Noisy FV-1?

Hardware questions and issues with the FV-1

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keithv
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Noisy FV-1?

Post by keithv » Mon Nov 09, 2015 4:15 pm

Image

I'm working on designing a very simple guitar reverb using the FV-1. So far it sounds good, but it's a bit noisy. Please take a look at my schematic and let me know if I'm doing something wrong or if there's something I can improve. Or is the FV-1 just kinda noisy?

frank
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Post by frank » Mon Nov 09, 2015 7:08 pm

You have the right output tied to ground, if unused it should be left open.

Layout has a lot to do with noise, post some pictures.
Frank Thomson
Experimental Noize

keithv
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Post by keithv » Tue Nov 10, 2015 9:56 am

Originally, I left both the right in and out open. Tying the outputs together caused some clipping, but aside from that, I didn't notice any difference as to whether or not the unused I/O was grounded, NC, or tied to the other.

frank
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Post by frank » Tue Nov 10, 2015 1:57 pm

keithv wrote:Originally, I left both the right in and out open. Tying the outputs together caused some clipping, but aside from that, I didn't notice any difference as to whether or not the unused I/O was grounded, NC, or tied to the other.
You never tie outputs directly together or to a power rail, that will damage a chip. If the output tries to go high but it is tied to ground (directly or through another output that is trying to go to ground) you have a short between power and ground through the pins and that will damage the chip.

You can generally tie inputs together since they are driven by an external signal.

At this point the FV-1 could be damaged or it may be a layout issue, pictures will help.
Frank Thomson
Experimental Noize

keithv
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Post by keithv » Wed Nov 11, 2015 10:30 am

Image

I think the chip is fine still. The outputs weren't initially tied together or to ground. I tried that later and it caused clipping or nothing at all, so I undid that and it went back to the way it was before.

The PCB is laid out almost like the schematic where the FV-1 is concerned. The 3.3V trace meanders around a bit, but the various components are about as close to their respective pins as can be. The audio signal is kept to the other half of the PCB and only intermingles with the FV-1 side of things to go to the I/Os.

keithv
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Post by keithv » Fri Nov 13, 2015 11:05 am

I just put it in the FX loop of an amp, and it's dead quiet. Does the FV-1 like to see a hot input signal?

frank
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Post by frank » Fri Nov 13, 2015 4:51 pm

First, sorry for not getting back to this. Been a crazy week, always gets this way from November till after NAMM.

As a general rule, all digital devices like hot inputs. You really want to drive the inputs of an ADC to just a few bits below clipping for best SNR.
Frank Thomson
Experimental Noize

keithv
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Post by keithv » Tue Nov 17, 2015 2:51 pm

I modified the input buffer to give a gain of +10 instead of +1 to drive the FV-1 input harder, and modified the output buffer to compensate to bring the dry level back to unity gain. The wet signal is now dead silent....I mean in terms of noise. The FV-1 is working perfectly and is extremely quiet. In fact, I'd go as far as to say it's actually reducing noise.

Do the app notes make mention that the FV-1 performs best with line level input rather than instrument level?

Sweetalk
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Post by Sweetalk » Wed Nov 18, 2015 9:54 am

keithv wrote:I modified the input buffer to give a gain of +10 instead of +1 to drive the FV-1 input harder, and modified the output buffer to compensate to bring the dry level back to unity gain. The wet signal is now dead silent....I mean in terms of noise. The FV-1 is working perfectly and is extremely quiet. In fact, I'd go as far as to say it's actually reducing noise.

Do the app notes make mention that the FV-1 performs best with line level input rather than instrument level?
Don't you get a lot of clipping?

keithv
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Post by keithv » Fri Nov 20, 2015 1:53 pm

No. None. I simply took the in/out buffer circuit from the Ibanez AD-80.

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