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Has anyone had issues using the power soak feature? When I go to use it, it works but after about 10 mins there is a nasty squealing sound coming from the head, when I turn the power soak off the squealing stops. I keep the gain on most of the channels around 5 or 6 and only have the volume halfway and master at maybe 3. If anyone has any solutions or even answers that would be much appreciated. Thanks!
3 posters
Power soak issues
zandafar- Posts : 1
Join date : 2019-12-02
bordonbert- Posts : 1790
Join date : 2015-01-28
Age : 72
Location : Southern England
Hmmm! The power soak itself certainly shouldn't have any way to affect the amp like that. What condition are your valves in? Any chance you have a microphonic one in there? (Try the chopstick tap test.) I could see that maybe you could have a power output valve going duff.
When you apply the power soak that first just removes the inner pair of EL84s from the circuit halving the available current and hence the power. Then when you set it lower again the power soak resistors are put in circuit to take out greater portions of the output power. If one of the current outer pair of EL84s is getting groggy the power soak will therefore put all of the work onto that alone. When you take out the power soak you bring the other pair of valves back in in parallel which may be enough to stabilise the situation.
It's a wild guess but that action might just be what is happening and it's simple to test. Just swap your outer pair of EL84s for the inner pair or better still, replace the outer pair with a known good pair and test it again. If it clears the problem then you have a bad valve in your current outer pair. Does that all make sense?
Incidentally what are you using for valves? You don't have 12AX7 "alternatives" (NOT!) or some sort of rare Russian esoteric "masterpiece" in there do you? There are cases of people "discovering" Russian equivalents to some valves and actually damaging their gear trying to make them work because it "adds mojo" and gets applause from other members of the priesthood.
When you apply the power soak that first just removes the inner pair of EL84s from the circuit halving the available current and hence the power. Then when you set it lower again the power soak resistors are put in circuit to take out greater portions of the output power. If one of the current outer pair of EL84s is getting groggy the power soak will therefore put all of the work onto that alone. When you take out the power soak you bring the other pair of valves back in in parallel which may be enough to stabilise the situation.
It's a wild guess but that action might just be what is happening and it's simple to test. Just swap your outer pair of EL84s for the inner pair or better still, replace the outer pair with a known good pair and test it again. If it clears the problem then you have a bad valve in your current outer pair. Does that all make sense?
Incidentally what are you using for valves? You don't have 12AX7 "alternatives" (NOT!) or some sort of rare Russian esoteric "masterpiece" in there do you? There are cases of people "discovering" Russian equivalents to some valves and actually damaging their gear trying to make them work because it "adds mojo" and gets applause from other members of the priesthood.
_________________
Newcastle Brown, can sure smack you down
You take a greasy wh*re, and a rollin' dance floor
You know you're jailhouse bound!
Rock On Humble Pie
jthom- Posts : 6
Join date : 2018-08-11
I had a similar issue a few months after purchase ( 2018 ), eventually it led to volume dropping out and various noise. Turned out it was a bad tube, but it wasnt visibly bad until i got the thing open and could look from another angle.
Easy and cheap to replace. Videos on youtube.
I should mention that i still have a strange issue that may be grounding. Sometimes when i power on and warm it up i have little to no volume. Pushing the Boost button ALL the way in til it bottoms out, turning it on or off is irrelevant, cures it. Weird but i dont gig so minor finicky stuff isnt a huge deal.
Does yours do this ?
Easy and cheap to replace. Videos on youtube.
I should mention that i still have a strange issue that may be grounding. Sometimes when i power on and warm it up i have little to no volume. Pushing the Boost button ALL the way in til it bottoms out, turning it on or off is irrelevant, cures it. Weird but i dont gig so minor finicky stuff isnt a huge deal.
Does yours do this ?
bordonbert- Posts : 1790
Join date : 2015-01-28
Age : 72
Location : Southern England
Hi Jthom. You Boost issue is intriguing. Best guess is that the Boost in the GM40 will work pretty much as the GM36 does, the family resemblance in functionality has proven to be very close up until now. The schematic for the GM36 is available on the internet if you search hard enough but the GM40 is still a closely guarded secret. So any advice I can offer is based on the GM36 circuitry, (with a smidgen of TM18 thrown in as their schematics are also available).
The Boost function is purely a digital one. The switch simply shorts down a line to ground and this tells the processor that Boost is to be applied. This does mean that there are no signal issues involved in that dicky switch of yours. It uses both wafers of the double pole switch in parallel so it would be unlikely that both would fail, a switch fault is not terribly likely, though not impossible of course. I would first start by resetting the software back to factory default. The procedure to do this is clear in the manual in section 8.3.
"Press 'Store' and 'FX Access' simultaneously while powering the amp up using the Power/On switch. Both buttons will flash three times to indicate the successful factory reset."
Do make sure to BACK UP ANY PRESETS YOU HAVE DEFINED BEFORE YOU DO IT! These are also set back to the factory default so you will lose them permanently if you don't back them up first. Resetting the software to pristine as new which this does, means that any temporary glitches which may have crept in which can happen in any software system are cleared out and the software is guaranteed to work as it should. We have had instances of niggling issues like your own being solved by this fix.
Try that first if you can and then let us know if the problem is sorted. If it is not the other next likely culprit is the switch itself of course.
The Boost function is purely a digital one. The switch simply shorts down a line to ground and this tells the processor that Boost is to be applied. This does mean that there are no signal issues involved in that dicky switch of yours. It uses both wafers of the double pole switch in parallel so it would be unlikely that both would fail, a switch fault is not terribly likely, though not impossible of course. I would first start by resetting the software back to factory default. The procedure to do this is clear in the manual in section 8.3.
"Press 'Store' and 'FX Access' simultaneously while powering the amp up using the Power/On switch. Both buttons will flash three times to indicate the successful factory reset."
Do make sure to BACK UP ANY PRESETS YOU HAVE DEFINED BEFORE YOU DO IT! These are also set back to the factory default so you will lose them permanently if you don't back them up first. Resetting the software to pristine as new which this does, means that any temporary glitches which may have crept in which can happen in any software system are cleared out and the software is guaranteed to work as it should. We have had instances of niggling issues like your own being solved by this fix.
Try that first if you can and then let us know if the problem is sorted. If it is not the other next likely culprit is the switch itself of course.
_________________
Newcastle Brown, can sure smack you down
You take a greasy wh*re, and a rollin' dance floor
You know you're jailhouse bound!
Rock On Humble Pie
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