1290 Build Thread

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Moderator: Joe Malone

htm
Posts: 17
Joined: Sun Jul 20, 2014 6:28 pm

Re: 1290 Build Thread

Post by htm »

htm wrote:
Tue Apr 18, 2017 4:20 pm
Hi Joe

I just ordered my set of 1290 kits and I'm about to order Carnhill input TX.

...

thanks, Hannu
Wow! Three years have passed quickly! Finally I'm back to this project. I have VTB9045 input TX, but I'm not sure about the wiring.
Here's the pdf for the Carnhill: http://www.audiomaintenance.com/downloa ... _guide.pdf

Do I just go like this: (I'm reading the Go between plus taps from left to right as the text "Primary" is the right way up)
Primary
Go between plus -> VTB9045
1 -> 10
2 -> 9
3 -> 8
4 -> 7

Secondary
Go between plus -> VTB9045
1 -> 5
2 -> 4
3 -> 3
4 -> 2

and pin 6 is ground
And I´m guessing the jumpers on the board go as pictured in the Go Between thread, since I´m not using a DI?

Thanks in advance!
Hannu

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Joe Malone
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Re: 1290 Build Thread

Post by Joe Malone »


Do I just go like this: (I'm reading the Go between plus taps from left to right as the text "Primary" is the right way up)
Primary
Go between plus -> VTB9045
1 -> 10
2 -> 9
3 -> 8
4 -> 7

Secondary
Go between plus -> VTB9045
1 -> 5
2 -> 4
3 -> 3
4 -> 2

and pin 6 is ground
And I´m guessing the jumpers on the board go as pictured in the Go Between thread, since I´m not using a DI?
You have the primary and secondary backwards and reversed it looks from the datasheet (which is very lacking in info) Primary is usually drawn on the left which would make

Primary
Go between plus -> VTB9045
1 -> 2+
2 -> 3+
3 -> 4-
4 -> 5-

Secondary
Go between plus -> VTB9045
1 -> 7+
2 -> 8+
3 -> 9-
4 -> 10-

For both input and output ratio fit one jumper to the centre two pins of the four pins. If no DI fit the 2 jumpers into the 10 pin socket as shown on overlay. pin 6 to 0v pad on the pcb.
Joe :-)
JLM Audio
Capturing Audio without Injury

htm
Posts: 17
Joined: Sun Jul 20, 2014 6:28 pm

Re: 1290 Build Thread

Post by htm »

Thank you for the advice Joe! I finished my 2x1290 and it works.
However one channel seems about 10 dB quieter.

I measured input and output connections resistances + to - and both to ground, and both channels are identical. So are the connections at the GoBetween Plus and the input and output transformers. Voltages are set to the same 24V. I couldn't find any shorts to ground in my wiring either. (that was the problem last time). It seems, the problem could be somewhere on the main board.
So is there something (voltages?)I should check, or where should I go from here?

Hannu

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Joe Malone
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Re: 1290 Build Thread

Post by Joe Malone »

htm wrote:
Mon May 18, 2020 7:43 pm
Thank you for the advice Joe! I finished my 2x1290 and it works.
However one channel seems about 10 dB quieter.

I measured input and output connections resistances + to - and both to ground, and both channels are identical. So are the connections at the GoBetween Plus and the input and output transformers. Voltages are set to the same 24V. I couldn't find any shorts to ground in my wiring either. (that was the problem last time). It seems, the problem could be somewhere on the main board.
So is there something (voltages?)I should check, or where should I go from here?

Hannu
HI Hannu
You need to find where the level changes. Set controls the same on both mic pres and output control on full on both. Put in a 1Khz that just doesn't clip the outputs to both channels at the same time. Preferably use one tone generator output via a Y cable to both channels and then check with AC volts multimeter or scope the AC level at input transformer primary and secondary out. Across the output pot and at primary of output transformer and secondary output. Let me know at which point the 2 channels have different levels so I can help. Try this on a minimum gain level first and then one above 50dB. Check both channels do 5dB level steps on the gain switch.
Joe :-)
JLM Audio
Capturing Audio without Injury

htm
Posts: 17
Joined: Sun Jul 20, 2014 6:28 pm

Re: 1290 Build Thread

Post by htm »

Hi Joe.
I got consistent readings with both channels, and it didn't make any sense. I tried different cables and even different inputs on my interface, but the difference was still there. It was driving me nuts until I checked the output jack, that had a loose "hot" connection. (I use jack i/o instead of XLR for convenient connecions to the patchbay.)

So the circuit itself was actually ok the whole time, Phew!

Now, time for beer. Then testing with different mics.

Thank you Joe!

Hannu

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Re: 1290 Build Thread

Post by Joe Malone »

htm wrote:
Fri May 22, 2020 4:44 am
Hi Joe.
I got consistent readings with both channels, and it didn't make any sense. I tried different cables and even different inputs on my interface, but the difference was still there. It was driving me nuts until I checked the output jack, that had a loose "hot" connection. (I use jack i/o instead of XLR for convenient connecions to the patchbay.)

So the circuit itself was actually ok the whole time, Phew!

Now, time for beer. Then testing with different mics.

Thank you Joe!

Hannu
HI Hannu. Cool great to hear you found the problem and it was simple fix :-)
Joe :-)
JLM Audio
Capturing Audio without Injury

joepus
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Joined: Thu Jan 11, 2018 8:06 am

Re: 1290 Build Thread

Post by joepus »

Hey Joe, I have a 1290 project I need some advice with. Testing with a SM7b and my voice, the mic pres starts to fizzle/hum/oscillate at a hi gain stage. I had better luck with an Audia Technica 4033. I wired the input transformers, t1452's like you described in your "Neve transformer info" so I assume that is one issue. I also read the layout might cause interference between components. It would be nice to get the 1290 performance out of these 1272 parts, I have duplicated the tests you have described and I can see and hear the difference. Anyway, let me know what you think.Thanks
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Joe Malone
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Re: 1290 Build Thread

Post by Joe Malone »

joepus wrote:
Tue Jun 09, 2020 6:40 am
Hey Joe, I have a 1290 project I need some advice with. Testing with a SM7b and my voice, the mic pres starts to fizzle/hum/oscillate at a hi gain stage. I had better luck with an Audia Technica 4033. I wired the input transformers, t1452's like you described in your "Neve transformer info" so I assume that is one issue. I also read the layout might cause interference between components. It would be nice to get the 1290 performance out of these 1272 parts, I have duplicated the tests you have described and I can see and hear the difference. Anyway, let me know what you think.Thanks
Are all 4 channels identical problem wise?

Best to email me a audio sample so I can hear and let me know what gain setting the mic pre is on for the sample.

Some photos of one channel inside so i can see all the wiring would be good so I could check it over.
Joe :-)
JLM Audio
Capturing Audio without Injury

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