[sdiy] DIY Mixer - please help!

Thu Sep 3 17:05:27 CEST 2009

BTW,

Here is a tube based "VCA/mixer/output module", part of a tube based
Synth....

- 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 8:58 AM
To: synth-diy
Subject: Re: [sdiy] DIY Mixer - please help!

Jerry,
there are several problems with this:
- tubes are not as easy to predict. You can't get new, 'great' tubes
nowadays unless you buy them from someone who regularly pulls them off
ebay and has a warehouse of ten thousand of them. The tube manufacture
market has mostly folded. And then he won't give you the best ones
anyways :)
- if this design is to be used by a lot of people, you can easily see
how resource problems would start happening with the insufficient
(negative) worldwide supply of tubes that we are experiencing
- solid state is, I guess, easier for people to DIY.. and I guess we
have more experts for this here!
- tubes seem to require impedance matching transformers, unless I'm wrong.

However a tube-based design could be very interesting sometime in the
future. There is no denying that this would be the next step after a
'clean and nice' solid state design is finished - a tube-based summing
bus would be the obvious choice for something that complements a
solid-state summer.

Thanks

D.

On Thu, Sep 3, 2009 at 2:39 PM, Jerry Gray-Eskue<jerryge at cableone.net>
wrote:
>
>
> 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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