Neve 1290 build completed!!

[bluezplaya]

Martin, I rewired the IP transformer with pin 5 going to shield on the board. No signal :? . Is there a schematic I could look at to help me see the signal flow and try to see where the signal stops?

 

[madriaanse]

Hi Adam,

From 55dB on, signal flow on the PCB is pretty much from right to left, starting with the switch and ending with 2N3055. If you have an oscilloscope it's pretty easy to track the flow by probing the transistors. Schematics are on the last two pages of: http://www.musiciansgig.com/ez1290/assembly.pdf

Did you also screw in 2N3055? (I edited my previous post and added that). The preamp won't work without that.

Best Regards,

M.

 

[bluezplaya]

I have screwed in the 2N3055 with heatsink and I when I tap hard on the 57 I can hear what sounds like the input transformers ringing as I hit the mic. When I listen with headphones I can hear a faint distorted signal with the input all the way up. It sounds to me that the input side is working but something on the output side is not. Is there a chance you would have voltages documented for the transistors? That way maybe I could check with my meter to see if all my transistors are getting proper voltages?

Thanks for all the help BTW,
Adam

 

[bluezplaya]

HOLY CRAP! :shock: When listening carefully for the slight ringing as I was tapping on the mic, I leaned over and determined that it was coming from the Carnhills. I then discovered that pin 5 was disconnected on the Carnhill and resoldered it. I HAVE SIGNAL! There's some sort of HF oscillation or ground or something like that, but most definitely a full, fat signal. I guess I never had the 2N3055 screwed in and grounded .

And let me add, damn this is a lot of gain!

 

[madriaanse]

Way to go Adam!!!

The HF oscillation probably/usually comes from either:

a) not using shielded wire (got a mic cable you can "shorten"?
b) having the input transformer too close to output transformer
c) having (unshielded) input wires running close to output wires.
d) a "funky" 2N3055
e) or any combination of the above

Lemme know how it goes, but it sounds like you're well on your way.:thumb:

M.

 

[bluezplaya]

I have some unused mic cable. I guess that makes sense to use that as shielded. Yeah, I'm well on my way to doing some more work...like installing phantom power :roll:

Adam

 

[gerardmanvuca]

Martin.....i just ordered 4 boards from u......canNOT WAIT to start building these beautys!! thanks so much 4 makin it available to the DIY community :grin:

i have a couple of questions:

i'm thinking i'm going to add the JLM go between and DI for recording guitars (pod) at home etc....maybe a silly question but the DI will be going through the preamp circuit, adding its lovely neve type colour right?

[EDIT: ok afer lookin at the JLM website i see the di connects directly to the preamp input so obviously it will go through the circuit.]

also i was thinkin a level meter would be cool....would i be able to use the pico led meter?

[EDIT: actually this one might be more appropriate- http://www.groupdiy.com/index.php?topic=26269&highlight=led+meter+metre maybe i could have one for input and one for output/Trim]

i also want to add a trim pot....but noticed u weren't a fan of them....is there a really high quality one someone could recomend?

will i need a different power supply to accomodate these extras?or just a modified JLM supply?(i will be building 2 separate dual preamp racks)

Please excuse my newbie knowledge of electronics.......cheers

 

[gerardmanvuca]

somthing like this would be awsome....prob need to space it out a bit more........

sheeesh im startin 2 get excited now :roll:


[/img]

 

[bluezplaya]

Alright Martin I have 2 EZ1290's working great and sounding great with no noticeable ground hum or hiss at the top volume. I ended up moving the 31267's on the opposite corner of the chassis from the toroid actually in between the trannies from the existing 2 Hot Rod 1272s. That completely silenced any and all noise. I ran shielded cable throughout except for the 24v and ground to the boards. I have to say, and I've said before...these 1290's have heaps of gain, more so than the Hot Rods. The only thing left to do is drill a 15/16 or 1" hole in the back panel for the XLR's for channels 3 and 4 . That'll be a bitch.

I do however need to add some phantom power to the channels. I think I will do that next.

Thanks for the help,
Adam

BTW: My channel 2 (Hot Rod) is acting kind of funky. The signal is clipping and sounds like the trimpot has been adjusted to make it REALLY clip. It will intensify as I turn the trimpot so I know the trimpot should be doing its job. However, without a scope I can't test. Would you say I have a "funky" transistor, starting with the 2N3055? Should I try to replace to get better results? Could it be a cap?

 

[bluezplaya]

I noticed on the 48v hookup diagram that 6K8 resistors are needed. I don't have any but I do have a bunch of 3K3's. I could pair those up but would 6K6 be sufficient?

Thanks,
Adam

 

[Siegfried Meier]

So, what are those of you using for the output pot, that are using the pot? I'd like the highest quality possible. Also, I'm putting the small grey N*ve knob on them, so I'd like to make sure that it actually fits properly. Any ideas?

Thanks,
Siegfried

 

[buschfsu]

i used these :wink:

http://www.groupdiy.com/index.php?topic=26413&highlight=ez1290

 

[madriaanse]

Hi Gerardmanvuca,

That's a pretty spiffy looking layout, but ditch the lights! This preamp don't need no steenkin' "idiot lights". :green: It's got such vast headroom; your A/D will be begging for mercy long before the 1290 clips!

Re: PSU; I use one AC/DC per pair.

Adam,

doubling up on the 3k3's could work as a temporary fix (as long as they're matched pairs), but I'm not sure why you'd want to take the shortcut; resistors are CHEAP.

Siegfried,

I'd look at Penny & Giles, TKD.

-------------

Also, for general troubleshooting I've prepared the following PDF:
http://www.musiciansgig.com/ez1290/transistor_voltages.pdf

All the best,

M.

 

[buschfsu]

martin,

thanks for the pdf, great help. so an update on my issue. preamps are working great sound really good. only problem is that in both channels gain settings 8, 9 , and 10 sound like they have a low pass filter on them. when i switch from position 7 to 8 i loose the top end, it comes back at position 11 and 12. i triple checked the solder work with a continuity checker and a magnifying glass. i also checked the resistor values and they are all spot on. is this normal or am i missing something???

 

[bluezplaya]

Adam,

doubling up on the 3k3's could work as a temporary fix (as long as they're matched pairs), but I'm not sure why you'd want to take the shortcut; resistors are CHEAP.

I know resistors are cheap but shipping is expensive and I didn't have any. So I used my resources.

BTW, I wired my board for a trimmer as per your diagram but it doesn't seem to taper the volume, only turn it off at the last bit of turn.

 

[madriaanse]

Hi Buschfsu,

That's definitely not normal; the preamp shouldn't start rolling off until about 40-45KHz - at any gain. Can you do a sweep and let me know at which frequency the HF rolloff starts?

Hi Adam,

Can you confirm that you removed the 10K resistor and check with a multimeter that you completely severed the trace (and jumper you put in) as noted in: http://musiciansgig.com/ez1290/trimmer.pdf

Best Regards,

M.

 

[Siegfried Meier]

Hey Martin,

Any reason for the extra ground pad just below the 0v on the PCB? I can't see anywhere I would connect this to.

EDIT:
Also Martin, I assume the P&G fader would be the best quality. Do you know what part number I need, or the value of the fader?

Thanks,
Sig

 

[buschfsu]

found some incorrect values around point U (.01uf vs 1500pf oops) once i clear this up it should take care of my problem!! ill post after the digikey box hits the porch.

thanks

 

[madriaanse]

Hi Siegfried,

Penny&Giles RF11/1/D/A looks like the right one; be prepared to spend some $$$!

The extra 0V point is there because it's handy to have when you're probing the transistor voltages with a DVM, clip your scope to it, etc.

Best Regards,

M.

 

[Siegfried Meier]

Thanks Martin. Those P&G's are $124.44 US each for 1-6 pieces, and $112.00 each for 6-19 pieces. YIKES. Maybe I'll pass for now.

Also, I am short 2 of the 82uF 25v - the ones just below the large 2N-3055 transistor. I was only able to find 100uF 25v locally, and axial at that. Will these be ok to use? Any negative effects?

Thanks!
Sig