EQN build thread

[peter purpose]

Joao,
If you saw off the 24v tab, you can ONLY run it off the 16v rails.

 

[jplebre]

I haven't yet, as I don't have +-24v rails yet running on my 51x. My question is do I have to?
(I have populated all the VPR 16v bits)

Was hoping I could swap it in case I run out of 16v juice at home or I need to go somewhere by removing the lambda and putting the jumper in.

 

[peter purpose]

Removing the dc-dc converter and putting in the jumper is fine for 24v operation. The other components will be happy going nowhere.
But as soon as the 24v tab is removed, you'll only be able to run it off the 16v rails.
Leaving the tab on... without the jumper inserted is fine for 16v.

 

[jplebre]

AWesome! Interchangeable between the 2 alliances! you are a genius! thanks!

 

[scott_humphrey]

It's been a cold, blustery winter, with dreams of multiple channels of Neve-style EQ swirling through the frosty air….

I finished 10 units the other week, and I just wanted to say thanks to Peter for making this possible. All units seem to work just fine. I haven't calibrated yet, but using them on a mix they all seem to do what they are supposed to do. Also, thanks to Mnats and canidoit for sharing their advice.

Speaking of sharing, I'll fess up to the stupid mistake that I made and tell you how I solved it. I ended up soldering the Q switch and the bypass switch to the wrong side of the board--and I repeated this mistake on each of the 10 boards! These switches are difficult to removed because the pins are a tight fit in the board even without solder, and I was really worried about damaging the circuit boards during the removal process. After some research, I ended up ordering the Quick Chip SMD-1 removal kit from eBay. I won't go into the details of the product, but for removing a part with multiple pins this worked great and none of the boards were damaged. Despite this, the plastic housing on some of the switches was damaged by the combination of heat and the mechanical force of having to pull them from the board with pliers.  I ordered replacement switches (Multicomp p/n 9473017) and all is well.

Another tip: mnats describes drilling holes so that the potentiometers will seat correctly. I was too lazy for this, and decided instead to clip the tabs off of the potentiometers. I then used the pliers to roughen (make small, superficial cuts in) the remaining metal that interfaces with the bracket, so it acts like a lock washer. This worked very well.

10 years ago I never would have dreamed it possible to own some of the equipment that I now have because of groupdiy. Thanks and cheers!

 

[jplebre]

Scott, I hear you!

Since I completed my 2 channels they have been used strapped permanently on vocals and I've had to bounce some OH and pianos through it.
They are still expensive to build but what a treat!

Thanks for the tip on the SMD removal

 

[pachi2007]

Hi. I was looking at those awesome pictures  and now Ive got a doubt about the input trafo.
Those two screws for holding it to the pcb... can they go all the way inside the trafo or is there a risk to short it inside?.
Thx a lot
Pachi

 

[peter purpose]

If you have to force it.... don't.
File them down, or pack them out.

 

[pachi2007]

Thx Peter.
I see some guys cut the screw, others put a nut and washer to gain some space to avoid cutting. My doubt was if there was a specific max to go inside the trafo before touching the core.
Doubt clear

 

[pachi2007]

Ok trouble here.

I´ve got one eq working first try,the other it´s not working fine.

I lose 12db FS when I insert the eq in Protools with the eq bypassed.
With the eq on I can recover the 12db drop with the trimmer.

I checked trafos wiring and seems ok. (I guess they should be ok otherwise I couldn´t recover gain with trimmer, am I right?)

I put a new clipping adj trimmer RV5 and same gain drop.

I noticed that the TR1/MJE3055 and the 47R/2w resistor don´t get warm even after 30min. Checked/resoldered all parts around and nothing.

MJE voltages left to right looking from the front: 1.6V, 23.39V,1.004V
The other working eq  voltages are: 2.17V, 23.14V, 1.571V (is this little bit higher a clue? ) Also this working one gets warm to touch after 5min or so.

Any advice would be apreciated.
Thx
Pachi

 

[jplebre]

If you recover with EQ on, did you check polarity of the 22uF cap and value of 39k resistor to ground on the bypass path?
The o/p trimmer should affect both paths (RV5) (bypassed and EQ'd)

What value did you throw in on R29?

You are sure that your connections are ok?

Trying to help didn't have to do any troubleshooting with mine and want to understand the design a bit more

 

[pachi2007]

Thanks for you help Jplebre.
Yes I checked both 22uf tant caps, both 39k and the 3k3 next to it.

I didn´t explained myself clearly about RV4. It works both with eq on and bypass. When eq is on and all bands at their off position I can set the trim at unity gain, but when I turn the eq to off there´s this 12db drop.
With the eq on in fact I can go up to a -4db drop (almost there)  but if I bypass then the output is 12db hotter than the input.
I hope this makes sense.

R29 is 680R on both eqs. Works ok on the other eq. The thing that pisses me of is the heat thing at the 2w resistor and the big transistor. It gets warm on the working eq, not on this one, that´s why I was looking over there.

RV4 is for in/out gain adjustment and RV5 just for clipping adj right?

Thx a lot

 

[pachi2007]

"With the eq on in fact I can go up to a -4db drop (almost there)  but if I bypass then the output is 12db hotter than the input. "

Sorry I meant the other way around. -4db eq off then +12db hotter than input with eq on

 

[pachi2007]

Reheated some stuff , rechecked values, played with the RV5 trimmer and now R32 (the 2w 47R) gets hot as hell in a few seconds. Had 2 turn off power as it was too hot to touch. I see no solder bridges though.
Time for a cigarette 

 

[pachi2007]

Back from cigarette.
Turned RV5 trimmer the other way again, heat is gone.
I can hear some laughs from the pros

 

[jplebre]

so it was RV5

 

[pachi2007]

No , still the same volume drop. I was just laughing at my troubleshooting and guessing
I´m not sure what to do next. I guess I´ll start taking voltage readings with the working one and compare. I dont want to start swaping things without knowing, just because.
I also checked ground continuity around the input trafo and some other random points (beep beep) I don´t really know if is ok to touch it with the 9V of the multimeter, maybe it´s wrong.
Still slowly learning 
Thx for asking

 

[jplebre]

well, if i get it correctly RV5 will bias the signal so will raise the DC. The resistor next to it will be dissipating a fair amount of current (12v/47r) roughly 3w (if i get it right)

Since your voltage rails measure fine, I would say the issue is in the bypass circuit or on the BA283 amp http://pds2.exblog.jp/pds/1/201202/15/96/f0039496_2356277.jpg

 

[pachi2007]

Thx a lot jplebre.
I´ll report back with my findings

 

[pachi2007]

Hey Jp have you ever noticed how much brown and red look alike in those resistor lines? 

This is a little embarrasing. As you suggested first it was a resistor (33k instead of 3k3) at the bypass. I checked again all those values and there it was.
Anyway, it´s ok now, no level drop.
Thanks a million for your help, I owe u one.