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

[ding]

I've been measuring wrong. I'm actually getting 49.5mV from R6. It seem like the voltage coming out of C12 is 49.5mV. That goes to R6 and R20. That seems way low. I pulled out C12 and it checks fine but I replaced it anyway and still???

 

[ding]

I am sure I am missing something elementary here. Should I be getting 49mV from the negative lead of C12?

 

[ding]

Transistor voltages are off.

Q4
c=23.8V
b=1.13V
e=670mV

Q3
c=1.13V
b=27.6mV
e=0.4mV

Q2
c=23.8V
b=670mV
e=49.4mV

AFAIK the should be Q4 22.6v, 3.1v, 2.5v Q3 3.6v, 0.9v, 0.4v Q2 22.6v, 3.6v, 3.1v I have checked for open resistors. My voltage is 23.8 so there is no voltage drop at either Q4 or Q2's collector. Still getting 29.8mV across R26. The hunt continues. 

 

[ding]

I'm really sad to say that I've run out of ideas troubleshooting this preamp. I have figured out what happens but I am not sure why. Here is the order of things.

1. Replace Q4
2. R26 starts at 95.5mv for 10 to 15 seconds
3. mv at R26 start rising until it reaches 328mv and stays there
4. If left turned on too long Q4 gets damaged.
5. Rinse and repeat.

All other voltages on all other transistors check out fine. I have replaced all three transistors on the output stage several times just to make sure. I replaced R23 for a 1 watt. Replaced R7 with 1 watt just in case. All resistors and caps test fine on the output stage. All resistors and caps are the correct value. Nothing is grounding that shouldn't be. Quadruple checked all solder joints with magnifier. Checked the 10k potentiometer R149.

I am not going to quit but I just don't know what else to do, what else to check, where to look next. I am really hoping someone can give me a clue as to what to check or test for. I am at a complete loss. I think I can draw out the output stage schematics with my eyes closed.  :'( If anyone has any ideas, no matter how strange they may sound, please let me know.

Thanks,
Alain

 

[bobtheninja]

Hi all,

I am about to start on this project, and I'm working on sourcing together the parts that are not included in the kit from AML. Has anyone compiled some sort of shopping cart, or excel spreadsheet, or whatever really, on the other stuff that's needed? That would make my head swim a little less from counting together M4 and M3 screws from the different pages of the colour book. I'm sure it'll be fine anyway if I order it all by my lonely self, but I also know that I will overlook something obvious and walk around for, at least, a whole day muttering "you're such an idiot" under my breath, and to be honest, I'd rather not do that.

Looking forward to diving into this project. A whole lot! I promise pictures and anecdotes from the process, and whatnot.

 

[allprod]

Hi Ding!

Did you find the solution to your problem with the ez1073?

 

[ding]

nope sure didn't. and since I am moving right now its going to be a couple of weeks before i can bash my head against a wall with this again.

 

[allprod]

The problem surely come from a transistor that ask too much for current as it is not working properly.
Test all the transistor dc voltage between base and emiter you should find 0.6V.
If you find a lot more then change the transistor.

 

[fripholm]

Hi all,
I've just finished soldering my first ez1073. Although everything worked from the get-go, I'm reading only +23.5 volts between J5 and J6 which is slightly out of the range of the 2 % tolerance of the 7824. But everything seems to work fine so far, line and mic input, phantom power as well as the EQ. The unit sounds great and even the amount of hum is negligible which I find a bit strange as I don't have an enclosure yet.

When adjusting the output bias I measured THD using a software scope when the unit was connected to my Fireface UFX. THD is at its lowest value when the voltage across R26 is just 55 mV - far below the recommended 120~130 mV. When I adjust R20 to get a reading of 125 mV, THD is getting much higher.

Could this be related to the low voltage on the +24V rail? After all, is something wrong with my build or are those readings within tolerance?

 

[haystack]

Just a thought-

What other output transformers could I try in the ez1073 (diy 1 unit version). Heritage Audio have a red/maroon transformer
in their 1073 clones. AML have a good range of these transformers in stock. Would they work in this preamp?

Haystack
::

 

[haystack]

EZ1073 output transformers:

Instead of VTB1847 would VTB2290 or VTB9049 work I wonder? Or are they the same?If not what are the differences?

thanks

Haystack

 

[Deepdark]

Hi

I was looking at the color assembly book and would like to confirm one thing. The pcb is made of 2 layers and the for the ground plane (analog gnd) it's the bottom surface of the pcb? So, when mounting, for exemple, the Q2 heat sink, we probably have to isolate the screw with some king of pad or washer??

 

[rob_gould]

Yep - you should pretty much always isolate the Vreg from the heatsink.  It is the correct habit to get into

 

[brewbacca]

Sooooo.... I've got 2 units built. And neither works  :'(

1. The first one powers up and I'm reading 24V and 48V, but the signal is really quiet. I've have to crank the mic input to get any sound, and that is negligible. Any suggestions on where to look?

2. The second one blows the fuse within a second of powering up. I'm getting around 33-40 ohms between the 24V rail and the ground rails, so I'm assuming there's some sort of short, or maybe I misplaced a resistor? Any suggestions there?

Thanks for all the future help guys! 

 

[rob_gould]

Sooooo.... I've got 2 units built. And neither works  :'(

1. The first one powers up and I'm reading 24V and 48V, but the signal is really quiet. I've have to crank the mic input to get any sound, and that is negligible. Any suggestions on where to look?

2. The second one blows the fuse within a second of powering up. I'm getting around 33-40 ohms between the 24V rail and the ground rails, so I'm assuming there's some sort of short, or maybe I misplaced a resistor? Any suggestions there?


Thanks for all the future help guys! 

Grab a magnifying glass, start checking for correct components values and also for bridges / solder splashes which are shorting connections together.

For #1, what happens when you try a different mic? And what about the line input? Does that work?

 

[brewbacca]

Sooooo.... I've got 2 units built. And neither works  :'(

1. The first one powers up and I'm reading 24V and 48V, but the signal is really quiet. I've have to crank the mic input to get any sound, and that is negligible. Any suggestions on where to look?

2. The second one blows the fuse within a second of powering up. I'm getting around 33-40 ohms between the 24V rail and the ground rails, so I'm assuming there's some sort of short, or maybe I misplaced a resistor? Any suggestions there?


Thanks for all the future help guys! 

Grab a magnifying glass, start checking for correct components values and also for bridges / solder splashes which are shorting connections together.

For #1, what happens when you try a different mic? And what about the line input? Does that work?

I've already looked for bridges / solder splashes and cleaned the board a few times, so I don't think it''s that. But I'll be sure to go through the components next.

For #1, I tried a dynamic mic that's usually pretty loud. I didn't have any success with the line in.

Also, for #2, I did find that if I took r26 out, I lost the short between the 24V rail and ground.

 

[brewbacca]

Ok, figured out #2. The heat sink on Q2 was causing a short for some reason. I fixed it by taking it off and putting it back on.  :-X  Maybe I just had it on too tight?

 

[brewbacca]

Any thoughts on what might cause the eq to pass a really distorted signal? With all the filters turned off and the HF around 0db, I'm getting a lot of distortion on the eq with a big volume drop. I'm assuming there's a problem with one of the the op-amps, but I wanted to see if anybody had a suggestion.

 

[brewbacca]

So while trying to troubleshoot my eq section, something must have gone wrong and now all I get is pops and static coming out of the ez1073. When I have a microphone plugged in, it seems to act like a speaker and I can hear the pops and cracks coming out of it. My voltage rails are reading fine. I've tried replacing a couple transistors (Q3, Q4) but that didn't seem to do anything. Does anybody have any ideas where to look? Not sure if I should just start emailing Colin.

 

[philipNL]

Does anyone know if this ez1073 sounds the same/as good as a pre built ez1073-500 in lunchbox format? Or are there different components used?