EZ Tube Mixer Support Thread

[Mike Cleaver]

Clean power supplies and grounding have always been a main concern in high end electronics.
We always used similar grounding bars to the one Holger is using in our radio station racks, connected to a very large grounding cable or thick flat copper strap that ran into every operational room in the station and then to a very solid main ground point.
Some of today's switching power supplies are indeed very quiet, others, not so much

 

[anjing]

How much of an effect on noise do unused windings on my torroidal have? I have 1x250v and 2x6.5 volts that i don't use and that are terminated with heat shrink. It's seems that by cleaning up my power supply cabling i have somehow woken up the 125hz hum i have been fighting with a few months back.

 

[ruffrecords]

How much of an effect on noise do unused windings on my torroidal have? I have 1x250v and 2x6.5 volts that i don't use and that are terminated with heat shrink. It's seems that by cleaning up my power supply cabling i have somehow woken up the 125hz hum i have been fighting with a few months back.

Assuming the mixer is remote from the PSU then I would not expect unused windings to cause a problem.

Cheers

Ian

 

[anjing]

Thanks Ian

 

[anjing]

I think one capacitor has gone bad in my HT350. It's 2 hours  since i turned off my power supply and i still have 160V at the positive leg of the last capacitor...
Forget my post, there was no card plugged in so nothing to drain the caps...

 

[ruffrecords]

I think one capacitor has gone bad in my HT350. It's 2 hours  since i turned off my power supply and i still have 160V at the positive leg of the last capacitor...
Forget my post, there was no card plugged in so nothing to drain the caps...

There's only the heater elevation pot divider to discharge those caps is there's no boards plugged in so it will hold up for a long time. If you check out my demo mixer blog you will see I have changed the values of the heater elevation pot divider in that mixer. I changed the 75K to 22K 0.5W type and replaced the 220K with two 33K 1W resistors in series. The lower resistance values mean the current is higher which is why higher wattage types are needed. The higher current also means the HT get discharged more quickly.

Cheers

Ian

 

[anjing]

Ok Ian, i will change those resistors....turns out i have a real problem, looks like the currents does not flow trough the HT350 anymore. When i tried a power up last night i read nothing at the different output points of the pcb. I tough i'd leave it off and redo all the solder joints this morning but i still have 270V at the positive of the first cap. I did check the resistor values and continuity last night and it seemed all right. What could be the problem? Do you have a trick to drain that left over current? Could i connect a resistor from the point were i have the current the other leg of the 75k

Thanks in advance Ian!

Pierre

 

[anjing]

Problem fixed! When i cleaned up the power supply i moved things around and one of the resistor was knocked a bit and it created a cold joint.

 

[anjing]

Good progress, Pierre.

I've reconceived my grounding scheme and I'm using a Rittal grounding bar as star ground now. I furthermore found that my 12V for relay switching adds too much noise, I need a new solution here.
So currently I only have post fader direct outputs because I removed the 12V rail.
I've improved my noise floor numbers. Direct out (post fader/EQ) of the channels are at -87 dBU. The best is my L/R master out:  -87 dBu when feeding my two channels to the stereo bus (fader set to 6 dBU output level position when signal is applied).
That's 7 dB less noise compared to my old grounding scheme. I'm confident now that it is possible to build a bigger mixer.

Hi holger would you mind giving more details about your grounding scheme?

 

[ruffrecords]

Ok Ian, i will change those resistors....turns out i have a real problem, looks like the currents does not flow trough the HT350 anymore. When i tried a power up last night i read nothing at the different output points of the pcb. I tough i'd leave it off and redo all the solder joints this morning but i still have 270V at the positive of the first cap. I did check the resistor values and continuity last night and it seemed all right. What could be the problem? Do you have a trick to drain that left over current? Could i connect a resistor from the point were i have the current the other leg of the 75k

Thanks in advance Ian!

Pierre

As a short term measure you could tack a resistor across each of the capacitors on the underside of the PCB so they have their own discharge path. A 330K 0.5W would be about right.

Cheers

Ian

 

[anjing]

Clean power supplies and grounding have always been a main concern in high end electronics.
We always used similar grounding bars to the one Holger is using in our radio station racks, connected to a very large grounding cable or thick flat copper strap that ran into every operational room in the station and then to a very solid main ground point.
Some of today's switching power supplies are indeed very quiet, others, not so much

I found some thick copper wire that i am attempting to run across the console. I am finding it hard to solder regular hookup wire to the copper bar(wire). I'm not sure how to go about this. I sanded the coating but still the solder won't stick...

 

[ruffrecords]

Problem fixed! When i cleaned up the power supply i moved things around and one of the resistor was knocked a bit and it created a cold joint.

After many years working in electronics I came to the conclusion that there was no such thing as a subtle fault. In 99.99% of cases the actual fault that causes all those puzzling symptoms turns out to be something quite simple like a dry joint. Now, whenever I have a puzzling fault, I look first for a simple fault that might cause it. It often works.

Cheers

Ian

 

[anjing]

Good day Ian,
  I totally agree with you! Things are always simpler then we want them to be! It seem's my hum problem was also a loose wire at pin 1 of one of the direct out's, i couldn't see it untill i moved the subracks around.
 
  Yesterday i was experimenting in measuring the noise floor of my mixer. The way i did it was feeding a 0 dBu sine wave in one of the input to adjust the fader's untill i had 0dBu at the main output of the stereo bus amp. With 4 mono modules, one stereo line and the main bus amplifier powered i could measure -78dBu for the noise floor.

  I found some red color button's that fit the phantom power pushbutton. Since the alps ones are difficult to find. The ones i found are C&K, they have a slight concave inwards curve. I can take a picture if anyone's interested.

I will be taking a few weeks vacation from work and hope to put some extra time on the eztube mixer. Looking forward to it!

Regards,

Pierre

 

[ruffrecords]

@Pierre - with 4 mono and one stereo source connected to the bus that's a total of 5 sources creating your measured -78dBu noise level. 10log5 is nearly 7 so that means the noise from each source is only -85dBu which is a very good result.

Cheers

Ian

 

[anjing]

I tough i'd share some progress. I started using my eztube mixer in it's prototype cabinet.

 

[ruffrecords]

Love the mouse mat Pierre!!!

Cheers

Ian

 

[anjing]

I started testing a mute implemetation with a simple dpdt switch. Now it's starting to ressemble a mixer!

 

[letterbeacon]

Holy smokes - that looks amazing!

 

[anjing]

While waiting for more funds i tough i'd play some music. I made this small video for fun, i'll make a better one eventually.

http://theworldin35mm.com/espressojazzdiy/some-fun-and-a-maiden-voyage/



(sound is fixed)

 

[letterbeacon]

That is one huge slice of awesome!