NE570-based NR compander (P-522) by JR

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JR.
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Re: NR compander (P-522)

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The cost of tooling IM has come down quite a bit thanks to our Chinese friends... While I expect it could be another zero added to my last version. The size of the package and complexity will make a difference. I will need to get up to speed in 3d cad since I want to take my best shot at a design, and then let the experts tell me why that won't work, rather they pay somebody else to do it from scratch. I will gladly pay them to finish my design to something they can fab.

I know enough to know that I don't know the idiosyncrasies of designing a proper IM but I have friends who can help advise me.

Regarding turnkey CM, They don't have a say in my retail price.. They negotiate a price to build based on their cost.., I set a retail sales price based on how much I need on top of that to effectively market and support the product, plus a little beer money. I will sell the product via my website, and tell them where to drop ship the units. If they try to jack me up on costs, I move the product somewhere else. They should make a good return and so should I.

I actually have another close friend, who used to work for me years ago and I mentored along the way.. He is now running his own CM division as part of a larger corporation and happy to cut me a very fair deal. Normally I would be too small to get good treatment from these folks.

JR
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Crusty
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Re: NR compander (P-522)

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Sounds like it will be a snap to assemble once the case design is worked out and you lose all that secondary machining. I think the "half or list price" must have been for the existing product line we were talking about. This guy shut down his factory and moved production to a contract manufacturer. He had one company employee there doing final QC.

So if I understand it, it's going to be some sort of two-piece case design that incorporates the rail guides into it? Let me know what you come up with for solid-modeling software - I've wanted to learn it but I have to choose my battles for now. I guess you have impact resilience in this design to contend with too...

As far as the original post in this thread, I'm gonna play with diode limiting idea on my eq this weekend and see if I can smooth the summing stage a bit as it starts to approach overload. I had never thought to try it before...
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JR.
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Re: NR compander (P-522)

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If you are talking about that diode break where above a P-P voltage another feedback path becomes active, that will was done to sound better that hard clipping, and IIRC with the 570- series gain cells the could get nasty if they are overdriven. So it was a lesser evil decision ands only expected to catch large transients.

JR
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mediatechnology
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Re: NR compander (P-522)

Post by mediatechnology »

JR. wrote:If you are talking about that diode break where above a P-P voltage another feedback path becomes active, that will was done to sound better that hard clipping, and IIRC with the 570- series gain cells the could get nasty if they are overdriven. So it was a lesser evil decision ands only expected to catch large transients.
I've seen that trick used in field recorders and modulators as well. I just saw one in the THAT 4320 wireless compander demo board. You can hit a diode pretty hard like that for soft-limiting and it not sound all that bad. Far better than a hard clip - or worse - polarity reversal.

John, the P-522 still amazes me due to it's simplicity.
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JR.
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Re: NR compander (P-522)

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The diode(s) in that circuit mainly create a threshold at roughly 10x a diode drop.. (because of the resistor divider 2k/20k). above about 5-6V p-p it just looks like a 20k feedback resistor added in parallel with the rest of the negative feedback. Below that p-p voltage it is just part of the DC feedback path.

JR

PS: Ironic that the 522 was IMO my best NR design, but the product failed in the marketplace because performance was not the most important thing, 3rd or 4th on the list...
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Crusty
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Re: NR compander (P-522)

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I got to play with this a little this weekend by scabbing into an eq. Not really needed as the opamp I used recovers quite nicely on its own. It does make for a nice effect when abused (!) I 'nested' a few sets across the feedback path and could get a nice and smooth limiting effect. I want to try some other 'diodes' too- LEDs, schottky, zeners, etc, and maybe put a ceiling control. Fun to play with something so simple for a change! LOL

JR. wrote:
PS: Ironic that the 522 was IMO my best NR design, but the product failed in the marketplace because performance was not the most important thing, 3rd or 4th on the list...
True of many industries - defense, medicine, education...
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mediatechnology
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Re: NR compander (P-522)

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Crusty wrote:I got to play with this a little this weekend by scabbing into an eq. Not really needed as the opamp I used recovers quite nicely on its own. It does make for a nice effect when abused (!) I 'nested' a few sets across the feedback path and could get a nice and smooth limiting effect. I want to try some other 'diodes' too- LEDs, schottky, zeners, etc, and maybe put a ceiling control. Fun to play with something so simple for a change! LOL
I think you'll find it to be dominate third harmonic "symmetrical" distortion if both poalrities are effected equally. Add a dash of asymmetry for a little second. Here's a cut I modified with diodes. IIRC THD measured about 10% (roughly even second and third harmonic) at the level I checked it. The brightness it adds to the guitar under this severe abuse is wicked.

http://www.ka-electronics.com/Content/E ... cessed.mp3

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Re: NR compander (P-522)

Post by Crusty »

mediatechnology wrote:
We would never go off topic here
Yes, where are the moderators?...

What do you think about adapting the sliding 'wow filter' hpf into a preamp? Seems like it might make for a sort of rumble filter...
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JR.
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Re: NR compander (P-522)

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Crusty wrote:
mediatechnology wrote:
We would never go off topic here
Yes, where are the moderators?...

What do you think about adapting the sliding 'wow filter' hpf into a preamp? Seems like it might make for a sort of rumble filter...
The sliding HPF might make some sense in a compressor, so when it is commanding a bunch of boost it trims away very LF. However to get flat nominal bandpass at unity, you want a bunch of boost range to play with. Subtle compression, won't cause much pole shift.

In a preamp there is a far simpler way to lose HF at high gain, and many of the already do it. The common topology for high gain preamps involves a low value R in the gain leg. A cap in series with this R automatically give a HPF that changes with gain.

I recall one popular mixer that I had to compete with, who would undersize this cap, resulting in less LF at high gain, then they would brag about how quiet their preamps were, because 1/F noise was attenuated relative to flat preamps (like mine).

JR
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Crusty
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Re: NR compander (P-522)

Post by Crusty »

Ah, I forgot about that effect - a plus maybe for keeping the cap there. Too bad it has to be so large...
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