All Tube Sidecar

[ruffrecords]

Hehe, Yeah with transformers in the monitor path you might end up making a terrible sounding album like Rubber Soul or Kind of Blue

If only it were that simple.

Cheers

Ian

 

[Timjag]

Personally (again) As someone that might use this kind of console I'd rather have some transformer colour, than farting about with cable capacitance, just for some type of purity that is subjective anyway. I know which ever transformers you select will be measured within an inch of their life anyway, I can't imagine anything I'd do particularly differently unless there was a huge discrepancy it bandwidth or at certain bands, and I don't think the transformers you'd choose would be like that.

Cost however is another issue, then I suppose there could be a choice between the two with a switch, but then you're getting into complications again.

 

[pvision]

I think if you created a tasty "tube" channel strip with mic / line, EQ, insert and a line out you'd find takers

How many takers you'd have for a full-featured monitor / speaker switching / output section I don't know, but it would be fewer

I think the addition of a channel compressor, or separate patchable compressor, would create a lot of interest and maybe attract more customers

Everyone has their own ideas about how best to setup routing, monitoring & etc so it might be hard to please everyone. However, with a "tube" channel strip you would definitely please everyone

Nick Froome

 

[ruffrecords]

Thanks for your input Nick. It is all too easy to get dragged the the road of creeping featurism so it is good to step back and look at the big, basic picture.

I am close to a basic tube channel strip design. Mic pre module with the usual pad, phase, phantom and mic/line switches plus a couple of AUX sends and a pan pot. This is followed by a three band EQ module with stepped boost/cut controls and three selectable frequencies per band. Lastly there is a fader module which includes mute and solo buttons. Monitor section can be considerably simplified because solo allows individual channels to be monitored so it can be little more than a master bus/2 track playback switch and a stepped level control and a couple of meters.

Anything else would be optional.

Cheers

Ian

 

[Brian Roth]

Thanks for your input Nick. It is all too easy to get dragged the the road of creeping featurism ....

.... Monitor section can be considerably simplified because solo allows individual channels to be monitored so it can be little more than a master bus/2 track playback switch and a stepped level control and a couple of meters.....

IMHO, at least two 2-track playbacks would be very useful.

Bri

 

[bluebird]

The passive 4 deck 10K monitor switch really does work well. There are a couple of the passive Colman units in the studio I work in. They are in some production rooms and get used for utility stuff here and there and there has never been a problem with them, hum, buzz, high end roll off wise. Most people will be driving powered monitors with standard high Z inputs.  Its a proven method of balanced/unbalanced attenuation for monitoring.

I think if you created a tasty "tube" channel strip with mic / line, EQ, insert and a line out you'd find takers

How many takers you'd have for a full-featured monitor / speaker switching / output section I don't know, but it would be fewer

Of course, no one was suggesting just a monitor controller. I'm saying in addition to the tube channels. And again it would be a bonus for someone who is looking for a small mixer and can sell whatever monitor controller they are using because the mixer will have all the monitor features they need included.

Personally (again) As someone that might use this kind of console I'd rather have some transformer colour, than farting about with cable capacitance, just for some type of purity that is subjective anyway.

Oh yea, there will be plenty of transformer/tube sound going on with the channel strips. But when you just want to hear the main out of your DAW your going to want to hear it as accurate as possible. If your A/B-ing a mix to an external source like a CD or media player you want the signal to be clean. And if you really want a transformer sound on your monitor feed, Just put some transformers in line with the output, your choice!

 

[scott2000]

Would polarity flip on the  channels be useful and also maybe allow for some type of mid side experimenting??

I see it was already brought up...... :-[

 

[ruffrecords]

Would polarity flip on the  channels be useful and also maybe allow for some type of mid side experimenting??

I see it was already brought up...... :-[

Polarity flip per channel is fitted as standard  There will be an insert point on the master bus so you can plug in a compressor, MS etc.

Cheers

Ian

 

[ruffrecords]

Here is my first stab at a block diagram for a channel. It is based on the Classic mic pre which is the only one I have right now in the new 35mm format. The only thing missing is an insert point. An unbalanced insert can be added just after either amplifier.

Cheers

Ian

 

[pvision]

In that diagram your pre-fader effects send & direct out are pre-EQ. This would limit their usefulness

Nick Froome

 

[ruffrecords]

Your pre-fader effects send & direct out are also pre-EQ in that diagram

Nick Froome

That is correct. It is a passive EQ so it needs a gain make up amplifier after it. You could change the fader to a 'gain' pot and put the 'proper' fader after the second amp but that means:

1. No post fader direct out
2. Fader has to drive the pan and post fader Auxes

A block diagram for this alternative is attached.

Edit: By the way, I forgot to mention the maximum mic pre gain of both version is about 55dB

Cheers

Ian

 

[pvision]

With insert

(How do you insert attachments in a message?)

 

[bluebird]

Or you could have a female XLR under the direct out XLR labeled "Fader in (unbalanced)"
So the insert  would be the (direct out  --> fader in) XLR combo.
All you would need is a DPDT insert switch  (or relay) to break the signal between the last amp stage and the fader, while attaching the hot pin of the female XLR to the top of the fader..

The advantage over the standard normaling 1/4" jacks is a truly balanced output for the insert. And not having to use xlr to 1/4" adapter cables for your gear if you arn't using a patch bay. 

The disadvantage would be the extra switch. And if you do it that way, you should probably have an associated LED so one can see that the insert is engaged.

 

[ruffrecords]

@bluebird.

I like that idea. I is a bit like the arrangement we used at Neve between channel amps and routing modules excpet the input to the fader was unbalanced by a transformer.

Two Three things about this are not clear to me right now.

1. Where do you connect pin 3 in the return XLR? You cannot leave it floating because transformer balanced sources would not work. If you connect it to 0V analogue you run the risk of blowing up poorly designed electronically balanced outputs.

2. The level at the direct out is 6dB lower than at the fader because of the 2:1 output transformer. A fix for this would be to replace the 2:1 transformer with a 1:1 one. This would men the output could not longer drive a 600 ohm load (no Pultecs) but it would increase the overall available gain by 6dB. An alternative fix would be to pad the bypassed feed the fader by 6dB but this worsens the signal to noise by 6dB. A third possibility, for those with plenty of money, would be to fit a 1:2 step up transformer on the return which would drop the return input impedance to 5K but I think we can live with that,

3. I guess the fader return actually goes to the mute relay rather than direct to the fader so that solo still works the same.

Cheers

Ian

Edit: Just had a thought. I can see an insert PCB that fits in the back of the mixer. I has two XLRs and a relay on it. It also has provision for  output and input transformers. This means the same  board could be built three ways:

1. Unbalanced insert. Just the relay is fitted and the transformer connections are wire linked.

2. Balanced out unbalanced in. The relay and a  1:1 output transformer are fitted. The input transformer connections are wire linked. This is not capable of driving 600 ohm loads

3. Totally balanced  600 ohm drive capable insert with a 2:1 output transformer and a 1:2 input transformer

Ian

 

[ruffrecords]

I have updated the channel block diagram to V3 to reflect the changes discussed above.

Cheers

Ian

 

[bluebird]

You are right about the unbalanced input. Its not a robust (or responsible) solution. The extra PCB is a smart "compromise" but a lot of work just to allow for a less than optimal solution.

My three way rebuttal:
1. The balanced direct out is a must. So your half way there. I would just add the extra 1:2 transformer and do it right.
I think another balanced input post EQ is a nice bonus. I think it is worth the extra expenditure to make it stock.

2. If you decide you don't want to spend for the extra 8 transformers you can just put in two normaling 1/4" jacks at the insert point to be used at the risk of the operator. This would just be a convenience I/O that would be better than nothing.

3. Skip the insert all together because most people will probably be fine putting outboard gear between the DAW/converters and the channel strip anyhow.

 

[ruffrecords]

You are right about the unbalanced input. Its not a robust (or responsible) solution. The extra PCB is a smart "compromise" but a lot of work just to allow for a less than optimal solution.

My three way rebuttal:
1. The balanced direct out is a must. So your half way there. I would just add the extra 1:2 transformer and do it right.
I think another balanced input post EQ is a nice bonus. I think it is worth the extra expenditure to make it stock.

2. If you decide you don't want to spend for the extra 8 transformers you can just put in two normaling 1/4" jacks at the insert point to be used at the risk of the operator. This would just be a convenience I/O that would be better than nothing.

3. Skip the insert all together because most people will probably be fine putting outboard gear between the DAW/converters and the channel strip anyhow.

I do not disagree with what you said but....

My tube pre designs do not have room on board for the direct out output transformer. It needs to be fitted somewhere near the output connector and hooked up to the backplane. I know from bitter experience that hand mounting and wiring output transformers and XLRs  at the back of a mixer is no fun so I would design a PCB to hold the two of them anyway. I would enjoy designing the PCB far more. So you might as well make provisions for the alternatives while you are at it.

PS. A few posts ago I said the monitor would need only to switch between the master bus and 2TK playback for A/B comparison because the Solo feature would let you set levels/check quality of individual channels. However, I forgot about the AUX sends. So a third postion on the switch is needed to accommodate these.

Cheers

Ian

 

[bluebird]

I would enjoy designing the PCB far more. So you might as well make provisions for the alternatives while you are at it.

I shouldn't forget you are a seasoned designer so you know what it would take to make the extra pcb, and if its not that big a deal for you, I think it is a great idea to give the buyer a choice, or to make future upgrades.

 

[ruffrecords]

I shouldn't forget you are a seasoned designer so you know what it would take to make the extra pcb, and if its not that big a deal for you, I think it is a great idea to give the buyer a choice, or to make future upgrades.

You are right, it is not that big a deal for me and will certainly simplify assembly which is a surprisingly long task.

Which begs a question which PCB mount XLRs to use. I don't like the plastic ones at all. Can you get male/female right angle PCB mounting metal XLRs??



Cheers

ian

 

[Brian Roth]

Which begs a question which PCB mount XLRs to use. I don't like the plastic ones at all. Can you get male/female right angle PCB mounting metal XLRs??

http://www.neutrik.com/en/xlr/xlr-chassis-connectors/d-series/


Bri