FW: [sdiy] DIY Mixer - please help!

[Jerry Gray-Eskue]

-----Original Message-----
From: Jerry Gray-Eskue [mailto:jerryge at cableone.net]
Sent: Thursday, September 03, 2009 8:39 AM
To: cheater cheater
Subject: RE: [sdiy] DIY Mixer - please help!




Given that, and assuming you would like the "tube" type distortion I would
say that you should go ahead and use a tube(s) for the summing buss, this
does leave you with the issues of scaling the output down for recording,
headphones, or other lower voltage applications, but it is all easily
"doable" and could make a very nice setup. The other advantage is this
system could drive speakers directly and would be a cool setup for live
performances.

If you want to max out the tube effects, you could use standard tube preamp
designs for your inputs and dump use of op amps altogether.

- Jerry



-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of cheater cheater
Sent: Thursday, September 03, 2009 8:29 AM
To: synth-diy
Subject: Re: [sdiy] DIY Mixer - please help!


I think Seb has mentioned a good point here, Jerry.

What seems to be a very important thing in analogue electronics
(especially mixers) is not *whether* they distort. There will always
be distortion and you can't escape it. You might even want to
introduce it by overloading channels - that happens quite often.

I think the important thing is *how* they distort.

So when designing the amplifier in the summing stage, it could be very
useful to have a lot of headroom, but to be able to dial in a little
bit of distortion by going higher.. and then the higher you go the
more distortion you get. I guess this requires some sort of
information on what sort of circuits distort the best.

Also I'm not very happy with using divide-down/resistors/whatevers in
the summing bus input. The first problem is that it changes the way
the mixer works depending on how many channels are in use (and the
additional complexity of added switches/relays/etc is not worth it).
The other problem is, as I understand it, that such approaches either
require an active element (which adds distortion) or a passive network
(which can easily create problems in impedance matching)

For example Manley seem to be using solid-state strips, but the
summing bus is a tube based circuit, which can easily run on high rail
voltage, since tubes like high voltages, and also distorts nicely,
since tubes, well, distort nicely. But I think that a similar approach
can be had with a discrete design based on solid state circuits, I
might be wrong of course (probably am).

So the question is - how do you make a summing stage that can work on
high voltages that reach, say up to 75V without distortion, and then
progressively starts being less and less linear, behaving like a nice
soft clipper? I think it would be nice if the behavior when you're
near the rails were similar to what I described.

I think it would also be nice to be able to dial in the symmetry
yourself by inputting a DC bias - instead of the circuit changing
symmetry in itself. For example I sometimes see this used for clipping
off 'spikes' on just one side of a signal. I understand that one trick
is that if you leave the spikes only in the 'negative' part of the
signal, they would happen when the tweeter 'pulls' and not when it
'pushes', giving you a mellower high-end.


>> I believe this is to achieve high headroom. Unconfirmed information
>> tells me that most op amp designs will distort more the closer you get
>> to the maximum output voltage.
>
> I doubt this is the case except when you're almost at the rails. A more
> important limitation is simply the maximum supply voltages audio opamps
will
> tolerate, which for the NE5532 (very low distortion opamp if the pcb is
> designed correctly) is +- 22V max. Not that having "only" 27 dBu max level
> is a problem IMO.

Thanks for your comment Antti. The NE5532 sounds interesting... how
does it behave near rail voltage?

Not that I expect it not to distort.. but does it distort in a nice way?

>> Do you think that a 741 will handle this sort of use?
>
> No. The comment about 741 was meant to show how poor some of the
electronics
> were in some respects.

- this just shows what sort of rube I am when it comes to real-life
parts and choices like that. :^)

Thanks
Damian

On Thu, Sep 3, 2009 at 2:07 PM, Seb Francis<seb at burnit.co.uk> wrote:
> Antti Huovilainen wrote:
>>
>> On Thu, 3 Sep 2009, Seb Francis wrote:
>>
>>> I guess it's a question of whether you consider a mixing desk to be
'part
>>> of the sound' or you simply want to mix your instruments, insert/send to
>>> effects, etc. and choose what colouration to add when desired.
>>
>> Sadly, these two options will rarely produce the same result. It's hard
or
>> impossible to reproduce the effect of dozens of small nonlinearities and
>> phase shifts in a single effect box.
>>
>> Whether you want "warm" or "clean" sound is a different question of
>> course. Both are valid choices.
>>
>
> I think I like "warm" & "clean" :)
> i.e. Some warm sound sources, but with an overall clean mix so that any
> 'clean' sounds can really come through.
>
> And even with a 'clean' signal path, judicious use of EQ (both analog and
> digital) can go a long way towards a 'warm' sound.
>
> Seb
>
>
>
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