BA BA2 BA4 BAD Dual99v Build Thread

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby Joe Malone » Tue Jun 09, 2015 1:52 pm

mikeyb wrote:Hi Joe, is there any reason why i couldn,t wire a bad pcb with separate gain pots for each section, i've not got any dual rev 10ks at the moment but have some single rev 10ks. I have some dual rev 5ks pots - could i use these instead?


You can run separate gain pots if you want.

Or to use the 5k rev log dual pot instead of the 10k rev log dual change

R8 & R12 from 10k to 5k1
RGain1 & RGain2 from 270R to 150R

This will give you to the same gain setup as the 10k dual pot with the original part values
Joe :-)
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Tue Jun 09, 2015 10:32 pm

Thanks Joe - as usual - a quick response :D

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Tue Jun 16, 2015 9:03 am

Hi Joe,
Was thinking about wether i should use my JLM Hybrid in Class A or A/B. Would it be possible to run a twisted pair or screened pair to a front panel switch or would that make it unstable or noisy? Could this be realised by changing a diode/diodes for a transistor and switching the junction on with the base of the transistor? I suppose the other option would be a localised sub minature relay.

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby Joe Malone » Tue Jun 16, 2015 10:01 am

mikeyb wrote:Hi Joe,
Was thinking about wether i should use my JLM Hybrid in Class A or A/B. Would it be possible to run a twisted pair or screened pair to a front panel switch or would that make it unstable or noisy? Could this be realised by changing a diode/diodes for a transistor and switching the junction on with the base of the transistor? I suppose the other option would be a localised sub minature relay.


You can add a switch with twisted pair for A to A/B switching but keep the wires well twisted and short as possible. It the wiring need to be longer add a 1uF mono cap across the wires on the switch.
Joe :-)

JLM Audio

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Thu Jun 18, 2015 12:18 am

Fantastic! - now i just want to solder :D

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Fri Jun 19, 2015 3:04 am

Gain of discrete opamps?
I'm currently (finally!) building various DOA kits, so far I got JLM hybrid, 990, SGA, GAR2520, GAR1731 and classicapi BB2521 for now to try out in my BAD builds
What sort of gain can each stage of the BAD circuit handle.
Looking at the JLM99V, that has it's open loop gain set at 60dB
I think I calculate the gain stage of the DOA on a BAN at 43.3dB with resistors 10k and 68R and the gain of each stage of the BAD at 31.6dB going with the resistor values of 10k and 270R.
What sort of gain can i safely obtain with stability from a single stage with the various DOAs.

Thanks in advance

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby Joe Malone » Mon Jun 22, 2015 4:01 pm

mikeyb wrote:Gain of discrete opamps?
I'm currently (finally!) building various DOA kits, so far I got JLM hybrid, 990, SGA, GAR2520, GAR1731 and classicapi BB2521 for now to try out in my BAD builds
What sort of gain can each stage of the BAD circuit handle.
Looking at the JLM99V, that has it's open loop gain set at 60dB
I think I calculate the gain stage of the DOA on a BAN at 43.3dB with resistors 10k and 68R and the gain of each stage of the BAD at 31.6dB going with the resistor values of 10k and 270R.
What sort of gain can i safely obtain with stability from a single stage with the various DOAs.

Thanks in advance


JLM99v usually will have a 43dB limit due to its low gain design which gives it a quieter noise floor.

All other opamps will be higher but stability depends on lots of the circuit and PCB layout.
Joe :-)

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Sat Jul 11, 2015 9:35 am

Yeah Joe - thought as much with the design layout.

Thanks for the reply

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Fri Nov 13, 2015 2:43 am

Just stuffing boards and noticed my 100uF are only 25V - are these ok or do i really need 35V. Got some 50V but they too big!

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby Joe Malone » Mon Nov 16, 2015 3:00 pm

mikeyb wrote:Just stuffing boards and noticed my 100uF are only 25V - are these ok or do i really need 35V. Got some 50V but they too big!


That is on the edge of the 25v that will be across the cap. 35v is best.
Joe :-)

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby mikeyb » Tue Nov 17, 2015 12:05 am

Hi Joe - had another root around and found 35V caps - thanks for the reply

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby ixox » Tue Feb 09, 2016 5:37 am

Hi Joe,

First thanks a lot for providing those great kits that taught me a lot about mic preamp.
I have 2 of them a BA and a BAD.

They don't have output transformer.
The BAD works perfectly with an OEP A262A3C and 2 x OPA2604. Lots of gain and very silent.

I have a question about my BA which uses a JLM14 in input.
. When used with a OPA2604 it's very silent and works great.
. When used with a JLM99v (and DIP8 4 to 7 pins wired) i can hear lots of noise, mostly electronic noise (such as when my computer downloads files).
It it expected ?
Could an output transformer fix that noise ?

Thanks,

Xavier

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby Joe Malone » Wed Feb 10, 2016 10:37 am

ixox wrote:Hi Joe,

First thanks a lot for providing those great kits that taught me a lot about mic preamp.
I have 2 of them a BA and a BAD.

They don't have output transformer.
The BAD works perfectly with an OEP A262A3C and 2 x OPA2604. Lots of gain and very silent.

I have a question about my BA which uses a JLM14 in input.
. When used with a OPA2604 it's very silent and works great.
. When used with a JLM99v (and DIP8 4 to 7 pins wired) i can hear lots of noise, mostly electronic noise (such as when my computer downloads files).
It it expected ?
Could an output transformer fix that noise ?

Thanks,

Xavier


HI Xavier
OK strange as JLM99v should be about 6 to 10dB quieter than OPA2604AP.
What A/D is the BA plugged into as it seems is is not liking the quasi-balanced noise cancelling output?
Are you plugged into the A/D with a balanced lead from the BA + output & - output?

Or the wiring is slightly wrong and making a ground loop. Need to see some photos to be sure.

Both above problems would be fixed with a output transformer as it will fully balance and float the output.
Joe :-)

JLM Audio

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby ixox » Wed Feb 10, 2016 6:03 pm

Hi Joe,

Thanks for your answer.
Yes my cable from the BA to my audio interface (Saffire 24 DSP) is balanced.
Didn't try to plug the BA in another Input... I'll try tonight my Berhinger AdA8000.
I'll also try to find an output transformer and will check if that fixes the problem.
I can also take a look to try to understand where this noise appear in the audio path.
Anyway thanks, i'll try to post an update later this week.

Xavier

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Postby ixox » Sat Feb 13, 2016 7:40 am

Hi Joe,

Unfortunately no good news : still the electronic/digital noise with the jlm99v.
I tried in another audio interface.. No success.
I added an output transfo... same thing.
(As i read somewhere 0v and +out from the BA to the input of the transfo...)

Reminder : The noise is only present when i use my jlm99v in my BA.
when used with an opa2604, i don't have this noise at all.
My BAD (2 * opa2604) does not have this noise neither.

I attached some pictures.
A sample of the noise sound is here :
https://www.dropbox.com/s/koeaklrt3y754ch/BA.mp3?dl=0

Let me know if you have any idea, else i'll go back with the OPA2604 and enjoy the few additional DB :wink:

Edited, additional info :
. Turning the gain pot modifies at the same time the volume of the noise.
. Modifying the inpug stage (phantom power, PAD, or unplug the mic) has NO impact.

Thanks,

Xavier
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