Help find source of distortion

[ginge6000]

Hi,

I have recently bought a Numa X Piano for playing gigs with the plan to hook it up to my Alto TS408 (also only 6 months old) for when I just need a keyboard amp for rehearsals etc.

I took this setup out for the first time to a band call for a show and was concerned to hear distortion / clipping when playing at not massively high volumes. I'm hoping some of you could help me locate the cause of this to help eliminate it going forward. Interestingly, it seems to be way worse with accoustic piano sounds than playing Rhodes / Wurly sounds.

When playing the keyboard through headphones - there is no distortion present which suggests it's not a problem with the actual sound generation so it's either (I think) the outputs of the keyboard being too hot, or the input stage of the speaker not being up to the job.....but which is it?!?

I have the speaker inputs set to line level which seems to result in me having to have the gain set almost full to get a decent level out of it. According to the Alto FAQs - on line level inputs, full is unity so not unsurprising? With the keyboard volume anything over 25%, there is clipping present at modestly loud playing from about D4 downwards (I think it is there also at higher octaves, just less obvious). At 25%, the volume isn't loud enough to play with other musicians so this isn't really workable.

I tried plugging the keyboard outs into my audio interface (UMC 204HD) and can only really get it to clip if the input gains are turned all the way up (in line level mode) which is way too loud anyway so I think this suggests it's not the output being too hot which is the issue?

So I'm leaning towards it being the speaker just not being sufficient....but would love to get any advice on how to narrow it down further. The show I had the band call for is next week and I'd rather not present the sound guy with too hot an output for his liking if I can help it (won't actually need my speaker for the performances, but do have a couple more rehearsals before then which will need it).

Any advice on how to approach trouble shooting much appreciated!

[Wonks]

I'd have thought a 12" speaker would be a bit better for full-range keyboard reproduction, but you have what you have.

How exactly are you connecting the keyboard to the speaker? Are you using the Left(mono) output?

TRS or TS cable? The outputs are TS (not mentioned in the manual but on the website), so a TS cable into the Alto will be best.

Have you tried different cables?

There is no technical info on the nominal output level of the Numa X, (which is a bit rubbish). Most keyboards tend to be -10dBV nominal rather than +4dBu, but if -10dBV, rather than +4dBu, then that explains some lack of volume.

But if it is hotter than +4dBu, (a lot of bassy piano sounds can have very strong signals), then have you tied turning the output down on the keyboard and the volume up on the speaker?

Have you checked that there isn't a weird boost setting on the speaker's onboard 6-band graphic (accessed via the app)?

Have you got a DI box? If so. you could try using that and setting the speaker input to mic level.

[ginge6000]

Thanks for replying Wonks!

I'd have thought a 12" speaker would be a bit better for full-range keyboard reproduction, but you have what you have.

I do have a bit of buyers remorse...! Already contemplating trading in for a TS410 (not sure I can swing the TS412) but don't want to throw bad money after bad!

How exactly are you connecting the keyboard to the speaker? Are you using the Left(mono) output?

TRS or TS cable? The outputs are TS (not mentioned in the manual but on the website), so a TS cable into the Alto will be best.

Using TS cable(s) I tried just the left output and both the left and right into the two inputs on the speaker, but similar results (worse when both are plugged in but I guess it's just doubling the problem?!)

There is no technical info on the nominal output level of the Numa X, (which is a bit rubbish). Most keyboards tend to be -10dBV nominal rather than +4dBu, but if -10dBV, rather than +4dBu, then that explains some lack of volume.

But if it is hotter than +4dBu, (a lot of bassy piano sounds can have very strong signals), then have you tied turning the output down on the keyboard and the volume up on the speaker?

I can only get a useable volume if the speaker volume is turned all the way up (also find that when using an audio interface when playing via my laptop for more complex setups) but I can't get the keyboard volume high enough to play with others before the clipping starts which is really odd - it's not like it's loud when it disorts - it's just there at medium volumes. The signal light on the speaker never indicates clipping either.

Have you checked that there isn't a weird boost setting on the speaker's onboard 6-band graphic (accessed via the app)?

I did wonder that but reset the EQ to flat with no improvement.

Have you got a DI box? If so. you could try using that and setting the speaker input to mic level.

I haven't tried this - I wasn't sure if it would make a difference but will give it a go for sure. Also couldn't rememer if the DI would output at line or mic level as I haven't used it in so long!

[Hugh Robjohns]

Acoustic piano is a very percussive, transient-rich sound and can carry a lot of energy at the low end. So my gut feeling is that the TS408 isn't really up to the job.

But I'm surprised the clip light isn't coming on.

It would be worth trying the DI box as Wonks suggested. It outputs mic level and you'll need an xlr-xlr cable.

This will present the keyboard with a high input impedance which might help if it doesn't like the speaker's line input for some reason, and may provide more gain.

But really, I think your best bet is to take the speaker and your keyboard to the shop and try a few different speakers to find one that means your needs.

[ginge6000]

Acoustic piano is a very percussive, transient-rich sound and can carry a lot of energy at the low end. So my gut feeling is that the TS408 isn't really up to the job.

But I'm surprised the clip light isn't coming on.

It would be worth trying the DI box as Wonks suggested. It outputs mic level and you'll need an xlr-xlr cable.

This will present the keyboard with a high input impedance which might help if it doesn't like the speaker's line input for some reason, and may provide more gain.

But really, I think your best bet is to take the speaker and your keyboard to the shop and try a few different speakers to find one that means your needs.

Thanks Hugh - your gut feeling is very much the same as mine...was so pleased with the TS408 for the last few months playing backing tracks for singing rehearsals (mostly via bluetooth or from a laptop) but the first time I used if for its intended purpose as a keyboard amp I was more than a little disappointed.

Will try the DI approach and keep my fingers crossed...

[James Perrett]

In my experience the Altos have a slightly weird top end which accents things that would be less noticeable through other speakers. I don't have any particularly good pianos here but I tried the U220 piano through my TS410s just now and didn't notice any distortion but they certainly highlighted the percussive attack of the note more than my studio monitors. I'm just waiting for someone to arrive so I can't crank them up at the moment but I'll try turning them up later and see if I notice anything untoward.

I know someone with some 8" Altos and, while they are very impressive for their size and price, I'm not sure I'd want to put full range piano through them at gig volumes. The TS410s have a more similar sound to the larger ones and I had someone playing reggae bass guitar through them the other day with no problems.

[forumuser931182]

You could try adjusting the keyboard velocity sensitivity curve so that it’s output is less dynamic… or feed the keyboard through a compressor to tame the signal somewhat. I used to use a Really Nice Compressor for this purpose. Do the speakers sound adequate if you play a solo piano track through them ( an audio file i mean )

[ginge6000]

In my experience the Altos have a slightly weird top end which accents things that would be less noticeable through other speakers. I don't have any particularly good pianos here but I tried the U220 piano through my TS410s just now and didn't notice any distortion but they certainly highlighted the percussive attack of the note more than my studio monitors. I'm just waiting for someone to arrive so I can't crank them up at the moment but I'll try turning them up later and see if I notice anything untoward.

I know someone with some 8" Altos and, while they are very impressive for their size and price, I'm not sure I'd want to put full range piano through them at gig volumes. The TS410s have a more similar sound to the larger ones and I had someone playing reggae bass guitar through them the other day with no problems.

Thanks James - I definitely wish I'd gone for the TS410 instead although no guarantee I wouldn't have the same issue as I'm guessing the share a lot of the same internals other than the woofer size. I'm tempted to buy a TS410 if I can't find one to try before my next rehearsal on Saturday but would love to hear your feedback if you get a chance!

Wondering if my better half will notice the slightly larger speaker in the living room.........

[ginge6000]

You could try adjusting the keyboard velocity sensitivity curve so that it’s output is less dynamic… or feed the keyboard through a compressor to tame the signal somewhat. I used to use a Really Nice Compressor for this purpose. Do the speakers sound adequate if you play a solo piano track through them ( an audio file i mean )

Nice idea - I've not tried a solo piano track - will give that a go. Thanks

[Wonks]

I have had three TS310s pass through my hands and I never had any distortion or volume problems with them. They had a definite smiley curve but nothing you couldn't live with.

The TS4xx series seem to sell for less than the TS3xx did, so I don't know whether there has been some cost cutting in the quality department or they've just managed to build them for less.

A pity you don't have a pair of the TS408s as then you could easily tell whether one has an internal electronic issue. It may all come down to a faulty component, maybe a power supply that can't provide all the current it should.

[ginge6000]

A pity you don't have a pair of the TS408s as then you could easily tell whether one has an internal electronic issue. It may all come down to a faulty component, maybe a power supply that can't provide all the current it should.

I really wanted to buy a pair....but just couldn't justify it for my use case (or to my wife!)

I do like the Alto speakers and am tempted to buy a TS410 from Amazon to try as nowhere near enough to get to has one in stock. I can always send it straight back if it has the same issue.

[ef37a]

I have to wonder if the speaker in the Alto has a slightly off centre voice coil?

As Hugh says, piano is a signal very demanding of "fidelity" and will show up faults in systems that "synth" sounds and rock and rock and roll may not.

As you have a computer setup and I am sure a microphone! Try some bassy,male speech through the speaker at a low level. That should show up VC rubbing very well.

Do you have access to a fairly powerful guitar amp? Something 30W+ (valves) and a 12" or two should be seriously loud although you will not get low bass tones. Should be good down to 70Hz or so.

Dave.

[James Perrett]

I have had three TS310s pass through my hands and I never had any distortion or volume problems with them. They had a definite smiley curve but nothing you couldn't live with.

I've not compared the 310s and 410s side by side but I've heard both a fair bit and they sound very similar to me.

I've also now tried my 410s at a high volume and they definitely show up the aliasing on the U220 piano samples much more than the studio monitors do, so if there are any imperfections in the source sound, it will probably be magnified.

[ginge6000]

I have had three TS310s pass through my hands and I never had any distortion or volume problems with them. They had a definite smiley curve but nothing you couldn't live with.

I've not compared the 310s and 410s side by side but I've heard both a fair bit and they sound very similar to me.

I've also now tried my 410s at a high volume and they definitely show up the aliasing on the U220 piano samples much more than the studio monitors do, so if there are any imperfections in the source sound, it will probably be magnified.

Thanks for checking James and reporting back.

[ajay_m]

Try cutting the low end and see if this helps. Often there's quite a bit of energy down there that you don't really need and it may be compromising headroom.

[AlecSp]

You may be hearing physical rattling. Not unheard of in some cabs - especially cheap ones like you have. Can be hard to identify and track down, and not always easily fixable.

Don't worry about your level when feeding a PA, any competent engineer should be able to handle pretty much any realistic output level you can give. That's what gain controls, pads, DI boxes, and high headroom pre-amps are there to help manage.

[Martin Walker]

Try cutting the low end and see if this helps. Often there's quite a bit of energy down there that you don't really need and it may be compromising headroom.

+1 to this advice.

[Dave Rowles]

I've got 5 TS310 that I use as monitor speakers, and I've used a TS410. I'll be honest, unless you're in a biiigggg room I can't see you needing the 12 or 15. The bottom end out of the 10s is insane. I've not used the 08s so can't comment,

Have you got access to a mixer? Try plugging in the keyboard into the mixer as you would to the TS408. Then use the headphone out of the mixer. If you still hear the distortion then you know for sure it's the output of the keyboard, if not, then it's the speaker.

Also try a different keyboard into the speaker if you can, or something else in the exact same way you plug the keyboard in. The key here is trying to find exactly where the distortion is coming from. If you can plug something in that's going to play uncompressed audio that's best as well. If you're not getting the same distortion from a mic, then it could be the jack input, not the XLR.

With one of my TS310s I got some distortion at one point, so I opened it up (it was 2 years old at this point) and the compression driver was a tiny bit loose from the horn. Literally just screwed it back on and the speaker worked perfectly from then and I've never had another problem.

[AlecSp]

With one of my TS310s I got some distortion at one point, so I opened it up (it was 2 years old at this point) and the compression driver was a tiny bit loose from the horn. Literally just screwed it back on and the speaker worked perfectly from then and I've never had another problem.

To be pedantic, that's not distortion (though it can sound very much like it) - it's a rattle. Often, though not always, triggered by certain frequencies.

[James Perrett]

The bottom end out of the 10s is insane. I've not used the 08s so can't comment,

I'd agree (from my reggae bass experience) that the bottom end on the 10s is amazing but I know someone with a 308 and the sound is somewhat different to the sound of the larger speakers. They sound fine on their own but, when compared to a larger version the bass is noticeably less - which possibly makes them better for vocals but probably not so good for piano.