It is currently Mon Mar 16, 2020 7:58 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 6 posts ] 
Author Message
Post subject: Volume 'pumping' problem, X2
Posted: Fri Mar 27, 2015 2:47 am
Offline
Hobbyist
Hobbyist

Joined: Fri Mar 27, 2015 2:28 am
Posts: 3
I've been using my X2 combo for about a month now and have started to hear an intermittent issue with volume pumping on both channels.

When I hit a chord the attack will come through clear and strong, but after about a second or so of sustain there is a defined and sharp drop in volume. Originally I thought this was something to do with the onboard compressor settings as it is similar to the 'pumping' sounds you can sometimes get with heavy compression, but after playing around with attack/release settings in Fuse and finally removing all effects the issue is still there. I then thought it might be an extreme noise gate kicking in, but I have noticed it when the noise gate is entirely turned off and it also affects Channel 1 which has neither noise gate nor compressor settings.

Turning the amp off and back on sometimes fixes this issue, sometimes it doesn't. There appears to be no pattern to this problem either; sometimes I can play for an hour and it will be fine, sometimes it appears within seconds of starting up the amp. Also occurs with multiple guitars and when using extension cabs so unlikely to be the speaker or other parts of my rig.

I think the X2 is a great little amp apart from this one thing and have really enjoyed using it up till now, but it's very frustrating and is becoming a bit of a dealbreaker for me. Has anyone else experienced this issue before? Is not does anyone have any tips or advice?

TLDR: Amp suffering from slight but sudden drops in volume. Not down to compressor, noise gate or other parts of my rig. Affects both channels and all models.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Volume 'pumping' problem, X2
Posted: Fri Mar 27, 2015 4:07 pm
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1022
I read the service manual and it seems that this effect is designed into the unit.
In the circuit description, it says'

Op-amp U6-A provides the high impedance instrument
input with 14db of gain. Op-amp U6-B is
configured as an active filter producing high frequency
pre-emphasis. U1-A provides another 20db :lol:
of gain. Its’ output is clamped to +/-2V.]The uDSP
PCB Assy. chooses either the low gain output from
U6-B or the higher gain output from U1-A depending
on the amplitude of the guitar input signal."


So as the signal decays, the computer changes the signal source between U6 & U1, which changes the volume, as you described.
You might try using more volume from your guitar to try to fool the computer into staying on one output longer.


Top
Profile
Post subject: Re: Volume 'pumping' problem, X2
Posted: Sat Mar 28, 2015 8:51 am
Offline
Hobbyist
Hobbyist

Joined: Fri Mar 27, 2015 2:28 am
Posts: 3
TimsAudio wrote:
I read the service manual and it seems that this effect is designed into the unit.
In the circuit description, it says'

Op-amp U6-A provides the high impedance instrument
input with 14db of gain. Op-amp U6-B is
configured as an active filter producing high frequency
pre-emphasis. U1-A provides another 20db :lol:
of gain. Its’ output is clamped to +/-2V.]The uDSP
PCB Assy. chooses either the low gain output from
U6-B or the higher gain output from U1-A depending
on the amplitude of the guitar input signal."


So as the signal decays, the computer changes the signal source between U6 & U1, which changes the volume, as you described.
You might try using more volume from your guitar to try to fool the computer into staying on one output longer.


First I'd just like to say that's a far more helpful and in depth answer than I was expecting, thanks for doing that research.

Secondly, what the hell were they thinking putting a feature like that into the software? I get that a lot of people wouldn't notice and it's probably not an issue for live shows once you take into account the tube compression and general noise of a live band, but it's basically written off any chance of me being able to use it for sessions or my own recordings.

Are there any workarounds for this I can look at? Not an electrician but I'm pretty comfortable with soldering and have a local guy who can walk me through any of the in-depth stuff.

Thanks again for your time and help with this, much appreciated.


Top
Profile
Post subject: Re: Volume 'pumping' problem, X2
Posted: Sat Mar 28, 2015 10:13 am
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1022
I wish I could tell you what they were thinking when they designed it. But it's not a mistake. From design concept to hardware to fussing over the software, them smart fellers at Fender thought they had come up with something special. It kept me up last night trying to figure out what they're so proud of.

There seems to be a disconnect between engineering and marketing departments. Special technical features are seldom described in a way that allows a picker to play to the strengths of an amp I don't know if its because the engineers don't want to be copied or the marketers don't think it's important.

Whatever the reason, its left up to the player to discover the feature. Some never do. I still meet 59 Bassman owners who don't know about its trick. Or owners of Dumble clones who donT know about, "singing harmonics" or how to acheive them.

With this circuit, it seems like it would act as a two speed transmission. If you want to play quietly in a bedroom, it would lower the gain for better tone. If you want it loud, it will kick into high gain. You seem to be running your levels on the threshold of switching.

The circuits involved in your amp are ahead of any volume controls, so their level would be entirely dependent on the volume setting of the guitar. Pedal levels would also affect it.
So keeping the volume on your guitar low and setting the amp volume high would tend to keep it in the low gain setting. This would be better for recording.
Turning the guitar volume high and the amp volume low would keep it in high gain mode..
Experiment with different guitar drive levels and see if you can recognize a pattern to the switching and then control it

The first approach to possibly fixing this issue is to reset the factory settings. While it will erase your custom settings, it will also reload the software that the CPU runs on.. All the decisions it makes about when and how much to change the gain are software controlled.
On the hardware end, you might be able to change the feedback resistor R59 on U1. It is currently 10K if you tack another 10K resistor on top of it, it would lower the gain of that stage and perhaps match the other stage a little better. That is, if it doesn't confuse the CPU. If it does help, you can fine tune the value of R59 to get the gain you want.

Good luck.


Top
Profile
Post subject: Re: Volume 'pumping' problem, X2
Posted: Tue Apr 18, 2017 5:51 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Mar 06, 2017 9:42 pm
Posts: 1
Has Fender addressed this problem at all since the original post? This has got to be the most frustrating problem I've ever had with any music product. A sustaining note or chord just drops in volume during it's decay like some sort of gate kicks in...or the note you're playing blasts really loud (volume spike) and scares the heck out of you. I live in an apartment with neighbors so am afraid the volume spike that randomly happens will get me in trouble.
Such a random occurence too. I can't seem to make it happen when I'm trying to show other people the problem.
I could certainly never gig with this amp.

I'm surprised more people haven't posted about this flaw if it's part of the design as TimsAudio has stated.
It must happen on every X2 ever built if it's part of the design. Or did I and the original poster just get a lemon?

When it happened last, I managed to make a video of the problem. I'll post it to Youtube in the next week so others' can get an example of what's happening.


Top
Profile
Post subject: Re: Volume 'pumping' problem, X2
Posted: Tue Sep 05, 2017 6:02 pm
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 05, 2017 5:54 pm
Posts: 2
I also have this problem of volume jumping
Worst of all, it is intermittent , and even if it is still under warranty and i have sent it to the dealer they could not fix it up.

I have changed the tubes. No improvement.

This is very disturbing and i cant believe it is designed to be so

I hope the Fender guys can look into this problem


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: