JLM AUDIO

Joe Malone wrote:

ajsteel wrote:Hi Joe,

IMG_1415.jpg

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?

Hi Joe, I removed the solder short at BD681 and I'm getting 7.8mV at +V across the Zener I'm getting 7.4mV

Joe Malone wrote:

ajsteel wrote:Hi Joe,

IMG_1415.jpg

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?

Hi Joe,

I have removed the short and replace the Zener and I get 2.9mV at +V on the opamp

ajsteel wrote:

Joe Malone wrote:

ajsteel wrote:Hi Joe,

IMG_1415.jpg

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?

Hi Joe, I removed the solder short at BD681 and I'm getting 7.8mV at +V across the Zener I'm getting 7.4mV

Remove the zener and see if you get close to +46v at +V. If so zener has gone short circuit and needs to be replaced.

ajsteel wrote:

Joe Malone wrote:

ajsteel wrote:Hi Joe,

IMG_1415.jpg

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?

Hi Joe,

I have removed the short and replace the Zener and I get 2.9mV at +V on the opamp

OK sounds like the short killed both the zener and BD681. Replace both and you should have 36 to 38v at +V.

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?[/quote]



Hi Joe,

I have re[laced the Zener and BD681 and now get 0.6mv at +N (unpowered unit, no opamp) and 38V powered. Also getting 19V at +N powered (no opamp).. seems like it's all good.

Shall I low ratio the primary by connecting the two centre pins on the primary (EA2622) and connect the two centre pins on the secondary (EA2622) to 0V on the BA?

OK sounds like the short killed both the zener and BD681. Replace both and you should have 36 to 38v at +V.

ajsteel wrote:
I have re[laced the Zener and BD681 and now get 0.6mv at +N (unpowered unit, no opamp) and 38V powered. Also getting 19V at +N powered (no opamp).. seems like it's all good.

Shall I low ratio the primary by connecting the two centre pins on the primary (EA2622) and connect the two centre pins on the secondary (EA2622) to 0V on the BA?

Cool. Good to hear you have the correct two voltages

Yes low ratio is the correct setting for 600ohm mics

Hi Joe,

Regarding the Low Ratio option and 600ohm mics, if using Dynamics and LDC's is really necessary? For instance the SM57 has an impedance 150ohm and I do have an Impedance pot on my pres? Am I missing out on anything by not using the low ratio on the Primary of the EA2622?

Thanks for all your great help. This has been a great learning curve in really understanding my gear and how and why it gives me the sound it gives me.

A.J.

ajsteel wrote:Hi Joe,

Regarding the Low Ratio option and 600ohm mics, if using Dynamics and LDC's is really necessary? For instance the SM57 has an impedance 150ohm and I do have an Impedance pot on my pres? Am I missing out on anything by not using the low ratio on the Primary of the EA2622?

Thanks for all your great help. This has been a great learning curve in really understanding my gear and how and why it gives me the sound it gives me.

A.J.

600ohm input is for 150ohm and 200ohm mics
150ohm input is for old 50ohm mics

But yes because you have variable impedance setup the centre detent on the Z pot is 600ohm on low ratio and 150ohm on high ratio.
You have a lot of impedance range so can experiment with high ratio if you want too.

I went with the low ratio. It seemed a little fatter. I've also added a 10k resistor before the 100k Impedance pot and only soldered the to back three legs and suggested earlier in this build thread. The pre seems more open and extended when the pot is all the way to the right. Two more pre's to build and I'll be away with four.

Hi Joe,

My 3rd channel I just finished doesn't seem to get any power. The phantom power LED will not light up either when I switch it on. I've compared it to the other two working channels and can't seem to find a difference. What have I missed? I'm going from +V on Channel 2 to +V on Channel 3.

I also destroyed a BD681 and got replacement but after I inserted it I saw that it was a BD681n. Is that a problem?

I thought I had these nailed now.


Thanks.

A.J.

This is the bottom side of my 3rd channel with no power.

Hi Joe,

I've fixed my problem with Channel 3. All good.. I didn'y have 0v from channel 2 connected to channel 3. Once connected I had power, LED cam on and correct Voltages at +N.

ajsteel wrote:Hi Joe,

I've fixed my problem with Channel 3. All good.. I didn'y have 0v from channel 2 connected to channel 3. Once connected I had power, LED cam on and correct Voltages at +N.

Cool good to hear you got it going so easy

Hi Joe,

I thought I had it going but I was wrong. My voltages aren't correct through the opamp amp circuit. What I get is;

+N 19V
-N 9V
Out 9V
1/2V 19V
+V 39V

When I first plugged in the 2520 I got a little smoke and a smell. Have I blown something up? Photos below; Also when I plug the 2520 in the power supply goes into protection mode. The LED flashes.

A.J.

ajsteel wrote:Hi Joe,

I thought I had it going but I was wrong. My voltages aren't correct through the opamp amp circuit. What I get is;

+N 19V
-N 9V
Out 9V
1/2V 19V
+V 39V

When I first plugged in the 2520 I got a little smoke and a smell. Have I blown something up? Photos below; Also when I plug the 2520 in the power supply goes into protection mode. The LED flashes.

A.J.

ba2_3 bottom.jpg

What voltages did you get when you did the votlage tests before the opamp was plugged in for -IN and OUT?

As long as there is no short on -IN or OUT to 0v there is no way the BA kit can damage the opamp so it should only be a opamp fault.

Is it a GAR2520 you built? And has it been tested in a good BA PCB before? I would be testing each new BA PCB with a known good opamp.