BA newbie's questions 2009

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pietro_moog
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Joined: Fri Mar 06, 2009 2:16 am

BA newbie's questions 2009

Post by pietro_moog »

Hi everyone!
i'm a newbie, and i need some help.

i found i have a 27k instead of a 68r (68r shold go into RG), what do i have to do with ?

in the on/off switch i have no diode. is this intended not to be there or i lost it?

thanks

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Joe Malone
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Re: BA newbie's questions 2009

Post by Joe Malone »

i found i have a 27k instead of a 68r (68r shold go into RG), what do i have to do with ?
27k is for OEP Rload when using fixed impedance. RG = 68R. (Latest batch of 100 BA kits were found to be missing 68R.)
in the on/off switch i have no diode. is this intended not to be there or i lost it?
The power switch kit doesn't have the diode marked on the PCB as it is only needed when switching AC volts. All of our mic pre kits now run on the 48vDC SMPS
Joe :-)
JLM Audio
Capturing Audio without Injury

jonte-72
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Joined: Fri Jul 10, 2009 3:39 am

Re: BA newbie's questions 2009

Post by jonte-72 »

Hi!

I am building my first BA so I thought this was the perfect headline for my question.

I bought a shielded 3-wire cable (with 0.23 mm^2 area per wire) for the output XLR jack and a shielded 2-wire cable (with 0.36 mm^2 area per wire) for the input XLR. Now I got a bit concerned that the area might be to small, especially the 0.23mm^2-cable. Q1:Are my concerns justified or is it of no matter for short leads (about 6 cm)? Q2:Could I use the 2-wire cable even for the output (using the shield for one of the pins as for the input) or is it better to have a separate shield around all three wires?

Cheers and thanks!

jonte-72
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Joined: Fri Jul 10, 2009 3:39 am

Re: BA newbie's questions 2009

Post by jonte-72 »

Hi again!

My, apologies. I missed that there were two more pages with forums. Should have posted my questions above in the BA wiring forum. Hopefully I will be excused as a newbie :-) Too late to move it, but I'm still wondering about these issues (however, now with my newly acquired knowledge that the output wires don't have to be shielded).

Best regards

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Joe Malone
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Re: BA newbie's questions 2009

Post by Joe Malone »

Really any thickness general hook up wire will do fine as remember this wire leads you to the input transformer winding which is super fine copper wire only as thick as hair.
Joe :-)
JLM Audio
Capturing Audio without Injury

Keagan
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Joined: Wed Sep 30, 2009 8:08 pm

Re: BA newbie's questions 2009

Post by Keagan »

Hey guys.

I just finished the BA4 kit. As a complete newcomer to the world of pcb's i thought i might throw up some things that had me puzzled the first time around, so that any people in my situation can get through this as easily as possible.

My kit was:
2 x JLM14 + 99v
2 x OPA + 99v

1. You need jumpers at the two spots marked BD681. Use some left over component legs. You need to link to centre hole with the hole marked E. You will see a little white tab between these holes to be sure.

2. You need a jumper on the socket where the OPA opamp would go (under the 99v). This goes between the first pin top row and the third pin bottom row. See the pink diagram on the BA page/jlm site, it will make sense.

3. The resistors marked RG, RPAD, and RL(oad) - these values are all on the yellow table on the BA page/jlm site.

4. If you are not using the ribbon cable, dont forget to use the jumpers. The locations are marked next to the socket on the board.

5. If you are using the OPA transformer, dont bother looking for the resistors to suit the high gain per the table on the website. Just go with the low gain, and again dont forget the jumpers that will be mounted on the pins to go between the transformer and the ribbon socket.

6. Test the voltages on the board without the opamp first (per the pink diagram). You should be missing voltage at a few locations. If everything is looking good to that point, plug the opamp in and the rest of the voltages should pop up. (This one burnt me for hours, when nothing was really wrong)

7. When i did the JLM14 transformer, the top bank of four holes (unused) above the transformer, marked on the pink voltage as being 48v with phantom, only every second one shows 48v. No worries.

8. The CZ, RZ, Zener, 47v slots all stay empty. Some of these get used if you make a BA2 with the impedance dial.

Generally, it is a process of elimination. All the parts are there, just work through what you know and it will make sense. I was left with one 220pF cap, and one resistor in each set. The resistor left over will vary based on the transformer and the values on the yellow table.

If any of these are wrong anyone please chime in. I just thought it would be good to have this because alot of this stuff seems common sense to alot of people here, but were the first things that left me unstuck. All in all though, the build could have been harder and im surprised with the results that someone with limited knowledge can achieve here.

Paul
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Joined: Sat Mar 24, 2007 5:16 pm

Re: BA newbie's questions 2009

Post by Paul »

Joe Malone wrote: 27k is for OEP Rload when using fixed impedance. RG = 68R. (Latest batch of 100 BA kits were found to be missing 68R.)
no wonder i couldnt find the 68R on my garage floor!! :)

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