Question About Low & High Pass Filter On BBD Based Chorus

[ElectricDruid]

I found my chorus distort with 9V, but clean with 15V

The significant figure is how big a signal you're feeding into it. As a rough guess, you'll have about 2V headroom at 9V and about 3V headroom at 15V. If you get distortion at one supply voltage and not the other, you're probably feeding in 2.5V or so.

(Depending on the BBD, these figures might vary a bit, but you get the idea).

Tom

[Rob Strand]

The significant figure is how big a signal you're feeding into it. As a rough guess, you'll have about 2V headroom at 9V and about 3V headroom at 15V. If you get distortion at one supply voltage and not the other, you're probably feeding in 2.5V or so.

For the hell of it:
Based on the DC transfer range in the datasheets, which I suspect are indicative of the hard limits, I get,
5V:   1.8Vp-p
9V:   3.1Vp-p (estimate)
15V:   5.0Vp-p

If your numbers are peaks then they look pretty close.  I've got some hard measurements in my files somewhere - I just don't want to go wading through them ...

[ElectricDruid]

For the hell of it:
Based on the DC transfer range in the datasheets, which I suspect are indicative of the hard limits, I get,
5V:   1.8Vp-p
9V:   3.1Vp-p (estimate)
15V:   5.0Vp-p

If your numbers are peaks then they look pretty close.  I've got some hard measurements in my files somewhere - I just don't want to go wading through them ...

Yeah, my numbers were peak-to-peak. That datasheet number of 1.8Vp-p at 5V is higher than what I measured, which was more like 1.2V or 1.3V. I remember because it was conveniently close to the level I could limit to with with a set of simple clipping diodes (1n4148/1n914s).
Either way - the point is that the BBD's headroom is *a lot* less than its supply, and you need to watch out for that.

T.

[Rob Strand]

which was more like 1.2V or 1.3V.

The lowest set of numbers from the datasheet corresponds to the range of the bias plot.   

Bias plot based:
5V:   1.2Vp-p
9V:   2.3Vp-p (estimate)
15V:   4Vp-p

It's a far stretch of my memory but I have this feeling when I looked at this stuff in detail even 4Vp-p seems high for a SAD-1024 running at 15V.

Either way - the point is that the BBD's headroom is *a lot* less than its supply, and you need to watch out for that.

Headroom and noise on those things are definitely the weak points.  Back in the day I made of point of getting the biasing just right.

I remember because it was conveniently close to the level I could limit to with with a set of simple clipping diodes (1n4148/1n914s).

Hmmm,  that rings a bell.   I remember lifting the diode limiter (before the BBD) out so I could get a better idea where the BBD clipped.