First Neurochrome Preamp Build

I dunno. You'd have to check the relay data sheet. Does the relay click and make contact when you apply the correct coil voltage?

The relay coil generally doesn't care about polarity. Some relays have a magnet inside to make the relay action a bit faster. Those relays do care about polarity. The only way to find out is to check the data sheet.

... and the easiest way to find the data sheet is to type the relay part number into Mouser/Digikey and click on the data sheet link.

Tom
Yeah I checked the data sheet, I haven’t powered it yet, mostly just want to know if the diode will do its job before I do. I plan to connect the feed to the volume control to pins 10 and 8

IMG_7324.jpeg
 
In that case you want + on the black wire and - on the green. The diode is connected correctly.

The relay will connect pin 4 to pin 5 when the coil is energized and connect pin 4 to pin 3 when it's not. Similarly, pin 9 will be connected to pin 8 when the relay coil is energized and to pin 10 when it's not.

If you connect the power supply for the volume control to pin 10 and the volume control at pin 8, the volume control will never be powered.

Tom
 
In that case you want + on the black wire and - on the green. The diode is connected correctly.

The relay will connect pin 4 to pin 5 when the coil is energized and connect pin 4 to pin 3 when it's not. Similarly, pin 9 will be connected to pin 8 when the relay coil is energized and to pin 10 when it's not.

If you connect the power supply for the volume control to pin 10 and the volume control at pin 8, the volume control will never be powered.

Tom
Got it! I was obviously misinterpreting the graphic, glad I asked, thanks!
 
I was thinking, couldn’t I just connect both the preamp supply and the Khozmo supply to the power switch? Maybe I don’t need the relay at all in that case?
 
Which power switch are you referring to? The low-voltage one that controls the Preamp Power Supply?

Tom
 
You can do that but then the Khozmo circuit is on at all times.

Tom
 
Well, it depends. The Preamp Power Supply supports the use of low-voltage switches, such as the nice-looking anti-vandal switches that are quite popular. In that application the power supply is always on and the voltage regulators are switched on/off. If you want to use this function then you need the relay if you want the Preamp Power Supply to turn on/off the Khozmo.

If you'd rather just switch the mains voltage, you can wire the Preamp Power Supply such that it turns itself on as soon as the mains power is applied. In that case you can just switch the mains voltage to both the Preamp Power Supply and the Khozmo.

Tom
 
Well, it depends. The Preamp Power Supply supports the use of low-voltage switches, such as the nice-looking anti-vandal switches that are quite popular. In that application the power supply is always on and the voltage regulators are switched on/off. If you want to use this function then you need the relay if you want the Preamp Power Supply to turn on/off the Khozmo.

If you'd rather just switch the mains voltage, you can wire the Preamp Power Supply such that it turns itself on as soon as the mains power is applied. In that case you can just switch the mains voltage to both the Preamp Power Supply and the Khozmo.

Tom
Got it, you’re right the aesthetics of the switch is a consideration. Thanks!
 
Comments from Tom from my layout...

Also suggestion to use an extender to keep wires short but maybe hard with the khozmo.

Scoot the Buffer down to the pot so the connections to its input become as short as possible. They're higher impedance than the output so easier to inject interference into.

The outputs of the Buffer are not very sensitive to interference, so they can be longer.


So stealing that knowledge...move the buffer down as close to the pot and run longer cables from the buffer to the back of the case?
 
Well I realized I bought the wrong kind of DPDT switch. It's momentary not latching. Doh.

Does anyone have a link to a good quality DPDT switch? I'm having trouble finding one with gold contacts.

EDIT: I decided to go the relay route, I'll get a basic quality DPDT switch to select between 2 TXS2 4.5v relays running off the 5v supply.
 
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You can scoot that buffer closer to the volume control. Maybe like this:
IMG_7338_TCedits.jpg

I would also swap the two power supplies so the Khozmo one gets closer to the side of the chassis. I'm counting gnats here, but the transformer is more likely to emit electromagnetic fields than the SMPS, so it would make sense to keep it as far away from the rest as possible. I doubt it'll make much, if any, difference in practice, but it's free to swap the two and it might reduce hum so why not?

Does anyone have a link to a good quality DPDT switch?
The ones by C&K are quite good. I get them through the usual suspects, Mouser/Digikey/et al.

Tom
 
Well I’m at a bit of a loss, I connected everything to power to test and tried it on a dim bulb tester and got no load whatsoever. I even tested across the iec jack and got nothing. Fuse is in place and not blown.

What am i missing?

IMG_7347.jpeg
 
Looks like you're missing a power switch.
Screenshot 2024-02-18 at 15.34.02.png

Or if you want the power supply to turn on when the AC power is provided, replace the power switch in the figure above with a piece of wire and select the TOGGLE option on the red jumper.

Tom
 
Looks like you're missing a power switch.
View attachment 189

Or if you want the power supply to turn on when the AC power is provided, replace the power switch in the figure above with a piece of wire and select the TOGGLE option on the red jumper.

Tom
I knew it!

Follow up question is how should I wire this switch in? In haven’t been able to find a clear wiring diagram online.

IMG_7348.jpeg
 
Well... I suggest looking up the data sheet for that switch. Have you tried contacting the vendor?

Another approach would be to grab your DMM and use the diode/continuity setting to figure this out.

The switch probably has a normally open and a normally closed position. It also has an LED. Typically red is (+) and black is (-) in DC circuits, so I wonder if those would be connected to the LED. If you use the diode setting on your DMM you should be able to get the LED light up, though probably pretty dimly. The meter should also give you some reading of the forward voltage of the LED.

If that guess is correct, that just leaves the three remaining wires. With the switch in the off position, I bet two of them will show continuity. That's your normally closed contact. Let's just say that's the green and the white wire. So one of those wires will be the common for the two switches (the NO and the NC ones). So push the switch and pick either the green or the white wire. That should then show continuity to the yellow wire. If it doesn't, then pick the other of the green or white and measure to yellow. That probably shows continuity.

Now you know all connections to the switch.

It looks like this on the inside:
Screenshot 2024-02-18 at 15.55.27.png

Tom
 
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