1290 Build Thread

Support for JLM Audio Kits

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

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

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

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

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

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

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
Posts: 3
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
You do not have the required permissions to view the files attached to this post.

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

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

LosinPwdr
Posts: 3
Joined: Wed Jan 19, 2022 12:58 am

Re: 1290 Build Thread

Post by LosinPwdr »

Hello. First post. Looking for some help regarding a second hand 1290 I bought with some issues.

Basically, thing are functioning Ok , however one channel is a couple of Db quieter than the other and it also has faint white noise in the background.The volume also appears to be slowly fluctuating ever so slightly in a cyclical manner.

Just wondering if anyone has any ideas.

I have swapped over the Micro PCB (The one which has the gain pot) and the problem follows it. So I'm guessing the issue is in this part.

I have done a little A/B ing between the good and bad pcb and the only thing I have found so far is that the 820R cap is reading 789R ...... The other PCB give a reading of 820R. I have swapped this cap out but the problem remains.

I am a little bit nervous about doing much more as I do not want to damage something that is working ok.

Any help from you guys would be great.

Thnx!

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: 1290 Build Thread

Post by Joe Malone »

LosinPwdr wrote:
Wed Jan 19, 2022 7:54 pm
Hello. First post. Looking for some help regarding a second hand 1290 I bought with some issues.

Basically, thing are functioning Ok , however one channel is a couple of Db quieter than the other and it also has faint white noise in the background.The volume also appears to be slowly fluctuating ever so slightly in a cyclical manner.

Just wondering if anyone has any ideas.

I have swapped over the Micro PCB (The one which has the gain pot) and the problem follows it. So I'm guessing the issue is in this part.

I have done a little A/B ing between the good and bad pcb and the only thing I have found so far is that the 820R cap is reading 789R ...... The other PCB give a reading of 820R. I have swapped this cap out but the problem remains.

I am a little bit nervous about doing much more as I do not want to damage something that is working ok.

Any help from you guys would be great.

Thnx!
Are the gains the same as minimum gain and change at some point in the gain switch stages?

Same for the noise is it the same at minimum gain and change at some point in the gain switch stages?

Not sure what 820R cap you mean as 820R would normally be a resistor?
Joe :-)
JLM Audio
Capturing Audio without Injury

LosinPwdr
Posts: 3
Joined: Wed Jan 19, 2022 12:58 am

Re: 1290 Build Thread

Post by LosinPwdr »

Joe Malone wrote:
Wed Jan 26, 2022 5:29 pm
LosinPwdr wrote:
Wed Jan 19, 2022 7:54 pm
Hello. First post. Looking for some help regarding a second hand 1290 I bought with some issues.

Basically, thing are functioning Ok , however one channel is a couple of Db quieter than the other and it also has faint white noise in the background.The volume also appears to be slowly fluctuating ever so slightly in a cyclical manner.

Just wondering if anyone has any ideas.

I have swapped over the Micro PCB (The one which has the gain pot) and the problem follows it. So I'm guessing the issue is in this part.

I have done a little A/B ing between the good and bad pcb and the only thing I have found so far is that the 820R cap is reading 789R ...... The other PCB give a reading of 820R. I have swapped this cap out but the problem remains.

I am a little bit nervous about doing much more as I do not want to damage something that is working ok.

Any help from you guys would be great.

Thnx!
Are the gains the same as minimum gain and change at some point in the gain switch stages?

Same for the noise is it the same at minimum gain and change at some point in the gain switch stages?

Not sure what 820R cap you mean as 820R would normally be a resistor?
Hi!

The db difference is consistently present at minimum gain and throughout all gain stages. It's always a bit quieter. Same goes for the noise. It's not something that kicks in beyond a certain point.

Sorry, I meant the 820R resistor yes.

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: 1290 Build Thread

Post by Joe Malone »

LosinPwdr wrote:
Thu Jan 27, 2022 6:23 am
Joe Malone wrote:
Wed Jan 26, 2022 5:29 pm
LosinPwdr wrote:
Wed Jan 19, 2022 7:54 pm
Hello. First post. Looking for some help regarding a second hand 1290 I bought with some issues.

Basically, thing are functioning Ok , however one channel is a couple of Db quieter than the other and it also has faint white noise in the background.The volume also appears to be slowly fluctuating ever so slightly in a cyclical manner.

Just wondering if anyone has any ideas.

I have swapped over the Micro PCB (The one which has the gain pot) and the problem follows it. So I'm guessing the issue is in this part.

I have done a little A/B ing between the good and bad pcb and the only thing I have found so far is that the 820R cap is reading 789R ...... The other PCB give a reading of 820R. I have swapped this cap out but the problem remains.

I am a little bit nervous about doing much more as I do not want to damage something that is working ok.

Any help from you guys would be great.

Thnx!
Are the gains the same as minimum gain and change at some point in the gain switch stages?

Same for the noise is it the same at minimum gain and change at some point in the gain switch stages?

Not sure what 820R cap you mean as 820R would normally be a resistor?
Hi!

The db difference is consistently present at minimum gain and throughout all gain stages. It's always a bit quieter. Same goes for the noise. It's not something that kicks in beyond a certain point.

Sorry, I meant the 820R resistor yes.
Does that channel click or pop while switching gain steps. The 470uF cap on the BAX83NV occasionally become leaky causing pops.
Joe :-)
JLM Audio
Capturing Audio without Injury

LosinPwdr
Posts: 3
Joined: Wed Jan 19, 2022 12:58 am

Re: 1290 Build Thread

Post by LosinPwdr »

Joe Malone wrote:
Thu Jan 27, 2022 7:33 am
LosinPwdr wrote:
Thu Jan 27, 2022 6:23 am
Joe Malone wrote:
Wed Jan 26, 2022 5:29 pm


Are the gains the same as minimum gain and change at some point in the gain switch stages?

Same for the noise is it the same at minimum gain and change at some point in the gain switch stages?

Not sure what 820R cap you mean as 820R would normally be a resistor?
Hi!

The db difference is consistently present at minimum gain and throughout all gain stages. It's always a bit quieter. Same goes for the noise. It's not something that kicks in beyond a certain point.

Sorry, I meant the 820R resistor yes.
Does that channel click or pop while switching gain steps. The 470uF cap on the BAX83NV occasionally become leaky causing pops.
No. No pops at all. Only the symptoms I mentioned previously. It seems like it must be something pretty small because the faulty channel is only slightly quieter and the noise is not super audible either.

Are there any parts on the mini pcb that would cause noise and gain loss ? Maybe a capacitor or one of the opamps ? I read someone previously had an issue on the DI (my DI's are fine although they are also affected when the faulty mini pcb is connected) due to an opamp- Maybe that's where I should be looking ??

User avatar
Joe Malone
Site Admin
Posts: 1823
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: 1290 Build Thread

Post by Joe Malone »

LosinPwdr wrote:
Thu Jan 27, 2022 11:38 pm
Joe Malone wrote:
Thu Jan 27, 2022 7:33 am
LosinPwdr wrote:
Thu Jan 27, 2022 6:23 am


Hi!

The db difference is consistently present at minimum gain and throughout all gain stages. It's always a bit quieter. Same goes for the noise. It's not something that kicks in beyond a certain point.

Sorry, I meant the 820R resistor yes.
Does that channel click or pop while switching gain steps. The 470uF cap on the BAX83NV occasionally become leaky causing pops.
No. No pops at all. Only the symptoms I mentioned previously. It seems like it must be something pretty small because the faulty channel is only slightly quieter and the noise is not super audible either.

Are there any parts on the mini pcb that would cause noise and gain loss ? Maybe a capacitor or one of the opamps ? I read someone previously had an issue on the DI (my DI's are fine although they are also affected when the faulty mini pcb is connected) due to an opamp- Maybe that's where I should be looking ??
Check the audio level at the output pots between outside pins with pot pulled out full CW and a AC meter and a 500Hz or 1khz tone. If the voltages are different then it is the preamp section. If they are the same it is the output amp and / or transformer.
Joe :-)
JLM Audio
Capturing Audio without Injury

Post Reply