Have Begun My First A12 Kit: Some Organized Questions...

[Great Magnet]

1.) I've already installed my Receptacles and resistors...no problem. BUT, the DIODES seem to use wire that is actually THICKER than the holes in the circuitboard! Is this common? I got around it by pre-trimming the wire ends to correct length (as opposed to trimming the extra AFTER it was soldered in place) and tapering each cut wire with my snippers so that there is a sharp point at the end. I lightly cram that sharp point into the hole in the circuitboard and then solder from the back until the hole fills with solder and locks the diode in place. Did I do good?

2.) In the headers section: What is a "shunt"? Is this the same as a jumper?

Okay I think that's it for now...thanks in advance!

Cheers,
Adam

[bkspero]

I think the approach you're using with the diodes is ok. Some risk that you will cut too short and wind up pulling too hard on the connection to the device to stretch deep enough into the hole. I trimmed the leads so that there was about 1/4-3/8 extra to fit thru the board and used the cut pieces to gently ream out the hole. I tapered one end of the short piece of wire as you described, pushed it thru the hole, and rotated it a few times to remove some of the excessing tinning. The diode leads fit well after that.

A shunt is the jumper block that fits over the pins of a header to complete a circuit between the 2 pins. A black square/rectangular piece of plastic with a copper metal insert that fits over the pins and is the conductor.

[tarnationsauce2]

I encountered this too. Just be careful and do not force the leads into the holes because you can lift the pad from the board.

I got around the problem by filing the diode's leads a little bit.

[lynyrd]

I used a micro drill bit with a hand vice (available at any good hobby shop) and drilled out the holes just a bit. Be careful though, to make sure your solder flows through properly or else the unit won't work. It took my tech 5 minutes to find the problem and about 5 seconds to fix it ( he just touched the joint with the soldering iron to re-heat it). This is the only glitch I have run into when building my SCA kits.

[Great Magnet]

A shunt is the jumper block that fits over the pins of a header to complete a circuit between the 2 pins. A black square/rectangular piece of plastic with a copper metal insert that fits over the pins and is the conductor.

So is this (photo below) the shunt, i.e. "jumper block" you speak of?


If it is, it leads me to an even bigger question: according to my (quite possibly incorrect) understanding of Instructions page 7, only locations J3, J4, and J6 receive headers at all. As in the photo below...


This is an actual pic of my kit as it now stands. Now, in my kit I was only given three headers, so that's where I put 'em. And then as you can see I put a jumper on J5, which was what I thought was meant by shunt at the time.

The instructions on Page 7 are really vague for the beginner...somebody help me understand where these headers do and don't go!

Thanks,
Adam

[tpryan]

You don't need a header at J6 unless you plan to use that isolated output for something. Better to install it at J5 in case you need to connect the output to a 600 ohm load some day. Also, make sure you install the headers with the long pins UP. It's hard to tell from your photos if they're in the right way.

[Great Magnet]

You don't need a header at J6 unless you plan to use that isolated output for something. Better to install it at J5 in case you need to connect the output to a 600 ohm load some day. Also, make sure you install the headers with the long pins UP. It's hard to tell from your photos if they're in the right way.

Hey Tim,

Yeah, I actually did install them with the long tines up...as I could tell that they were meant to marry (snap) to those plastic parts which have since been explained to me are the shunts.

So, put simply: what I should do is desolder and remove that header I placed at J6, then re-install it at J5 (in place of the jumper I made there) and then put the plastic shunt over it? And thusly the shunt on the J5 header acts as a sort of jumper until I "need to connect the output to a 600 ohm load some day"?

Cheers,
Adam

[bkspero]

Correct about installing a header at J5 and connecting a shunt (jumper) across the pins (at least that's how my son and I read and did it and the pre's sound fine going into modern equipment).

I made the same mistake of soldering a header at J6 on the first of my A12's. I decided it was safer and easier to leave the header in J6 and buy another 2 pin header to install at J5. With all the stuff already installed nearby J6 and with needing to unsolder 2 pads simultaneously to get out the header, it wasn't worth the risk to me of damaging something important to save a few cents (even a few dollars) worth of a part.

Its easier to unsolder the wire shunt you installed at J5. There's more room to work. And you can snip the wire so each end can be removed separately. Or just leave the wire there and use it as-is. You can always go back and install a jumper at some later time.

[Great Magnet]

With all the stuff already installed nearby J6 and with needing to unsolder 2 pads simultaneously to get out the header, it wasn't worth the risk to me of damaging something important to save a few cents (even a few dollars) worth of a part.

Yeah it's pretty tight in there but yesterday I went down to Radio Shack and bought one of those spring-loaded desoldering vacuums and then went home and did the switch and it went just fine.

[honkyjonk]

Just thought I'd attatch a question to this thread since it is related.

What is the harm of leaving off the jumper to J5 EVEN if you are using a modern high impedence recorder?

I'm not exactly sure what Jumping or not jumping J5 does to the output impedence, but this is my situation:

I have an Alesis HD24 Hard Disk recorder that I use a lot. So, having the "shunt" on J5 wouldn't be a problem, but I also have an old Ampex 440B 8-track that I'm fixing up that I intend to use some day. I can look up the input impedence and make sure, but I think I remember it being 600 ohms, so if I were using both recorders on a frequent basis, it would be a bummer to have to open up the SC preamp and remove this thing all the time.

If the output is looking for a 600 ohm input, but finds a much higher input impedence, then that is a lot better than the other way around, no?

So what's the harm in just leaving it off?

[tpryan]

If the output is looking for a 600 ohm input, but finds a much higher input impedence, then that is a lot better than the other way around, no?

Definitely.

So what's the harm in just leaving it off?

No harm at all. You'll notice a slight increase in output and you'll be able to measure a slight rise in HF response, but not until you get way out of the audio band.

If you're using both recorders regularly, you can always arrange your patch bay so that the preamps drive both machines simultaneously.