Feeler: Classic Solo

[ruffrecords]

how did you managed the input transformer screen connection? Is it connected to the signal ground or connected to a mounting standoff pad?

It is connected to the ground plane of the PCB which is signal 0V.

Cheers

Ian

 

[Deepdark]

ok. I thought it was best to tie the screen (pin 7, actually, the mumetal can, right?) of the input transformer to the chassis (as any shield) and tie pin 6 to the signal ground.

Am I wrong?

 

[ruffrecords]

ok. I thought it was best to tie the screen (pin 7, actually, the mumetal can, right?) of the input transformer to the chassis (as any shield) and tie pin 6 to the signal ground.

Am I wrong?

This is a difficult one.  The first thing to note is that as far as suppressing magnetic fields is concerned, there is no need to ground the mu metal can. Usually the transformer will already be inside a metal box which provides screening of external interfering E fields. Interference currents will flow in this screen. The transformer can will provide screening of any interference INSIDE the box. If the can is connected to the main box, all the interference currents are coupled to it and potentially to the transformer windings. So, I  usually connect it to the local signal 0V.

Cheers

Ian

 

[ruffrecords]

Which XLRs do you recommend?

Any good quality metal bodied ones should be fine. I personally prefer Neutrik.

Cheers

Ian

 

[Deepdark]

Thanks Ian. I was aware of that one because, speaking with David from Cinemag, he highly suggest me connecting pin 7 (the can) to the chassis with the shorter run possible (on the CMM1-10APC, that one is sent to chassis, at least it puts the chassis symbols) and pin 6 (Inside screen??) is sent to signal ground. So there is no real importance as where we connect it or I would be better off to tied it to signal ground? In case the input transformer don't touch at the chassis, too.

 

[Deepdark]

Just found this: https://www.edcorusa.com/xpwr018

Probably too low, but maybe edcor could wind a custom one, if the toroid end up being too expensive. Ofcourse, we would have to instal it outside the case to be safe. Just an idea

 

[ruffrecords]

Just found this: https://www.edcorusa.com/xpwr018

Probably too low, but maybe edcor could wind a custom one, if the toroid end up being too expensive. Ofcourse, we would have to instal it outside the case to be safe. Just an idea

Yes, the 40V winding is probably too low. The 48V/50V I normally use gives about 70V dc across the reservoir capacitor which means the TL783 has about 20V across it which is necessary to ensure good regulation and ripple rejection.

I have now received a quotation for 10 custom toroid transformers. The price is not confirmed yet because I am not sure if mounting kits are included but it looks like it will be close to 30 Euros.  I will have a couple myself so if 8 more are taken we can have a group buy.

Cheers

Ian

 

[Deepdark]

Just found this: https://www.edcorusa.com/xpwr018

Probably too low, but maybe edcor could wind a custom one, if the toroid end up being too expensive. Ofcourse, we would have to instal it outside the case to be safe. Just an idea

Yes, the 40V winding is probably too low. The 48V/50V I normally use gives about 70V dc across the reservoir capacitor which means the TL783 has about 20V across it which is necessary to ensure good regulation and ripple rejection.

I have now received a quotation for 10 custom toroid transformers. The price is not confirmed yet because I am not sure if mounting kits are included but it looks like it will be close to 30 Euros.  I will have a couple myself so if 8 more are taken we can have a group buy.

Cheers

Ian

30 euros is quiet a good deal, i would be in for 1. It's a custom toroid with phantom tap included? Does it have some form of shielding or it's a regular toroid with 3 coils?

 

[ding]

I am too except I'm sure shipping would be expensive to the US. Either way I would be very interested to know the final tally and shipping.

 

[ruffrecords]

Thanks Ian. I was aware of that one because, speaking with David from Cinemag, he highly suggest me connecting pin 7 (the can) to the chassis with the shorter run possible (on the CMM1-10APC, that one is sent to chassis, at least it puts the chassis symbols) and pin 6 (Inside screen??) is sent to signal ground. So there is no real importance as where we connect it or I would be better off to tied it to signal ground? In case the input transformer don't touch at the chassis, too.

It is important that the can is connected only to the signal 0V OR the chassis but it must definitely not be connected to both. So, if it happens your can gets mechanically (and hence electrically) connected to the chassis you should not connect it to signal 0V. Given a choice, I would go for signal 0V. If you get a chance, try both and let us know if there is any difference.

Cheers

Ian

 

[ruffrecords]

30 euros is quiet a good deal, i would be in for 1. It's a custom toroid with phantom tap included? Does it have some form of shielding or it's a regular toroid with 3 coils?

Yes, it has the three secondary windings we need and also dual voltage primaries so it should work anywhere. The Carnhill I used in the prototype has no screening so I decided not the include any. I got a price for one with an inter-winding screen and that added nearly 50% to the price.

Cheers

Ian

 

[ruffrecords]

I am too except I'm sure shipping would be expensive to the US. Either way I would be very interested to know the final tally and shipping.

It is unfortunate that transformers are so heavy. I have a spare Carnhill that is the same size so I will weigh it and find out the US shipping cost.

Cheers

Ian

 

[Deepdark]

Thanks Ian. I was aware of that one because, speaking with David from Cinemag, he highly suggest me connecting pin 7 (the can) to the chassis with the shorter run possible (on the CMM1-10APC, that one is sent to chassis, at least it puts the chassis symbols) and pin 6 (Inside screen??) is sent to signal ground. So there is no real importance as where we connect it or I would be better off to tied it to signal ground? In case the input transformer don't touch at the chassis, too.

It is important that the can is connected only to the signal 0V OR the chassis but it must definitely not be connected to both. So, if it happens your can gets mechanically (and hence electrically) connected to the chassis you should not connect it to signal 0V. Given a choice, I would go for signal 0V. If you get a chance, try both and let us know if there is any difference.

Cheers

Ian

Thanks Ian.  I will give it a try in my LA2A. It's possible it causes some minor ground loop I guess.

 

[ruffrecords]

I just weighed the small Carnhill toroid mains transformer at 375 grams. Allowing for packing I have checked out the post office prices for a 500gm parcel shipped to various places around the world. The results are as follows:

Germany £10.15
USA  £12.45
Australia £12.90

This is around 50% of the cost of the transformer. I'll leave it up to you guys to judge if it is cost effective for you.

Cheers

Ian

 

[Deepdark]

I just weighed the small Carnhill toroid mains transformer at 375 grams. Allowing for packing I have checked out the post office prices for a 500gm parcel shipped to various places around the world. The results are as follows:

Germany £10.15
USA  £12.45
Australia £12.90

This is around 50% of the cost of the transformer. I'll leave it up to you guys to judge if it is cost effective for you.

Cheers

Ian

GBP to CAD is about twice. So probably something like 30$CAD for shipping and 30euro is about 47$ so it end up to cost about
80$, more or less. Not bad. If we go with the EI Hammond, it's the price it will cost but we will have to buy another transformer for the phantom supply

 

[ding]

If I were thinking of being able to use this as a gain makeup for a passive summing mixer wouldn't it be best to add a stepped 1k output pot between the transformer and output XLR? I was thinking of using one of these to achieve that.

http://capi-gear.com/catalog/product_info.php?cPath=51_133&products_id=238

I think I'm going to do without the meter and instead put a mic XRL jack and a stepped output pot where I had the meters. I imagine that would be more useful. I hate reaching around back to plug in a mic.

 

[ruffrecords]

If I were thinking of being able to use this as a gain makeup for a passive summing mixer wouldn't it be best to add a stepped 1k output pot between the transformer and output XLR? I was thinking of using one of these to achieve that.

For a passive summing gain make up amp that is the only sensible place to put a level/trim control.

http://capi-gear.com/catalog/product_info.php?cPath=51_133&products_id=238

That should work. It is not a balanced control so you would have to use what I call the Neve trick to use it with a balanced output.

I think I'm going to do without the meter and instead put a mic XRL jack and a stepped output pot where I had the meters. I imagine that would be more useful. I hate reaching around back to plug in a mic.

Is this going to be a summing mixer and a mic pre?

Cheers

Ian

 

[ding]

No. Just a mic preamp that I'm going to use to amplify the passive summing mixer I plan to make in the future. Since I'm building 2 in a 2u rack that should work nicely. Although a preamp summer would be an interesting thing for someone else.  So about the output. Should I then make a T-pad 600 ohm attenuator instead? Strait or bridged?

 

[ruffrecords]

No. Just a mic preamp that I'm going to use to amplify the passive summing mixer I plan to make in the future. Since I'm building 2 in a 2u rack that should work nicely. Although a preamp summer would be an interesting thing for someone else.  So about the output. Should I then make a T-pad 600 ohm attenuator instead? Strait or bridged?

OK, if it is a mic amp then you do not really need an output level control unless you want to try deliberately driving the second stage harder to get more tube tone. All you need is the 10K log pot between the two stages.

Cheers

Ian

 

[ruffrecords]

The V2 PCBs arrived in the post this morning. I have added them to the PCB emporium. They are £14 each. Place your order in the usual fashion.

Cheers

Ian