BA BA2 BA4 BAD Dual99v Build Thread

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htm
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Joined: Sun Jul 20, 2014 6:28 pm

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

Hi!

One more question about the BA. I got all of my four API-type BA:s finished and racked. They sound really good, especially on vocals (a little surprise there). I'm wondering about the gain range though. When using a tube condenser mic, that is plenty loud on other pres, I have to crank the gain all the way up to get a usable level. On drums with dynamic mics I have to go about half the way up. With a ribbon mic I thought I'd had something broken.
Is it just that one gain stage pres are like this, or could there be some kind of impedance issue with the non standard input tx I'm using?

Or should I just get the output transformars...


Thanks, Hannu

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:Hi!

One more question about the BA. I got all of my four API-type BA:s finished and racked. They sound really good, especially on vocals (a little surprise there). I'm wondering about the gain range though. When using a tube condenser mic, that is plenty loud on other pres, I have to crank the gain all the way up to get a usable level. On drums with dynamic mics I have to go about half the way up. With a ribbon mic I thought I'd had something broken.
Is it just that one gain stage pres are like this, or could there be some kind of impedance issue with the non standard input tx I'm using?

Or should I just get the output transformars...


Thanks, Hannu
The output transformer will give you 6dB extra gain. But remind me which input transformers and opamp you are using?

Because depending on the opamp type RGain could be made smaller than 68R to give you more gain.
Joe :-)
JLM Audio
Capturing Audio without Injury

htm
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

Hi

I'm using 1:8 input transformer with JLM25HV. How much smaller could I go from 68R?

- Hannu

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:Hi

I'm using 1:8 input transformer with JLM25HV. How much smaller could I go from 68R?

- Hannu
If the transformer is wired as 1:8 properly and loaded correctly you should have almost 60dB of gain already without adding the output transformer.

What info do you have on the input transformer? If none measure all the winding for dc resistance and let me know the measurements and which winding's are connected to each other etc.
Joe :-)
JLM Audio
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htm
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

The tx's are from an old AKG Tapco 6100 series mixer. No markings on them, and the manual doesn't say much.
"Custom built high nickel alloy"
"Microphone impedance matching 30 to 600 ohms"
"Common mode rejection 105 db"

I wired them the same way they were in the mixer. Three taps on each side.
Primary side: 1 + 3 for signal, 2 N.C.
Secondary : 1 ground, 2 + 3 for signal

I tested them the other way around and tried also the middle tap on the primary. The way mentioned above was the one that worked.
I'll get the multimeter out, when I get home from work and post the measurements.

htm
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

Ok. Here we go. I hade a spare one to test.

Primaries
1+2 is 12,2 ohm
2+3 is 12,2 ohm
1+3 is 19,2 ohm

Secondaries
1+2 is 83,5 ohm
2+3 is 83,5 ohm
1+3 is 3,3 ohm

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:Ok. Here we go. I hade a spare one to test.

Primaries
1+2 is 12,2 ohm
2+3 is 12,2 ohm
1+3 is 19,2 ohm

Secondaries
1+2 is 83,5 ohm
2+3 is 83,5 ohm
1+3 is 3,3 ohm
Something strange about the secondary 1+ 3 = 3.3ohms ? Should be 169ohms?? Can you check that is correct or not?
Joe :-)
JLM Audio
Capturing Audio without Injury

htm
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

It thought it was weird too, but I checked, and its 3,3

I took another one I had lying around an it reads:
8,5 + 8,5 /15,5 primary
80,5 + 80,5/2,3 secondary

i changed the multimeter battery and the readings are the same +/- 2 ohm

the earlier reads about the same with the new battery

If you want to look at the 6100 mixer schematic, its here:

https://www.google.co.uk/url?sa=t&rct=j ... 2846,d.ZWU

The input schematic is on page 13


Should I just get AE2622's from classicapi or can I get more gain out of these? I kinda wanted tu use them.

- Hannu

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:It thought it was weird too, but I checked, and its 3,3

I took another one I had lying around an it reads:
8,5 + 8,5 /15,5 primary
80,5 + 80,5/2,3 secondary

i changed the multimeter battery and the readings are the same +/- 2 ohm

the earlier reads about the same with the new battery

If you want to look at the 6100 mixer schematic, its here:

https://www.google.co.uk/url?sa=t&rct=j ... 2846,d.ZWU

The input schematic is on page 13


Should I just get AE2622's from classicapi or can I get more gain out of these? I kinda wanted tu use them.

- Hannu
Yes the transformer only gives 6db so is only 1:2 ratio which why you have low gain
Joe :-)
JLM Audio
Capturing Audio without Injury

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Joe Malone
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:It thought it was weird too, but I checked, and its 3,3

I took another one I had lying around an it reads:
8,5 + 8,5 /15,5 primary
80,5 + 80,5/2,3 secondary

i changed the multimeter battery and the readings are the same +/- 2 ohm

the earlier reads about the same with the new battery

If you want to look at the 6100 mixer schematic, its here:

https://www.google.co.uk/url?sa=t&rct=j ... 2846,d.ZWU

The input schematic is on page 13


Should I just get AE2622's from classicapi or can I get more gain out of these? I kinda wanted tu use them.

- Hannu
manual says the transformer only gives 6db so is only 1:2 ratio which why you have low gain
Joe :-)
JLM Audio
Capturing Audio without Injury

htm
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Joined: Sun Jul 20, 2014 6:28 pm

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by htm »

Darn. I must have missed that. Seems that I have to get new ones.

Thank you so much for the quick answers.

- Hannu

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

htm wrote:Darn. I must have missed that. Seems that I have to get new ones.

Thank you so much for the quick answers.

- Hannu
Since the input transformer is so low you should be able to make RGain maybe as small as 10R which would give you about 15dB extra gain. Just need to try it and see if you any oscillation or not.

Also this transformer would need Rload 10k or variable impedance 2k2 in seres with 50k log pot. If you have variable impedance the oscillation is most likely to happen at high impedance.

Also Cload of 220pF to 440pF maybe needed if you get oscillation to stop it.
Joe :-)
JLM Audio
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Dais3
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Dais3 »

Hi Joe
Would it be possible to use an LL1528 instead of the LL1538 for the BA? Just because I have a couple of LL1528s lying around.
Many thanks
Dave

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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

Dais3 wrote:Hi Joe
Would it be possible to use an LL1528 instead of the LL1538 for the BA? Just because I have a couple of LL1528s lying around.
Many thanks
Dave
You can use the LL1528 but its pinout doesn't line up on the PCB so would have to be wired to the PCB. The four input pins do line up but the rest do not.
Joe :-)
JLM Audio
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mikeyb
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by mikeyb »

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?

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