JCM2000 DSL100 hums when standby switched.

TheRuleOfThree · 10-20-2009, 06:34 AM

Hi,
I was wondering if anyone can point me in the right direction in respect to my JCM2000 DSL100. After bringing it home from a jam, it's suddenly developed a hum through the cab when standby switch is switched on (not on standby). Otherwise the only audible hum is from the transformers and no cab hum at all. The hum is loud enough to be annoying at very low levels, especially when using the clean channel but it's volume does not change at all no matter what volume I'm running at or what channel I'm using.

I always have a spare set of valves handy and thought that I'd try and change the output valves first (and Bias adjust) but the "hum remains the same" (pardon the pun) This also goes for the preamp valves. No good....

I've had a bit of a look across the internet, and because this hum remains the same regardless with what I do to the pre-amp section, I'm suspecting the main filter capacitors in the HT rectifier section, in my case C38, C39, C34 & C35. Easily enough done, but are there any other caps that could cause this problem while I've got it open and exposed?

Any help would be greatly appreciated!!

Danny.

jcmjmp · 10-20-2009, 08:00 AM

You should also replace the DC Heater filter capacitors. The actual part ref may be different depending on which HW revision of the board you have - i.e. JCM2-60-00 vs JCM2-60-01 vs JCM2-60-02

If that doesn't help, it could just be that your PT has developed an internal hum. The only real solution is to get a proper PT in there. I'm working on a high quality drop-in replacement for the DSL.

The transformers that Marshall uses are slightly below average quality IMO and aren't built to last like the old ones.

TheRuleOfThree · 10-20-2009, 08:23 AM

Thanks for the pointer jcmjmp! It's funny that you mentioned this part of the the circuity, as I once had that very bridge rectifier package fail on me! The amp would play fine for 10 minutes and then slowly fade away, then fade back in again. It wasn't until I noticed the heaters in V1 and V2 fade with the sound that knew I had a problem with this. The component was fine cold, but when it heated up it would fail, and then cool down again and work.... I'll change those caps too and see if it's bearable enough not to have to change the PT.

Thanks again!

mc_guitar · 10-20-2009, 05:25 PM

Hey,

Also check the BridgeRecifier used for the DC-Heating. They have been known to be quite weak currentwise.

Cheers Michael

jcmjmp · 10-20-2009, 06:34 PM

Quote:

Originally Posted by mc_guitar

Hey,

Also check the BridgeRecifier used for the DC-Heating. They have been known to be quite weak currentwise.

Cheers Michael

They're rated for 6.0 DC amps (1997 JCM2-60-00 main board, issue 1). For two 12AX7s, its actually overkill since each 12ax7 draws 300ma (0.3A).

http://www.datasheetcatalog.org/data...nents/BR68.pdf

Maybe the newer DSLs have a different component?

MartyStrat54 · 10-20-2009, 10:47 PM

I agree with jcmjmp about the quality of the transformers. The DSL and the TSL have what I call bargain transformers. Just looking at them and you can tell they aren't as good as the prior one's. I like to see bells on my transformer. Not the insulation wrap around the windings.

I think they do the job. I just think they are a little cheesy.

Wilder Amplification · 10-21-2009, 01:14 AM

One guy over on another forum had great results upgrading the output transformer to a Mercury Magnetics type. Marshall has been using bargain transformers on their stuff for quite some time...even the 1959 reissue responds to an MM tranny upgrade quite well from what I've read from other people who've had it done.

TheRuleOfThree · 10-21-2009, 01:28 AM

Thanks guys.... When I changed the bridge rectifier package after the first failure, I did opt for the next current size up when choosing a replacement as I thought heat might have been a factor in it's failure in the first place.

The funny thing is I've just spent all day looking for 330uF 315wv electrolytic capacitors the same size as the originals. These bloody things are 22mm in diameter and do you think I can find any in Australia? No Way... All I can find is 30mm up! and 30mm is too big to fit where the others sat....

I used to be able to buy parts here in Australia through Yamaha Aust. but not anymore and the parts distributor now will only deal with music shops.... What tha? Does anyone know where I can get parts for Marshall amps in Australia without being treated like the enemy?

Thanks again for the advice!

Wilder Amplification · 10-21-2009, 01:51 AM

Quote:

Originally Posted by TheRuleOfThree

Thanks guys.... When I changed the bridge rectifier package after the first failure, I did opt for the next current size up when choosing a replacement as I thought heat might have been a factor in it's failure in the first place.

The funny thing is I've just spent all day looking for 330uF 315wv electrolytic capacitors the same size as the originals. These bloody things are 22mm in diameter and do you think I can find any in Australia? No Way... All I can find is 30mm up! and 30mm is too big to fit where the others sat....

I used to be able to buy parts here in Australia through Yamaha Aust. but not anymore and the parts distributor now will only deal with music shops.... What tha? Does anyone know where I can get parts for Marshall amps in Australia without being treated like the enemy?

Thanks again for the advice!

Is that an axial lead or radial lead? If you don't know the difference, axial lead is where the capacitor's leads are on opposite ends whereas the radial type has its leads on the same end.

mc_guitar · 10-21-2009, 02:02 AM

Quote:

Originally Posted by jcmjmp

They're rated for 6.0 DC amps (1997 JCM2-60-00 main board, issue 1). For two 12AX7s, its actually overkill since each 12ax7 draws 300ma (0.3A).

http://www.datasheetcatalog.org/data...nents/BR68.pdf

Maybe the newer DSLs have a different component?

I have to admit I don't know the ratings of the original type. But I had quite a few DSLs and TSLs with that problem on my bench. But He already upgraded that part.

Regards,

Michael

TheRuleOfThree · 10-21-2009, 02:10 AM

Radial type, 330Uf 315WV 22mm dia. X 50mm long. 10mm pitch on the "snap on" type leads.

P.S. After jcmjmp's advice, I have been looking into Mercury Magnetics OT's and PT's also.

Wilder Amplification · 10-21-2009, 02:21 AM

Quote:

Originally Posted by TheRuleOfThree

Radial type, 330Uf 315WV 22mm dia. X 50mm long. 10mm pitch on the "snap on" type leads.

P.S. After jcmjmp's advice, I have been looking into Mercury Magnetics OT's and PT's also.

Perfect...let me see what I can dig up.

Wilder Amplification · 10-21-2009, 02:36 AM

I didn't happen to have any so I went in search of, found some, and went ahead and ordered up a couple...if nothing else just to have them on hand.

They are a 330uF 350WV snap in electrolytic cap, measuring 22mm x 45mm with a 10mm pitch on the snap in leads.

So if you'd like to buy one from me I'll let you know as soon as I get them in.

TheRuleOfThree · 10-21-2009, 08:53 AM

Thanks for the info, Jon.

Between posts I have been searching and I think we come up with the Panasonic product at the same time as yourself! I have not only left the search for these caps to one of my local music stores with contacts to the Marshall parts distributor here in Australia, but have emailed Panasonic themselves with the specific part No.s as well in the hope that they can recommend a seller here in Melbourne.

Thanks again to all who contributed to solving my dilemma!

Wilder Amplification · 10-21-2009, 11:57 AM

Quote:

Originally Posted by TheRuleOfThree

Thanks for the info, Jon.

Between posts I have been searching and I think we come up with the Panasonic product at the same time as yourself! I have not only left the search for these caps to one of my local music stores with contacts to the Marshall parts distributor here in Australia, but have emailed Panasonic themselves with the specific part No.s as well in the hope that they can recommend a seller here in Melbourne.

Thanks again to all who contributed to solving my dilemma!

Good to hear you may have found one closer to ya. If in the event something falls through on your end with that cap, just keep in mind that I will have them as something to fall back on if need be.

Buggs.Crosby · 10-21-2009, 12:15 PM

Quote:

Originally Posted by Wilder Amplification

One guy over on another forum had great results upgrading the output transformer to a Mercury Magnetics type. Marshall has been using bargain transformers on their stuff for quite some time...even the 1959 reissue responds to an MM tranny upgrade quite well from what I've read from other people who've had it done.

Jon i think you are referring to me and i have to say the MM tranny is Awesome
if and when my 59RI needs a new i will go to MM again....i cannot say enough about how much better this head sounds with their Tranny and choke there is a lot of false hype about equipment on the net....this is no hype
and so everyone knows Jon was a huge help getting my head back up and running and he continues to spend time helping others what a great asset to Marshall community

i have been wondering if there are any upgrades for the caps on a DSL
is bigger better in this case? i don't even care if i had to top mount them like on my plexi as i dont ever plan on getting rid of it
so please post the results of your cap switch and your opinion on how they sound....good luck

Randy

Wilder Amplification · 10-21-2009, 12:20 PM

Quote:

Originally Posted by Buggs.Crosby

Jon i think you are referring to me and i have to say the MM tranny is Awesome
if and when my 59RI needs a new i will go to MM again....i cannot say enough about how much better this head sounds with their Tranny and choke there is a lot of false hype about equipment on the net....this is no hype
and so everyone knows Jon was a huge help getting my head back up and running and he continues to spend time helping others what a great asset to Marshall community

i have been wondering if there are any upgrades for the caps on a DSL
is bigger better in this case? i don't even care if i had to top mount them like on my plexi as i dont ever plan on getting rid of it
so please post the results of your cap switch and your opinion on how they sound....good luck

Randy

Thanks for the kind words! I wasn't aware that you were on this board as well. And for the record, the false hype, misinformation and technical myths are what I aim to get rid of, which is why I like sharing my knowledge with others in hopes that eventually people will understand enough to filter out the bullshit.

In regards to a filter cap upgrade, they already use a 330uF for the first stage, which is MORE than plenty and I doubt you'd hear much of a difference if any at all going any bigger than this.

The only time you'll notice the difference is if the amp had low filtering to start with and you stepped the filtering up, making the power supply more efficient and allowing it to perform more optimally by having more current in reserve. But once the power supply has more than enough current available to draw, stepping the filtering up beyond that to have even more current available becomes a moot point.

10-20-2009, 06:34 AM	#1 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	JCM2000 DSL100 hums when standby switched. Hi, I was wondering if anyone can point me in the right direction in respect to my JCM2000 DSL100. After bringing it home from a jam, it's suddenly developed a hum through the cab when standby switch is switched on (not on standby). Otherwise the only audible hum is from the transformers and no cab hum at all. The hum is loud enough to be annoying at very low levels, especially when using the clean channel but it's volume does not change at all no matter what volume I'm running at or what channel I'm using. I always have a spare set of valves handy and thought that I'd try and change the output valves first (and Bias adjust) but the "hum remains the same" (pardon the pun) This also goes for the preamp valves. No good.... I've had a bit of a look across the internet, and because this hum remains the same regardless with what I do to the pre-amp section, I'm suspecting the main filter capacitors in the HT rectifier section, in my case C38, C39, C34 & C35. Easily enough done, but are there any other caps that could cause this problem while I've got it open and exposed? Any help would be greatly appreciated!! Danny.

10-20-2009, 08:00 AM	#2 (permalink)
jcmjmp Senior Member Join Date: Nov 2008 Posts: 2,725	Re: JCM2000 DSL100 hums when standby switched. You should also replace the DC Heater filter capacitors. The actual part ref may be different depending on which HW revision of the board you have - i.e. JCM2-60-00 vs JCM2-60-01 vs JCM2-60-02 If that doesn't help, it could just be that your PT has developed an internal hum. The only real solution is to get a proper PT in there. I'm working on a high quality drop-in replacement for the DSL. The transformers that Marshall uses are slightly below average quality IMO and aren't built to last like the old ones.

10-20-2009, 08:23 AM	#3 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	Re: JCM2000 DSL100 hums when standby switched. Thanks for the pointer jcmjmp! It's funny that you mentioned this part of the the circuity, as I once had that very bridge rectifier package fail on me! The amp would play fine for 10 minutes and then slowly fade away, then fade back in again. It wasn't until I noticed the heaters in V1 and V2 fade with the sound that knew I had a problem with this. The component was fine cold, but when it heated up it would fail, and then cool down again and work.... I'll change those caps too and see if it's bearable enough not to have to change the PT. Thanks again!

10-20-2009, 05:25 PM	#4 (permalink)
mc_guitar Member Join Date: Dec 2008 Location: LE / Germany Posts: 50	Re: JCM2000 DSL100 hums when standby switched. Hey, Also check the BridgeRecifier used for the DC-Heating. They have been known to be quite weak currentwise. Cheers Michael __________________ Marshall Rules...

10-21-2009, 01:28 AM	#8 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	Re: JCM2000 DSL100 hums when standby switched. Thanks guys.... When I changed the bridge rectifier package after the first failure, I did opt for the next current size up when choosing a replacement as I thought heat might have been a factor in it's failure in the first place. The funny thing is I've just spent all day looking for 330uF 315wv electrolytic capacitors the same size as the originals. These bloody things are 22mm in diameter and do you think I can find any in Australia? No Way... All I can find is 30mm up! and 30mm is too big to fit where the others sat.... I used to be able to buy parts here in Australia through Yamaha Aust. but not anymore and the parts distributor now will only deal with music shops.... What tha? Does anyone know where I can get parts for Marshall amps in Australia without being treated like the enemy? Thanks again for the advice!

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10-21-2009, 02:10 AM	#11 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	Re: JCM2000 DSL100 hums when standby switched. Radial type, 330Uf 315WV 22mm dia. X 50mm long. 10mm pitch on the "snap on" type leads. P.S. After jcmjmp's advice, I have been looking into Mercury Magnetics OT's and PT's also.

10-21-2009, 08:53 AM	#14 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	Re: JCM2000 DSL100 hums when standby switched. Thanks for the info, Jon. Between posts I have been searching and I think we come up with the Panasonic product at the same time as yourself! I have not only left the search for these caps to one of my local music stores with contacts to the Marshall parts distributor here in Australia, but have emailed Panasonic themselves with the specific part No.s as well in the hope that they can recommend a seller here in Melbourne. Thanks again to all who contributed to solving my dilemma!

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