8 Channel, 3U NEVE 1073 completed

[Enchilada]

Genius! Probed all the way through the audio path and the signal was fine right up to the output transformer. Perhaps I've got a dud because it looks like it's wired fine. Pins 6 and 7 are connected, there's a 0.01 polypropylene cap in series with a 1K5 resistor between pins 5 and 8, pin 2 of my XLR out is connected to pin 5 and pin 3 of my XLR is connected to pin 8.

Could I have a dud VTB9049?

 

[Enchilada]

Oh, and XLR pin 1 is connected to shield.

 

[tmuikku]

Enchilada - This is my favourite problem to answer
Might be bad cable or the device you are connecting into doesn't have pin 3 (or 2?) connected.

I had soundcard with unbalanced input and still it had TRS sockets. The soundcard input TRS socket ring was not connected to anything and thus with balanced cable there wasn't connection on pin 3!  Output tx secondary was connected only from the other end (pin 2, or Tip of the TRS cable). The exact symptom, no low end at all. Boy did I spent hours debuging the DIY device before catching the soundcard problem up

Try another cable and another device to hook into before pulling hair with 1290

 

[Enchilada]

MY HERO!!!!

Tried an XLR to mono 6.5mm cable and BOOM, bass in the place.

It is particularly noisy though. Not ground hum but white noise. I reckon it's the cheap Jaycar transistors I'm using. I'll switch back to the eBay ones and see how it goes.

That's sort weird though, my Alctron MP-100 works no problem with my XLR to stereo 6.5mm jack cable into the unbalanced input of my Tascam M-3700. Maybe the Alctron is specially wired.

Thanks for the help mate!

 

[tmuikku]

Alctron MP-100 might have electronically balanced output instead of a transformer?

The extra noise is propably coming from the cable shield now connecting the pin1 of your 1290 output to audio input (or ground, pin 2 or 3 hot??) of your tascam board = no advantage of cable shielding and a ground loop.

Best  thing would be to make special cable to hook 1290 to your Tascam board.
Use standard mic cable but don't connect cable shield at the TS jack end, only at the XLR pin 1.
XLR pin 2 to goes to tip and pin 3 to sleeve.

This way 1290 handles the cable shielding and no ground loop occurs between the devices.

 

[Enchilada]

Sorted! Cheers for the help dude  8)

 

[Enchilada]

Thanks again for everyone's help with my build. I'm pretty good with tube mics but this was my first preamp build.

Switched transistors back and now it's sounding very quiet and very sweet  ;D

 

[tomnowell]

I managed to get hold of a scope and tested my output again, and following the procedure outlined in the assembly guide I am still getting clipping on only one side and moving the trim pot does not clip the top of the waveform.  Has anyone had this problem?  At one end of the trim pots range the signal goes into a very weird pumping type thing, and for the next 10 or so turns the waveform is clipping less below the middle.  After 10 turns or so the waveform hardly changes at all and I cannot make the top and bottom symmetrical at all, in fact I can't get the top to clip at all without seriously overdriving the input.

I used BC550s (could that be the problem? - does my trim pot need to be logarithmic?  I have measured my transistor voltages and everything seems spot on.

Any advice would be greatly appreciated!
Tom

 

[Whoops]

I managed to get hold of a scope and tested my output again, and following the procedure outlined in the assembly guide I am still getting clipping on only one side and moving the trim pot does not clip the top of the waveform.  Has anyone had this problem?  At one end of the trim pots range the signal goes into a very weird pumping type thing, and for the next 10 or so turns the waveform is clipping less below the middle.  After 10 turns or so the waveform hardly changes at all and I cannot make the top and bottom symmetrical at all, in fact I can't get the top to clip at all without seriously overdriving the input.

I used BC550s (could that be the problem? - does my trim pot need to be logarithmic?  I have measured my transistor voltages and everything seems spot on.

Any advice would be greatly appreciated!
Tom

That's really strange,
I don't think the BC550 are the problem, and if your voltages are spot on I really dont know what could be the solution.

Maybe Martin can help

 

[tomnowell]

Sincere apologies!! I got the wrong value for resistor R5 in BA183AM - somehow I had 51k instead of 3k3 - I had double checked all before populating the board, but it must've been a friday night soldering session or something and I messed up - sorry if anyone else has been scratching their head on my behalf, it now sounds amazing, is correctly biased and I can't wait to start the next project!  I'd take some photos but mine is not exactly beautiful its sort of rammed in the cheapest case I could get, I haven't really done it justice this will have to be a temporary case until I can pimp it up a bit

thanks for encouraging me to get a scope Whoops, Ive always wanted one and it certainly helped a lot in locating the region of the problem!

I do have one more question, sorry to be a pain.

Is it correct that I have mounted my transformers directly to the chassis with conductive bolts? I have no idea whether they have any part of their windings intending to or not connect to the mains earth.  As I said the unit sounds fine, I just don't want to have problems in the future if I have inadvertently bypassed the 10R gap between ground and earth by mistake...

 

[Potato Cakes]

So in my attempts to even further quiet the buzz on channels 3&4 of my four channel EZ1290, I wound up pulling the PSU and placing in an separate enclosure. It would still have been fine on loud sources and the transformer shielding did help quite a bit, but in my pursuit trying to make anything I build the best I can, I just did what everybody else here has done and put the PSU outside of the rack and of course fixed the buzz. Maybe at some point I may revisit keeping everything internal, but I have too many other projects to finish. I think the only way I can see to build 4 channels with an internal PSU would be to redo the panel so the cards mounted on their side and condensed down to one side and the PSU would be on the opposite end. Basically how Martin built his 8 channel version, but with half of the cards. Unfortunately I don't see my self being able to do this in the foreseeable future, but maybe someone else here who is aspiring to build one of these great preamps might want to give this a go.

And as always, thanks to Martin for this super sweet project.


Thanks!

Paul

 

[guisquil]

Hello,

Both of the places mentioned in the original post are sold out of the EZ1290 PCB, are the boards available anywhere else?

Thanks

 

[madriaanse]

Hello,

Both of the places mentioned in the original post are sold out of the EZ1290 PCB, are the boards available anywhere else?

Thanks

Hello,  I have a new batch of boards scheduled to arrive tomorrow.  New boards will be back in stock at those stores soon after that.

Thanks for your patience!

M.

 

[Pusch3l]

hey and good morning,
after hitting the searchfunction and nothing to find i need someone to point me in a direction how to locate the fault i produced..

i built a 2 channel 1u version of the ez1290 and everything went fine on channel 1.
started with 22.66v (measured on 2n3055) on both channels and after that i used the scope to finetune the clipping.
as mentioned before on channel 1 everything went well but on the other channel 2 i ran into problems with the waveform.
after being totally pissed i put away the unit and started over the next morning with a fresh mind and found 2 things:

-a tantalum cap soldered wrong
-a voltage drown from 24.05v (psu) to 16-17v (measured on the 2n3055) which cannot be raised on the trimpot

i did desolder the tantalum cap and switched sides so the polarity is now like the silkscreen on the pcb
but i have no idea where to start on the voltage drown...
maybe someone had the same problem and can point me in a direction where to start

greets

 

[Spencerleehorton]

Always check all resistors first, then double triple check. Check voltage form source this should hopefully then give you some idea of where it starts to go wrong.
Change tants has worked for me on start of gain stages before when I have had funky voltages.

Regards

Spence.

 

[Whoops]

hey and good morning,
after hitting the searchfunction and nothing to find i need someone to point me in a direction how to locate the fault i produced..

i built a 2 channel 1u version of the ez1290 and everything went fine on channel 1.
started with 22.66v (measured on 2n3055) on both channels and after that i used the scope to finetune the clipping.
as mentioned before on channel 1 everything went well but on the other channel 2 i ran into problems with the waveform.
after being totally pissed i put away the unit and started over the next morning with a fresh mind and found 2 things:

-a tantalum cap soldered wrong
-a voltage drown from 24.05v (psu) to 16-17v (measured on the 2n3055) which cannot be raised on the trimpot

i did desolder the tantalum cap and switched sides so the polarity is now like the silkscreen on the pcb
but i have no idea where to start on the voltage drown...
maybe someone had the same problem and can point me in a direction where to start

greets

I would start as Spencerleehorton told,
check all the resistor values.
Then visually inspect all the polarized capacitors direction (tantalums and electrolytic)
Then Visually inspect all the transistor placement, are all the legs correct?

After that You should get the chart of transistor voltages that Martin has in the build manual, and measure all your transistor voltages and compare. Then you might know the place were the problem is.

Also if you had a polarized capacitor with the wrong orientation, thee might be some other thing damaged close to it.

 

[Pusch3l]

after some measuring i managed to narrow it down to the 100uf 25 axial caps near the 2n3055.
ordered new ones, we will see after xmas what happens

thanks for the help so far

greets

 

[madriaanse]

after some measuring i managed to narrow it down to the 100uf 25 axial caps near the 2n3055.
ordered new ones, we will see after xmas what happens

thanks for the help so far

greets

Sorry to be chiming in so late. Glad you're making some progress on this. Please let me know how it works out. You might need a new 5k trimpot and 47R 1W resistor as well.

Best,

Martin

 

[XAXAU]

Yes, I did think about adding the line-in section, but it doesn't really make sense to add it unless you are also incorporating the EQ section. Very few people need line gain, but (almost) everyone  needs a mic preamp.  Hi-Z input can be added to the EZ1290 using a JLM Go Between.

I did make a 1073 line board (with proper 31267 input transformer) a few years ago but discontinued it because there was very little interest in it. Please see: http://groupdiy.com/index.php?topic=34292.0

Best,

M.

Hey Martin, you don´t have any plans to revive the line in board with VTB9046? There´s a lot of people wanting to build mini mixers and summers these days!

 

[madriaanse]

Hey Martin, you don´t have any plans to revive the line in board with VTB9046? There´s a lot of people wanting to build mini mixers and summers these days!

I'd be delighted to do another run, but will need sufficient interest to keep the board prices reasonable. How many would you like?

M.