#1
My friend came to me yesterday wielding his JCM2000 DSL100 head, he said he wanted me to take a look at it because the tubes were glowing and no sound came out.

One the back of DSL there are three speaker jacks, two of which can be used at either 4 or 8 OHMS and the third is a dedicated 16 OHMS output, i plug my 1960 cabinet in, first at 4 OHMS, then Stereo at 8 OHMS and every time i struck a chord, it would last for a split second then the sound would abruptly cut out.

i then changed the cab over to 16 OHMS and ran it from the dedicated 16 OHM output and it worked fine.
could someone explain to me what exactly could be going on with the head for this to happen?

Cheers!
some guitars
some amps
some pedals
some crabs
Last edited by Mech-cannibal at Apr 9, 2011,
#2
Because the 1960 cab is 16 ohm mono, 8 ohm stereo or 4 ohm mono. I'm assuming you have the 16 ohm mono.. the cab won't be able to handle 4 ohms.. it could blow even.. or atleast rattle.. the 8 ohms won't work unless you have two cabs and go in stero..

16 ohms ismore resistance than 4 ohms and restricting the power so the speakers won't have as much 'stress.'
If reply to me...P.M me.
#3
well the thing is, the cab is switchable stereo, i ran two speaker leads into both 8 OHM inputs, and if you switch back to mono, those inputs become 4 and 16 ohms respectively.

the issue here is the head, we've tried it with other cabinets too.
some guitars
some amps
some pedals
some crabs
#4
also, the cab could still potentially run at low volume with the wrong impedance, i've done it by accident before.
some guitars
some amps
some pedals
some crabs
#5
Quote by Mech-cannibal
well the thing is, the cab is switchable stereo, i ran two speaker leads into both 8 OHM inputs, and if you switch back to mono, those inputs become 4 and 16 ohms respectively.

the issue here is the head, we've tried it with other cabinets too.

you aren't running stereo with one head. You're running Mono.
Current Gear:
LTD MH-400
PRS SE Custom 24 (Suhr SSH+/SSV)
Ibanez RG3120 Prestige (Dimarzio Titans)
Squier Vintage Modified 70s Jazz V
Audient iD22 interface
Peavey Revalver 4, UAD Friedman BE100/DS40
Adam S3A monitors
Quote by Anonden
You CAN play anything with anything....but some guitars sound right for some things, and not for others. Single coils sound retarded for metal, though those who are apeshit about harpsichord probably beg to differ.
#6
2 8 OHMS out of the head, into 2 8 OHMS Cabinet inputs, stereo.

still not the issue, the problem is within' the head, as i have stated previously, it has been tested with various cabinets with all three impedance options.
some guitars
some amps
some pedals
some crabs
#7
Output transformer?

Not to ask a stupid question, but have you tried it with the 16 ohm mono out?
Current Gear:
LTD MH-400
PRS SE Custom 24 (Suhr SSH+/SSV)
Ibanez RG3120 Prestige (Dimarzio Titans)
Squier Vintage Modified 70s Jazz V
Audient iD22 interface
Peavey Revalver 4, UAD Friedman BE100/DS40
Adam S3A monitors
Quote by Anonden
You CAN play anything with anything....but some guitars sound right for some things, and not for others. Single coils sound retarded for metal, though those who are apeshit about harpsichord probably beg to differ.
#8
I've just looked at the manual for this amp. The amp is mono not stereo. The 16 ohm output is just that and you are clear about that. The other two output jacks are wired in parallel. This means that when you plug two speakers in the impedance is halved as far as the amp is concerned, and as you know the impedances have to be matched in a valve amp.

If you plug a single 8ohm in the switch needs to be set at 8 ohms and at 4 ohms for a single 4.

If you plug in two 8ohm speakers then the load is 4ohms and you switch to 4 ohms. Since both speakers share exactly the same signal it isn't stereo.

If you have two 16ohm cabs then they plug into the paired 8/4 sockets and not the 16. Two 16's in parallel make 8ohms so set the switch to 8.

I hope this is clear or you will damage your mates amp.

There may also be a fault with the amp but it may be a protection mechanism which is keeping the amp safe from your mistakes or even a faulty lead. Get the impedances right and see if the fault goes away.

Set your 1960 to either 16 and use the 16 out or set it to 4 and use one 4 output with the switch set to 4. There is no point to using stereo with a single mono amp but it would work with the speaker set to mono, the amp set to 4ohms and two leads between speaker and amp.
#9
i've tried it with the right impedances and the fault still seems to be there. any idea what it may be?
some guitars
some amps
some pedals
some crabs