Loss of input signal, amp functions quiet, NEED HELP

American Viking · 09-26-2009, 12:04 PM

Hello and thanks for viewing.

Some of you may remember when I had a post about the Laney GH100L earlier. Ok, so what ended up happening was I fixed the amp by swapping out a bad component, changing the output tubes and biasing. It worked perfectly for about 30 minutes, I was jamming on it and was really surprised at how great it sounded. Then I put it the chassis back in the head case and went to go jam on it again five hours later and it didn't sound right. The problem is that the amp still plays, but it sounds like it has a loss of input, like if I were to turn down the volume knob on the guitar severely, sounds like that. It's a single channel amp and with the gain all the way up it still sounds clean. Just like I said, like somewhere in the amp there's a loss of signal somewhere but I can't find it.
I've done all the simple stuff, swapped ALL tubes, examined all internal fuses, solder joints on all tube sockets, checked cables, changed guitars, the problem still persists. I don't understand why it would work great, then next time I fire it up it sounds ill. The only strange thing I did was when putting the little metal covers on the preamp tubes I tapped one of them on with a pair of needle nose pliers because it wouldn't go down all the way. All the tubes have been swapped so it's not that and the tube socket does not appear to be damaged in any way. I didn't HAMMER it down or anything just kind of tapped the top of it a few times. Just figured I'd mention it since it may be relevant. Thanks for reading and hope you can help me out. Peace.

Procter2812 · 09-26-2009, 12:26 PM

Quote:

Originally Posted by American Viking

Hello and thanks for viewing.

Some of you may remember when I had a post about the Laney GH100L earlier. Ok, so what ended up happening was I fixed the amp by swapping out a bad component, changing the output tubes and biasing. It worked perfectly for about 30 minutes, I was jamming on it and was really surprised at how great it sounded. Then I put it the chassis back in the head case and went to go jam on it again five hours later and it didn't sound right. The problem is that the amp still plays, but it sounds like it has a loss of input, like if I were to turn down the volume knob on the guitar severely, sounds like that. It's a single channel amp and with the gain all the way up it still sounds clean. Just like I said, like somewhere in the amp there's a loss of signal somewhere but I can't find it.
I've done all the simple stuff, swapped ALL tubes, examined all internal fuses, solder joints on all tube sockets, checked cables, changed guitars, the problem still persists. I don't understand why it would work great, then next time I fire it up it sounds ill. The only strange thing I did was when putting the little metal covers on the preamp tubes I tapped one of them on with a pair of needle nose pliers because it wouldn't go down all the way. All the tubes have been swapped so it's not that and the tube socket does not appear to be damaged in any way. I didn't HAMMER it down or anything just kind of tapped the top of it a few times. Just figured I'd mention it since it may be relevant. Thanks for reading and hope you can help me out. Peace.

Was it the V1 tube that you tapped down?

Maybe its a thermal issue with the tube socket... try retensioning it?

Alex

American Viking · 09-26-2009, 12:45 PM

It was V3 I tapped on. Re-tensioning, huh? Sounds like it couldn't hurt to try. Is that just squeezing the little female metal parts of the socket back together a bit? What's the best tool for the job, little screwdriver or small ice/dental pick?

jcmjmp · 09-26-2009, 12:59 PM

Have you checked heater voltages on the preamp sockets? B+ Voltages?

Any op-amps in there? Check for +- 15v on those too.

Procter2812 · 09-26-2009, 01:09 PM

Quote:

Originally Posted by American Viking

It was V3 I tapped on. Re-tensioning, huh? Sounds like it couldn't hurt to try. Is that just squeezing the little female metal parts of the socket back together a bit? What's the best tool for the job, little screwdriver or small ice/dental pick?

Yeah use a small screwdriver or even a needle.

I did it on my TSL and you just basically push the contacts towards each other.

What Pre-amp tubes are you using? Also how many are there?

i think these CP pre-amp tubes are just too fat!

I bought one the other day and it was a real tight squeeze in my 800...

Its even worse when the pins are not parrallel to the tube itself!!

Alex

***Adwex*** · 09-26-2009, 02:47 PM

What about testing continuity from the tube socket contacts to the wire. Maybe a solder joint got damaged?

TPR · 09-27-2009, 04:36 AM

+1 on the retension, but I think you need to drain the caps first or use something non-conductive.

belch · 09-27-2009, 06:47 AM

Is this the schem that corresponds with your amp.

http://www.schematicheaven.com/newamps/laney_gh100l.pdf

If so it would appear your prob lies around V1, as others have mentioned check all conns from the valve base to the board & that the valve sits tight.

After that check relay 1 to make sure it is switching correctly,this should be able to be checked with the amp in standby mode i think, the led may work but the relay could be sticking. With a meter set for continuity testing place one probe on r16 leg that goes to relay & alternate the other probe between gain & drive pot input lugs which go to relay wiper.

If your prob persists a scope would make it easier to track down the signal loss.

American Viking · 09-30-2009, 05:44 AM

I had retensioned all the sockets today, no help there, but it never hurts to have a little routine maintenance like that anyway.

I'm going to try more of the continuity testing tomorrow. I tried today a little but but I didn't turn the amp on while doing it. I suppose that may be why I didn't get continuity on higher resistance parts.

Sorry for the silly question, but I could not find relay 1 on the schems, unless that's what R1 stands for. I'm sure it's one of those things that I've managed to overlook a hundred times.

I keep thinking the problem is with V1 as well as I've had similar problems before in other amps with faulty tubes but I've switched this tube out with others I've verified in other amps to be fine.

I would love to hear any new ideas I can try out before I head back to the shop tomorrow. I've got a few other amps I'm working on too so I'm trying to divide my time evenly. This one is giving me the most headache so far. Thanks for the help thus far, fellows. You know I appreciate it.

belch · 09-30-2009, 06:07 AM

The relay is shown in the top left quarter of page 2 ( the 3rd page down ) & is marked RLY 1, it's just a sealed dpdt switch, these are normally a rectangular black or blue box that's operated by a small voltage that's triggered by a remote switch ie footswitch.

American Viking · 11-04-2009, 10:30 AM

I finally figured it out so I can bring closure to this thread...

A brown wire coming to point P22 (goes to a lug on the Gain pot) was off. The wire was sitting in the hole in the PCB but wasn't visibly loose. After tapping on the relay with a screwdriver I noticed the sound would get louder for a few seconds and stop. Then I started moving the wires near the relay and the wire going into P22 completely pulled out. I guess that was it all along. I didn't feel like lifting the board so I just soldered the wire directly to the lug. Amp sounds great now. I still can't find P22 on the schematics and I've been looking for a while.

Anyway, thanks for all the help guys.

09-26-2009, 12:04 PM	#1 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Loss of input signal, amp functions quiet, NEED HELP Hello and thanks for viewing. Some of you may remember when I had a post about the Laney GH100L earlier. Ok, so what ended up happening was I fixed the amp by swapping out a bad component, changing the output tubes and biasing. It worked perfectly for about 30 minutes, I was jamming on it and was really surprised at how great it sounded. Then I put it the chassis back in the head case and went to go jam on it again five hours later and it didn't sound right. The problem is that the amp still plays, but it sounds like it has a loss of input, like if I were to turn down the volume knob on the guitar severely, sounds like that. It's a single channel amp and with the gain all the way up it still sounds clean. Just like I said, like somewhere in the amp there's a loss of signal somewhere but I can't find it. I've done all the simple stuff, swapped ALL tubes, examined all internal fuses, solder joints on all tube sockets, checked cables, changed guitars, the problem still persists. I don't understand why it would work great, then next time I fire it up it sounds ill. The only strange thing I did was when putting the little metal covers on the preamp tubes I tapped one of them on with a pair of needle nose pliers because it wouldn't go down all the way. All the tubes have been swapped so it's not that and the tube socket does not appear to be damaged in any way. I didn't HAMMER it down or anything just kind of tapped the top of it a few times. Just figured I'd mention it since it may be relevant. Thanks for reading and hope you can help me out. Peace. __________________ -I'd rather be a good liver than have one...

09-26-2009, 12:45 PM	#3 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Loss of input signal, amp functions quiet, NEED HELP It was V3 I tapped on. Re-tensioning, huh? Sounds like it couldn't hurt to try. Is that just squeezing the little female metal parts of the socket back together a bit? What's the best tool for the job, little screwdriver or small ice/dental pick? __________________ -I'd rather be a good liver than have one...

09-26-2009, 12:59 PM	#4 (permalink)
jcmjmp Senior Member Join Date: Nov 2008 Posts: 1,341	Re: Loss of input signal, amp functions quiet, NEED HELP Have you checked heater voltages on the preamp sockets? B+ Voltages? Any op-amps in there? Check for +- 15v on those too.

09-26-2009, 02:47 PM	#6 (permalink)
*Adwex* Super Moderator Join Date: Sep 2006 Location: Long Island, NY Posts: 1,631	Re: Loss of input signal, amp functions quiet, NEED HELP What about testing continuity from the tube socket contacts to the wire. Maybe a solder joint got damaged? __________________ http://www.youtube.com/MarshallLesPaul

09-27-2009, 04:36 AM	#7 (permalink)
TPR Senior Member Join Date: Sep 2009 Posts: 109	Re: Loss of input signal, amp functions quiet, NEED HELP +1 on the retension, but I think you need to drain the caps first or use something non-conductive. __________________ The awesome tone coming out of my amp almost makes up for my inability to play. '91 JCM 900 Head w/ EL34s '68 Bassman Head- Blackfaced Hand Built 2x12 Classic 30 Gibson LP Studio w/ PAFs Epi LP Standard w/ G 57s The usual assortment of pedals and stuff

09-27-2009, 06:47 AM	#8 (permalink)
belch Member Join Date: Sep 2009 Location: Brew town UK Posts: 40	Re: Loss of input signal, amp functions quiet, NEED HELP Is this the schem that corresponds with your amp. http://www.schematicheaven.com/newamps/laney_gh100l.pdf If so it would appear your prob lies around V1, as others have mentioned check all conns from the valve base to the board & that the valve sits tight. After that check relay 1 to make sure it is switching correctly,this should be able to be checked with the amp in standby mode i think, the led may work but the relay could be sticking. With a meter set for continuity testing place one probe on r16 leg that goes to relay & alternate the other probe between gain & drive pot input lugs which go to relay wiper. If your prob persists a scope would make it easier to track down the signal loss.

09-30-2009, 05:44 AM	#9 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Loss of input signal, amp functions quiet, NEED HELP I had retensioned all the sockets today, no help there, but it never hurts to have a little routine maintenance like that anyway. I'm going to try more of the continuity testing tomorrow. I tried today a little but but I didn't turn the amp on while doing it. I suppose that may be why I didn't get continuity on higher resistance parts. Sorry for the silly question, but I could not find relay 1 on the schems, unless that's what R1 stands for. I'm sure it's one of those things that I've managed to overlook a hundred times. I keep thinking the problem is with V1 as well as I've had similar problems before in other amps with faulty tubes but I've switched this tube out with others I've verified in other amps to be fine. I would love to hear any new ideas I can try out before I head back to the shop tomorrow. I've got a few other amps I'm working on too so I'm trying to divide my time evenly. This one is giving me the most headache so far. Thanks for the help thus far, fellows. You know I appreciate it. __________________ -I'd rather be a good liver than have one...

09-30-2009, 06:07 AM	#10 (permalink)
belch Member Join Date: Sep 2009 Location: Brew town UK Posts: 40	Re: Loss of input signal, amp functions quiet, NEED HELP The relay is shown in the top left quarter of page 2 ( the 3rd page down ) & is marked RLY 1, it's just a sealed dpdt switch, these are normally a rectangular black or blue box that's operated by a small voltage that's triggered by a remote switch ie footswitch.

11-04-2009, 10:30 AM	#11 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Loss of input signal, amp functions quiet, NEED HELP I finally figured it out so I can bring closure to this thread... A brown wire coming to point P22 (goes to a lug on the Gain pot) was off. The wire was sitting in the hole in the PCB but wasn't visibly loose. After tapping on the relay with a screwdriver I noticed the sound would get louder for a few seconds and stop. Then I started moving the wires near the relay and the wire going into P22 completely pulled out. I guess that was it all along. I didn't feel like lifting the board so I just soldered the wire directly to the lug. Amp sounds great now. I still can't find P22 on the schematics and I've been looking for a while. Anyway, thanks for all the help guys. __________________ -I'd rather be a good liver than have one...

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