Wein Bridge

How about Wien ?
Don't want to be a d*ck, I just want you to score more hits.

But I'm not 100% sure Wein is the same as Wien but then just spelt differently (as in wrong).

SSL EQ is another example.

Keith

Do you mean connected in series resistor, capacitor, and paralleled resistor & capacitor?

[quote author="buttachunk"]I've been looking for Wein-bridge EQ designs... does anyone have or know of any designs ?[/quote]

While I don't have a schematic handy the eq in a console I did back in late '80s (AMR 600/1600/2400) used Wein Bridge topology. Very nice, transparent approach because of low noise gain compared to state-variable or other conventional EQ topologies.

Downside as I recall was the oddball potentiometer needed to execute a sweep EQ section (we had to tool up a special part using the wiper to shunt between two parallel screened resistive tracks per pot wafer). Because of the topology any wiper bounce or intermittence resulted in parasitic oscillations (clicky, scratchy pot noise). It was worth the trouble but I'm not sure how to accomplish with off the shelf parts.

JR

PS: The same EQ topology (dialed in for different Q) was also used in Peavey Mark VIII SR consoles from around same time period (shared same tooled potentiometers and a few other common components). The owner's manuals for both consoles came with full schematics so there are surely schematics out there.

Buttachunk, FWIW, Wien bridges are often used as band-reject filters in distortion analyzers. I designed a simple manually-tuned analyzer about ten years ago that accomplished the tuning with a dual linear pot and three switched capacitor decade ranges... This is a pretty conventional setup.

I believe I've seen some Wien-derived sweepable midrange EQs in Soundcraft products.

I used them for cheap simple oscillators, with a light bulb in gain stabilizing network.

Here's something pertinent...



(Cleeeek for Beeeeg Pickcha.)

Keef

wein bridge :?

does'nt he play for chelsea?





sorry could'nt resist

I need to retract my caution about requiring a special pot. Upon reflection my former difficulty was trying to squeeze a dual (freq) pot and a single (boost/cut) pot into one dual concentric component. Thus the Rube Goldberg dual element on a single wafer.

JR

[quote author="buttachunk"]

JohnRoberts, thank you. I have heard excellent reviews of the AMR eq. are dual-concentric pots currently available ?

[/quote]

I can't recall the exact schematic but still remember that damn PIA potentiometer's PN [71190557]. It was actually a pretty nice part after they got it right. The dual elements screened on one substrate tracked unusually well as you would expect, but it is an older, physically large, pot family and obsolete by now from both vendors. We scratched one vendor back when the consoles were still in production over wiper issues. Any parts still in Peavey service stock are probably best used to keep old consoles happy in the field.

I am not up on what's available in low quantities with mixed elements. You want a linear taper for boost/cut, but a log taper is probably best for wider frequency adjustment range.

have fun.

JR

May be a discrete frequency switch is the way to go?
I've discovered that actually I need only 2 frequencies to boost on my consoles (the top secret, don't ask which)

> retract my caution about requiring a special pot.

Thanks for saving my brain. I couldn't figure anything other than a dual reverse-audio taper would be needed. Yeah, getting that PLUS a boost-cut pot all in one hole would be "special". And as Keef's plan shows, that cut/boost pot's wiper is risky.

> cheap simple oscillators, with a light bulb in gain stabilizing network.

I know some boys got PhDs for the light-bulb, but light-bulb alone will NOT stabilize the oscillator. It's gotta have a signal-rate gain-droop. This was assured with sloppy biasing of H and P's vacuum tubes, or Heath's 5-transistor oscillator. But when you "improve" these "mis-biased" amplifiers, the oscillation becomes increasingly hard to tame.

The light bulb does get you from 2% THD down well below 1%, but it is not sufficient.

There is a very different oscillator which amplifies its output to a full-rail square-wave, and filters back to a sine. Just one pot, though only about a 4:1 range. Damsite more stable than an H-P. http://www.national.com/ms/LB/LB-16.pdf

> actually I need only 2 frequencies to boost on my consoles

I can't remember when a bell-shape boost actually improved a sound. I work all with dips and slopes and cut-offs.

[quote author="buttachunk"] :guinness: is this the low-mid band ? (15nf) also, how would one "shelf it" ? :green: [/quote]

They don't shelf this one... The manufacturer instead uses a 4-gang reverse-log pot and makes a second filter which tracks alongside the first, in shelf mode. -if you want shelf, you simple switch over to that output... but making one requires 4-gang rev-log pots, and if people have a hard-time finding 2-gang versions for the 9k preamp, then this is only going to be tougher...

Keef

[quote author="JohnRoberts"]While I don't have a schematic handy the eq in a console I did back in late '80s (AMR 600/1600/2400) used Wein Bridge topology.[/quote]

This wouldn't be the DDA AMR 24 console? If so, I would have the schemos.

Michael

the sony 3000 has some wein-bridge eq design as some eq options. The eq's themselves sound nice especially the semi parametric design. The full parametric sounds like crap IMO.

Its the Peavy AMR...
Nice tread over at gearslutz
http://www.gearslutz.com/board/showthread.php?t=97606

[quote author="JohnRoberts"]I can't recall the exact schematic but still remember that damn PIA potentiometer's PN [71190557]. [/quote]
Damn...

I have five of those consoles in storage, and many of them have worn tracks on those pots, which has led to a little "squeal' as you turn past specific dead-spots. I did look briefly into sourcing replacement parts, but drew a blank and they went into non-air-conditioned storage here in humid Florida, where I'm sure they haven't improved with age. -That was perhaps 3 years ago.

I think we have a buyer for them (or most of them) now, and I'm hoping that I don't have to service them first... Not a design issue, so much as a part-sourcing headache that I really don't care for...

Keith

[quote author="SSLtech"][quote author="JohnRoberts"]I can't recall the exact schematic but still remember that damn PIA potentiometer's PN [71190557]. [/quote]
Damn...

I have five of those consoles in storage, and many of them have worn tracks on those pots, which has led to a little "squeal' as you turn past specific dead-spots. I did look briefly into sourcing replacement parts, but drew a blank and they went into non-air-conditioned storage here in humid Florida, where I'm sure they haven't improved with age. -That was perhaps 3 years ago.

I think we have a buyer for them (or most of them) now, and I'm hoping that I don't have to service them first... Not a design issue, so much as a part-sourcing headache that I really don't care for...

Keith[/quote]

Best chance for repair parts is Peavey service but I have no idea what they might have left these days. Like I said it was a special design. The Alps version was the better of the two originally tooled up as they made a new wiper with more individual fingers in the right places. The second source cheated and used a stock wiper so there were only a couple of fingers over each track and contact quality varied some with concentricity of element screens, etc. As I mentioned contact bounce could cause audible parasitics. I suspect either version will degrade with wear and tear.

Note: if it ever comes down to harvesting parts from kited out old modules the Peavey Mark VIII SR consoles from same time era used the same pot series. I would advise a strong preference for old Alps parts as they will be more robust over time.

JR

[quote author="PRR"]
> cheap simple oscillators, with a light bulb in gain stabilizing network.

I know some boys got PhDs for the light-bulb, but light-bulb alone will NOT stabilize the oscillator. It's gotta have a signal-rate gain-droop. This was assured with sloppy biasing of H and P's vacuum tubes, or Heath's 5-transistor oscillator. But when you "improve" these "mis-biased" amplifiers, the oscillation becomes increasingly hard to tame.

The light bulb does get you from 2% THD down well below 1%, but it is not sufficient.
[/quote]

No, I used them with one resistor, in feedback of a single power amp chip.

There is a very different oscillator which amplifies its output to a full-rail square-wave, and filters back to a sine. Just one pot, though only about a 4:1 range. Damsite more stable than an H-P. http://www.national.com/ms/LB/LB-16.pdf

Click to expand...

One integrator and one comparator with a hysteresis loop will do the job. Now, shape then filter a triangle, instead of a square, it is simplier. However, National's approach from your link with oscillating filter is a good idea as well.


[quote author="PRR"]
> actually I need only 2 frequencies to boost on my consoles

I can't remember when a bell-shape boost actually improved a sound. I work all with dips and slopes and cut-offs.[/quote]

Because it is as I said, a top secret.
Ancient Romans stole it from Egyptean prists and called Balkanto.