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Yamaha FB-01 Headroom Issue? Keyboard Synthesizers
Old 17th February 2016
  #1
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Yamaha FB-01 Headroom Issue?

I picked up an FB-01 the other day for $50. Yay. I like it a lot. It reminds me a lot of the DX100 but with a much smaller footprint and a lower pricetag.

The only problem I am noticing is that with the output set to the max of 127, single notes are OK, but playing 3-4 notes at a time results in distortion. Lowering the output to 100-110 fixes this, so it seems like an internal headroom issue.

Is this a common problem? The unit is in pristine shape on the outside.

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Old 17th February 2016
  #2
I haven't noticed this on mine. Can you put up an audio clip of this?
Old 18th February 2016
  #3
Gear Nut
 

Mine does this too. I also blame it on internal clipping.
Old 18th February 2016
  #4
Gear Guru
Maybe the patches themselves are a bit low?

I noticed that on my Korg 707. Turned them up.
Old 18th February 2016
  #5
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Quote:
Originally Posted by djugel View Post
Maybe the patches themselves are a bit low?

I noticed that on my Korg 707. Turned them up.
No, they're set to max already. Problem is, that makes them distort straight out of the machine. If I turn down the internal volume, it goes away.
Old 18th February 2016
  #6
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Quote:
Originally Posted by jochenp View Post
Mine does this too. I also blame it on internal clipping.
Good to know. I wonder how widespread this is and if there's a fix. I can live with it, but it's already hissy, so turning down the patch volume just decreases the S/N ratio.
Old 18th February 2016
  #7
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Quote:
Originally Posted by midiquestions View Post
Good to know. I wonder how widespread this is and if there's a fix. I can live with it, but it's already hissy, so turning down the patch volume just decreases the S/N ratio.
The bad S/N ratio is part of the charm
Old 18th February 2016
  #8
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I do remember when i had a FB-01 a long time ago, there was a modification by removing 2 transistors in the signal path circuit that cleaned up the FB-01's output.
Old 18th February 2016
  #9
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Quote:
Originally Posted by Syn303 View Post
I do remember when i had a FB-01 a long time ago, there was a modification by removing 2 transistors in the signal path circuit that cleaned up the FB-01's output.
It the lowpass filter on the output stage to filter out the high frequency artifacts.
You could remove the filter, but it won't simply 'clean up' the output.

See here:
FB-01—Help with ways to stop treble roll-off—What is FB-01G? - Yamaha Forums UK
Old 18th February 2016
  #10
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Nah wasn't that dude, i did the mod long before that, was somewhere around 2008 i did it to my FB-01. That forum thread you linked to is 5 years later in 2013.
Old 18th February 2016
  #11
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Quote:
Originally Posted by Syn303 View Post
Nah wasn't that dude, i did the mod long before that, was somewhere around 2008 i did it to my FB-01. That forum thread you linked to is 5 years later in 2013.
Here's the service manual on the off chance that you can remember which 2 transistors. I'd love to know.

http://www.bleeps-and-peeps.com/imag...vicemanual.pdf
Old 18th February 2016
  #12
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Quote:
Originally Posted by Syn303 View Post
I do remember when i had a FB-01 a long time ago, there was a modification by removing 2 transistors in the signal path circuit that cleaned up the FB-01's output.
The easiest fix I know is to increase the gain in the final output amp by using a larger feedback resisitor. Also worth swapping out the opamp for something nicer.

I don't really think the low output and hiss is really much of the charm.

Quote:
change resistor r13 and r6 to 10ks, and replace the JRC4558. I put a socket in and tried everything I had on hand. OPA2888 won.
The op-amp actually played a huge part of the sound in this one. 2888 had a similar woody tone to the original, but less ringing in the highs. Really nice now, and the levels are proper. >85db S/N. :-)
Old 18th February 2016
  #13
Quote:
Originally Posted by bluegreengold View Post
The easiest fix I know is to increase the gain in the final output amp by using a larger feedback resisitor. Also worth swapping out the opamp for something nicer.

I don't really think the low output and hiss is really much of the charm.
Those two transistors are for muting the outputs. I wouldn't remove them as it could worsen the noise problem.

I'd change those transistors though as they could be degraded from static electricity from the output jack when plugs are inserted.
And a new + better opamp isn't going to hurt things either compared to that relic that is in there.

In the service manual they explain an on-board test for AMP Characteristics. It may shed some light to perform that test.

Looking at the schematic, that is one drastic filter there. I don't blame people for removing it. Though that will increase noise.

IC1 and 4 have a big load on their outputs already through R64, R65 and R5, R67. No wonder the output circuit has difficulties. I would play with the values here. Try higher resistances in the same ratio given for R64 and R65. Maybe 1.4K and 1.3K. Then reduce R12 and R66 down to 100 ohms.
Old 19th February 2016
  #14
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Just did a couple of simple mods to my FB01 and I like it much more now! I just had a look at the service manual and copied what these guys on the Yamaha forum were talking about:
FB-01—Help with ways to stop treble roll-off—What is FB-01G? - Yamaha Forums UK
FB-01 noise/loudness issue - Yamaha Forums UK

Increase the output level:
Change resistor R13 and R6 to 10KOhm.

This has increased the output level to a more usable range. About 6dB higher I'd guess.

Raise the Lowpass filter cutoff from ~3.6 kHz to just over 20 kHz.
Change capacitors C4, C9 and C14, C16 to 3.3 nF.

This is the value shown in the schematic but for some reason Yamaha decided to fit 18nF ones resulting in a muffled sound.
This upgrade is a big improvement in my opinion and you can always lowpass filter the sound to get the original vibe.

I've attached a WAV showing before and after. Don't think I'm gonna bother with anything else - it's meant to be a bit grungy! So far I've just modified one output so I can choose between original and upgraded that way.
Attached Files
File Type: aif FB01 upgrade.aif (2.02 MB, 153 views)

Last edited by explorer; 19th February 2016 at 02:28 PM..
Old 21st February 2016
  #15
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Quote:
Originally Posted by explorer View Post
Just did a couple of simple mods to my FB01 and I like it much more now! I just had a look at the service manual and copied what these guys on the Yamaha forum were talking about:
FB-01—Help with ways to stop treble roll-off—What is FB-01G? - Yamaha Forums UK
FB-01 noise/loudness issue - Yamaha Forums UK

Increase the output level:
Change resistor R13 and R6 to 10KOhm.

This has increased the output level to a more usable range. About 6dB higher I'd guess.

Raise the Lowpass filter cutoff from ~3.6 kHz to just over 20 kHz.
Change capacitors C4, C9 and C14, C16 to 3.3 nF.

This is the value shown in the schematic but for some reason Yamaha decided to fit 18nF ones resulting in a muffled sound.
This upgrade is a big improvement in my opinion and you can always lowpass filter the sound to get the original vibe.

I've attached a WAV showing before and after. Don't think I'm gonna bother with anything else - it's meant to be a bit grungy! So far I've just modified one output so I can choose between original and upgraded that way.
Interesting, but actually I think the FB fits really well in a track partly because of the roll-off, at least when it's used for bass. Would you be willing to post up some more A/Bs with different instruments and playing actual melodies? It's hard to get a sense of the significance of the change from just the four notes.
Old 21st February 2016
  #16
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Quote:
Originally Posted by midiquestions View Post
Interesting, but actually I think the FB fits really well in a track partly because of the roll-off, at least when it's used for bass. Would you be willing to post up some more A/Bs with different instruments and playing actual melodies? It's hard to get a sense of the significance of the change from just the four notes.
I've modified both outputs now so I can't record any more unmodified examples. It basically sounds like the unmodified version if I use a 12dB low pass filter at 3.6kHz.

I understand the FB01 is unusual out of all the Yamaha FM synths in having such a muffled output as standard. DX100, DX21, and DX27 use very similar chips but sound brighter.

I'd much rather have the full bandwidth and use a filter or EQ to reduce the high end in the mix if necessary.

It even seems like Yamaha originally designed the FB01 to have the full bandwidth because the capacitor has a different value on the schematic (the one I have changed it to). Maybe they just used a different one for cost-cutting reasons or something?

Last edited by explorer; 21st February 2016 at 02:05 AM..
Old 5th March 2016
  #17
Quote:
Originally Posted by explorer View Post
......
Increase the output level:
Change resistor R13 and R6 to 10KOhm.

This has increased the output level to a more usable range. About 6dB higher I'd guess.

Raise the Lowpass filter cutoff from ~3.6 kHz to just over 20 kHz.
Change capacitors C4, C9 and C14, C16 to 3.3 nF.

This is the value shown in the schematic but for some reason Yamaha decided to fit 18nF ones resulting in a muffled sound.
This upgrade is a big improvement in my opinion and you can always lowpass filter the sound to get the original vibe.
......
I changed out those four caps to 3.3 nF back in 2015. I never got around to posting my results. This looks like a good place as any. The Audio Comparison Sound File at the link below contains four pairs of before and after clips back to back. The waveform image of a portion of the sound file shows some noise increase which is my guess as to why Yamaha opted to use 18 nF caps for the production run. Even so, my FB-01 sounds SOOOO much better for my use in the studio now. I used Nichicon P/N: QYX1H332KTP 3.3nF 50V Polyester Film Capacitors (0.0033uF)

I have created an webpage with part numbers and info for this DIY here:
FB-01 DIY HOMEPAGE



Audio Comparison Sound File (Before/After):

https://soundcloud.com/mrmojorisin-267423905/yamaha-fb-01-mods-beforeafter
(Note: This audio file has been updated to include samples of the FB-01 with the capacitor mods + upgraded audio filter IC's + the 10k Resistor mod for increased audio output. The wave image below only details the capacitor mod)


Waveform With Capacitor Mods Only (Before/After):




Waveform With All Mods (Before/After):




Schematic Segment:


Last edited by Mr_Mojo_Risin; 1st April 2016 at 12:01 AM.. Reason: Updated audio file and waveform image
Old 13th July 2016
  #18
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Thread Starter
Quote:
Originally Posted by explorer View Post
Just did a couple of simple mods to my FB01 and I like it much more now! I just had a look at the service manual and copied what these guys on the Yamaha forum were talking about:
FB-01—Help with ways to stop treble roll-off—What is FB-01G? - Yamaha Forums UK
FB-01 noise/loudness issue - Yamaha Forums UK

Increase the output level:
Change resistor R13 and R6 to 10KOhm.

This has increased the output level to a more usable range. About 6dB higher I'd guess.

Raise the Lowpass filter cutoff from ~3.6 kHz to just over 20 kHz.
Change capacitors C4, C9 and C14, C16 to 3.3 nF.

This is the value shown in the schematic but for some reason Yamaha decided to fit 18nF ones resulting in a muffled sound.
This upgrade is a big improvement in my opinion and you can always lowpass filter the sound to get the original vibe.

I've attached a WAV showing before and after. Don't think I'm gonna bother with anything else - it's meant to be a bit grungy! So far I've just modified one output so I can choose between original and upgraded that way.
Hey, I missed this part the first time around as I got caught up in the mod that opens the filter which I do not want to do as I like the somewhat mellow sound of the FB-01. There is a mod which simply raises the volume, and I'm going to give it a shot. Here's the link:

FB-01 DIY HOMEPAGE
Old 20th July 2016
  #19
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Quote:
Originally Posted by midiquestions View Post
Hey, I missed this part the first time around as I got caught up in the mod that opens the filter which I do not want to do as I like the somewhat mellow sound of the FB-01. There is a mod which simply raises the volume, and I'm going to give it a shot. Here's the link:

FB-01 DIY HOMEPAGE
I just changed out R6 and R13 but did not do the other two mods. It may or may not be louder, but it's still distorting above volume values of 110 or so. My thought is that the distortion is actually tied to the HF rolloff.
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