BA500 Mic Pre Amp BUILD THREAD 500/51X

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Joe Malone
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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Joe Malone » Tue Dec 18, 2018 10:59 am

Warbler wrote:You are so helpful! I really appreciate that.

Image


Build looks good. Start with the below and answer the questions and we should be able to get you going ASAP.

OK check the 10pin plug going into the GO between input as it doesn't look fully plugged in. Sitting out a few mm.

Do you have an extender cable? Y/N

First check you have all 3 power rails +/-16v and 48v at the back edge connector of the BA500? Y/N.
(Pin 13 is 0v for black meter probe, Pin 15 = 48v, Pin 14 = -16v, Pin 12 = +16v.

When you plug a jack into the DI input slowly can you hear the white relay click on and off? Y/N

With nothing plugged into the BA500 input turn up your monitors and see if the output hiss level goes up when you turn up the BA500 gain pot? Y/N

Did you get a dummy plug in your kit (10 pin header with hot melt glue on the back)? Y/N
Joe :-)
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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Warbler » Fri Dec 21, 2018 10:45 am

Thanks Joe. I’ll be able run those checks after the holidays and get back to you.

I do have an extender card.
I did get a dummy plug.
Merry Christmas!

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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Warbler » Fri Dec 28, 2018 9:17 am

Ok, back at it.

I have 16+ & 16- & 38v phantom. (This is low for phantom I know. I can adjust that.)
I can hear the relay click when plugging in the DI
When I turn the gain all the way up, there's a funky spot towards the top (just under max) where all of a sudden my gain is there. Bad pot maybe?

Warbler
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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Warbler » Fri Dec 28, 2018 9:26 am

Pot checks out smooth.
And strike that previous comment on the gain being "back". Just makes some noise when the pot is turned past few clicks to max.

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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Warbler » Thu Jan 03, 2019 10:44 am

Turns out this mic pre is totally fine. There was a combo of diagnostic stupidities, on my part, leading me astray. My apologies, and thanks for your willingness to help.

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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Joe Malone » Mon Jan 07, 2019 4:59 pm

Warbler wrote:Turns out this mic pre is totally fine. There was a combo of diagnostic stupidities, on my part, leading me astray. My apologies, and thanks for your willingness to help.


Finally back to work today for start of 2019. Great to to hear the mic pre is working :-)
Joe :-)

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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Hynek » Sat Feb 16, 2019 2:03 am

Hi, Joe--

Just finished the BA500 that arrived a couple of days ago from you. The build was a breeze and everything works great!

I purchased the sweepable HPF mini module along with the BA kit with the intent to integrate it in place of the unused DI. Can you throw me some suggestions as to where the HPF would be best inserted in the circuit? I know you touch upon this subject on the first page of this thread but my situation differs in the fact it is an active LPF circuit rather than just a capacitor.

I already have the HPF powered up so my question is just on
- best insertion point
- any IN and OUT impedance concerns (should I change the Zin of the HPF or is 10k good?)
- the HPF's output is DC blocked, any need to add a cap at the input as well?

Thanks for your help.

PS: What's the deal with the floods we see on the news here? I hope you're staying out of the way!

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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Joe Malone » Mon Feb 18, 2019 10:38 am

Hynek wrote:Hi, Joe--

Just finished the BA500 that arrived a couple of days ago from you. The build was a breeze and everything works great!


Cool great to hear :-)

I purchased the sweepable HPF mini module along with the BA kit with the intent to integrate it in place of the unused DI. Can you throw me some suggestions as to where the HPF would be best inserted in the circuit? I know you touch upon this subject on the first page of this thread but my situation differs in the fact it is an active LPF circuit rather than just a capacitor.

I already have the HPF powered up so my question is just on
- best insertion point
- any IN and OUT impedance concerns (should I change the Zin of the HPF or is 10k good?)
- the HPF's output is DC blocked, any need to add a cap at the input as well?


Easy one.

Cut the red wire in the short cable from the GO between 500 pcb to BA500 main pcb as shown in the link below.
viewtopic.php?f=2&t=188#p2021

Wire HPF input to wire coming from the GO between 500 pcb and HPF output to wire going to the BA500 main pcb

Remove R4 10k or replace with 1MEG otherwise is will overload the variable impedance pot from working properly.

Since the HPF is before the main gain stage you need to use a low noise dual opamp like OPA2134. A NE5532A may even work quieter but may add a bit of variable frequency pot noise while sweeping the frequency.

Thanks for your help.

No Problems. Neat idea :-)

PS: What's the deal with the floods we see on the news here? I hope you're staying out of the way!


All good hear. Flooding above us and fire below us. Seems the wrong way around.
Joe :-)

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Hynek
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Re: BA500 Mic Pre Amp BUILD THREAD 500/51X

Postby Hynek » Wed Feb 20, 2019 8:42 am

Glad you're safe and thanks for the guidance!
Will proceed as instructed.

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