Speaker Swap kills V15G. Help

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
Starting with a stock Rogue V15G 15 Watt faux-tweed bedroom/practice amp, I did the following:

1 Removed everything from the cabinet - Chassis, Speaker, Baffle, Bling

2 Coated the faux-tweed with some amber shellac to make it appear somewhat less faux. (probably not the issue)

3 Enlarged the 6 in speaker exit hole in the baffle to accomodate an 8 inch, 4ohm, 25 watt Jensen 8-20 Speaker.

4 Re-mounted the baffle and screen inside the cabinet

5 Mounted the speaker on the baffle.

6 Installed the chassis (with all electronics untouched) on the cabinet back.

7 Used copper foil to provide a ground plane on the inside of the cabinet back and on the open ends of the chassis frame. Attempt to keep noise out of the amp.

8 Wired the speaker. (paid attention to + and - on the speaker.)

9. Buttoned up the Amp and put the bling (except the logo) back on.

The amp acts as follows:

When plugged in, guitar jacked in, power is applied.

When Drive and Master pots are brought up above about 20% a high pitched whine comes out of the speaker. The higher the volumne knobs are set the louder the whine.

No guitar string strum sounds come out of the speaker at any settin.

Turn the Drive and Master knobs all the way down, the whine diminishes eventually to zero.

No guitar, just whine

Where do I start to trouble shoot this one?

Thanks in advance.
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
1. Did it work before you disassembled it?
2. Is it possible something is shunting out to your shielding foil?
1. The incredibly unthinking part is That I cannot be sure. I never tested it out of the box. Moron.

2. ‘Shunting’? You mean some signal carrying wire shorting to ground? Certainly a possibility, although I took care applying. Will take it off to test.
 

Refugee

Tele-Afflicted
Joined
Mar 8, 2021
Posts
1,216
Age
53
Location
Hot Springs, AR
I expect anything selling for $70 to function out of the box.

Once you break the seal it voids the factory warranty. I do hope you can fix it, but maybe you should've played it for a while. Like at least 30 days to see if anything goes wrong, then you can return it for a full refund.
 

Old Verle Miller

Tele-Meister
Joined
Apr 7, 2022
Posts
301
Location
Texas
Shielding in amp cabinets? Start with that.

If the symptoms diminish as you describe rather than cut off instantly that means there's some kind of resonance involved.

And a speaker can't cause that kind of problem no matter what way you connect the polarity (it would only be out of phase).

Just my guesses.
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
Once you break the seal it voids the factory warranty. I do hope you can fix it, but maybe you should've played it for a while. Like at least 30 days to see if anything goes wrong, then you can return it for a full refund.
Yes that is some common sense I did not apply.
 

Milspec

Poster Extraordinaire
Silver Supporter
Joined
Feb 15, 2016
Posts
7,204
Location
Nebraska
Doesn't sound like you did anything wrong, but my guess is the foil shielding. Just reverse course, remove the shielding and all should be good to go.

We all tend to over-think it a bit and just get ourselves into trouble. Enjoy the amp and the new speaker.
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
Shielding in amp cabinets? Start with that.

If the symptoms diminish as you describe rather than cut off instantly that means there's some kind of resonance involved.

And a speaker can't cause that kind of problem no matter what way you connect the polarity (it would only be out of phase).

Just my guesses.
OK.. a bit of investigation.

Popped the back off, took the foil shielding off the open ends of the chassis. Noticed a couple of both signal and ground wires near the transformer (red and black) were touching the ground shield on the inside of the cabinet back. Not bare wire, the coated insulation. On the possibility that the hot wire was inducing something into the ground shield magnetically and from there back into the ground wire, i took the copper foil off the back, hooked up the brand new Bullet Squier and tried a test. No speaker response from the amp at all. High pitched squeal out of the amp (I think it is coming from the chassis, not the speaker at this point) tracked the Drive and Master pots.

Downloaded a spectrum analizer/DB meter app to the iPhone and let it listen to the squeal. There is a main spike around 5300 Htz:
9CBC9A02-F40A-44AB-ADDB-44FCFBFBAEE4.png


There is a secondary spike around 10630 Htz:
67055B73-3DEF-449C-90BF-9336C1F2BCF5.png


There is a tercentenary spike around 16000 Htz:
AE1095C3-A0E8-411F-A3BF-B7F53B65D222.png


These all rise/fall in proportion to the volume of the squeal and in the same relation to each other.

There is nothing coming out of the speaker in response to a strum on the Bullett. For that matter, I don't think there is any hum at all.

Fuse looks good. No smell of hot components coming from the chassis.

All solid state, no tubes.

Had to extend the speaker wires coming out of the chassis and elected to just solder them to the speaker, figuring I'd seldom have to disconnect the speaker.

Any thoughts on how to trouble shoot the signal?

For starters, how do I measure the signal coming out of the Bullet? Multimeter on the end of the cable, but what to look for?
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
In the garbage can. It's a Rogue.

DON'T buy another one. You've heard the definition of insanity I suppose.
I'm not going to argue water under the bridge or religion with anyone. The rogue came highly recommended in the reviews or I would not have selected it. Telling me you think it is garbage does not help the truble shooting process - I can cite others that think it is not.

When any amp gives a 5300Hz squeal instead of a tone, what does that indicate? How do I check with my scope or VM to see where the signal chain jumps off the tracks?
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
Doesn't sound like you did anything wrong, but my guess is the foil shielding. Just reverse course, remove the shielding and all should be good to go.

We all tend to over-think it a bit and just get ourselves into trouble. Enjoy the amp and the new speaker.

I agree. Tried to solve a theoretical problem I did not know existed. That backfired. Took off the shielding. Did not change anything.
 

Milspec

Poster Extraordinaire
Silver Supporter
Joined
Feb 15, 2016
Posts
7,204
Location
Nebraska
If there is zero speaker response, start there and work your way back. Check those speaker wires for continuity to make sure the signal is reaching the speaker and keep working backwards.
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
If there is zero speaker response, start there and work your way back. Check those speaker wires for continuity to make sure the signal is reaching the speaker and keep working backwards.
OK. Thanks.
 

Milspec

Poster Extraordinaire
Silver Supporter
Joined
Feb 15, 2016
Posts
7,204
Location
Nebraska
Squeeling is often due to electromagnetic issues, so that gives you places to start as well.

Test with the original speaker. I have had a new speaker once that was fubar and the spider was stuck.

Test the amp in a different room in case you have some dirty power or other interference. I have seen some trigger squeeling although it normally went away when you touched the strings.
 

AcroCaster

TDPRI Member
Silver Supporter
Joined
Sep 3, 2021
Posts
23
Age
70
Location
Arizona
I have seen some trigger squealing although it normally went away when you touched the strings.

Absolutely no speaker hum that I can discern. When I touch the strings or strum, there is no difference whatsoever in the sound. Not 60 Hz hum. 5300 Hz squeal and unrelated to the guitar at all. Happens if the guitar is plugged in or not.
 

InstantCoffeeBlue

Tele-Holic
Joined
Feb 20, 2012
Posts
667
Age
36
Location
Milwaukee, WI
When any amp gives a 5300Hz squeal instead of a tone, what does that indicate?

From a new SS amp with no frills and (theoretically) little to go wrong? Really, really poor build quality.

Honestly, I know you don't want to hear this, especially since you seem to have sunk a lot of time into this already, but all this time spent trying to diagnose something that was never meant to be serviceable is time not spent playing guitar. This is why as a teacher it always pains me when beginners or parents ask for gear recommendations and then totally disregard it and buy something junky just because it had a few good reviews on amazon and they figure it's better to play it safe in case they or their kid quits.

So you voided the warranty. Ok, lesson learned. At least it was only a $70 lesson instead of a $700 one. I commend your persistence, but I would suggest setting a time limit, after which you throw your hands in the air, say "I'm done" and then scrape together a couple hundred bucks for something that was made with decent quality control, even if it's used.
 




Top