8 Channel, 3U NEVE 1073 completed

[madriaanse]

Thanks for the tips on transformer placement and shielding Mr. Whoops! I should add those to the FAQ!

M.

 

[Whoops]

Thank you for this project Martin!

It's a really well designed and conceived Board.

 

[phelar]

Hi!
My output transformer is singing :-\ I hear the 1khz in the transformer at low gain settings. With 2,2ppv from the function generator i can hear it at the 20db step and getting real evil at higher gain settings.
Need some help...

 

[madriaanse]

Hi!
My output transformer is singing :-\ I hear the 1khz in the transformer at low gain settings. With 2,2ppv from the function generator i can hear it at the 20db step and getting real evil at higher gain settings.
Need some help...

Completely normal. No worries.

 

[phelar]

Here is another screen dump. 1khz 0,1Vpp on the input at max gain.
This is how it looks on the output. The bias trim doesnt respond at all btw.

This cant be normal..

 

[Harpo]

Here is another screen dump. 1khz 0,1Vpp on the input at max gain.
This is how it looks on the output. The bias trim doesnt respond at all btw.

This cant be normal..

??? Just do the math for 0.1Vpp input * 70dB gain (=factor 3162, giving more than your local AC mains voltage). Thankfully your power supply set the 24V upper limit, else your connected gear/converters would already be toast.

 

[phelar]

:-\ Ok, my function generator does 0.1Vpp minimum. So i have to get a new function generator or a voltage divider to bias this preamp?

 

[madriaanse]

If you have a DI box you should be good to go.

EDIT: or use less input gain on the mic pre.

 

[North]

Mine looks pretty much the same on my Goldstar scope. I had wondered about this too.

 

[madriaanse]

I should add that you want to adjust bias at a level where the preamp is barely starting to show clipping on one side of the waveform. You won't accomplish anything by trying to do this when the mic pre is heavily overdriven - as shown in the pictures above.

 

[phelar]

Thanks!

 

[phelar]

Is this a properly biased preamp?

 

[Whoops]

Is this a properly biased preamp?

I would say it looks Good!

 

[madriaanse]

Is this a properly biased preamp?

I would say it looks Good!

Me too. Congrats!

 

[phelar]

Is this a properly biased preamp?

I would say it looks Good!

Me too. Congrats!

I say thanks!
(Made a 40db pad and 200ohm load of a xlr and some resistors)

 

[mtw]

Hi Folks - I'm in need of some assistance getting the grounding / PSU hookups correct.

I am using a FiveFish 1848 PSU (http://www.fivefish.net/diy/PSU1848/pdf/PSU-1848AssemblyGuide.pdf) to power 2 channels.  The 1848 has indeed been updated to produce 24v.

When I connect the 0v pad to the GND pads of the PSU, I get 24v at the +24v pad.  Cool.

However, this means that there is no connection from the 0v pad to chassis ground, so when I measure the resistance from chassis to 0v, I don't get 10ohms (I get something in the MOhm range).  Not so cool.

When I connect the 0v pad to the chassis star ground (using a 10Ohm resistor) I don't get any voltage at the +24v pad.  Definitely not cool at all.

So, I have I chosen the wrong power supply?  Is there a way to make this work?

Could I run leads from 0v to PSU GND and 0v to chassis ground with 10Ohm resistors?

 

[Whoops]

Hi Folks - I'm in need of some assistance getting the grounding / PSU hookups correct.

I am using a FiveFish 1848 PSU (http://www.fivefish.net/diy/PSU1848/pdf/PSU-1848AssemblyGuide.pdf) to power 2 channels.  The 1848 has indeed been updated to produce 24v.

When I connect the 0v pad to the GND pads of the PSU, I get 24v at the +24v pad.  Cool.

However, this means that there is no connection from the 0v pad to chassis ground, so when I measure the resistance from chassis to 0v, I don't get 10ohms (I get something in the MOhm range).  Not so cool.

When I connect the 0v pad to the chassis star ground (using a 10Ohm resistor) I don't get any voltage at the +24v pad.  Definitely not cool at all.

So, I have I chosen the wrong power supply?  Is there a way to make this work?

Could I run leads from 0v to PSU GND and 0v to chassis ground with 10Ohm resistors?

I don't think you've chosen the wrong PSU, You need +24V at aprox 1 Amp for 2 channels, so that PSU should work fine

Isn't the 0V the same as the PSU GND?

Do you have the PSU bolted to the case with metal standoffs? make sure there's no short circuit there

It would be easier to troubleshoot if you draw your ground connections layout and show us

 

[mtw]

Hi Folks - I'm in need of some assistance getting the grounding / PSU hookups correct.

I am using a FiveFish 1848 PSU (http://www.fivefish.net/diy/PSU1848/pdf/PSU-1848AssemblyGuide.pdf) to power 2 channels.  The 1848 has indeed been updated to produce 24v.

When I connect the 0v pad to the GND pads of the PSU, I get 24v at the +24v pad.  Cool.

However, this means that there is no connection from the 0v pad to chassis ground, so when I measure the resistance from chassis to 0v, I don't get 10ohms (I get something in the MOhm range).  Not so cool.

When I connect the 0v pad to the chassis star ground (using a 10Ohm resistor) I don't get any voltage at the +24v pad.  Definitely not cool at all.

So, I have I chosen the wrong power supply?  Is there a way to make this work?

Could I run leads from 0v to PSU GND and 0v to chassis ground with 10Ohm resistors?

I don't think you've chosen the wrong PSU, You need +24V at aprox 1 Amp for 2 channels, so that PSU should work fine

Isn't the 0V the same as the PSU GND?

Do you have the PSU bolted to the case with metal standoffs? make sure there's no short circuit there

It would be easier to troubleshoot if you draw your ground connections layout and show us

Hi Whoops - thanks for the reply!  I do have the PSU bolted to the chassis with metal standoffs.  I'll work on drawing out the ground connections.  (I don't know how to correctly draw schematics, so I'll do my best with a descriptive drawing.)

 

[Whoops]

[/quote]

Hi Whoops - thanks for the reply!  I do have the PSU bolted to the chassis with metal standoffs.  I'll work on drawing out the ground connections.  (I don't know how to correctly draw schematics, so I'll do my best with a descriptive drawing.)
[/quote]

Just a simple drawing with lines and notes is fine.

Unsrew the PSU PCB from the case and put some non conductive thing underneath it, like a card.

Check again the connection of the PSU GND to the Chassis through a 10ohms resistor, or for the sake of testing you dont have need a ny resistor just connect direct.

Sometimes metal standoff touch a component in the PCB under the board itself and then you have a short.

 

[madriaanse]

Sounds like perhaps your voltage regulator (LM317) is shorting to the chassis. If so, consider giving the regulator its own heatsink and insulating it from chassis.

M.