BA500v2 Mic Pre Amp BUILD THREAD 500/51X

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slb1959
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by slb1959 »

Hi Joe

The values for VTX or oep a262a3e componentes are the same?
I have caps 100uf 25V. Can i use it instead 35V?

Thanks, Luís

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Joe Malone
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

slb1959 wrote:
Tue Dec 05, 2023 11:03 pm
Hi Joe

The values for VTX or oep a262a3e componentes are the same?
I have caps 100uf 25V. Can i use it instead 35V?

Thanks, Luís
Yes transformer values are the same. Yes 100uF 25v is perfect.
Joe :-)
JLM Audio
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caoimhin
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by caoimhin »

hi Joe, I had this email exchange with you back in 2022:
[me]I'd love to replace the DI with an output volume knob - can you tell me about how to do this, and is there anything i need to do at the ordering stage via your website?
[you] Basically you will need one of our dual 1k log pots + resistor to set the range of the output attenuator. I will have to draw up a new way of doing this in the new BA500 version as the transformer directly plugs into the pcb.
I'm only getting round to building my BA500v2 now (life and kids intervened!) - can I ask you to tell me how to connect the dual 1k log pot / transformer, and what resistor value I should use? Thank you!

caoimhin
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by caoimhin »

Am I right in guessing that you think the output attenuator is simply not a good idea, Joe? I found this old thread that quotes you as saying you "would never put an output control on a baby animal because it will take away from headroom and adds output damping" (https://gearspace.com/board/geekzone/50 ... nimal.html).

I'm an electronic newbie and ignoramus, so if you think it's a bad idea, then I'll listen to you and just not do it.

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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

caoimhin wrote:
Tue Jan 23, 2024 3:23 am
Am I right in guessing that you think the output attenuator is simply not a good idea, Joe? I found this old thread that quotes you as saying you "would never put an output control on a baby animal because it will take away from headroom and adds output damping" (https://gearspace.com/board/geekzone/50 ... nimal.html).

I'm an electronic newbie and ignoramus, so if you think it's a bad idea, then I'll listen to you and just not do it.
You have to watch output headroom when you turn down the output control but otherwise, it can be useful. Yes it does vary output impedance and therefore damping but it can still sound ok. Headroom clipping and noise are the 2 main things to watch out for.

I am making up the drawings to show how to do the wiring with the new pcb transformers but it will take a little while as we are just back to work and trying to clear 300 emails and a truck load of orders.
Joe :-)
JLM Audio
Capturing Audio without Injury

caoimhin
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by caoimhin »

Super, Joe, thank you so much!

jaaperdany
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by jaaperdany »

Hi,

I have a question, I am using JLM14 as input transformer, JLM99V or JLM Twenty 5 Twenty SMD as Opamp, would do some tests and decide to go with the better sounding opamp. My output transformer is the JLM2503. Now the question is in the PCB GB500v2, for Cload, should I use 390pF or not ?.

Please do let me know what I should be doing here.

Greetings
Jasper

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Joe Malone
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

jaaperdany wrote:
Mon Mar 11, 2024 8:20 am
Hi,

I have a question, I am using JLM14 as input transformer, JLM99V or JLM Twenty 5 Twenty SMD as Opamp, would do some tests and decide to go with the better sounding opamp. My output transformer is the JLM2503. Now the question is in the PCB GB500v2, for Cload, should I use 390pF or not ?.

Please do let me know what I should be doing here.

Greetings
Jasper
The JLM14 is very flat so it doesn't need a CLoad but depending on the opamp it may need a CLoad for better opamp stability. JLM99v should be fine without any Cload at all and Twenty 5 Twenty CLoad of 100pF or 220pF
Joe :-)
JLM Audio
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jaaperdany
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by jaaperdany »

Hi Joe,
Thanks for the reply, then for what kind of opamps/transformer combinations then do I need the 390pf ?

Greetings
Jasper

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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

jaaperdany wrote:
Tue Mar 12, 2024 3:35 am
Hi Joe,
Thanks for the reply, then for what kind of opamps/transformer combinations then do I need the 390pf ?

Greetings
Jasper
Kit 2520 opamps are usually very unstable especially if used with VTX / OEP highi ratio transformers and any opamp you see oscillation on the output of the opamp at any gain level.

"CLoad can be not fitted or up to 390pF in value depending on the opamp used has stability problems."
Joe :-)
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trispembo
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by trispembo »

Hi Joe, first time posting and building one of your (or any) audio kits. Really enjoying the experience so far.

There are two BA500 v2 kits on my bench, with builds completed (or so I thought). I'll focus on unit 1 to begin with before tacking the other one later.

Unit 1 seems to be powering up ok (VU light on, 48v LED comes on, takes signal on XLR & DI with VU meter and gain pot active, pad works) but is not passing any signal to lunchbox output. No noise, nothing. Usual trouble shooting with lunch box confirms slots are working with other gear.

Currently I only have a multimeter for tests, but am happy to procure a signal generator if needed. Any help would be most graciously received!

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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

trispembo wrote:
Sun Oct 20, 2024 3:53 pm
Hi Joe, first time posting and building one of your (or any) audio kits. Really enjoying the experience so far.

There are two BA500 v2 kits on my bench, with builds completed (or so I thought). I'll focus on unit 1 to begin with before tacking the other one later.

Unit 1 seems to be powering up ok (VU light on, 48v LED comes on, takes signal on XLR & DI with VU meter and gain pot active, pad works) but is not passing any signal to lunchbox output. No noise, nothing. Usual trouble shooting with lunch box confirms slots are working with other gear.

Currently I only have a multimeter for tests, but am happy to procure a signal generator if needed. Any help would be most graciously received!
Ok since VU meter is showing level all active mic pre electronics is working and can only be soldering to do with the output transformer. Or if running a dip8 dual opamp with no output transformer the 2 wire links to get audio to the output are not fitted. Are you running a balanced XLR lead out from the 500 rack to another balanced input ?

Best to put up a couple of photos of the built BA500 so I can see the main pcb setup.
Joe :-)
JLM Audio
Capturing Audio without Injury

trispembo
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by trispembo »

Joe Malone wrote:
Mon Oct 21, 2024 9:20 am
Ok since VU meter is showing level all active mic pre electronics is working and can only be soldering to do with the output transformer. Or if running a dip8 dual opamp with no output transformer the 2 wire links to get audio to the output are not fitted. Are you running a balanced XLR lead out from the 500 rack to another balanced input ?

Best to put up a couple of photos of the built BA500 so I can see the main pcb setup.
Thanks so much for your prompt response Joe!
I'm using your twenty 5 twenty op amp.
Yes, balanced xlr lead to a balanced input (Metric Halo 2882).
Photos attached.

Image
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by Joe Malone »

trispembo wrote:
Mon Oct 21, 2024 11:04 am
Joe Malone wrote:
Mon Oct 21, 2024 9:20 am
Ok since VU meter is showing level all active mic pre electronics is working and can only be soldering to do with the output transformer. Or if running a dip8 dual opamp with no output transformer the 2 wire links to get audio to the output are not fitted. Are you running a balanced XLR lead out from the 500 rack to another balanced input ?

Best to put up a couple of photos of the built BA500 so I can see the main pcb setup.
Thanks so much for your prompt response Joe!
I'm using your twenty 5 twenty op amp.
Yes, balanced xlr lead to a balanced input (Metric Halo 2882).
Photos attached.

Image
I cannot see it in the photos but have you jumpered the output transformer ratio as 1:2 or 1:3 (as that is the only extra difference on the 2503 pcb to our JLM111DC version). The 3 pads are next to the output transformer. Add a wire from centre pad to either 1:2 which gives 6db transformer boost or 1:3 which gives 10dB transformer boost and more fat 2nd harmonic :-)
Joe :-)
JLM Audio
Capturing Audio without Injury

trispembo
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Re: BA500v2 Mic Pre Amp BUILD THREAD 500/51X

Post by trispembo »

Joe Malone wrote:
Mon Oct 21, 2024 11:10 am
trispembo wrote:
Mon Oct 21, 2024 11:04 am
Joe Malone wrote:
Mon Oct 21, 2024 9:20 am
Ok since VU meter is showing level all active mic pre electronics is working and can only be soldering to do with the output transformer. Or if running a dip8 dual opamp with no output transformer the 2 wire links to get audio to the output are not fitted. Are you running a balanced XLR lead out from the 500 rack to another balanced input ?

Best to put up a couple of photos of the built BA500 so I can see the main pcb setup.
Thanks so much for your prompt response Joe!
I'm using your twenty 5 twenty op amp.
Yes, balanced xlr lead to a balanced input (Metric Halo 2882).
Photos attached.

Image
I cannot see it in the photos but have you jumpered the output transformer ratio as 1:2 or 1:3 (as that is the only extra difference on the 2503 pcb to our JLM111DC version). The 3 pads are next to the output transformer. Add a wire from centre pad to either 1:2 which gives 6db transformer boost or 1:3 which gives 10dB transformer boost and more fat 2nd harmonic :-)
Ah, no I haven't. Sorry, just followed the build map. The ratio is right next to the JLM logo?

Here's a photo of that part of the PCB.
IMG_8593.JPG
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