Custom Tube Console help???

[HappyHourStudio]

Hi Folks,
First timer here… hi!
So last year I decided to build a little tube console and have come across some of the input transformers I used, so now I’m going to turn the 5 channel 2 bus console into a 10 channel 2 bus console with direct outs and an echo send.

***Disclaimer! I dig the way the one I’ve already put together sounds and the attached schematic could be a little off. I drew that up today to sort of avoid the more modular design of the old one.***

Now… I’m teaching myself how to do this with some much appreciated advice from friends when I get stuck, so there are some weird bits…

The weirdest being how in the old design, instead of a pan pot, I have two volume controls on each channel that go to the left and right cathode follower, which controls the stereo image in a groovy way.

I know for certain that I will have to redo bits of the schematic once I dig into the old design because I ventured off a little on that one…

Want to be able to switch between the solo and summing modes, as I assume that would be the easiest way to go about it. “Solo” mode being a direct out that hits its own cathode follower and summing mode being the Left and Right cathode followers. I kind of wing it on things sometimes… so I know some ideas are probably kooky, but I wouldn’t know! ha It would be great to maybe have a three position switch with one being “solo”, one being “both”, and one being “sum”.

Sorry, long winded… long story short, could anybody be of assistance on a few things:

1.) How and where to add an echo send in the circuit. Would love to be able to go out and back in two a split left and right volume control with a master volume control after that.

2.) What resistors to play around with in the summing network.

3.) I would just love to know what you guys would think in general about it! Ideas and thoughts, criticisms, anything!

4.) Forgot… might as well ask… I haven’t decided if I want to just build two more of the same 12AU7 cathode followers for the left and right “sum mode” or try building something different on the output.

PS-The green board is just my initial layout mock up.

Thank you!

 

[ruffrecords]

The schematic you posted s basically a tube mic pre. There are no pan pots, buses etc shown. Without knowing how these were done it is hard to give any specific advice about implementing additional mixer options.

Cheers

Ian

 

[gyraf]

The .1 and the .01/400V in series looks very wrong.

 

[HappyHourStudio]

The .1 and the .01/400V in series looks very wrong.

I thought so too! This was just combining the schematics I used to put together the old design. When I start the project, I’m sure that’ll end up making a little more sense. If it happens to actually be part of how the old design works, it sounds pretty groovy to me! But yeah… agree 100%. Doesn’t look right.

 

[HappyHourStudio]

The schematic you posted s basically a tube mic pre. There are no pan pots, buses etc shown. Without knowing how these were done it is hard to give any specific advice about implementing additional mixer options.

Cheers

Ian

Hi Ian!
Thank you! Yeah, I haven’t finished the entire schematic because I wasn’t sure where to tap the preamp circuit for the echo send. Like I’d mentioned before, there are no real “pan pots” in the entire project. The stereo image of each channel is controlled by a left volume control and a right volume control on each preamp. I want to say those were 10k, but I’d have to go literally digging into the old design to recall... it’s the most difficult part to get to in the old design.

Anyway, I appreciate you taking a look! I’m just trying to get some ideas for mapping it all out.

 

[ruffrecords]

Echo send is usually post fader and you should preferably drive its pot from a low source impedance so I think after the final cathode follower would be a good pick off point. I wouls use a 47K pot and a 47K bus feed resistor. You should also drive the pan pot(s) from the same point.

Cheers

Ian

 

[HappyHourStudio]

Echo send is usually post fader and you should preferably drive its pot from a low source impedance so I think after the final cathode follower would be a good pick off point. I wouls use a 47K pot and a 47K bus feed resistor. You should also drive the pan pot(s) from the same point.

Cheers

Ian

Thank you Ian! Really appreciate your advice!

 

[HappyHourStudio]

Thank you Ian! Really appreciate your advice!

I’ll be coming up with a more rounded out schematic soon.

 

[heatwalk]

I thought so too! This was just combining the schematics I used to put together the old design. When I start the project, I’m sure that’ll end up making a little more sense. If it happens to actually be part of how the old design works, it sounds pretty groovy to me! But yeah… agree 100%. Doesn’t look right.

A switchable series cap like that is sometimes how I implement a HPF. If you are flat with both these in series already you could just replace with the single equiv value which is effectively .01

 

[HappyHourStudio]

A switchable series cap like that is sometimes how I implement a HPF. If you are flat with both these in series already you could just replace with the single equiv value which is effectively .01

I was advised by a pal that, given the old modular system I based the schematic off of, the manufacturer didn’t know if customers would be building units the same way each time and that’s why those two caps were in series. He said I could just ditch the .01 and use the .1 instead.

Thank you for your reply!

 

[heatwalk]

Ok. Makes sense if there potentially was no output cap coming off of the previous stage, the designer would want one on the input of a modular style arrangement so stages aren’t DC coupled. If you are flat freq response with them in series currently the single smaller value should be fine. If you want to implement a simple HPF with series caps, experiment with a smaller value than .01. You can use a switch that shorts it for HPF off or puts it in series for HPF on. Not a steep slope filter but you may like it. Or just switch between diff single caps (but make sure DC not on switch)

 

[ruffrecords]

@MidnightArrakis: I have to say, I do not like your version of the schematic. A basic rule of schematics is that signal should flow from left to right, In yours it goes from the transformer to the second triode, then backwards to the first, then forwards to the fourth and backwards again to the third triode. I find it very difficult to read. The main reason for this is that your schematic symbols do not break out the three major function blocks (triode1, triode2 and heaters) into separate parts of the schematic symbol. which is normal schematic practice for double triodes.

Edit: And why do the cathode and grid connections of the left triode have to cross over? It is not to preserve the pin order of the part because the sequence is AGK (123) and yours goes AKG(132)

Cheers

Ian

 

[ruffrecords]

[I do not like your version of the schematic] -- Can't please everybody, right???

Indeed not.

[A basic rule of schematics is that signal should flow from left to right] -- I am more than well aware of that!!!

To ensure this rule is followed is why a double triode tube symbol normally has several parts. Why is this a rule - because it considerably aids understanding of the operation of the circuit and that is the primary purpose of a schematic.

[your schematic symbols do not break out the three major function blocks (triode1, triode2 and heaters) into separate parts of the schematic symbol] -- I have always created/drawn my schematic symbols for vacuum-tubes based upon how they are drawn within the various manufacturers tube databooks. From what you are telling me, following that criteria is incorrect, right???

That is exactly what I am saying. The schematic symbol is exactly that - a symbol - not a direct representation of the pin out of the tube. The purpose of the symbol is to aid understanding of the circuit not as a duplicate of the datasheet.

[which is normal schematic practice for double triodes] -- I have been completely unaware of any "normal schematic practice" for drawing vacuum-tube schematic symbols for, at least, the past 60-years!!! Dumb, dumb me!!!

I have just quickly looked though my copy of Tape Recorder Servicing Manual published in 1965. Of the more that 100 schematic diagrams in that book that show double triodes, only five show both triodes in the same symbol. All the rest show the two triodes separately so I think the normal schematic practice is well established. Nobody would create a TL072 dual op amp symbol with both op amps in the one symbol, and even less so for a TL074. Splitting a multi-part component into several separate but related symbols is very well established practice.

Cheers

Ian

 

[heatwalk]

Im going to support Ian here. Following a datasheet drawing seems like an unnecessary standard to try and adopt. Its hard to understand what each triode is doing as shown. In the time when tubes were king look at most any legacy amp schematic and you’ll see triodes split up and shown as the OP displayed in their version. When triodes are shown together in a single package/ symbol it is for a sensible reason. (DC cathode follower, paralleled, a phase inverter etc)

Look at a fender schematic or an RCA broadcast console preamp schematic. The signal flow is easy to follow and stuff is spaced out. Volume control is given some space between stages so you can see what stages it is placed between as you go left to right. In marshall schematics triodes are drawn together (Im thinking of Marshall 1959 schematic) but it makes sense because of the application of tubes. V1 on that is an exception because it is two different channel voicings but they sum together before V2

Heaters sometimes arent even shown in the signal path area of the schematic, they appear in the PSU section

 

[C.B. - Boudio]

I do appreciate MidnightArrakis' efforts, however, I am leaning more towards Ians point.

I know of generally three or four standards of vacuum-tube drawing; the German/European (with the cathode either as an arch or a big dot), which seems the most common, the Fender (and other American manufacturers') style, and the old French one, with the valves displayed on their 'side'.
Other differences in the methods lie in resistors, electrolytic capacitors, grounds and transformers, like we all know nor have trouble to understand when we see it (I'm not at all accustomed to solid-state above a simple transistor).

I personnally think, that none of them are hard at all to read, interpretate, follow in real-life, etc - however, the French one can be a bit harder, and they usually drew double triodes and such in one!

For those who don't know the old French way of drawing valves, because it's become a bit obscure and hopelessly obsolete (those damn Frenchmen, always forcing to do it differently! and probably some Belgian manufacturers have followed too, in a distant past):


But, that's all just my opinion!

(I hope that we are not stealing this thread!)