Feeler: EZ Tube Lunch Box

[ruffrecords]

Thanks Ian, great work on the pdf! Wasnt there talk at one point to have the foot print for a carnhill input trafo?


Regards Ian,

Pierre

Not that I recall but I have been known to be wrong.  I have had a quick look at lower cost line input transformers for another project and I was thinking along the lines of an adaptor PCB that would allow them to be used with the current range of PCBs.

Cheers

ian

 

[G-Sun]

I'm still thinking about the insert post preamp, pre eq.

As I see it I have three choices
a) No insert (not ideal for me, but maybe a good choice)
b) transformer balanced out/in
c) IC balancing board out/in

Then it's a question of switching type.
1) DPDT switch, mounted on front (preamp > eq  ;  preamp | eq )
2) Relay switched
2) Switching jacks mounted on front

Ideally it would be an IC based balancing in out with relay switching.
But then it's a question about psu and pcb (for the relay). Adding a second psu-board for this is not impossible.
Balancing boards like this http://www.diyrecordingequipment.com/products/balanced-input
seems good.
Is floating ground an option and using one of the rails to create e.g +-3V?

If cost was no objection I guess transformers are ideal.
I don't know how the switching best should be done.
Anything better than wiring to/from a DPDT-switch on front?

Any thoughts and pointers are helpful

 

[ruffrecords]

I'm still thinking about the insert post preamp, pre eq.

As I see it I have three choices
a) No insert (not ideal for me, but maybe a good choice)
b) transformer balanced out/in
c) IC balancing board out/in

There is a fourth choice - post EQ - you already have the output transformer there anyway so the insert is free.

Then it's a question of switching type.
1) DPDT switch, mounted on front (preamp > eq  ;  preamp | eq )
2) Relay switched
2) Switching jacks mounted on front

I am not sure any of these is possible within a 3U module. There are not enough spare pins on the 32 way for 1) or 2) and 3) takes up a lot of real estate on the front panel.  Holger ended up designing a special module for insert switching.

Cheers

Ian

 

[rmaier]

Another question about parts for the Classic pre: what should I be looking for in a relay? Please feel free to school me (or point me in the right direction).
Thanks!
Ralph

 

[ruffrecords]

Another question about parts for the Classic pre: what should I be looking for in a relay? Please feel free to school me (or point me in the right direction).
Thanks!
Ralph

I recommend something like the NEC EA2-12NU. It has gold plated contacts and is rumoured to be the ones Neve use. Available just about everywhere.

Cheers

Ian

I have included this in the classic pdf and also made a note about minor differences between the V2 and V3 PCBs. New version 1.1 pdf attached.

 

[G-Sun]

I'm still thinking about the insert post preamp, pre eq.

There is a fourth choice - post EQ - you already have the output transformer there anyway so the insert is free.

Then it's a question of switching type.

I am not sure any of these is possible within a 3U module. There are not enough spare pins on the 32 way for 1) or 2) and 3) takes up a lot of real estate on the front panel.  Holger ended up designing a special module for insert switching.

Thanks!
Insert post eq is not suitable for my needs, as it's most about using the preamp and fx as separate units.

But, I was thinking it over, and I can us ch1 preamp, the use ch2 for lineamp, eq and comp.
When recording mono that is. For those small percentages of stereo tracking I can live with non-ideal workflow for tweaking vs. recording.

So, then I'm cutting the cost of 4 transformers and my modules will be like one (So, eg doing preamp-eq in one build is not that problematic.)

 

[ruffrecords]

I think I mentioned some time ago some tests I did to compare the low cost Edcor XSM2.4k/600 output transformer with the Carnhill VTB2291 that I normally use. I concluded that, even when loaded with 600 ohms, the Eurochannel card runs out of steam before either of the transformers do. Both transformers gave near identical frequency response and distortion figures. On that bais I was happy to recommend the Edocr as an alternative to the Carnhill.

To complete the comparison, today I measured the primary and secondary inductance of both transformers at 100Hz and also the DCR of both windings when connected 2400:600. The results were:

Primary Inductance: Edcor 26H, Carnhill 28.2H
Secondary Inductance: Edcor 9.8H,  Carnhill 11.6H
Primary DCR: Edcor 150R, Carnhill 162R
Secondary DCR: Edcor 79R, Carnhill 42R

Apart from the relatively low secondary DCR of the Carnhill, these paramaters are very similar. Not surprising that their performance is near identical.

Cheers

Ian

 

[rmaier]

Very reassuring! I'm waiting for an order of four Edcors that I placed a few weeks ago. It seems that there tends to be a bit of a wait for orders to get filled, so it's good to hear that they'll work well. The price is pretty hard to beat.

 

[G-Sun]

On that bais I was happy to recommend the Edocr as an alternative to the Carnhill.

Thanks for these tests Ian!
That's really a buget-friendly xformer.

 

[G-Sun]

Norwegian krones to GBP has declined very much lately,
so I don't buy in GBP before I need to these days.
Concentrating on plan, bom and sourcing.

Same with USD to NOK.
Eur to NOK is ok.

It has a rather big impact on the final sum

 

[G-Sun]

What is a typical choice/pcb-mount for mic input transformer for the Eorochannel preamp?
http://cinemag.biz/mic_input/mic_input.php
Other brands?

 

[ruffrecords]

What is a typical choice/pcb-mount for mic input transformer for the Eorochannel preamp?
http://cinemag.biz/mic_input/mic_input.php
Other brands?

The PCBs are designed to take any one of three different mic input transformers - Sowter 1948,  Jensen JT-115K-EPC or a Cinemag CMMI-10-PCA.

The Sowter 1948 is a special made for me but Sowter will supply it to anyone. It is basically their 1:10 Helios mic transformer without the 600 ohm tap on the secondary.

Cheers

ian

 

[G-Sun]

The PCBs are designed to take any one of three different mic input transformers - Sowter 1948,  Jensen JT-115K-EPC or a Cinemag CMMI-10-PCA.

The Sowter 1948 is a special made for me but Sowter will supply it to anyone. It is basically their 1:10 Helios mic transformer without the 600 ohm tap on the secondary.

Thanks!
Any practical, performance or sonic differences between them as you're aware of?

 

[anjing]

I have been using both sowter and cinemag. The sowter i use is not the same as Ian tought mine is the 9610c.
I prefer the sowter, even the difference is rather subtle. Eventually i'am gonna try the 1948.
Regards,
Pierre

 

[G-Sun]

Ian: Any planned revisions for the pcbs: eurocard, LBPSUV2 (psu) and 2MODMOTHER before I order some from you?

 

[ruffrecords]

Ian: Any planned revisions for the pcbs: eurocard, LBPSUV2 (psu) and 2MODMOTHER before I order some from you?

Any day now I am expecting a batch of a 6modmother PCB - a 6 module version of the 2 module motherboard. You might want to hang on for one of them.

The LBPSUV2 is the external power supply board and at present I do not envisage any changes to it.

As noted in my white market thread I only have two of  the eurochannel V3  boards left. This means there will be none available until the V5 versions arrive in a few weeks.

Cheers

Ian

 

[G-Sun]

Any day now I am expecting a batch of a 6modmother PCB - a 6 module version of the 2 module motherboard. You might want to hang on for one of them.

The LBPSUV2 is the external power supply board and at present I do not envisage any changes to it.

As noted in my white market thread I only have two of  the eurochannel V3  boards left. This means there will be none available until the V5 versions arrive in a few weeks.

Thanks! v3 vs v5, what's the difference?

 

[ruffrecords]

Any day now I am expecting a batch of a 6modmother PCB - a 6 module version of the 2 module motherboard. You might want to hang on for one of them.

The LBPSUV2 is the external power supply board and at present I do not envisage any changes to it.

As noted in my white market thread I only have two of  the eurochannel V3  boards left. This means there will be none available until the V5 versions arrive in a few weeks.

Thanks! v3 vs v5, what's the difference?

V5 has:

1.Molex connector provision for internal connections rather than plain solder pads.
2. Added HT decoupling to fix the oscillation problem.
3. 1N4007 series diode in HT to prevent smoke escaping from capacitors if you connect the HT the wrong way round (which I have managed to do).
4. Second stage gain trim pot brought to front of PCB so EQ gain can be adjusted thru front panel.
5. Gain setting resistors ground referenced rather than floating at about 90V which also allows amps to be used as virtual earth mixers if you wish.
6. Tubes moved so as not to foul Fischer extruded aluminium cases. First stage output cap moved to as not to be cooked by 6922 tube

Functionally the two are identical as is the 32 way connector pinout. In other words they are plug compatible.

Cheers

Ian

 

[G-Sun]

V5 has:

1.Molex connector provision for internal connections rather than plain solder pads.
2. Added HT decoupling to fix the oscillation problem.
3. 1N4007 series diode in HT to prevent smoke escaping from capacitors if you connect the HT the wrong way round (which I have managed to do).
4. Second stage gain trim pot brought to front of PCB so EQ gain can be adjusted thru front panel.
5. Gain setting resistors ground referenced rather than floating at about 90V which also allows amps to be used as virtual earth mixers if you wish.
6. Tubes moved so as not to foul Fischer extruded aluminium cases. First stage output cap moved to as not to be cooked by 6922 tube

Functionally the two are identical as is the 32 way connector pinout. In other words they are plug compatible.

Thanks! I'm in no hurry, so I'll wait for the 6modmother and eurocard v5

 

[ruffrecords]

Thanks! I'm in no hurry, so I'll wait for the 6modmother and eurocard v5

OK, I'll post here and in the white market when they arrive.

Cheers

ian