Feeler: an "Eee-Zzz" christmas present...ez1073 and ez1073-500

[deveng]

I've done some research on the 60Hz ripple I'm seeing on my 1073's.  This appears to be a "normal" thing.  Now my noise measurement of -99.8dB seems pretty respectable!

To quote Geoff Tanner: 
"If we take the 1073 as a classic example, one of the biggest flaws in its design is that it takes the negative feedback for the output stage from the collector of the 2N3055 which puts it the primary winding impedance and a 12 ohm resistor away from the dc supply. So, if you don't have gobs of capacitance after that 12 ohm resistor, then the noise and crud on the power supply can get into audio via the feedback". 

This may explain why moving my transformer or experimenting with grounding had no effect.  Adding more capacitance to the supply filtering may have an impact where moving the 24v supply to remote may not necessarily reduce the ripple!  So no external for me.  I'd love to drop this down another 3-6dB though.  My custom API's are at -105dB and its not audible. 

regards,
Jeff

 

[haystack]

Just been reading about the 2n3055 and the possibility of it shorting underneath the pcb. Would it help if nylon washers were used?

Also, for the IEC, do you use a separate fuse holder after the IEC inlet then add a rocker switch?

Thanks for any feedback...

Haystack

 

[deveng]

I reduced the hum just a bit by disconnecting the shield from chassis on the output XLR.  Will try reconnecting that and disconnecting the input shields as that's the "preferred" method.  But something happened to one of the units.  Now I don't have signal at the output of the line input transformer (at R30 termination resistor).  Absolutely nothing at pin 2 of PL11 even though there's continuity between them.    I doubt I could damage the transformer as they should be hard to break, especially if I haven't moved or un-soldered them!    I didn't remove the pcb and I wasn't even close to working in that area.  Oh well, more debug on unit 2.

Anyone have a working one open to measure the resistance across R30?

 

[saxmonster]

I have noticed the hum in my 1073 too.  I have to put the headphones up really loud in order to hear it.  Sounds like a ground loop type of sound.  The gain settings don't increase or change it.  I don't hear it when i record because the headphone are not up that loud.  The eq section does change the sound but not the volume of it. 

Would love to get rid of it to just to have the cleanest signal.

-Scott

 

[deveng]

Scott,

There could be more than one source of hum.  One is described by Geoff Tanner in post 700 and is related to power supply ripple.  That's the tough one to tackle.  Another source for me was from the shields on the in/out connectors.  You can try disconnecting the input shields or disconnect the output shield.  Then try your headphone test again.

Regards,
Jeff

 

[deveng]

Issue solved.  Trying to debug when there are 3 issues at once is a challenge.  Found them all finally and the both units are working.  No transformer problem as it turns out.  Just a bad connection for that one.  Now for the fun stuff....making some music.

Regards,
Jeff

 

[haystack]

Deveng

What were your issues and how did you fix them?

cheers

Hay

 

[saxmonster]

Deveng

What were your issues and how did you fix them?

cheers

Hay

are you talking about the shield in the wires that connects\ the xlr's to the pcb or the wire that connects the ground to all the xlr's outer metal parts.

 

[haystack]

Hi Saxmonster

I have not yet turned  my 1073 on as it is awaiting the chassis and wiring-up. So I wondered about various issues people were having with theirs.

Deveng seemed to resolve his issues and I was interested in how/what.

Incidentally, what are the shields in the wires that you refer to?

As for hum, it looks as if that is inherent with the 1073 design??

cheers

Haystack

 

[deveng]

Saxmonster, Hay,

My triple issues were a single cold solder joint on the line input transformer (nothing to do with buzz), an intermittent cable and finally a bonehead wiring issue (output XLR mis-wire).  So you would not likely have these issues.  The buzz I hear is very low at about -102dB now when measuring noise with RMA.  In most recording uses this is not a problem. 

The shields I was referring to are the pin 1 connections at the XLR's.  Typically these are wired to chassis at the star ground point (and I've disconnected the shield running from pin 1 to the pcb).  If you have ground loops the best way to get rid of them is to diagnose your system, but if you absolutely have to, you can disconnect this pin at the receiving end.  My problem turned out to be a wrong connection at my output XLR.  That's why I shouldn't wire them at 2am! 

As for 1073 inherent hum, its all about the power supply ripple and the design.  Colin's design is good and these units sound and work great.  Get them running and have a listen.  If your noise measurement is above -100dB you probably have a wiring issue or ground loop in your system. 

Regards,
Jeff

 

[haystack]

That's great Deveng, thanks for the reply. Interesting to know about the issues folk have be it soldering problems or wiring etc.
The trick is know how to diagnose the problems should they occur.

Cannot wait to fire mine up!!

Haystack

 

[saxmonster]

I don't think my issue is a ground loop hum its just the inherit hum of the machine like you said.  I don't hear it at all unless I turn up the headphone amp all the way and then it is still far in the background but I would never ever monitor at those levels any ways.  How can i measure how many DB the noise is in my daw.  I have digital performer.  Do a need a scope to measure it? 

Thanks
-Scott

 

[deveng]

Scott,

If you have an Intel based DAW you can download RMAA (Rightmark audio analyzer) for free.  It uses your sound card for measurements.  For MAC, I think Fuzzmeasure does the same thing. 

Since you can only hear the "buzz" when your level is at extreme, what you're probably hearing is power supply ripple.  Measure it with the above mentioned analyzers and if you're down in the -100dB or better you're going to have a battle to get it any lower.  The best these 3 terminal regulators can do is about 75dB so the rest has to be filter caps.

Regards,
Jeff

 

[haystack]

Ok, just finished everything on ez1073. Sounds great (and a relief of course that it works).

Does anyone use the LED as I found it impossible to solder in and align and stay in the chassis. Now I think I have damaged it after trying to re-arrange it to fit into the tiny hole on the chassis in the corner. Everything else works great, so I assume the led doesn't affect the 'pre circuit generally.
I will get another and re-solder but it is nice to have some kind of mains lamp.

Haystack

 

[deveng]

Haystack,

Yes I use the LED.  It is a bit difficult to line up with the hole in the front panel.  What I do is bend the leads so the LED will feed through the front panel hole correctly.  Then solder to the pcb from the top side.  You can then "tweak" the leads if you need to. 

Its not required to have the LEDs in place for the unit to work but it is nice as it will not only let you know the unit is on but also let you know both the 24v and the phantom power are working.

Regards,
Jeff

 

[haystack]

Thanks Deveng for your reply. Yes I will sort the LED out. It's good to know all is well with the unit by looking at
a healthy light!

I have really enjoyed building the unit and collecting the bits and bobs- IEC, spacers etc etc and ending up
with a great unit as this. lovely sounding thing.

cheers haystack

 

[stribor1]

I found it not so difficult to align the LED, I aligned the LED with the hole in the faceplate (not to deep, just to enter the hole slightly) and used a marker pen on the LED leads to mark the position of the LED lead holes in the PCB.  Then take the LED out and bend the leads in the marked positions to a 90 degree angle, trim off the leads to get the needed height (they shouldn't be to long or they will ground with the case bottom, some 5mm from the bending mark should be just enough) then just place the LED in the PCB, fix it slightly in the LED hole on the faceplate and solder from top.

 

[Meyer]

Hi

I've bee lurking here for a while, reading and learning, but now I have a issue with my ez1073 that I can't solve.

It worked fine at first, until I turned on the phantom power. There where some strange noises and distortion and now my bias is stuck at about 260mV. By adjusting R20 I can only bring it up higher but not lower.

Everything else is working, there is sound coming from the unit, but it is distorted. I checked for shorts and reflowed solder joints, but there has been no improvement. There are no visual clues for burnt components, but maybe something shorted to 48V and got damaged, but I have no idea what.

Any suggestions are much appreciated

Thanks

Meyer

 

[spneca]

Hello all,

I just finished a build, and the line input and eq works great.  I checked the power voltages and adjusted the output bias and everything was fine.  My problem is that the Mic Pre section is not passing any signal.  I did some probing and found that there is continuity between pins 2 and 3 of the mic in.  Looking around the board , I could not find any obvious short.  I did some trace cutting and the short does not appear to be near the connectors.  One thing I noticed is that all of the contacts of SW4 (the impedance switch) have continuity.  Could it be that I have a bad switch?  Could this be the cause?

 

[stribor1]

Hello all,

I just finished a build, and the line input and eq works great.  I checked the power voltages and adjusted the output bias and everything was fine.  My problem is that the Mic Pre section is not passing any signal.  I did some probing and found that there is continuity between pins 2 and 3 of the mic in.  Looking around the board , I could not find any obvious short.  I did some trace cutting and the short does not appear to be near the connectors.  One thing I noticed is that all of the contacts of SW4 (the impedance switch) have continuity.  Could it be that I have a bad switch?  Could this be the cause?

Hi there, I'm by no means an expert but I can share my experience after two successful builds, since I had similar issues.
Continuity on the mic input between pins 2 and 3 is normal as these pins are connected through the mic input transformer which has a low DC resistance. I have the same on my two builds and everything is working fine. One hint if you are using a dynamic mic, make sure the phantom power is not on. The 48V switch pointing downwards is the phantom power on position, so if you are using a dynamic mic it should be pointing upwards otherwise it wont pass any signal. The labeling on the frontplates (from both Dan's) are a little bit confusing regarding this, and there is no led indicator for the 48V on/off position.
J.