DB25 summing PCB - MK2??

[ruffrecords]

wow! Interesting!... anyone else in for a Poor Man's SSA-2B?

I am sure you could beat the Sweetwater $3999 price!!!

Rough BOM:

[b]Item                                                 Price GBP[/b]

Twin Line Amp plus input and output transformers       250GBP
 2 X db25 cards plus connectors and resistors           30GBP
2U Case                                                 50GBP
Custom Front Panel                                      50GBP
23 position switch pot                                  50GBP
Power Supply (guess)                                   200GBP

Total                                                  630GBP
[b]Total                                                 1000USD[/b]

Cheers

Ian

 

[erikb1971]

still not very low budget... but my guess is that that would be a fine piece of kit!

 

[bruce0]

It would be a very different approach no? 

This would passive summing with a tube make up stage?

That summer has 12 stereo inputs each transformer balanced line level input - so you might need 2 dozen OEP line trafo's or something.  The manual implies the transformers are in the feedback loop for the input stage, so it seems like that isn't a passive summer.  I don't know what you have in mind for the 1:10 trafo's.  As far as trafo's, not sure they are using anything too special (whole unit weighs 5.4kg 11.8 pounds).

Still even if you did the whole thing with OEP it would be 26 *$16 .. $416 in trafo's. 

 

[ruffrecords]

It would be a very different approach no? 

This would passive summing with a tube make up stage?

That summer has 12 stereo inputs each transformer balanced line level input - so you might need 2 dozen OEP line trafo's or something.  The manual implies the transformers are in the feedback loop for the input stage, so it seems like that isn't a passive summer.  I don't know what you have in mind for the 1:10 trafo's.  As far as trafo's, not sure they are using anything too special (whole unit weighs 5.4kg 11.8 pounds).

Still even if you did the whole thing with OEP it would be 26 *$16 .. $416 in trafo's.

I may be wrong but I very much doubt this has  24 input transformers in it. The feedback I think they are referring to is zero field feedback in the summing bus transformer. It would be interesting if someone could get the lid off one of these and take a photo of the insides. You mention the manual - do you have the actual product? could you take the lid off??

Cheers

Ian

 

[bruce0]

No sorry, no product ($4k !)
Manual and specs are minimal but they exist online.
b

http://www.tube-tech.com/filer/ManSSA2A-1.pdf

They are kind of fuzzy about the term "channel" but it seems to be a 12 "channel" stereo thing that can have 2 channels operate as 4 mono.

From the manual
"All inputs are balanced by two zero field transformers (one for each channel)."


http://www.tube-tech.com/filer/tekniskespecifikationer/webspecs/SSA%202B%20specs%20WEBsite%20100211.pdf

 

[ruffrecords]

Well, the zero field thing can only be done by feedback so there would need to be an active circuit for each input if every input (channel) had a transformer. Yet there are only 8 tubes in it.

I agree they are fuzzy about the term channel. I strongly suspect it means left and right. I guess we are not going to resolve this until we see inside one. I'll look for reviews of it.

Cheers

Ian

 

[bruce0]

Yes... maybe we can find one, but I couldn't find any reviews.  But the manual does have instructions for adjusting +15 and -15 rails, so there is an op amp in there somewhere. The site says
"The power supply and the sidechain circuits are based on a solid-state circuit."... I can't imagine what a sidechain is on a summer.

 

[bruce0]

Ian:  Please put me down for 4. 

I was thinking I could put 2 in a wide 500 series faceplate, and do makeup gain using the JLM INX5 dInGo card (if I can figure out how to make the output virtual ground).

Or I could just keep it passive and do makeup gain in a pair of mic pre's.

 

[ruffrecords]

Yes... maybe we can find one, but I couldn't find any reviews.  But the manual does have instructions for adjusting +15 and -15 rails, so there is an op amp in there somewhere. The site says
"The power supply and the sidechain circuits are based on a solid-state circuit."... I can't imagine what a sidechain is on a summer.

I couldn't find any reviews either. Several people on gearslutz had owned the A model for a few years. I might askt hem if they will take the lid off. I did see mentioned the fact that the VU meters are buffered by op amps  to 'prevent distortion due to VU loading' which explains why they need +- 15V supplies but I agree the 'side chain' reference is puzzling.

Cheers

Ian

 

[helterbelter]

eeehhhhhhrrrr.... I obviously missed this. Am I too late to order 4 of these ?

greetings,
Paul

I had a feeling this might prove popular so I ordered plenty. I'll put you down for four of them.

Cheers

Ian

Nice ! That saves me the hassle of doing this :
http://www.groupdiy.com/index.php?topic=43999.msg585983#msg585983

And PCB's look a lot more professional as well

 

[ruffrecords]

I asked on gearslutz about the number of transformers in a Tube-tech SSA-2B and  got this reply from MattS.

Hi
There are 2 'zero field' transformers which provide 2 balanced, earth free 'virtual earth' mix buses.
The various inputs are simply resistors onto these 2 buses.
There are 2 valves associated with each zero field transformer which then feed the level attenuator switch (balanced) and then into 2 more valves for each output stage.
Thus overall there are 2 bus mix transformers, 8 valves and 2 line output transformers.
The VU meters use an op amp buffer circuit so that there is no distortion added to the audio path from the metering.
The whole unit is 'balanced' from input to output.
Matt S

Cheers

Ian

 

[erikb1971]

I asked on gearslutz about the number of transformers in a Tube-tech SSA-2B and  got this reply from MattS.

Hi
There are 2 'zero field' transformers which provide 2 balanced, earth free 'virtual earth' mix buses.
The various inputs are simply resistors onto these 2 buses.
There are 2 valves associated with each zero field transformer which then feed the level attenuator switch (balanced) and then into 2 more valves for each output stage.
Thus overall there are 2 bus mix transformers, 8 valves and 2 line output transformers.
The VU meters use an op amp buffer circuit so that there is no distortion added to the audio path from the metering.
The whole unit is 'balanced' from input to output.
Matt S

Cheers

Ian

so... ours is better?

 

[bruce0]

I asked on gearslutz about the number of transformers in a Tube-tech SSA-2B and  got this reply from MattS.

Hi
There are 2 'zero field' transformers which provide 2 balanced, earth free 'virtual earth' mix buses...etc

Cheers

Ian

Well that makes more sense.  Thanks Ian.

 

[ruffrecords]

so... ours is better?

Similar and just as good in its own way.  We have relatively expensive mic transformers, they have cheap transformers and a couple of extra tubes - just different ways of achieving the same thing. They have a balanced attenuator in the middle of the circuit and we have it on the output. This means their noise performance could be worse at some gain settings, ours gets better as you turn down the gain. They have a push pull output stage capable of +26dBu (into 600 ohms I presume) at the cost of a large expensive output transformer (and it is not large and expensive then they lose bass performance). We have a low cost un-gapped output transformer driven by the Eurocard amp which will do +22dBu into 600 ohms. They have a passive mix bus and so do we. They have a whole bunch of not cheap XLR connectors and we have a couple of dB25 connectors. They need a PSU to power 8 tubes, we need one for just three.

Also, I have been contacted by Dan Deurloo of collectives cases who is willing to do a case for  a summing box project if anyone is interested.

Cheers

Ian

 

[erikb1971]

cool.. and maybe two of these:

would be cool...

 

[ruffrecords]

The db25 PCBs arrived in the post this morning. If you want some email me your shipping address and quantity and I'll send you a Paypal invoice (5GBP each +shipping).

Cheers

Ian

 

[nmp]

I have changed the labelling of the resistors to hopefully make it more obvious which is which and also to reflect the Tascam input numbering system. So, for a regular alternate left/right assignment you just fit the resistors whose label begins with a letter 'R'. The second character is the Tascam channel number 1 thru 8 and the last character is either 'H' or 'C' to indicate if it is the hot or cold connection. So:

R1H is channel 1 hot
R7C is channel 7 cold

If you want to make any channel into mono then just fit the corresponding resistors whose labels begin with the letter 'M' (for mono). So:

M1H and M1C make channel one into a mono channel.
M4H and M4C do likewise for channel 4

So normally you would fit all the resistors beginning with the letter 'R'. For any channel you want to make mono you fit the corresponding resistors beginning with the letter 'M'.

Hope that makes sense.

Cheers

Ian

This is great! Exactly the PCB I was after!! Such a great way of offering mono options too!

I am not the best with reading PCB layouts, so just had one question.... I noticed quite a big difference in terms of the grounding between V2 and V3, and the green links going to J6 are no longer visible. Where is this link happening and getting to the J6 terminal?

Also, do you still have a few of these PCBs? I'd be keen for 4-6 of them if you do.

Thanks,
Nick.

 

[bruce0]

Could you please share the overall dimensions of the card?  I want to see if it will fit in front of an INX5

 

[ruffrecords]

Could you please share the overall dimensions of the card?  I want to see if it will fit in front of an INX5

The card is 61mm wide and 50mm deep.

Cheers

Ian

 

[sharpeleven]

Received the cards a couple of days ago. Great work!! Thanks!!