8 Channel, 3U NEVE 1073 completed

[delir66]

Yesterday I brought for first time my two finished channels to the studio.
Recorded with a 414 on a digidesign 02, then on a Universal audio 610 , then with the neve.... amazing!
Just makes 02 sound stupid and UA to sound as it's small dumb brother (speaking about presence and clarity). It's so clear  and present on it's highs... really happy man!!

On the other side, I'm having a problem in one of my channels.
It's like a bit deff. At low gain values it's fine compared to the other (the sound is just identique), but when I go further that the fourth step, it will only amplify when there's a big input (when I put a lot of pressure on the diaphragm of the mic). At the beggining I thought it could be a mistake on the switch resistor, but everythin fine there.
Could that be related to a power issue?
Could anybody point me someway? Thanks.

 

[sr1200]

Did you check that your voltages are correct for your transistors?  Also, how did you check the rotary switch?

 

[delir66]

First of all thanks for your reply.

When I say checking the resistors on the switch I mean check the values. After forth step the sound gets much lower, at the beggining I thought I just misplaced any of the resistors, but then I realised that behavior mentioned before, the sound only gets to the correct level when lot of diaphragm movement.
I also checked the solders in there.

As for the transistors values, as soon as I get the pre back from the studio I'll check the values. i remember seeing a value table somewhere on this post, I'll compare them with that values. Do I need to input the 1khz sine while checking?

I'll update my process when I get the pre back. Thanks.

 

[sr1200]

first things first, check the pre with a dynamic mic and see if you get the same issue. If not you might have an issue with the phantom power (which might not be related to the rotary switch at all)  As for checking the switch, (dont have the schematic infront of me) but on it, find the point after the switch and resistors and measure from there to right before the switch.  if youre finding you have some "off" numbers, you might have a solder bridge on the switch (which isn't that hard to do being the pins are so damned close together and small) and a cold solder on there might not be apparent to the naked eye. (check with a magnifying glass)

 

[delir66]

In fact when I compared both channels, did it with the 414. Will check with dynamic mic.
Thanks again. I'll update when I have the pre back. 

 

[indiehouse Recording]

Hi, Can someone recommend an oscilloscope that would be appropriate to use for biasing these pres? Preferably one under a hundred dollars (used) that will work for this. Thanks!

 

[sr1200]

If you find a usable scope for under $100 let me know please!  You can (kinda) bias them using just a multimeter.

 

[indiehouse Recording]

I do have a multimeter. I just don't have a use for a scope other than to bias these pre's. I want them to be set up properly, but I don't really want to spend a few hundred bucks on something that I'll probably not use very often.

 

[desol]

I found a Tektronix 2215 locally on Kijiji for $50 from a recent university grad...who was more into digital...and had no use for it anymore.

 

[sr1200]

My 4 channel unit was biased using a multimeter and sounds just as good as the 2 channel unit that was biased with a scope.

 

[mikerl]

Hello all,

Im putting together a mouser cart with the parts on the v2.4 BOM.  The BOM seems to have many redundant parts, and perhaps too many to fit on the board.  are all of the parts listed on the BOM for ONE complete channel?  are some of the parts substitutes for other parts?

i see two pre stages, and a driver stage, which i believe makes up one channel, but below that i see EH10023-2, and EK20032, with many parts listed under each.  Do i need all parts listed in these categories as well?  i question it, because i see r3 r4 and r5 (just as examples) listed under EK20032, but also under the "driver stage" section.

I am a newbie, so i guess im just a bit confused by the layout of the BOM.  I am building 4 channels of ez1290. 

i already have chassis, transformers, transistors, switches, power supply.  Most of my questions here are in regards to the resistors and caps on the BOM.

 

[desol]

My 4 channel unit was biased using a multimeter and sounds just as good as the 2 channel unit that was biased with a scope.

Let's not start validating that a multimeter is the equivalent of a scope.

 

[sr1200]

Not at all, just saying that at normal operating levels, I dont hear a difference from using the 2 methods.

 

[alexidoia]

BC184C is now obsolete. What should I do?

You should be able to find them on eBay if you're really wanting to use BC184. Another option is to use MPSA18. One important detail about using MPSA18 in place of BC184C is that MPSA18 will need to be mounted backwards (rotated 180 degrees on its vertical axis) on the PCB. Other than that it is a great substitute: http://www.digikey.com/product-detail/en/MPSA18RLRMG/MPSA18RLRMGOSCT-ND

Hello,
I am just starting a 4 channels piece !!
Just a question regarding the MPSA18 : when you say to mount them backwards, you mean having the actual transistor underneath the PCB and having its pins to be sold on the top ?

Thanks a lot.
I am very excited.
Alex

 

[drAk]

No, you just need to spin them 180 degrees and mount on the top. So where the board shows |) you would mount the MPSA18 like (| in that spot.

 

[alexidoia]

Thanks for the drawing  :

 

[alexidoia]

I have  some doubts:
My PCB is version 2.1 and I have the 1290BOM24.xls

1) In both pre-stage: C13 is 150uF /  16 volts 20 %
On the board I have 150uF/6.3v

2) In the driver-stage: C4, C6 and C7 are 100uF/25V whether it is written 82u/25v on the board ?

3) What does EH10023-2 section refers to  ?

Thank you for your help.
Alex


Thanks a lot.

 

[desol]

I have  some doubts:
My PCB is version 2.1 and I have the 1290BOM24.xls

1) In both pre-stage: C13 is 150uF /  16 volts 20 %
On the board I have 150uF/6.3v

2) In the driver-stage: C4, C6 and C7 are 100uF/25V whether it is written 82u/25v on the board ?

3) What does EH10023-2 section refers to  ?

The reason alex is that the old capacitor axial packages are difficult to find. 82uf is non-existant....so 100uf is used instead.
As long as the capacitor fits and at least meets the minimum voltage it will be ok. Keep the capacitance values the same for all the capacitors except the 82uf's.

I specifically found some nice BC capacitors(originally used) that not only fit the lead spacing and met the voltage rating...but also were the higher 125 degree temp rating! Plus they look nice. I'm assuming that EH10023-2 is the changed schematic from the 1073.

 

[mikerl]

I am building a 4 channel unit.  I have the carnhill input transformers..

any reason i can't mount the input transformers on their side, underneath each board?  twords the front near the swithes, and far away from the output trannies.. which would be at the rear of the unit.

thanks.

 

[desol]

You could if wanted i guess...i'd probably mount them to the side where they wire in to the board, or whatever...just for ease of getting at them if i needed to. As long as they're away from the outputs.