BP Net EQ vs Behringer T1951

[tonedude]

      ehhh, anyway...

Is this some kind of a secret... ?

I was searching for a decent stereo EQ to mod and when looking at schematics I found that the implementation of the filters (or is it called gyrators?) is kind of... ...the same in the Net EQ and in the T1951 Behringer (different values but they essentially look the same to me). I read somewhere that one or two of the bigger manufacturers got a little to much inspiration from BP Net EQ and this must be one of them. Surprised? Probably not! Just bought one of from Ebay, will be a fun project modding this with a little more inspiration from the Net EQ.

Ps. I'm sorry for the "ugly" subject header...    :-[ 

 

[tonedude]

Net EQ:

 

[tonedude]

T1951:

 

[dagoose]

To me they look pretty different. OK, they both use 2 opamps but the filter circuit looks quite different, at least in my eyes.
Though it's behringer so it would not surprise me.  8)
I had a tubevitalizer (t1953?) a long time ago and found out that the tubes are glowing (at least it looks like that) because they have simple lightbulbs behind them.  ???
I bought it back then because 'm.. it was cheap  ;D

 

[tonedude]

I had a tubevitalizer (t1953?) a long time ago and found out that the tubes are glowing (at least it looks like that) because they have simple lightbulbs behind them.  ???

Lightbulbs are cool... 

But regarding the circuit, if you take a closer look (and if we would redraw the T1951 schematic), it's clear that the topology is mostly the same. Some components are rearranged, values are changed, some components are added, but it's actually more or less the same.

 

[tonedude]

I'll try to redraw the essential part of the T1951 schematic in a day or two to clarify the similarities.

If someone want to have a look at the full T1951 schematic you can download it here

// Mattias

 

[tonedude]

Ok, the above T1951 part redrawn to make it a little clearer... maybe I'll do more of the surrounding circuit later. When the redrawn part is put in its context it becomes pretty clear that the "heart" (the gyrator design and how they are implemented in the rest of the circuit) of the T1951 is very influenced by the Net EQ. I'll start a mod thread when the fun starts.


Ps. I'm no EE just a hobbyist having fun and learning along the way... 

 

[tonedude]

Just a comment on the full T1951 schematic. When looking at the original T1951 schematic it almost looks as if they drawn it in a way just to complicate the discovery of the resemblance with the Net EQ. 

 

[Harpo]

: and the colour of the pen used to draw the schematic was influenced by (insert name)...
It is a state variable filter. TI once (1992) had these functions inside a single chip (UAF42).
Difference in filter implementation is in the details, FI just try to get close matched neg.log stereo pots and see Barrys workaround for linear taper pots ...

One funny thing in the Behringer unit is its magic power supply. With 7815/7915 voltage regulators and single 1N400x standoff diodes they already round up to +/-16V at psu-out and arrive at +/-17V for the parts to supply.

 

[tonedude]

Still learning... 

Where in the circuit does the T1951 use neg.log stereo pots, is it the 100kC for frequency selection? Regarding pot codes, does anyone know what 50kG stand for. Thanx!

 

[Harpo]

Where in the circuit does the T1951 use neg.log stereo pots, is it the 100kC for frequency selection?

Yepp.

Regarding pot codes, does anyone know what 50kG stand for.

Got a broken pan-pot?
Some Panasonic definitions and taper curves http://www.panasonic.com/industrial/components/pdf/AOK0000PE1.pdf
Europe/US/Asian manufacturers might use a different taper labeling, so better measure resistance at different rotation angles.

 

[tonedude]

Ok, got the t1951 and started the modding, or should I say rebuilt.

Big case but whats inside?

 

[tonedude]

... Air!  :

New slogan for Behringer: "Behringer, room for improvement"!

 

[tonedude]

Its all SMD components and therefore not so modfriendly, not to me at least. The only thing I use from the t1951 right now is the parallell arrangement of the state variable filters. I connected them to a veroboard containing three "parts" of the Net EQ, the input and output circuit, and also the circuit that sits in between the in and out circuits, the part that connects to the parallell filters of the t1951. So if I bypass the filters, its actually a Net EQ without filters...  8) ;D

HOw does it sound? To my ears, very very nice! Price? 200euro including parts for rebuild.

Next step in the rebuild is to beef up the PSU. And next to that do something nice with the tubes that, at the moment, just glowing in there.

Two of these containing in/out and the "circuit in between" sits in the case right now.

 

[tonedude]

The veroboard contains those parts. I did exclude the HPF.

 

[tonedude]

And i did change the knobs to something more "userfriendly".

 

[tonedude]

One more thing, I did use the peak sensing circuit of the t1951. It measures the signal both before and after the filters as far as I can tell, witch is kind of a nice feature.

 

[okgb]

Looks better right away !  thanks for posting your investigations
Do you use the valvex much ?

 

[tonedude]

You are welcome.   

I bought the Valvex with the intention of using it as a summing tool for mixes but this far it's main use has been summing external effects. After uppgrading the PSU caps, with the effect of lowered noise floor and extended headroom, it sounds more than great though.