8 Channel, 3U NEVE 1073 completed

[evilcat]

Very nice build remsouille!

 

[KDE]

Hey there fellas!
I'm about to complete my 6 channel unit, and I must say I'm quite pleased about the way it came together:
Can't wait to silkscreen it!!!
I used a screened power transformer to be able to put it in the case, and I have on ACDC for every two channels. All channels are functional, however I seem to have a little problem...
My 48v rail works fine, but when I tried to hook up two of the leds to one of the acdc's, the damn 47ohm resistor on the acdc blew  . When I disconnect the wire that goes to the led - to 0v, everything's fine.
Resistance between 0v and chassis reads 3,7ohm on every acdc .
Anyone have an idea where I should look into?
Thanks!!

You forgot to screen print some numbers!

 

[Harpo]

I used a screened power transformer to be able to put it in the case, and I have on ACDC for every two channels. All channels are functional, however I seem to have a little problem...
My 48v rail works fine, but when I tried to hook up two of the leds to one of the acdc's, the damn 47ohm resistor on the acdc blew  . When I disconnect the wire that goes to the led - to 0v, everything's fine.

What is the value of the current limiting resistors to each LED ?
Did you use single pole or dual pole switches for activating phantom voltage per channel ?
If dual pole, what is the LEDs supply voltage (with a free pole at the switch you might have used the unused negative rail for your LED supply).
If single pole, do your current limiting resistors have the power rating needed to stand the heat generated by (48V - LED Vfwd)*ILED ? If your build is missing these resistors, expect the LEDs to be blown once powered on. This short could also kill your voltage regulator, so double check, the phantom rail is still delivering +48VDC.

 

[remsouille]

Very nice build remsouille!

Thank's a lot!!

You forgot to screen print some numbers!

It's getting printed tomorrow!

So I figured part of my 0v-chassis resistance problem. It might come from the fact that I daisy chained the acdc's, though I don't quite understand why.. Anyway, when they're not chained the reading is correct. I still didn't try to star-power them, but still, even with only 1 acdc wired, the damn 47ohm keeps frying!

What is the value of the current limiting resistors to each LED ?
Did you use single pole or dual pole switches for activating phantom voltage per channel ?
If dual pole, what is the LEDs supply voltage (with a free pole at the switch you might have used the unused negative rail for your LED supply).
If single pole, do your current limiting resistors have the power rating needed to stand the heat generated by (48V - LED Vfwd)*ILED ? If your build is missing these resistors, expect the LEDs to be blown once powered on. This short could also kill your voltage regulator, so double check, the phantom rail is still delivering +48VDC.

I used a 3,9k, as specified in martin's building instructions, although it's only a 1/4w which maybe might be the problem (?).
I used C&K SPDT switches, and yup, the rail is still delivering +48! The leds take the 48v through the resistor at the switches' upper pole (where the phantom goes to my input xlr) and the led's anode is connected to the 0v connecter right next to the 48v on the acdc.

EDIT: That was it! I changed the resistors to 1w and it works like a charm!! Thank you very much Harpo!
I'll post beauty shots when the frontplates are screened!!

 

[madriaanse]

Wow! VERY nice looking build Remsouille! Did you end up using the MPSA-18s?

Martin

 

[remsouille]

Wow! VERY nice looking build Remsouille! Did you end up using the MPSA-18s?

Martin

Thanks a lot martin! WIthout you, of course, this wouldn't simply have been possible!
Yes, I used mpsa's on 4 of them (on the two first channels I built I still had bc184s). I'll report ASAP with my thoughts on the differences (if any) between the 2 of them.
The module plates are getting screened this afternoon, I'll post detailed pictures very soon!! I think it already looks pretty good, thanks to the correct RAF blue paint and awesome knobs from classic api!!

 

[digistu]

I've just completed four channels of ez1290 - what a brilliant project!  The boards were an absolute pleasure to work on, and thanks to the comprehensive assembly guide and the absolute mine of information here, all four channels worked perfectly when I fired them up for the first time.

I do however have a query about the biasing process.  Initially I just biased using a multimeter - to my ears (and without anything to compare them to) they sounded pretty special.  However I recently borrowed a scope so decided to do a proper job.  My question is, at what point after you make the clipping symmetrical should you stop turning the pot?  I found the waveform looked symmetrical at the 22.66v I had biased to with the multimeter, but I could turn a fair way until it started to go asymmetrical.  Going 'up' the scale (i.e. decreasing the value of the 5k pot) from the bottom, I found the point at which the wave first clips symmetrically to be around 18.12v, which seems much lower that I originally had them.  Is this the point at which I should stop?  Can someone talk me through the exact process to find the correct level to bias them at?

Thanks a lot!

 

[remsouille]

It's coming  8)

 

[remsouille]

There you go!!

Came out pretty good uh?  :-*

 

[madriaanse]

Wow! Pro build! Beautiful finishing touch!


Digistu: With the mic pre at max gain, keep creeping up the output of the signal generator (1KHz tone) until you barely see clipping starting to happen on one side of the waveform. Adjust the biasing trimmer so that clipping happens equally on both sides of the waveform as it begins to clip. That's all the adjustment you need - you don't want to keep turning the trimmer any more past this point as it will start clipping the other side of the waveform.

M.

 

[desol]

What's the best output impedance for the signal generator to be set at Madriannse?

I suppose it should match the input impedance of the primary of the transformer...

 

[digistu]

Thanks Martin, that's pretty much what I thought, just wanted to check given that my voltages were significantly less than the 'field' guide.  Really looking forward to using these preamps in anger!

 

[madriaanse]

What's the best output impedance for the signal generator to be set at Madriannse?

I suppose it should match the input impedance of the primary of the transformer...

Correct. My signal generator puts out line level, so I use a DI.

M.

 

[remsouille]

Hey All, I seem to have a wee problem after all.On one module, on The 70db position (2nd to last) I get a very distorted sound with sometimes lots of noise. Where should I look into?
Cheers!

EDIT: Actually, it's even weirder than that    The problem occurs on two modules powered by the same acdc, and they  send the problem to each other, which means one will distort if the other is set at 70db, and if they're both set at 70db, I'm deep into Fuzz Mayhem. Grounding issue? Where should i look?

EDIT 2: I've been doing some more testing, and the problem definitely comes from only one module, the other is affected by the fact that they're powered by the same acdc. Still, i checked my soldering in the grayhill switch area and didn't notice anything.

 

[madriaanse]

Does the problem preamp also exhibit these symptoms at 75dB? If so, you might have an oscillation issue related to transformer placement or not using shielded wire in the proper places. If it only does it at 70dB I'd check for improper resistor values around the switch or a possible solder bridge somewhere.

M.

 

[remsouille]

Does the problem preamp also exhibit these symptoms at 75dB? If so, you might have an oscillation issue related to transformer placement or not using shielded wire in the proper places. If it only does it at 70dB I'd check for improper resistor values around the switch or a possible solder bridge somewhere.

M.

You're right, the problem also happens at 75, not always though. I already removed the power transformer from the case, and ruled it out. I've been using shielded wire for everything audio, and 22awg wire for everything 0v 24v and 48v. Could it be the proximity of this module to the power supplies?

 

[madriaanse]

Hi there, I wouldn't worry too much about the power supply transformer (unless you're getting hum), but rather experiment with the placement of the audio transformers (10468, LO1166).

M.

 

[dmp]

I'd suggest checking that the 10468 transformer shield is grounded to the chassis with a multimeter. I built one of these and without the transformer shield grounded it would feedback at high gain.
A quick test is to ground the input on the pcb to ground and see if the problem goes away.

 

[remsouille]

I'd suggest checking that the 10468 transformer shield is grounded to the chassis with a multimeter. I built one of these and without the transformer shield grounded it would feedback at high gain.
A quick test is to ground the input on the pcb to ground and see if the problem goes away.

I haven't yet find the problem, though I have tried this and it didn't work. Still more testing to be done! I have another problem on another unit, though...
I accidentally shorted the trace going from the 12ohm 1w res (R56) to C7/C8 and M point to the chassis.... R56 blew, I replaced it, but no sound is coming out anymore..... I can still read 22,66v on 2N3055 enclosure... I hope I haven't blown the LO1166  :'( ... What do you guys think?
EDIT: well... that's it: I blew an L01166  8)

 

[desol]

Youch. A real one?

Do you have fuses on everything while you go?