[r2d2]

hey
about the 48v led  (pdf making guide v4)
it is 5 or 2 volt?
then the 3k9 resistor value
depend from the led voltage ?

the 24-48v power supply need to have some chassis-case ground connection?
peace
(all over)

[Siegfried Meier]

Hey guys,

I have a dual channel 1290 here that has one channel humming and has a thin output, no low end.  I've built up a number of these, but have never encountered something like this.  I've scoured the thing for hours on end, checked solder joints etc.  Any clue where to look for what might be wrong?

Thanks!
Sig

[herrmann]

Try to swap input transformer.

[ilfungo]

Excuse me
how can I add  clipping indicator  on preamp?
Thanks

[adam1176]

I'm putting together my psu and I just read something that I need clarification on. Do I need to insulate the voltage regs from the psu case? I read something about using the rubber adhesive between the regs and the case and using a nylon standoff. If that is the case, do i even need to screw the regs to the case at all? If it's secure then do i need to bother with that? Or did i get it all wrong and I'm just supposed to screw the regs directly to the psu case?

[adam1176]

and can/should I use mic cable for the run from the ground on the outlet to the case and pcb?

[snipsnip]

yes you need to isolate them, otherwise you will cause a short.

You need to attach them to the case so it can act as a heatsink, otherwise they will shut down.

[Chrome Heart]

I'm putting together my psu and I just read something that I need clarification on. Do I need to insulate the voltage regs from the psu case? I read something about using the rubber adhesive between the regs and the case and using a nylon standoff. If that is the case, do i even need to screw the regs to the case at all? If it's secure then do i need to bother with that? Or did i get it all wrong and I'm just supposed to screw the regs directly to the psu case?

Yes. Definitely insulate them from the case, otherwise, fireworks. Or you can heatsink them inside the PSU with stand alone heatsinks. I did that in mine and it works fine

[Chrome Heart]

and can/should I use mic cable for the run from the ground on the outlet to the case and pcb?

If you mean inside the PSU case, I dont see a reason for that.

[beatnik]

Hi there,

I'm building a two channel EZ1290. Being oscillation problems very usual, I want to be very careful about placement of the transformers and the internal layout.

I attached a picture with some notes to show you my actual idea, but want to ask your opinion before starting to drill the chassis.
Please don't mind channel two, and its input transformer position, and its xlr mounting wooden piece  it was mounted in a testing case.
The reference layout is shown on channel 1.

I have read that one important thing is to mount the audio transformers far from each other. Being my chassis quite tight, it's not easy.

Then, I tried to keep the unbalanced connections (from input transformer to pcb and from pcb to out transf) as short as possible.

One of the doubts I have, is if the output transformers too close to in/out xlr can cause noise problems.

About the power supply section, I really don't like the idea of mounting it in an external case. I know it's better for hum problems, but i thinked that a similar result regarding isolation/shielding could be mounting a piece of alluminium inside the case (connected to ground), to separate and shield the power supply section from the audio circuitry. What do you think about this?

Any input is highly appreciated, thanks in advance.

[briomusic]

Hi there,

I'm building a two channel EZ1290. Being oscillation problems very usual, I want to be very careful about placement of the transformers and the internal layout.

I attached a picture with some notes to show you my actual idea, but want to ask your opinion before starting to drill the chassis.
Please don't mind channel two, and its input transformer position, and its xlr mounting wooden piece  it was mounted in a testing case.
The reference layout is shown on channel 1.

I have read that one important thing is to mount the audio transformers far from each other. Being my chassis quite tight, it's not easy.

Then, I tried to keep the unbalanced connections (from input transformer to pcb and from pcb to out transf) as short as possible.

One of the doubts I have, is if the output transformers too close to in/out xlr can cause noise problems.

About the power supply section, I really don't like the idea of mounting it in an external case. I know it's better for hum problems, but i thinked that a similar result regarding isolation/shielding could be mounting a piece of alluminium inside the case (connected to ground), to separate and shield the power supply section from the audio circuitry. What do you think about this?

Any input is highly appreciated, thanks in advance.

Looks good to me, I have a similar layout and not even a shield from the PSU - no hum problems here.

[erikb1971]

Hi all

Iam soldering the parts on my EZ1290 at this moment but I have run into a little problem:

I did not recieve R56 (resistor 12 Ohm 1W). But I got two extra R98 (resistor 10 Ohm 1W).

Can I use the 12 Ohm in place of the 10 Ohm?

Tnx

Erik

[DIY-solder]

I have a question regarding adding the TRIM pot described here http://s3.amazonaws.com/EZ1290/trimmer_v2.3.pdf

If I understand this correctly one can lower the 10K resister value to get the same effect as if using a 10K log pot, right?

For a test I used a rotary and tried 10K vs 100R to see if this was right. I discovered that only low end under 100Hz to my ear
was lowered when I switched to 100R. It worked as a HPF not as volume TRIMMER. Anyone has any idea why?

Another question is, is this trimmer effecting the input or the output stage?

[MagnetoSound]

I have a question regarding adding the TRIM pot described here http://s3.amazonaws.com/EZ1290/trimmer_v2.3.pdf

If I understand this correctly one can lower the 10K resister value to get the same effect as if using a 10K log pot, right?

Probably a question for Martin (my experience is with the actual Neve stuff, not the EZ1290 build), but I would say no. It looks to me like the 10k resistor was put there just to give the second gain stage some moderate loading. A pot is a voltage divider - ie two resistors in series with the signal taken from the node in between. You might want to read here for some insight on how the original circuit was intended to work.

For a test I used a rotary and tried 10K vs 100R to see if this was right. I discovered that only low end under 100Hz to my ear
was lowered when I switched to 100R. It worked as a HPF not as volume TRIMMER. Anyone has any idea why?

Yes, there is a blocking cap at the output of the second gain stage. The resistor loading this stage forms a high-pass filter with this cap. By reducing the resistance you are raising the cutoff point of this filter into the audio band. The stock value for the trimmer is designed for a reason - ie the cutoff point of the filter should be well out of the way of the audio passing through it.

Neve had a 5k pot in this position. 10k is marginally easier to source and is fine. You might get away with 1k (never tried it). Too low and you lose the bottom end.

Another question is, is this trimmer effecting the input or the output stage?

It is bridging the two stages. Specifically, it is attenuating the signal at the input of the output stage.

Hope this helps. 

[DIY-solder]

Probably a question for Martin (my experience is with the actual Neve stuff, not the EZ1290 build), but I would say no. It looks to me like the 10k resistor was put there just to give the second gain stage some moderate loading. A pot is a voltage divider - ie two resistors in series with the signal taken from the node in between.

This explains my result. I basically just switched the 10K as it is with the 100R and this doesn't work the same as using the pot. Looks like different wiring is needed if one wants to use rotary switch with resistors instead of the pot. Maybe I'll just go with the pot or leave fake knobs in the place for the trimpot.

Thanks for the help.

[DIY-solder]

One more question.

I wired my unit with Marinair L31267 on the input, wired as explained in the JLM webpage. Would I gain anything if using the recommended 10468?   

[desol]

Less chance of noise.

[DIY-solder]

Less chance of noise.

OK, but no sound difference. I thought so...   

[DIY-solder]

Here is a link to a nice 10K log, if anyone needs it  http://uk.farnell.com/vishay-sfernice/p11s1v0flsy00103kl/potentiometer-10k-log/dp/1141610

[MRecords]

Happy new Year to all 

I wrote colin yesterday about the difference between the VTB9045 and the VTB9045M. He wrote back but i just got an failure mail telling me his ID was blocked. Can someone explain me the difference between this two?  I don´t think there is a difference soundwise and they cost the same. So would it be better to go with the Mu version?

Thanks

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