BA Dramas

Support for JLM Audio Kits

Moderator: Joe Malone

MattyTwo
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Joined: Tue Nov 14, 2017 4:22 pm

BA Dramas

Postby MattyTwo » Tue Nov 14, 2017 6:23 pm

Hi Joe,

I've recently purchased the BA mic preamp kit with the following options;

JLM14 - Input Transformer
JLM99V - Opamp
JLM11DC - Output Tranformer

I'm a bit confused about a few things. I've searched the forum for answers to help myself but haven't been able to find any?

1. Do I need to fit the Opamp Volts Trimmer? If so how do I set the voltage? Opamp in or out? If not, do I install a jumper and across which terminals?

2. My kit has been supplied with a 100K impedance pot and no 2K2 resistor. I've installed the 100K pot with the 10K resistor. I'm unsure as to whether this is a change made by you to give me the 100K pot and no 2K2 resistor deliberately as a mod?

3. I have the Mean Well GS25A48-P1J 48V 540mA power adaptor. Do I need to install the soft start mod? I have broken my BD681 transistor removing it as I thought I didn't need it. I guess if I get one I can just grab one from Jaycar?

Regards,

Matt.

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Joe Malone
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Re: BA Dramas

Postby Joe Malone » Tue Nov 14, 2017 6:43 pm

MattyTwo wrote:Hi Joe,

I've recently purchased the BA mic preamp kit with the following options;

JLM14 - Input Transformer
JLM99V - Opamp
JLM11DC - Output Tranformer

Answers from email I sent earlier

I'm a bit confused about a few things. I've searched the forum for answers to help myself but haven't been able to find any?

1. Do I need to fit the Opamp Volts Trimmer? If so how do I set the voltage? Opamp in or out? If not, do I install a jumper and across which terminals?

You can leave off trimpot and BD681 and link C to E in BD681 position as shown by white line on all BA BAD pcbs if running 48v or +/-24v opamp type like JLM99v. If setting volts for lower volts opamp always set before fitting opamp. Example if opamp is +/-18v set 36v at +V or pin 8 if DIP8 type measured to 0v.

2. My kit has been supplied with a 100K impedance pot and no 2K2 resistor. I've installed the 100K pot with the 10K resistor. I'm unsure as to whether this is a change made by you to give me the 100K pot and no 2K2 resistor deliberately as a mod?

[Joe] OK strange there was no 2k2. I will check the batch of kits. The 100k pot is dual and is wired in parallel for 50k. (Front row of legs joined to back row of legs to make 50k log pot) New black PCB fit 2k2 to RLoad and plug in 2 pin header and wire to impedance pot so impedance pot is shorted when fully counter clock wise.

3. I have the Mean Well GS25A48-P1J 48V 540mA power adaptor. Do I need to install the soft start mod? I have broken my BD681 transistor removing it as I thought I didn't need it. I guess if I get one I can just grab one from Jaycar?

[Joe] No Soft mods needed on any new builds ever. You can leave off trimpot and BD681 and link C to E in BD681 position as shown by white line if running 48v or +/-24v opamp type like JLM99v.

Let me know if you have any more questions
Joe :-)
JLM Audio
Capturing Audio without Injury

MattyTwo
Posts: 3
Joined: Tue Nov 14, 2017 4:22 pm

Re: BA Dramas

Postby MattyTwo » Wed Nov 15, 2017 11:49 am

Thanks.

Definitely no 2K2 resistor. It's not even listed on the bag. I'll grab one on the way home from Jaycar.

MattyTwo
Posts: 3
Joined: Tue Nov 14, 2017 4:22 pm

Re: BA Dramas

Postby MattyTwo » Wed Nov 15, 2017 9:12 pm

Hi Joe,

I've fitted the 2K2 resistor.

At first I had no sound. I came to the realisation that I had the connector on the IC cable around the wrong way. I changed it and I got some sound however...

The sound is heavily distorted. There's no hiss. You don't really get any sound until you turn it all the way up and turn the input on my interface all the way up. Even then the level is very low.

The sound is somewhat like an octave up fuzz pedal through the DI pedal. The mic signal is similar. I've been over and over and over the connections, no to mention the forum...

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Joe Malone
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Re: BA Dramas

Postby Joe Malone » Thu Nov 16, 2017 7:58 am

MattyTwo wrote:Hi Joe,

I've fitted the 2K2 resistor.

OK we can send you one if you need as well. I have fixed the BA kit packing now now thanks so future kits will have 2k2

At first I had no sound. I came to the realisation that I had the connector on the IC cable around the wrong way. I changed it and I got some sound however...

ok that would dead short the power supply and make the 48v smps go into hiccup mode (green light flashing)

The sound is heavily distorted. There's no hiss. You don't really get any sound until you turn it all the way up and turn the input on my interface all the way up. Even then the level is very low.

The sound is somewhat like an octave up fuzz pedal through the DI pedal. The mic signal is similar. I've been over and over and over the connections, no to mention the forum...


Ok Email me a couple of photos of the top and bottom of each PCB and your wiring with opamp removed so I can check them over for you and answer the questions below.

Best to test one thing at a time. So unplug DI and fit the 2 jumper shunts in the 10 pin header as shown on the BA overlay PDF.

Do you have 48v a +V opamp pin measured to 0v?

Does the 48v phantom led turn on and off with the 48v phantom switch?
Joe :-)

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