EQN build thread

[corgan4321]

Thanks for your response Paul! I have read through all the posts on this thread a few times and have also successfully built 4 EZ1290 preamps so I do know what to look for when it comes to achieving proper bias.
The problem I'm having now is that when I do achieve proper bias with RV5, I get low frequency noise that only goes away when i turn RV5 CW, but when I do so, I get very uneven clipping on my output waveform (only clipping on the negative swings).
I've double checked that I stuffed the PCBs (opamps and main boards) correctly and I'm using MPSA18 transistors in lieu of BC184c (flipped around 180 degrees of course).

If the wiper for RV5 is too far to one side (CW?) you will get oscillation. Put RV5 in the middle of it's range and do the same for RV4. Read some of the posts on this thread about how the input trim affects the bias and then proceed accordingly.

Thanks!

Paul

 

[Potato Cakes]

When you adjust RV5 to get rid of noise, have you then tried adjusting RV4 to change the input gain and see if that helps? I distinctly remember that being the issue for someone building these. I recently finished my pair and I had the same issue with the LF oscillation because RV5 was turned too far CCW. One is built with MPSA18 and the other with BC184C's, both running on +24V (51X).

See if RV4 is the answer and let us know.

Thanks!

Paul

 

[corgan4321]

Hi again Paul,

Still having some issues with the EQNs... I had some BC184c's in the mail on the way to me already so I put them in one of the EQNs I have.  I also reflowed some joints around the output stage. Whereas before I was getting loud oscillation at the proper bias current, I'm not getting softer noise (around -63dbFS into my interface). It's definitely better now, but I have verified that the issue is coming from the output stage by listening to the positive leg of C48 - here I have no low frequency noise like I do on the output.

To answer your previous question, it doesn't seem that RV4 (the volume trimmer) affects the noise at all.

Since I've now replaced the two BC184cs in the output section, are there any other components around there that may be bad like a noisey resistor or capacitor?

Thank you,
Will

 

[corgan4321]

I've done more work on the boards and discovered that the issue is certainly in the DC-DC circuit. When bypassing the DC-DC converter and powering the boards with 24v, I get clean operation!

I'm assuming it will be an issue with the TDK/Lamda converter so hopefully I'll have replacements for those soon to verify, otherwise I'm looking towards Q1 and surrounding components...

thank you

 

[Whoops]

I'm cleaning my workshop and found 1xEQN pcb plus 4x front pannels and 4x L-backets for this units.
I put the stuff for sale in the black market in case someone is interested:

https://groupdiy.com/index.php?topic=76070.0

 

[Brizco]

id like to upgrade both my LAZ EQN's with center detent potentiometers, but i have troubles to find potentiometers in that small quantity...

can someone please guide me to a source, or the correct part number for the 10K and 50 pots?

thanks!!

 

[gyraf]

I think reichelt.de has ALPS RK27 in centre-detended version..

 

[Brizco]

I think reichelt.de has ALPS RK27 in centre-detended version..

Thanks Jakob! Do RK27 really fit? not to large?

 

[gyraf]

I have no idea - I don't know what the mechanics of this project is like..

/Jakob E.

 

[Whoops]

id like to upgrade both my LAZ EQN's with center detent potentiometers, but i have troubles to find potentiometers in that small quantity...

can someone please guide me to a source, or the correct part number for the 10K and 50 pots?

thanks!!

do a search in audiomaintenace, they have some Omeg center detent pots offerings

Also do a search in Farnell and Mouser for "Center Detent" or "Center ident"

 

[Potato Cakes]

id like to upgrade both my LAZ EQN's with center detent potentiometers, but i have troubles to find potentiometers in that small quantity...

can someone please guide me to a source, or the correct part number for the 10K and 50 pots?

thanks!!

Is there really a need for a center detent? I thought I would want them as well for my builds but since all of the individual frequency bands can be turned off then that essentially does what a center detent is supposed to do.

If you had to have them, then Jeff at CAPI sells 10k Bourns with center detents which should be small enough but I do not know where you would find 50k pots with the necessary dimensions.

Thanks!

Paul

 

[Whoops]

Is there really a need for a center detent?

Yes, always
At least for me personally, I would not use any other type of pot.

But I was not the one asking...

 

[Potato Cakes]

Yes, always
At least for me personally, I would not use any other type of pot.

But I was not the one asking...

Usually I would agree if it was the full EQ circuit being switched in/out, but this design has individual band bypass so it effectively does what a center detent is supposed to do. I also am using this particular EQ to boost frequencies only as it sounds great. If precision is a desired feature then this is the wrong circuit. Also, the issue still remains that finding the correct size potentiometers with the correct values and center detent is difficult to find as an off the shelf product is very difficult. I don't want to discourage further searching for them but it would stand to reason that maybe they might be redundant in the EQN.

Thanks,

Paul

 

[Whoops]

Also, the issue still remains that finding the correct size potentiometers with the correct values and center detent is difficult to find as an off the shelf product is very difficult.

Yes, that can be problematic sometimes, not a lot of choices of Center Detent pots, well if you don't find them them it's a dead end and have to resort to normal pots.

I was happy the day audio maintenance ordered the Center Detent pots for the Night EQ project, it really improved my units.

Best regards

 

[stylesforfree]

Looking forward to trying out a pair of these! Especially on drums

 

[Rob Flinn]

Looking forward to trying out a pair of these! Especially on drums

If you look at the date of the original post you will find this project is now 14 years old. Peter hasn't produced this kit for probably 12 years & hasn't been here for ages. I last saw him about 10 years ago when we necked a few beers in London & I got my 2 kits from him. However, you may be lucky to get some unused kits in the black market. If not there are some other options if you look around.