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Post subject: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Fri May 02, 2014 5:22 am
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[edited/abbreviated post to provide much simpler/shorter explanation]

New Super-Sonic 22. Amp works fine (if somewhat noisy: hum/hiss) with nothing plugged into fx-loop.

With anything plugged into the fx-loop (eg just a patch lead plugged between fx-send and fx-return), and with nothing plugged into the amp input, turning the volume up more than about half-way (on clean channel, haven't tried on 'burn' channel) sometimes causes runaway screeching feedback. Turn volume down, it stops. Turn volume up, it starts again. Doesn't always happen, but enough to be a problem.

It can't be conventional audio feedback - there's nothing going into the amp input. Something after the fx-loop seems to be feeding back (internally, electrically) to something before the fx-loop. Reverb settings don't seem to make a difference.

Before I take the amp back to the store, any opinions? Known issue, expected behaviour, faulty valve vs other fault...? Many thanks for all and any replies.


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Wed May 07, 2014 7:39 am
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OK, I guess the lack of any reply means no-one else has experienced this, which further suggests it isn't normal/expected behaviour. So time to go back to the store. Shame, love the amp's tone apart from the hum/hiss/screech. I hope they can furnish me with a replacement SS22 that doesn't have these problems, rather than having to choose a different amp.


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Wed May 07, 2014 2:32 pm
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Your best bet, since the amp is new, might be to return/exchange it. Just a possibility, something easy to try, is maybe a faulty tube or two. The last tube before the effects loop is V4 (12AX7), and the first tube after the effects loop is V5 (12AT7) which is the PI, you could substitute known good tubes in these positions. Or, the reverb driver V3 (12AT7), or the reverb recovery V4 (12AX7) are a couple of possibilities. Note that for V4, half is used for reverb recovery and half is a gain stage before the effects loop. Maybe the hum that you have is from a tube, and the problem is amplified when using the effects loop.

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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Wed May 07, 2014 3:00 pm
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scott-uk wrote:
[edited/abbreviated post to provide much simpler/shorter explanation]

New Super-Sonic 22. Amp works fine (if somewhat noisy: hum/hiss) with nothing plugged into fx-loop.

With anything plugged into the fx-loop (eg just a patch lead plugged between fx-send and fx-return), and with nothing plugged into the amp input, turning the volume up more than about half-way (on clean channel, haven't tried on 'burn' channel) sometimes causes runaway screeching feedback. Turn volume down, it stops. Turn volume up, it starts again. Doesn't always happen, but enough to be a problem.

It can't be conventional audio feedback - there's nothing going into the amp input. Something after the fx-loop seems to be feeding back (internally, electrically) to something before the fx-loop. Reverb settings don't seem to make a difference.

Before I take the amp back to the store, any opinions? Known issue, expected behaviour, faulty valve vs other fault...? Many thanks for all and any replies.


You say with anything plugged into the fx-loop, does this include a delay pedal?


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Mon May 12, 2014 12:59 am
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shimmilou - thanks for the info about the valve/tube functions. I'm going to keep that it's really useful for the future. But as the amp is still so new, on this occasion I'll let the store figure it out.

relicgman - I hadn't tried a delay pedal, and when I did it didn't make any difference. I'm curious what you thought might be relevant to a delay-effect here? Could be useful info for me for future troubleshooting?

With further testing, the feedback seems possibly connected to the reverb unit (which I see from other topics several people have experienced), although on different occasions, different things seem to trigger it - notably the fx loop. Or maybe (as per shimmilou) all this points at V4 being the culprit, as that's common to both the reverb and fx-loop.

So anyway, amp went back to the store, they agreed it was faulty on all counts so it's now being shipped back to Fender who'll hopefully sort it out. I was briefly tempted just to swap it for a Super-Sonic Twin, until I tried to lift the Twin :shock:


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Tue May 13, 2014 9:04 pm
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I was just wondering what a patch cable between send and return does on the 22.


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Wed May 14, 2014 4:07 pm
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Quote:
wondering what a patch cable between send and return does on the 22

I tried this. Switching the effects loop on/off (via the amp's footswitch) with a patch cable connecting fx-send to fx-return, makes no (pereptible to me) difference to the guitar sound, either in tone or volume. There is a slight audible 'click' when turning the fx-loop on or off, but not too intrusive. The amp's fx-loop circuitry seems pretty neutral, in particular no (detectable to me) increase or decrease in volume. Note the SS-22 doesn't have any controls to adjust the level on the fx-loop (unlike the higher-powered SS models).

(Of course this is all when things are working normally on an amp with no faults)


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Thu May 15, 2014 3:57 am
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While I wish the 22 did have the tube-driven fx loop with level controls like the old original SS60 did, the fx loop works great with a boost in the loop. I do this for a volume boost for solos, using a BBE Boosta Grande, and it works great - without having to hit V1 any harder, meaning it's more of an actual volume boost instead of a gain boost.


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Post subject: Re: Super-Sonic 22 - screeching feedback with fx-loop
Posted: Fri May 16, 2014 12:38 am
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Quote:
the fx loop works great with a boost in the loop

Thanks for mentioning that, that's really helpful. For brevity I hadn't included it in my original post, but when I had tried any sort of boost in the fx-loop, that immediately triggered the runaway internal feedback (ie amp feeds back within itself, even with nothing plugged into the input).

I had wondered if it was simply that this amp's fx-loop wasn't meant to cope with a boosted signal - your experiences suggests this is supposed to work fine. So I'll make a point to test that explicitly when I get my amp back. Thanks again for raising this.


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