DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

Hi Owel and others.

I've put my Sc-1 together, but I have been having a few problems.

To start with I thought there was something wrong, but I measured the voltages and found that the little pin plug I'd put on the -ive side of the powersupply wasn't actually delivering any current. Easy fixed. Microphone started working.

Last night I got more seriously into getting this thing going proper. I was getting noticeable RFI. I tried a different ac out let and still not much different. I decided to rewire the input and output section, paying more attention to braiding the wire for the input/output and re-soldering the neutrix side. The output no longer presents RFI, I can't hear any SBS radio anymore on it when waggling it. After that I found I was still getting radio off the input side, so I rewired that side this morning. And now I have a problem. No microphone sound. And yes I have checked that the pins and wires match.

1) I've checked the voltages across both ends of the 48v and 18v+/- and they are fine going into the preamp, at both points, out of the powersupply and at the pcb itself. I still get a nice "thump" when I turn the preamp on and off.

2) Since I had a problem I cut off the output wires and put some test clip wires in place. I'm getting the following voltages across the pins:
1 pin and 3 pin I get about 0.3volts (mic connection end of cable)
Between pin 2 and pin 3 I get 0.1volts (mic connection end of cable)

I've tried clipping the XLR input to the test wires and am still getting the same voltage readings, but yet again no working mic input. Is that the correct voltage? I now get "noise" out of the preamp (which I think is to be expected as there's no grounding on either output and it's obviously not "seeing" the microphone either).

Any tips or hints about this would be helpful.

Stratman

Do you have a photo of the whole thing? Is it in a case? or not? Is the case grounded?

Are the PSU voltages proper? 48V, +18, -18V?

Wiring correct for the XLRs in and out? pin 1, 2, 3 connected to the correct pin 1, 2, 3 of the Neutrik Jack? Note, the locations of 1,2,3 on the input and output XLR are different.

Are your input and output wires twisted? or just hanging?



I'm not sure what you're trying to do here? Are you measuring if you have phantom power voltage?

Between pin 1 and 2 should be 48V.
Between pin 1 and 3 should be 48V.
Between 2 and 3 should be 0V.

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SC1 in case.
Case is grounded to the IEC via a terminal ring. I'll try and get some photos to you soon.



Yes. All looking pretty good.



Yes. Pretty sure.

So on the input Neutrik that you sell:

Pin 1 Left, Pin 3 middle, Pin 2 right (From back)

PCB -> Pin 1, Pin 2, Pin 3

So on the output Neutrik that you sell:

Pin 2 Left, Pin 3 middle, Pin 1 right (From back)

PCB -> Pin 1, Pin 2, Pin 3



I had them twisted. The output is still in place and still twisted. The input is now connected via some test cables to the jack.



Just using a dynamic, Shure SM58 - I don't own any condensors right now.

On hooking up the cable and switching on phantom power with no microphone connected:

Pin 1 and Pin 2 --> 47.3v
Pin 1 and Pin 3 --> 47.3v
Pin 2 and Pin 3 --> Near 0, 0.1v (I think this meter and probe set is not entirely accurate but close enough generally)

Just trying to figure out what's going where across ground and not across ground.

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Without Phantom:

Pin 1 and Pin 2 --> 0.1-0.3v (fluctuates)
Pin 1 and Pin 3 --> 0.1-0.3v (fluctuates)
Pin 2 and Pin 3 --> About 0v, 0.1v

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More stuff

Tested microphone with a portable M-Audio Audio Buddy and I know the microphone isn't dead, nor the 2.1 speaker set things are hooked upto.

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I'll see what I can do about a picture later tonight. I'm still scratching my head.

Spratty

A bunch of recent pictures. Hope they help.













Spratty

Thanks for the photos. Yes, they do help.

I see the cause of your RFI problem. Your case isn't really grounded.



On this picture, you'll see a small tab on the XLR case. This is the grounding for the XLR jack's case. It's beside/nearest the Pin1 terminal. You should get some solder (or wire), and bridge the gap between this metal tab and Pin1 of the XLR jack. Either use a wire,or just a good blob of solder.

You may also play whether connecting the ground of both the XLR in or output wire together will improve noise or not.

I assume those temporary alligator test leads will not be in the final assembly?

This is a 1 channel in a rack I did,


and this is what the above assembly/rack sounds like:
http://www.fivefishstudios.com/audio/kol/Silence.mp3

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Thanks Owel. The photographs are appreciated

I notice you have a nice rainbow ribbon thing to connect things up - I've never seen these at any stores around here, can you tell me what they're called?



No, the clips are not for final assembly. Right now I'm just trying to get the unit going, then I'd like to add a second SC-1 and tidy everything up.



Ah yes, I understand what you're talking about here. Previously when I had it all wired up I had a tiny set of clips pinning that little "flange" to pin one. I've now soldered it and it's quieter than when I had clips on it. The clips are obviously not perfect for such an application. Anyone else building an SC-1 --> It's a good idea to solder the flange first. No temporary clips.

Now what the real problem was.....I found this hard to believe....I thought something was stuffed. But it's not. And I tried to solve this by being naive and inexperienced and probably a bit paranoid.

What has happened:

Because the board is not solidly supported AT THE BACK right now it seems that the 1510P THAT! chip had shifted in its socket at some point (either when SC-1 was removed from case or when the gain stages were toggled through) and wasn't operating properly as a result. I just reseated the thing and low and behold, I have mic! And not only that but it's pretty quiet (probably quieter when I hook it up to a proper piece of audio equipment and not just some cheap speakers with a cheap y cable). It's quieter EVEN WITH the alligator plugs on the input, which I will replace soon. And there I was thinking that there was something seriously wrong. My only worry now is perhaps there's something not quite right with the stiffness of the IC legs on the 1510P - I put it in carefully the first time, I am scared of damaging IC's and I'm not sure I want to play with it, without having another one on hand in case of accidents.

Thank you Mr Owel!

Stratman! (Somewhat happier and having solved one mystery! And seriously thinking about buying a second channel!)

Glad it's a good happy ending for you.

I would suggest that you insert the IC chips on the PCB before you mount the board to the case.

As for the support on the back, there are 2 holes on the PCB, just need to drill some 1/8" holes on the case that aligns with the PCB, and use some 1/4" nylon spacer stand. That would give a solid footing.

The IC chip if inserted properly should just sit about 1mm above the IC socket. And all the legs securely in the hole. It's a good thing you did not damage the chip when it got loose with power on.



They're called wiring harness. I haven't had time to put it on the online store. But I've sold them to a few people via email (after they saw it in pictures).

On your next order, I can include and send you the cables with your order and just Paypal separately the extra cost of the cables.

The nice thing about the cable is you can easily detach your PSU wires from the preamp board. In case you need to work on the preamp, and it's just neater.

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Just wondering what wiring harness you're referring to. I don't recall noticing it in any pics. I'd be interested in something like that as well. Do you mean that molex like connector?

Ahh yes. The 4 wires with the connector.

4 wires don't necessarily need to be called a harness

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Hi Owel



That's what I did strangely enough. I didn't think it'd be a clever idea to do anything different.



Should be doable. I'll have to look into where to buy these, as I haven't seen any local. Have you found the standard sorts are the right size?



Yes, I was lucky. From turning it off and switching things around a lot it looks like it's possible that it just lifts from the socket when there is minimal support on the back of the pcb. Some support appears to make it hold and not move. I imagine putting a knob on the trim will help too.



If they're not expensive then that's not an issue. With regards to the harness, I assume it's possible to use multiple harnesses against the powersupply to power more than 1 SC-1 I'd imagine? It's hard to guess from this picture what your approach is for multiple SC-1's/multi-connections.

Edit:Bought another channel + 2x harness wiresets

Cheers!
Stratman

Thanks. Yes, the PSU can power several channels. No problem.

Since the PSU has (2) sets of connection, what I do is use (1) harness for 2 SC-1 channels, and another harness for the other (2) channels.

This picture should explain it.

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