DIY Front End 2022

[Aleph5]

Ceramic capacitors if Class 1 dielectric. C0G/NP0.

 

[ghitus]

If I chose mica? https://www.mouser.it/ProductDetail/5982-15-500V10J

Gaetano.

 

[rickmcinnis]

Got my two FE2022s working over the weekend. Powered by a perfboard version of Ben Mah's regulator - the two make a very tidy package each mounted in its respective amplifier. Did not want to buy capacitors since these will be used while I make a version of ra7's latest SCG; they will be retired after those are made - only using them on the bass side of the MEH - all I had laying about were DYNAMICAP loudspeaker caps which, while not huge, are much larger than what the pads would accommodate - the caps are bigger than the FE2022 and the regulator.

Maybe I will brave enough to take a picture of one of them for the HOW NOT TO DO IT section of the forum? My rationale is "why go to lots of trouble for something you know will not be around for too long"? One of those corollaries to the litany of procrastinators.

Certainly is a neat project that comes in handy. AD infinitum THANKS to the mentor, proprietor, and all around fine fellow.

Funny how the artist can also be the patron in the rare case? How often has that happened in human history?

 

[Dneu2011]

How bad of an idea is this? Thinking of experimenting to see if there is any improvement over smps.

Another option could be to change the VRDN to take an AC Wall Wart and remove the transformer.

 

[Dneu2011]

Can anyone recommend a switch that can be used with a 48V dc 1.5A SMPS?

Can I use a 12 volt DC 20A switch or will a 240VAC 20A switch work?

I’ve noticed the ones I use for 24V builds don’t last.

 

[Mark Johnson]

Here's the one I used: (link) . Specs are included.

 

[Ben Mah]

Here are some I found at Mouser.com:

Mouser.com 48VDC switches

 

[Centurion53]

Question about the shielded cable used in these FE projects like this one and the BA2018. I see where Jim used Mogami 2330, which has a 28 gauge conductor and he used Mogami 2381 in other circuits which is a 30 gauge conductor. Not sure what currents these conductors are carrying but is 30 gauge big enough to use on the FE. I ask because thats what I have on hand.

 

[Mark Johnson]

Assume the signal is a 50 volt square wave and the load is 5K ohms. Then the current flowing in the cable is 10 milliamperes. 30 AWG wire resistance is 0.104 ohms per foot of length, so if your cable is 5 feet long (!) that's 0.52 ohms from end to end. Power dissipated in the cable's resistance is (I * I * R) = (52 one-millionths of a watt). The cable and the 5K load resistance form a resistive voltage divider which attenuates the signal; (Vout / Vin) = [5000 / (5000 + 0.52) ] = 0.999896. Or if you prefer dB, -0.000903 dB.

So you need to decide: are you comfortable pushing 10 mA through the cable?

Are you comfortable dissipating 52 microwatts in the cable resistance?

Are you comfortable allowing the cable to attenuate the signal by 0.01 percent?

OBTW (this table) says the max current you can safely squirt thru a short (< 10 meters long) AWG-30 wire, is 860 milliamps. And the max current you can safely squirt thru a long (>10 meters) AWG-30 wire, is 142 milliamps.

 

[GKTAUDIO]

OBTW (this table) says the max current you can safely squirt thru a short (< 10 meters long) AWG-30 wire, is 860 milliamps. And the max current you can safely squirt thru a long (>10 meters) AWG-30 wire, is 142 milliamps.

Thanks for that, Mark.

For most of my umbilicals, I've used 20ga. or 22ga. conductors out of these exact concerns.

 

[Centurion53]

Thanks for the quick reply Mark! and thanks for the link to the table, very useful to have.

 

[Skip Pack]

Off topic, but the 2330 looks suitable for interconnect duty. I need to make up some long cables (10 foot and 7 foot) Is the capacitance (35pf/foot) likely to be an issue (fairly high amp input impedance).

 

[dliscomb]

@Skip Pack
Using this a question as a springboard to start using LTSpice, I think this cable can be modeled by a 350pF cap in series with a 0R.7 resistor. Assuming I did this right, and the target device has 10KR impedance, the phase shift should be well under 40 microdegrees for most of the listening spectrum.

 

[Skip Pack]

Thanks a bunch, @dliscomb! I'd done the simple reactive impedance calc and thought all would be well. Your phase analysis contribution cements that. I expect that the input impedances Ill be using this with will be at least 20K. I'll make some interconnects up.

 

[dliscomb]

increasing the load to 20kR decreases the phase shift scale on the right by a factor of two; the divisions range from 0 to 22

to be clear: I'm not super confident that my analysis is reasonable. I would love to get some validation, either positive or negative.

Kind regards,
Drew

 

[dliscomb]

Oh! I forgot to mention that this analysis was for the 10-foot cable, hence the capacitance = 10 ft * 35pF/ft = 350pF. the 7-foot cable should have less phase shift, I think, because its capacitance would drop to 245pF.

The resistance of the cable is dwarfed by the input impedance, rendering it negligible for all practical purposes in this frequency range.

Kind regards,
Drew

 

[Skip Pack]

I forgot to mention that this analysis was for the 10-foot cable, hence the capacitance = 10 ft * 35pF/ft = 350pF.

Understood!, I've ordered the bulk cable and hope to make up any new ones I need with it. It's a less visually-obvious alternative and that's useful in my new living room 3ch installation -- lots of cables. I'll stop my off topic excursion here.

 

[dliscomb]

Hold on.

I was messing about, and now I get the following:

Not sure what changed, as the circuit looks the same to me, albeit with a 20K load.

The NET file:
* /Draft1.asc V1 N001 0 0 AC 50 R1 OUT 0 20K C1 OUT N001 350p Rser=0.7 .ac dec 10 30 100k .backanno .end

 

[dliscomb]

apologies; this is hijacking the thread unnecessarily

 

[Skip Pack]

As the OH (original hijacker) I should bear most of the blame. Still, I sure appreciate your contribution.

Skip