old trojan records, am I right.
and yes that is a solid description of a good Jamaican sound system

Seems like the reggae sound system places speaker effiency above all other concerns , each cab tends to be tuned to a particular frequency band where SPL is maximised , distortion doesnt come into the equation ,maybe even adds to the effect .

I like the old stories about Macintosh amps driving short circuits just fine and the Trenchtown street lights dimming and brightening with the rhythm (of current draw)...
Also in love with Jamaican Ska (up there with the great 60´s soul Motown, Deep City etc.) and also Dub Dub Dub Dub Dub