Some things I've learned about the FV-1
Moderator: frank
Some things I've learned about the FV-1
OK, I typed up this LONG response, and in the process the board logged me out, and I lost the whole thing. So this is my second and last attempt.
I've been asked to post some things about my research/dev with the FV-1.
A little about myself. I've worked with delta sigma converters for the last 15 years. I've gotten some patents. I've built products for pro audio (recording), guitar, and stage/DJ/live performance, including custom stuff used on albums you've no doubt listened to. The FV-1 was my first attempt at DSP. Enough boring things, though. Let's get to the good stuff.
Because my FV-1 design is currently being used in a commercially available product, I can't share specifics with this forum. That means no schematics, no measurements, no Bode plots. I can point everyone in the right direction though. I hope you understand.
First, the thermal noise. I've seen people make comments about this. I think the published spec is -97dB typ? I can't remember. In my experience, If you're using a standard 78xx regulator in your design, it's going to be noisy. Consider using a modern LDO or an LM431 shunt, and split the supplies into separate VDD and VCC. Using split power supplies, I was able to get the noise floor so low that it's inaudible at max gain. this includes two opamps, one of which is a makeup gain stage. I built my power supply using some research that Philips EMC Labs in Eindhoven published some years back, so my results might differ from yours.
Second, I experimented with a variety of power supply levels in my initial attempts to control noise. I found that 3.3v offers the best sonic performance, and keeps the FV-1's internal stages from overdriving. For reasons I'm not sure of, it really opens up the mid-range response as well. Maybe this has to do with the internal decimation filter behavior?
Third, use the fully differential IO, otherwise you're robbing yourself. You can tie your inputs together, and sum the outputs into a differential opamp stage. The difference in sound between single pin IO and differential IO is pretty amazing.
Fourth, the watch crystal clock is awesome. Seriously. I tried all kinds of fancy approaches including third order, wide Q XO's with fancy divider networks. The watch crystal sounds the best IMO.
Fifth, use a four layer board. This is technically a mixed-signal design, so four layer boards are your friends. If you're trying to save money on your design, consider using JLC PCB. They'll do low-volume four layer boards with parts placed for super cheap.
Anyway, I hope this helps someone here.
I've been asked to post some things about my research/dev with the FV-1.
A little about myself. I've worked with delta sigma converters for the last 15 years. I've gotten some patents. I've built products for pro audio (recording), guitar, and stage/DJ/live performance, including custom stuff used on albums you've no doubt listened to. The FV-1 was my first attempt at DSP. Enough boring things, though. Let's get to the good stuff.
Because my FV-1 design is currently being used in a commercially available product, I can't share specifics with this forum. That means no schematics, no measurements, no Bode plots. I can point everyone in the right direction though. I hope you understand.
First, the thermal noise. I've seen people make comments about this. I think the published spec is -97dB typ? I can't remember. In my experience, If you're using a standard 78xx regulator in your design, it's going to be noisy. Consider using a modern LDO or an LM431 shunt, and split the supplies into separate VDD and VCC. Using split power supplies, I was able to get the noise floor so low that it's inaudible at max gain. this includes two opamps, one of which is a makeup gain stage. I built my power supply using some research that Philips EMC Labs in Eindhoven published some years back, so my results might differ from yours.
Second, I experimented with a variety of power supply levels in my initial attempts to control noise. I found that 3.3v offers the best sonic performance, and keeps the FV-1's internal stages from overdriving. For reasons I'm not sure of, it really opens up the mid-range response as well. Maybe this has to do with the internal decimation filter behavior?
Third, use the fully differential IO, otherwise you're robbing yourself. You can tie your inputs together, and sum the outputs into a differential opamp stage. The difference in sound between single pin IO and differential IO is pretty amazing.
Fourth, the watch crystal clock is awesome. Seriously. I tried all kinds of fancy approaches including third order, wide Q XO's with fancy divider networks. The watch crystal sounds the best IMO.
Fifth, use a four layer board. This is technically a mixed-signal design, so four layer boards are your friends. If you're trying to save money on your design, consider using JLC PCB. They'll do low-volume four layer boards with parts placed for super cheap.
Anyway, I hope this helps someone here.
Re: Some things I've learned about the FV-1
Thanks for the info, what do you think about the LM1117?
Re: Some things I've learned about the FV-1
Good question. I have not tried that particular part, but looking at the datasheet I think it might be fantastic for an analog circuit.
It has pretty high output current capacity compared to the requirements of the FV-1.
Typically these kinds of regulators will offer higher current performance in exchange for (relatively) higher noise when compared to a low-current output LDO.
So, if the datasheet noise figure is to be believed...I would consider using it as a pre-regulator but not a local regulator for the FV-1. The reason is that noise performance is spec'ed at .003% of input (a weird way to specify it IMO) from 10Hz to 10kHz.
But Delta Sigma will suffer most performance degradation from thermal noise between 1Hz and 10Hz. I'm assuming the figure below 10Hz isn't included for performance reasons. I think there are better options out there for noise behavior in that band.
Does that make sense?
Re: Some things I've learned about the FV-1
Obviusly makes sense. Is one of the most common regulators around with the 78L33. Any recommendations about an LDO?.
Re: Some things I've learned about the FV-1
Are you here suggesting using separate LDOs for the analog and digital power supply pins on the FV1 chip? If so would you consider the REFP (Positive Reference) as part of the analog or digital power? I feel the datasheet could have gone into greater detail when describing the pinsmportnoy wrote: ↑Sat Jun 13, 2020 1:42 pm First, the thermal noise. I've seen people make comments about this. I think the published spec is -97dB typ? I can't remember. In my experience, If you're using a standard 78xx regulator in your design, it's going to be noisy. Consider using a modern LDO or an LM431 shunt, and split the supplies into separate VDD and VCC. Using split power supplies, I was able to get the noise floor so low that it's inaudible at max gain. this includes two opamps, one of which is a makeup gain stage. I built my power supply using some research that Philips EMC Labs in Eindhoven published some years back, so my results might differ from yours.
Found some info in this thread:
http://www.spinsemi.com/forum/viewtopic ... dvdd#p3380
Re: Some things I've learned about the FV-1
i really appreciate you posting all of these thoughts, thank you!!
now i feel a bit silly for always using a 78Lxx regulator just because all the boutique builders do
now i feel a bit silly for always using a 78Lxx regulator just because all the boutique builders do
Re: Some things I've learned about the FV-1
My apologies, I've been traveling a lot this summer and haven't been on this board.
I have seen that thread. In fact, very early on, I asked specifically about splitting up the supplies, and was given similar answers. Being the stubborn jerk that I am, I didn't listen to the advice and tried it on my own . Because I've worked with mixed-signal designs for a number of years I simply used circuitry that I've come to rely on. I was pretty amazed at the difference in noise performance.
I wouldn't use the 78L33 mentioned in that thread, there are several LDO regs out there with significantly better noise performance. Remember to keep an eye on the 10Hz noise figure!
Yes I am.knutolai wrote: ↑Sat Jul 04, 2020 4:56 am
Are you here suggesting using separate LDOs for the analog and digital power supply pins on the FV1 chip? If so would you consider the REFP (Positive Reference) as part of the analog or digital power? I feel the datasheet could have gone into greater detail when describing the pins
Found some info in this thread:
http://www.spinsemi.com/forum/viewtopic ... dvdd#p3380
I have seen that thread. In fact, very early on, I asked specifically about splitting up the supplies, and was given similar answers. Being the stubborn jerk that I am, I didn't listen to the advice and tried it on my own . Because I've worked with mixed-signal designs for a number of years I simply used circuitry that I've come to rely on. I was pretty amazed at the difference in noise performance.
I wouldn't use the 78L33 mentioned in that thread, there are several LDO regs out there with significantly better noise performance. Remember to keep an eye on the 10Hz noise figure!
Last edited by mportnoy on Wed Aug 26, 2020 5:57 am, edited 1 time in total.
Re: Some things I've learned about the FV-1
For most applications that part is fine. But I've grown used to avoiding it for anything that has a delta sigma converter or clock in it.
Aside from the LM431 shunt reg, I don't have any suggestions off the top of my head--I know that Analog Devices, TI, and Linear Tech make some suitable parts. Maybe reach out to their tech teams, or use their LDO product tree? Sorry I don't have better specifics.
Re: Some things I've learned about the FV-1
i gave the AP2205-33Y LDO a shot, and i can't hear any difference, but to be fair i'm not using proper test equipment. i'll try the LM431 as a shunt regulator next. but i do wonder if having separate analog and digital supplies was a lot more significant than the specific part used?
Re: Some things I've learned about the FV-1
Those are decent, but I think there's lower noise regs than that out there. IMO, based on my work with delta sigma converters over the years, I found that regulator noise (power supply noise) was a dominant factor in converter performance. In this case, I chose to split supplies in order to help limit noise, but I think the regulator choice itself was the primary reason.smear wrote: ↑Sat Aug 29, 2020 8:26 pm i gave the AP2205-33Y LDO a shot, and i can't hear any difference, but to be fair i'm not using proper test equipment. i'll try the LM431 as a shunt regulator next. but i do wonder if having separate analog and digital supplies was a lot more significant than the specific part used?
If you're looking for a decent inexpensive audio analyzer, checkout QuantAsylum's QA401. I've built production test rigs for a multi-site electronics assembly house using the QA stuff. Sure it's not as feature-rich as a Prism or an Audio Precision, but it's also not $5k-$15k.
Re: Some things I've learned about the FV-1
Thank you for the useful advices but i've a doubt about the separate power supply. What's the point of doing that knowing that there is no dedicated AGND and DGND on the FV1?
The return current would be on a single ground plane. Usually we separate analog and digital ground but in the FV1 case,it's impossible
The return current would be on a single ground plane. Usually we separate analog and digital ground but in the FV1 case,it's impossible
Re: Some things I've learned about the FV-1
That's a valid point, but my experience in working with this part has shown otherwise. And that's all I'm doing here, is sharing my experience. You might find it useful, or you might not.alassg wrote: ↑Fri Oct 09, 2020 6:20 am Thank you for the useful advices but i've a doubt about the separate power supply. What's the point of doing that knowing that there is no dedicated AGND and DGND on the FV1?
The return current would be on a single ground plane. Usually we separate analog and digital ground but in the FV1 case,it's impossible
Re: Some things I've learned about the FV-1
I've never said that is was a useless advice, i just wanted to point what i said. I just made a PCB using a single power supply and ordered it. I'll share my feedback on it as soon as i receive it.mportnoy wrote: ↑Sat Oct 17, 2020 10:35 amThat's a valid point, but my experience in working with this part has shown otherwise. And that's all I'm doing here, is sharing my experience. You might find it useful, or you might not.alassg wrote: ↑Fri Oct 09, 2020 6:20 am Thank you for the useful advices but i've a doubt about the separate power supply. What's the point of doing that knowing that there is no dedicated AGND and DGND on the FV1?
The return current would be on a single ground plane. Usually we separate analog and digital ground but in the FV1 case,it's impossible
Re: Some things I've learned about the FV-1
So, here is my feedback on FV1 and noise:
- I have used juste one 3.3v supply on my PCB (REG113NA)
- No noise at all when using a 5V power supply adapter to supply my op amps (OPA1642)
- Noisy when using a 9V power supply adapter to supply my op amps (OPA1642)
I have other issues but not related to the power supply. For example, i tied the audio right and left output with two 10kohm resistors and it seems that my signal is too much attenuated.
- I have used juste one 3.3v supply on my PCB (REG113NA)
- No noise at all when using a 5V power supply adapter to supply my op amps (OPA1642)
- Noisy when using a 9V power supply adapter to supply my op amps (OPA1642)
I have other issues but not related to the power supply. For example, i tied the audio right and left output with two 10kohm resistors and it seems that my signal is too much attenuated.
Re: Some things I've learned about the FV-1
this seems odd to me. the opa1642 should be fine with either of those voltages, so maybe you had a noisy 9v adapter? and was the same supply used to power the reg113na as well?alassg wrote: ↑Tue Nov 10, 2020 5:51 am So, here is my feedback on FV1 and noise:
- I have used juste one 3.3v supply on my PCB (REG113NA)
- No noise at all when using a 5V power supply adapter to supply my op amps (OPA1642)
- Noisy when using a 9V power supply adapter to supply my op amps (OPA1642)
I have other issues but not related to the power supply. For example, i tied the audio right and left output with two 10kohm resistors and it seems that my signal is too much attenuated.