BA500v2 Mic Pre Amp BUILD THREAD 500/51X

[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

[Joe Malone]

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.

[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]

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.

[Joe Malone]

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.

[caoimhin]

Super, Joe, thank you so much!

[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

[Joe Malone]

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

[jaaperdany]

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

Greetings
Jasper

[Joe Malone]

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."