Ohm question for DSL20 head?

Richardr_fit

New Member
Joined
Feb 4, 2022
Messages
2
Reaction score
5
Hi,

I bought Marshall DSL 20 head.

It has 3 input jacks:

1 - 16ohm

2 and 3 with description - 1 - 8ohm or 2x16ohm

Please answer this questions:

1. Does it mean I can put one 8ohm cab in 2 or 3 jack without difference in which one?
2. Can I put in 2 and 3 jack 16ohm cabs in same time ?
3. I’m going to buy speaker with G12T-75 but seller might don’t know if it’s 8ohm or 16ohm.
If I put into 1 8ohm/2 16 ohm it should be safe right ?
If put only 1 16ohm cab into jack described 1 8ohm/ 2 16ohm will it be safe or it always has to be 1 8ohm or 2 16ohm ?
 

Attachments

  • 450A371B-891B-46A0-A820-A0D0EEBE50F0.jpeg
    450A371B-891B-46A0-A820-A0D0EEBE50F0.jpeg
    309.9 KB · Views: 2

PelliX

Well-Known Member
Joined
Jun 16, 2020
Messages
2,095
Reaction score
4,090
Hi and :welcome: to the MF!

1: You can connect an 8 Ohm cab to either jack 2 or jack 3. You are not supposed to connect an 8 Ohm cab to both at once (because two 8 Ohm cabs would result in a 4 Ohm load which is too low for the tap). You could connect them in series to achieve a 16 Ohm load and connect that to the 16 Ohm tap (presuming one of the cabs has the right jacks for this).

2: Yes, two 16 Ohm cabs (in parallel, so using jacks 2 and 3) result in an 8 Ohm load. That's why the tap is labeled "1x8" and "2x16". Really, it's just an 8 Ohm tap, so whatever you connect should be an 8 Ohm load in total.

3: I'm not quite sure what you mean. The seller should be able to snap a pic of the back of the speaker, though - c'mon... ;) If it's not clearly visible, measure the speaker with a multimeter on the resistance setting. Whatever the result is will be 'close' to either 8 or 16 Ohms. Impedence is not resistance, but in this case the approxiation of a multimeter is fine to go by.

Perhaps a generic pointer will help you: When you connect multiple equal speakers/cabs in parallel you halve the impendance. So two 16 Ohm speakers in parallel result in an 8 Ohm load. Two 8 Ohm speakers in parallel result in a 4 Ohm load. If you connect them in series the impendance adds up. So two 8 Ohm speakers in series becomes a 16 Ohm load. Add another one and you get a 24 Ohm load, etc. Be careful mixing speakers in parallel - if you connect an 8 and a 16 Ohm speaker in parallel you get a load of ~5.3 Ohms - this is not intuitive to your average Joe.

Then a little note about taps. Mismatching is not a 'good' thing, but remember that a load higher than the rating of the tap is generally OK if you don't go totally nuts. A 16 Ohm cab on an 8 Ohm tap is no problem, really. Don't reverse this; you don't want a 4 Ohm load on an 8 Ohm tap for too long at high volume. If in doubt - get your multimeter, measure the resistance. If you don't have one, get one. It's a lot cheaper than replacing an output transformer or even just your output valves.
 

Richardr_fit

New Member
Joined
Feb 4, 2022
Messages
2
Reaction score
5
Hi and :welcome: to the MF!

1: You can connect an 8 Ohm cab to either jack 2 or jack 3. You are not supposed to connect an 8 Ohm cab to both at once (because two 8 Ohm cabs would result in a 4 Ohm load which is too low for the tap). You could connect them in series to achieve a 16 Ohm load and connect that to the 16 Ohm tap (presuming one of the cabs has the right jacks for this).

2: Yes, two 16 Ohm cabs (in parallel, so using jacks 2 and 3) result in an 8 Ohm load. That's why the tap is labeled "1x8" and "2x16". Really, it's just an 8 Ohm tap, so whatever you connect should be an 8 Ohm load in total.

3: I'm not quite sure what you mean. The seller should be able to snap a pic of the back of the speaker, though - c'mon... ;) If it's not clearly visible, measure the speaker with a multimeter on the resistance setting. Whatever the result is will be 'close' to either 8 or 16 Ohms. Impedence is not resistance, but in this case the approxiation of a multimeter is fine to go by.

Perhaps a generic pointer will help you: When you connect multiple equal speakers/cabs in parallel you halve the impendance. So two 16 Ohm speakers in parallel result in an 8 Ohm load. Two 8 Ohm speakers in parallel result in a 4 Ohm load. If you connect them in series the impendance adds up. So two 8 Ohm speakers in series becomes a 16 Ohm load. Add another one and you get a 24 Ohm load, etc. Be careful mixing speakers in parallel - if you connect an 8 and a 16 Ohm speaker in parallel you get a load of ~5.3 Ohms - this is not intuitive to your average Joe.

Then a little note about taps. Mismatching is not a 'good' thing, but remember that a load higher than the rating of the tap is generally OK if you don't go totally nuts. A 16 Ohm cab on an 8 Ohm tap is no problem, really. Don't reverse this; you don't want a 4 Ohm load on an 8 Ohm tap for too long at high volume. If in doubt - get your multimeter, measure the resistance. If you don't have one, get one. It's a lot cheaper than replacing an output transformer or even just your output valves.
Thanks, this is what I need.
So putting 16ohm cab in 8ohm amp is safe but putting 8ohm cab into 16ohm amp is dangerous ?
Sorry for asking twice. Your answers fully answer my questions, just want to be sure.
 

Gemon

Member
Joined
Apr 9, 2021
Messages
25
Reaction score
45
Location
Milano IT
I have the same sockets combination on my Origin20 head, but it's clearly indicated that the middle one is for 8ohm. I think should be the same on DSL20H; so:
Socket 1 - 1 speaker 16ohm
Socket 2 - 1 speaker 8ohm
Socket 2 & 3 - 2 speakers 16ohm.

Never put speakers with an impedance lower than that indicated in the socket
Never use socket 1 & 2 at the same time
 
Last edited:

PelliX

Well-Known Member
Joined
Jun 16, 2020
Messages
2,095
Reaction score
4,090
So putting 16ohm cab in 8ohm amp is safe but putting 8ohm cab into 16ohm amp is dangerous ?

Replace the word 'amp' with 'tap', as an amp generally has multiple taps - as does yours, but "yes". My rule of thumb is that doubling the load on a tap is OK (but don't go much further), and go no lower than perhaps 75% of the tap rating for a load in the other direction. A 12 Ohm load isn't going to cause damage on a 16 Ohm tap, for example, but it's still not a 'good setup', honestly.

Also, to complicate matters a little bit more, if you intend to use multiple taps at once, you want to (or maybe 'have to') consider the balance towards the valves. The output transformer has a primary (which the valves connect to, simply put) and a number of secondaries (the 'taps' we're referring to). If you're using multiple taps (so an 8 and a 16 Ohm tap, for example, not just both 8 Ohm jacks) you would ideally want to balance that correctly, so the valves 'see' the right load. If you'll only use one tap at a time, you can forget this bit (or read up on it, get smart and be prepared in case you ever want to do just that). :)

Never use socket 1 & 2 at the same time

Well, that's what the manual states. Actually it's a little more complex. To be honest, you can get away with a 16 Ohm load on the 16 Ohm tap and an 8 Ohm load on the 8 Ohm tap. Would I recommend this for long periods of time, cranked and dimed? No, generally not.

Technically you want a 20 - 30 Ohm load on your 16 Ohm tap and something like a 16 Ohm load on the 8 Ohm tap to balance things correctly, because they add up on the primary side to over simplify it. TL;DR: Can you use all jacks at once? Yes, though it will stress the valves a little more. I've done this plenty on my DSL20 and never had any adverse effects.
 
Last edited:

Georgiatec

Well-Known Member
VIP Member
Joined
Apr 23, 2010
Messages
5,968
Reaction score
6,109
Location
Looking for something I don't remember what.
Hi,

I bought Marshall DSL 20 head.

It has 3 input jacks:

1 - 16ohm

2 and 3 with description - 1 - 8ohm or 2x16ohm

Please answer this questions:

1. Does it mean I can put one 8ohm cab in 2 or 3 jack without difference in which one?
2. Can I put in 2 and 3 jack 16ohm cabs in same time ?
3. I’m going to buy speaker with G12T-75 but seller might don’t know if it’s 8ohm or 16ohm.
If I put into 1 8ohm/2 16 ohm it should be safe right ?
If put only 1 16ohm cab into jack described 1 8ohm/ 2 16ohm will it be safe or it always has to be 1 8ohm or 2 16ohm ?
If your cab is 16 ohm, no problem it goes in the 1 x 16 output, however as Gemon stated be careful with an 8 ohm cab as the 2 x 16 / 1 x 8 sockets may not be the same. On the Origin 20h you can ONLY use the centre socket for an 8 ohm cab. This may or may not be the same on the DSL20h. If you quickly try both and they are the same, then no problem, use either or. However if one is noticeably quieter with lousy tone then use the other one....before your OT starts to melt (smell of cooking kippers)
 

PelliX

Well-Known Member
Joined
Jun 16, 2020
Messages
2,095
Reaction score
4,090
Doesn't the use of the 1x16 tap switch off the other two taps on these amps?

Nope. Marshall don't use a lot of switching jacks for their speaker taps. I know there are some amps that have them, but not this one.

On the Origin 20h you can ONLY use the centre socket for an 8 ohm cab.

From having had DSL20's apart, I can assure you that both 8 Ohm outputs are in fact simply in parallel, so it doesn't matter which one you use.
 

Latest posts



Top