BA BA2 BA4 BAD Dual99v Build Thread

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ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe, underside of the PCM attached. When I say insert, I mean when I place the 2520 into the opamp slot
On the pcb the power supply goes into hiccup mode.

If I have three channels running all good. When I have all four channels running I have problems. However I have placed a
Working opamp from one of the other channels in this channel and I had sound, but when I add a newly built 2520 to this channel and have all 4 channels running there is an issue. Hope this is a little clearer. :)

Thanks so much for your help.
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ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

I'm not sure the other picture was that great for checking for shorts. This one should be better. :)

Thanks AJ
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

Looks ok to me. Could do with a bit of alcohol and old toothbrush cleaning to remove the flux residue.

Black wiring is blocking some of the solder joints. Also not sure why you think you need to have the black wire there? As both points should already be ground.

What power supply have you got to run the 4 of these BA PCBs. The 48v 40W one?

You can measure the voltage across the 10R resistor on each BA PCB to check the current each module is drawing.
Joe :-)
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ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

I read somewhere on the forum that the EA2623 needed to be wired to the ground at the 0V on the PCB so the internal shields worked properly. Obviously misinterpreted the post. I will remove it. I guess the 0V just behind the secondary is the one, not 0V at the back of the PCB.

Yes I have the 48V 40W power supply.

Voltages across the 10r as follows;

Channel 1: 0.413V
Channel 2: 0.426V
Channel 3: 26mV ?????
Channel 4: 0.414V

Should I upload another picture without the black wire?

Thanks for your help. :)
AJ

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

ajsteel wrote:Hi Joe,

I read somewhere on the forum that the EA2623 needed to be wired to the ground at the 0V on the PCB so the internal shields worked properly. Obviously misinterpreted the post. I will remove it. I guess the 0V just behind the secondary is the one, not 0V at the back of the PCB.

Yes I have the 48V 40W power supply.

Voltages across the 10r as follows;

Channel 1: 0.413V
Channel 2: 0.426V
Channel 3: 26mV ?????
Channel 4: 0.414V

Should I upload another picture without the black wire?

Thanks for your help. :)
AJ
Looks like channel 3 isn't drawing any current? Does it have the opamp plugged in? Does the 10R measure 10R? With the opamp in do you get the correct voltage at +V pin?
Joe :-)
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ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

I plugged an OPAMP in that works and got 38V at +V, I then plugged in the new OPAMP I built and the power supply went into hiccup mode even though only three had OPAMPS were in three channels. I think it may be the OPAMP and not the BA Circut. I plugged suspect OPAMP into a working channel and the power supply went into hiccup mode again. I am building another OPAMP now and will see what happens.

Thanks
AJ

ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

I built a new 2520 and I think it's definitely my OPAMP building. This one didn't work in a working channel. The power went in hiccup mode again when the OPAMP was in this working channel. But, when I placed a working OPAMP in Channel 3(not working I thought) I get clean signal as before. I assume is definitely my opamp. I might buy a pre built and tested OPAMP and plug that into my channel 3 and see what happens. If I'm right everything should work fine.

Will I need to make any adjustments to my BA Channel which is set up for a GAR 2520 if I use your 2520 OPAMP?

A.J. :)

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

ajsteel wrote:Hi Joe,

I built a new 2520 and I think it's definitely my OPAMP building. This one didn't work in a working channel. The power went in hiccup mode again when the OPAMP was in this working channel. But, when I placed a working OPAMP in Channel 3(not working I thought) I get clean signal as before. I assume is definitely my opamp. I might buy a pre built and tested OPAMP and plug that into my channel 3 and see what happens. If I'm right everything should work fine.

Will I need to make any adjustments to my BA Channel which is set up for a GAR 2520 if I use your 2520 OPAMP?

A.J. :)
Sounds like a dead GAR 2520 opamp then. Our JLM25HV will plug straight in and work without changes. But if you remove the zener the JLM25HV can also run on the full 48v (+/-24v)
Joe :-)
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ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

All fixed! :) You'll never guess what, I was checking my GAR2520 assembly instructions and saw that two transistors were in the wrong positions. I swapped them over and everything works. All four channels, no power issues, clean gain and quiet operation. I now have two spare 2520's. Cool. :) May have to build some more API flavour pre's!

Thanks for all your help.

A.J.

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

ajsteel wrote:Hi Joe,

All fixed! :) You'll never guess what, I was checking my GAR2520 assembly instructions and saw that two transistors were in the wrong positions. I swapped them over and everything works. All four channels, no power issues, clean gain and quiet operation. I now have two spare 2520's. Cool. :) May have to build some more API flavour pre's!

Thanks for all your help.

A.J.
That would do it. Good to hear you got all the mic pres going :D 8)
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tazwolf
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by tazwolf »

Hi
Iam building a BA using a beyer 1:10 input transformer and a Freed 32035 600:600 output tranformer, opamp is a jlm hybrid..
i wanted to add an output attenuator after the output transformer.

I found this schematic for an input attenuator
http://www.jlmaudio.com/PAD.gif

which looks cool but it is an input attenuator so i was wondering if it would work as an output attenuator as well?
I assume that as an input attenuator the resistor values are chosen for attenuation of a mic (150ohms?) to
mic pre input (1500ohms?) but when I try to confirm this using the many attenuation calculators on the web
i dont get the same values as the ones on the schematic.

So my question is

can I use the schematic for line level attenuation, 600:600?
How do I calculate the resistor values?
Does it make a difference if sometimes the mic pre will go straight into my audio interface (10k) but sometimes into an
eq or compressor (600ohm) before going into the audio interface.

Grateful for any help.

regards
/Taz

ajsteel
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ajsteel »

Hi Joe,

I was wondering if you could tell me how I can test the Output voltages on the BA Mic pres so I can be sure there all on par. They all seem to be working well but I'm not convinced channel 3 is giving me the truth. When I measured between the 0V and the output on each channel with the unit on and gain full I got 0.2mv at the output to the transformer?

Thanks
A.J.

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

tazwolf wrote:Hi
Iam building a BA using a beyer 1:10 input transformer and a Freed 32035 600:600 output tranformer, opamp is a jlm hybrid..
i wanted to add an output attenuator after the output transformer.

I found this schematic for an input attenuator
http://www.jlmaudio.com/PAD.gif

which looks cool but it is an input attenuator so i was wondering if it would work as an output attenuator as well?
I assume that as an input attenuator the resistor values are chosen for attenuation of a mic (150ohms?) to
mic pre input (1500ohms?) but when I try to confirm this using the many attenuation calculators on the web
i dont get the same values as the ones on the schematic.

So my question is

can I use the schematic for line level attenuation, 600:600?
How do I calculate the resistor values?
Does it make a difference if sometimes the mic pre will go straight into my audio interface (10k) but sometimes into an
eq or compressor (600ohm) before going into the audio interface.

Grateful for any help.

regards
/Taz
Best to only allow a set amount of dB atten on the output as you are removing the headroom of the BA output so driving gain harder will just result in clipping on the BA output.
The below 2 ways are the best if you want a output atten pad on a BA or BAN.

ImageImage
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Joe Malone
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

ajsteel wrote:Hi Joe,

I was wondering if you could tell me how I can test the Output voltages on the BA Mic pres so I can be sure there all on par. They all seem to be working well but I'm not convinced channel 3 is giving me the truth. When I measured between the 0V and the output on each channel with the unit on and gain full I got 0.2mv at the output to the transformer?

Thanks
A.J.
No DC can get to the output transformer as there is a isolating capacitor between the opamp output and output transformer.

+in and -in and out on the opamp should all be sitting around half of the power rail at the opamp +V pin.
Joe :-)
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tazwolf
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by tazwolf »

On the groupdiy mega thread there was this posting by Dirk666.


Do you fit a jumper across amp BA PCB pins (4-7) when using a hybrid for the baby animal with the jlm 1:1:1 output tran?


Joe said on page 25;
‘WHEN USING HYBRID WITH BA PCB, LEAVE OFF the 47uF cap which is on the opposite side of the PCB to the LED. As this can override the power supply filtering and let noise into the pre.’

I could not find the answer to these questions so I was wondering if someone here could help.

I am getting buzz/oscillation at 500hz on mine and am wondering if these coul dbe the cause.

Regards
/Taz

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