ruffrecords

Re: Poor Man's Tube Mixer
« Reply #160 on: July 30, 2020, 04:22:05 AM »
Very interesting project.
Following with attention.
Have you got any board available (maybe spare prototypes)?
I made all the spare protoype main PCBs available here at cost. I have one left if you are interested
Quote
To keep costs down what are output transformers options?
I see in other of your projects you suggested Edcor or Carnhill.
But I can't recognise this particular output transformers in photo.
I checked all the thread but maybe I missed something.
I found OEP a very good option as input transformers.
Perform well together with other expensive options.
There are lots of transformer options. I suspect the transformers will be the parts most often changed by constructors.

On the input side the design uses OEP transformers for the mic input and bus expansion inputs to keep costs down.

On the output side you can use no transformer at all and instead use an impedance balanced output. Or you can use the  normal Carnhill (VTB2291) and Edcor  (XSM2K4/600) types that go with my designs. The transformer you do not recognise is one that was designed here by CJ and which I have manufactured by a local company. Its costs lies somewhere between that of the Edcor and the Carnhill types. It has the advantage of being PCB mounted. I am happy to pass some of these on at cost if people want them.

Lastly, you should know that I am not proceeding any further with those particular PCB designs. As I have said in an earlier post, the sheer volume of wiring between the main board and the two panels makes them impractical and very difficult to service. This has caused me to re-evaluate the method of interconnect and revert to the motherboard method I use in the EZTubeMixer project.  I have also been disussing the project with several potential customers whose input has been invaluable. This has cause me to revisit the overall design several times in an attempt to reduce cost yet retain flexibility. The schematic posted above is the latest attempt.

I am currently working on a new enclosure design that is compatible with the EZTubeMixer motherboards which actually looks like a mixer (you can fit real faders to it if you wish) and I hope the have something to show in a few weeks time.

Cheers

Ian

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


scott2000

Re: Poor Man's Tube Mixer
« Reply #161 on: July 31, 2020, 09:11:30 AM »
I made all the spare protoype main PCBs available here at cost. I have one left if you are interestedThere are lots of transformer options.

Lastly, you should know that I am not proceeding any further with those particular PCB designs. As I have said in an earlier post, the sheer volume of wiring between the main board and the two panels makes them impractical and very difficult to service. This has caused me to re-evaluate the method of interconnect and revert to the motherboard method I use in the EZTubeMixer project.  I have also been disussing the project with several potential customers whose input has been invaluable. This has cause me to revisit the overall design several times in an attempt to reduce cost yet retain flexibility. The schematic posted above is the latest attempt.


Cheers

Ian


Is the drawing in the beginning of this thread relevant to the prototype board? the MiniMixer drawing?

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #162 on: July 31, 2020, 01:13:17 PM »

Is the drawing in the beginning of this thread relevant to the prototype board? the MiniMixer drawing?
Not any more. The design has gone through several iterations since then generally getting simpler each time.

Xheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

scott2000

Re: Poor Man's Tube Mixer
« Reply #163 on: July 31, 2020, 01:53:21 PM »

Not any more. The design has gone through several iterations since then generally getting simpler each time.

Xheers

Ian
Thanks..I'm following that...... I was just referring to the original prototype boards that were the first run.... is there a drawing that is more or less relevant to them?

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #164 on: July 31, 2020, 04:49:45 PM »
Thanks..I'm following that...... I was just referring to the original prototype boards that were the first run.... is there a drawing that is more or less relevant to them?

Hi Scott,

I have been through the entire thread and it is now clear to me that I never posted the actual schematic of the prototype main board (although it was described in detail). Any way, to put that right I have attached it to this post. The only different between this schematic and the actual prototype PCBs is that the mic pre relays have been ditched and replaced with regular toggle switches. The main PCB use seven tubes.

The very latest version of the design (not yet in PCB form) first changes the left and right buses to balanced ones, then feeds the DB25 inputs direct to these buses (thus eliminating two tubes), the mic pre pan pots are changed to LCR types and also feed the balanced bus and lastly the transformer balanced line inputs at the bottom no longer need input transformers because the bus is balanced thus saving two transformers.

Cheers

Ian
« Last Edit: July 31, 2020, 04:54:44 PM by ruffrecords »
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #165 on: July 31, 2020, 05:08:22 PM »
I do not wish to confuse people but the latest mechanical design will use good old EZTubeMixer plug in modules. This means you only need to build the boards you use rather than partially populate one huge PCB. One advantage of this is that completely different alternative mixers become possible. I have recently been talking to a prospective customer about a line input only version with AUX sends and pan on every channel. It turns out you can pretty much do this passively with just a pair of tube based bus amps (3 tubes max). The block diagram of the final version looked like this:



The design uses a very low cost OEP 10K:10K input transformer per channel and a couple of TLAs for bus amps for a total of 6 tubes. At a push these could be replaced by a pair of Classics for a reduced tube count of 4. Using the new mechanical design (roughly this one):



You could built an 8 line input version of this for about £2K all up.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

scott2000

Re: Poor Man's Tube Mixer
« Reply #166 on: July 31, 2020, 05:15:40 PM »
This is great!
Thanks!

scott2000

Re: Poor Man's Tube Mixer
« Reply #167 on: August 01, 2020, 11:07:10 AM »
One more question regarding the original prototype boards and drawing.  Are the MU stages considered to be your Tube Gain Make Up circuit mentioned here? With the drawing attached in the first post?

https://groupdiy.com/index.php?topic=43973.20

Or something else. ? Sorry if I missed it....


ruffrecords

Re: Poor Man's Tube Mixer
« Reply #168 on: August 02, 2020, 04:00:16 AM »
One more question regarding the original prototype boards and drawing.  Are the MU stages considered to be your Tube Gain Make Up circuit mentioned here? With the drawing attached in the first post?

https://groupdiy.com/index.php?topic=43973.20

Or something else. ? Sorry if I missed it....

It is the same basic topology but instead of the 6CG7 I now use a 6922 tube. This has a lower plate resistance and, via a 2K4:600 transformer will drive +20dBu into a 600 ohm load. There is also a couple of dB increase in gain. This version was first used in the Classic Solo project.

Edit: Here is a link to the Classic Solo document which includes a schematic:

https://drive.google.com/file/d/0B_n67A1hN3qtUWhWUjVoOXVxU28/view?usp=sharing

Cheers

Ian
« Last Edit: August 02, 2020, 04:15:30 AM by ruffrecords »
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

scott2000

Re: Poor Man's Tube Mixer
« Reply #169 on: August 02, 2020, 08:15:12 AM »
Thanks Ian!


ruffrecords

Re: Poor Man's Tube Mixer
« Reply #170 on: August 19, 2020, 05:56:36 PM »
Today I received the new custom designed metalwork for the poor man's tube mixer. This now has a proper 3U space for modules and backplane plus a sloping front 4U section for faders and misc controls:



I fitted it with a few old EZTubeMixer modules and a fader just to give you an idea of what could be built with it:



Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #171 on: September 18, 2020, 06:22:38 PM »
I got the panels from the new low cost UK supplier I recently found. here's how they look fitted in the back of the mixer:



The pair of mic inputs with their direct outs is on the right. Next are the 24 line level balanced stem inputs on DB25 connectors plus the bus expansion inputs. The third panel has the main and monitor outputs. Far left is the mains input panel with voltage selector switch and fused/filtered IEC inlet. You can see there are two blank panels. This would typically be replaced by addition pairs of mic pre inputs meaning that fully loaded you could make a 6  mic + 24 line into 2 bus tube mixer. Alternatively you could fit sets of line inputs each with its own level and pan controls.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #172 on: October 01, 2020, 03:06:47 PM »
I have just finished a mock up mechanical build of the basic Poor Man's Tube Mixer (pic attached). When I first started putting it together the basic build had a very sparse front panel and fader section so I decided to add four line inputs with pan and fader in addition to the two mic inputs. There are also 24 stems coming in on 3 x db25 connectors plus a couple of bus expansion inputs for a total of 32 inputs.

From left to right you have two tube mic pres with the usual switches, a HPF and gain and pan pots. The four line input with pan pots (a HPF might also be possible). These six inputs all have their own faders. Next is the bus master currently with two faders but normally you would just have the one stereo fader. The we have the stems trim that adjusts the overall level of the 24 stems reaching the bus with a monitor level control above which feeds a separate monitor output (the stems trim would have been a fader if I could find an affordable 500 ohm one.) The last module houses the power supply. This base level version needs a minimum of four transformers (two for the mic pres and two for the bus amp). Output transformers are optional. The space to the right of the faders is pre to fit whatever you wish. I still looks like a £2000 BOM is possible.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Poor Man's Tube Mixer
« Reply #173 on: October 03, 2020, 09:57:50 AM »
Ooops, correction, it currently looks like  BOM cost of £1400 is possible which means if I was building one it would have a selling price of £2100.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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