Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! - Page 3

American Viking · 11-03-2009, 04:35 AM

Quote:

Originally Posted by American Viking

Although a higher number on the head and lower on the cabinet is less damaging than the other way around.

Quote:

Originally Posted by Wilder Amplification

This is backwards. Too low of a load will cause the load to pull too much current from the OT.

Too high of a load mismatch increases flyback voltage on the OT beyond its limits. This is why open loads will fry an OT.

You're absolutely right. I think I've been repeating this info way too many times. I've been fumbling a lot here lately.

Gtrman58 · 11-03-2009, 02:45 PM

Great thread Viking!

It should be repeated monthly and I bet tons of people will still be blowing up their gear. As I stated in another post, you would not believe the stuff I have seen seasoned veterans to their gear through the years!!!!

What were they thinking? Or were they??

Noone · 11-03-2009, 08:49 PM

Sorry that you have to repeat yourself (no sarcasm.) People everyday are getting their very first head and cab. A lot of them are bought used and either don't have the manual or the seller 'mickey-moused' something and the buyer doesn't know it. That's why people like me really appreciate this forum and definitely appreciate your repeating yourself. I personally don't want to damage my amp. If you guys say don't mismatch impedances than I SHALL NOT! So, I have another question. Is there anything wrong with running a head at 4 ohms into one 8 ohm cab and one 1960 lead cab switched to stereo which runs at 8 ohms on one side? I realize I'd only be using one side of the Marshall. I'm trying to get some sound off of the floor by stacking cabs. We have a very small practice space

Again, thank you for go over this again with a newbie!

American Viking · 11-04-2009, 10:17 AM

Quote:

Originally Posted by Noone

Sorry that you have to repeat yourself (no sarcasm.) People everyday are getting their very first head and cab. A lot of them are bought used and either don't have the manual or the seller 'mickey-moused' something and the buyer doesn't know it. That's why people like me really appreciate this forum and definitely appreciate your repeating yourself. I personally don't want to damage my amp. If you guys say don't mismatch impedances than I SHALL NOT! So, I have another question. Is there anything wrong with running a head at 4 ohms into one 8 ohm cab and one 1960 lead cab switched to stereo which runs at 8 ohms on one side? I realize I'd only be using one side of the Marshall. I'm trying to get some sound off of the floor by stacking cabs. We have a very small practice space

Again, thank you for go over this again with a newbie!

That would be fine. As long as both speaker loads were 8ohms and the amp is set to 4ohms that would be matched.

I'm glad you're finding this helpful. I don't mind repeating it, I just fouled up twice this week in typing out the wrong thing. Sometimes I feel like I'm answering these threads in my sleep! lol.

nielsdaugaard · 11-04-2009, 11:09 AM

I just bought the randy roads full stack, and when i try it at the store the amp was on 16 ohm and plugget in to the left side in the two cabs, that`2ohm load :-( i thange it to the right side and 8ohm on the head, they told me that it hasen`t played loud, so my q are will it blow op now ? seem to work fine at the moment

American Viking · 11-04-2009, 11:34 AM

Being played loud is really inconsequential to having the impedance mismatched. You should refer back to the first post. If both cabinets are plugged into the right side input with the cabinet set to Mono and the head at 8ohms you should be in good shape. As long as the amp plays fine it should be alright for the future. Being mismatched in the store was definitely not good for it, but it seems as it has survived. Transformers won't necessarily go bad immediately, but if the mismatch was continued damage will have taken place. It should be all good.

nielsdaugaard · 11-05-2009, 04:56 AM

Hi are there anyway to messure the trafo to see if it is ok ??

Wilder Amplification · 11-05-2009, 11:21 AM

Quote:

Originally Posted by nielsdaugaard

Hi are there anyway to messure the trafo to see if it is ok ??

Yes and no. You can read the DC resistance of the primary and secondary coils. If they're not what they should be, it's bad. But if they are what they should be, it doesn't necessarily mean it's any good and should be checked by a tech with the proper equipment.

Primary side should read the same amount between the center tap and each outside winding give or take an ohm or two. It should read double these two readings between the two outer windings.

Secondary side should be less than an ohm on all 3 taps relative to the common/ground wire. Relative to common, it should read slightly higher on the 8 and 16 ohm taps than it does the 4, but still be less than 1 ohm.

Aerostar2005 · 11-05-2009, 08:53 PM

Here's my question: I have a MF350 head (The Infamous Mode Four). I want to run a second 1960B cab using it. The amp is at 16oms, the cabs are set to 16 as well. Can I do this safely? (I've been waiting 2 months for an answer from Marshall Support)

Wilder Amplification · 11-05-2009, 09:56 PM

Quote:

Originally Posted by Aerostar2005

Here's my question: I have a MF350 head (The Infamous Mode Four). I want to run a second 1960B cab using it. The amp is at 16oms, the cabs are set to 16 as well. Can I do this safely? (I've been waiting 2 months for an answer from Marshall Support)

Yes but there is a certain way to do it.

Straight from the Mode 4 Manual -

For half stack operation (running single cabs), Output I is for a 16 ohm cab whereas Output II is for an 8 ohm cab.

For full stack connection, you connect two 16 ohm cabinets to the amp by connecting one cab into Output I and the other 16 ohm cab into Output II. This means that the ONLY way to run a full stack is with two 16 ohm cabs.

Do not connect any less than 8 ohms or you will trigger the output protection circuitry of the amp on the Mode Four.

DO NOT connect anything to Output I while using an 8 ohm cab on Output II.

DO NOT connect anything other than a second 16 ohm cab to Output II while you have a 16 ohm cab connected to Output I.

It's either -

* One 16 ohm cab on Output I

* One 8 ohm cab on Output II

* Two 16 ohm cabs...one on Output I and the other on Output II

Aerostar2005 · 11-17-2009, 11:07 PM

Quote:

Originally Posted by Wilder Amplification

Yes but there is a certain way to do it.

Straight from the Mode 4 Manual -

For half stack operation (running single cabs), Output I is for a 16 ohm cab whereas Output II is for an 8 ohm cab.

For full stack connection, you connect two 16 ohm cabinets to the amp by connecting one cab into Output I and the other 16 ohm cab into Output II. This means that the ONLY way to run a full stack is with two 16 ohm cabs.

Do not connect any less than 8 ohms or you will trigger the output protection circuitry of the amp on the Mode Four.

DO NOT connect anything to Output I while using an 8 ohm cab on Output II.

DO NOT connect anything other than a second 16 ohm cab to Output II while you have a 16 ohm cab connected to Output I.

It's either -

* One 16 ohm cab on Output I

* One 8 ohm cab on Output II

* Two 16 ohm cabs...one on Output I and the other on Output II

Thank you so much for your advise. I can now drive my bandmates crazy!

BluesDisciple · 11-18-2009, 07:45 PM

O.K., new guy question here...

My new JCM 2000 TSL 60w head has, on the back, a switch for 16 ohm or 8 ohm. It also has two jacks for cabinet leads.

The 1960 cabinet has a switch on the plate for stereo (8ohms) or mono(16ohms). I will ignore the 4ohm designation over the left hand jack for now. The switch on the cab, right now, is set to the right for mono at 16 ohms. The switch on the back of the head is set at 16 ohms. I have one lead running from one of two output jacks down to the cab.

The question: To run stereo out of one cabinet, would I be doing any damage to run two leads out of the two jacks on the back of the JCM 2000 TSL 60w head, into the two jacks on the back of the 1960 cab, if I have both switches set at 8 ohms?

Your thoughts please...

***Adwex*** · 11-18-2009, 07:48 PM

Quote:

Originally Posted by BluesDisciple

O.K., new guy question here...

My new JCM 2000 TSL 60w head has, on the back, a switch for 16 ohm or 8 ohm. It also has two jacks for cabinet leads.

The 1960 cabinet has a switch on the plate for stereo (8ohms) or mono(16ohms). I will ignore the 4ohm designation over the left hand jack for now. The switch on the cab, right now, is set to the right for mono at 16 ohms. The switch on the back of the head is set at 16 ohms. I have one lead running from one of two output jacks down to the cab.

The question: To run stereo out of one cabinet, would I be doing any damage to run two leads out of the two jacks on the back of the JCM 2000 TSL 60w head, into the two jacks on the back of the 1960 cab, if I have both switches set at 8 ohms?

Your thoughts please...

The TSL60 is not a stereo amp. You need two amps (more specifically, two POWER amps to run stereo).
Use the cab in mono, 16 ohms.

BluesDisciple · 11-19-2009, 09:34 AM

Quote:

Originally Posted by Adwex

The TSL60 is not a stereo amp. You need two amps (more specifically, two POWER amps to run stereo).
Use the cab in mono, 16 ohms.

Then why the two output jacks? And how do I know which to plug into?

movo · 11-19-2009, 10:02 AM

Hmm I'm currently running a JCM800 set on 16ohm trough two 8ohm Valvestate speakers. Is that correct?

***Adwex*** · 11-19-2009, 11:32 AM

Quote:

Originally Posted by BluesDisciple

Then why the two output jacks? And how do I know which to plug into?

"Stereo" means there is a left and a right channel. There are two output jacks on most amp heads so you can connect two speaker cabs. They will not be stereo, just two speaker cabs in mono. They are wired in parallel, you can use either one, it doesn't matter.

***Adwex*** · 11-19-2009, 11:36 AM

Quote:

Originally Posted by movo

Hmm I'm currently running a JCM800 set on 16ohm trough two 8ohm Valvestate speakers. Is that correct?

No. Two 8 ohm cabs in parallel will equal 4 ohms.

movo · 11-19-2009, 12:13 PM

Quote:

Originally Posted by Adwex

No. Two 8 ohm cabs in parallel will equal 4 ohms.

But they are seperated, in series. Both speakers got their own speakercable which goes in both outputs of the amp. Or...?

***Adwex*** · 11-19-2009, 01:14 PM

Quote:

Originally Posted by movo

But they are seperated, in series. Both speakers got their own speakercable which goes in both outputs of the amp. Or...?

They're not in series, they are wired in parallel inside the amp.

For 1 cab, you can use either jack it doesn't matter which one. If the cab is 8 ohms, set the amp for 8 ohms.

For 2 cabs, you use both jacks, one for each cab. If both cabs are 8 ohms each, set the amp for 4 ohms.

BluesDisciple · 11-19-2009, 01:22 PM

Aha! Thanks for the clarification. I scoured the Marshall lit. that is downloadable, but could not find a reasonable answer. Yours makes the most sense. I appreciate your time on this.

BD

Wilder Amplification · 11-19-2009, 01:22 PM

Quote:

Originally Posted by movo

But they are seperated, in series. Both speakers got their own speakercable which goes in both outputs of the amp. Or...?

Adwex is correct about the speaker jacks being paralleled inside the amp.

***Adwex*** · 11-19-2009, 01:25 PM

Quote:

Originally Posted by BluesDisciple

Aha! Thanks for the clarification. I scoured the Marshall lit. that is downloadable, but could not find a reasonable answer. Yours makes the most sense. I appreciate your time on this.

BD

My pleasure. Just doing my part to make the world a better place, one Marshall at a time.

Rev-al · 11-19-2009, 03:45 PM

Hello and Thank You for great info - Hope this isn't a duplication of an earlier post - but -
How do I connect both my 16 ohm 4x12 AND my 1936 2x12 cab to my '72 super lead 100 ?
Think the 1936 would have to be on the 4 ohm mono setting, ??
So what do I set the head output to please ??
Many thanks
al

Wilder Amplification · 11-19-2009, 03:50 PM

Quote:

Originally Posted by Rev-al

Hello and Thank You for great info - Hope this isn't a duplication of an earlier post - but -
How do I connect both my 16 ohm 4x12 AND my 1936 2x12 cab to my '72 super lead 100 ?
Think the 1936 would have to be on the 4 ohm mono setting, ??
So what do I set the head output to please ??
Many thanks
al

You would have to do some rewiring to make that work. If that 2x12 is 4 ohms when set to mono, that leads me to believe that the speakers are 8 ohm, which can be wired to 16 ohms in mono mode by wiring them in series. Then you could run it with the 16 ohm 4x12 and set the amp to 8 ohms.

If you try to run it as a 4 ohm in mono mode, you CANNOT add any more cabs once you're down to 4 ohms as adding another cab would drop the imepdance down lower than 4 ohms and would not pose enough of a load to the amp's output, which would cause the amp to go overcurrent and blow your OT.

movo · 11-19-2009, 04:06 PM

Quote:

Originally Posted by Adwex

They're not in series, they are wired in parallel inside the amp.

For 1 cab, you can use either jack it doesn't matter which one. If the cab is 8 ohms, set the amp for 8 ohms.

For 2 cabs, you use both jacks, one for each cab. If both cabs are 8 ohms each, set the amp for 4 ohms.

http://94.100.113.216/785150001-7852...58_6_vwN8.jpeg

This is my setup for now. Maybe I'm completely wrong but those two speakers got their own jacks so, speaker 1 has a cable and jack, same with speaker 2..

Sorry for the convenience

***Adwex*** · 11-19-2009, 04:23 PM

Quote:

Originally Posted by movo

http://94.100.113.216/785150001-7852...58_6_vwN8.jpeg

This is my setup for now. Maybe I'm completely wrong but those two speakers got their own jacks so, speaker 1 has a cable and jack, same with speaker 2..

Sorry for the convenience

Take a close picture of the back of the amps.

Wilder Amplification · 11-19-2009, 04:26 PM

Quote:

Originally Posted by movo

http://94.100.113.216/785150001-7852...58_6_vwN8.jpeg

This is my setup for now. Maybe I'm completely wrong but those two speakers got their own jacks so, speaker 1 has a cable and jack, same with speaker 2..

Sorry for the convenience

Right, and by plugging each speaker into each speaker jack on the back of the amp, this places them in parallel. Cut the impedance of one of the two speakers in 1/2 and that's where you'll set your impedance switch to.

***Adwex*** · 11-19-2009, 04:27 PM

Quote:

Originally Posted by Rev-al

Hello and Thank You for great info - Hope this isn't a duplication of an earlier post - but -
How do I connect both my 16 ohm 4x12 AND my 1936 2x12 cab to my '72 super lead 100 ?
Think the 1936 would have to be on the 4 ohm mono setting, ??
So what do I set the head output to please ??
Many thanks
al

The 1936 2x12 cab is 8 ohms. You cannot match the impedance if you use both cabs, the result will be 5.33 ohms, you will risk damaging the amp....and you don't want to damage a '72 super lead.

movo · 11-19-2009, 04:42 PM

Thanks for the answers Adwex and Wilder. And sorry for being stupid :P Never dealth with this before..

http://img43.imageshack.us/img43/7495/dsc00363lb.jpg

http://img684.imageshack.us/img684/9291/dsc00364d.jpg

Wilder Amplification · 11-19-2009, 04:58 PM

Quote:

Originally Posted by movo

Thanks for the answers Adwex and Wilder. And sorry for being stupid :P Never dealth with this before..

http://img43.imageshack.us/img43/7495/dsc00363lb.jpg

http://img684.imageshack.us/img684/9291/dsc00364d.jpg

Yeah that switch is obviously set wrong unless you have 32 ohm speakers, and in the case of guitar speakers they don't make such an animal.

If your two speakers are 16 ohm a piece, set the selector on the amp to 8 ohms.

If they're 8 ohm a piece, switch it to 4 ohms.

Rev-al...since Adwex just clarified that your 2x12 is an 8 ohm cab, this means that the speakers are more than likely 16 ohm speakers wired in parallel for 8 ohm and this would in fact create a slight mismatch on the 4 ohm setting. 8 ohm stuff is finicky in that they can't be wired to a different usable impedance without changing speakers out with speakers of a different rated impedance. If those were 8 ohm speakers, you could wire them in series for 16 ohms. But for 2 speakers to arrive at a total 8 ohm impedance, you'd either have to series wire two 4 ohmers or parallel wire two 16 ohmers, which knowing Marshall/Celestion is more than likely how yours is done.

Now, in regards to running a 5.3 ohm load on the 4 ohm tap...yes this does pose a SLIGHT mismatch. My personal opinion, I wouldn't worry about it. I used to run an 8 ohm KMD cab on a Fender Pro Reverb set up for 4 ohms and I never once had an issue.

11-03-2009, 02:45 PM	#62 (permalink)
Gtrman58 Senior Member Join Date: Sep 2009 Location: St. Louis, Mo. Posts: 148	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Great thread Viking! It should be repeated monthly and I bet tons of people will still be blowing up their gear. As I stated in another post, you would not believe the stuff I have seen seasoned veterans to their gear through the years!!!! What were they thinking? Or were they?? __________________ 2009 JCM 2000 Dsl 100 MLB MC412A 1951 Fender Deluxe 2006 Hot Rod Deluxe 1995 Blues Junior 1994 Blues Deville Vox Path Finder 1982 Legend A 30 1980 Gibson Herritage Cherry Sunburst Standard 1980 Explorer White with gold HW 2000 52 Telecaster USA RI 1983 57 Strat LH USA RI 2003 57 Strat USA RI 1960 Silvertone Danelectro 1994 Fender P-bass 68 RI Acoustic guitars....not enough space to list !!!!!

11-03-2009, 08:49 PM	#63 (permalink)
Noone Junior Member Join Date: Nov 2009 Posts: 6	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Sorry that you have to repeat yourself (no sarcasm.) People everyday are getting their very first head and cab. A lot of them are bought used and either don't have the manual or the seller 'mickey-moused' something and the buyer doesn't know it. That's why people like me really appreciate this forum and definitely appreciate your repeating yourself. I personally don't want to damage my amp. If you guys say don't mismatch impedances than I SHALL NOT! So, I have another question. Is there anything wrong with running a head at 4 ohms into one 8 ohm cab and one 1960 lead cab switched to stereo which runs at 8 ohms on one side? I realize I'd only be using one side of the Marshall. I'm trying to get some sound off of the floor by stacking cabs. We have a very small practice space Again, thank you for go over this again with a newbie!

11-04-2009, 11:09 AM	#65 (permalink)
nielsdaugaard Junior Member Join Date: Nov 2009 Posts: 2	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! I just bought the randy roads full stack, and when i try it at the store the amp was on 16 ohm and plugget in to the left side in the two cabs, that`2ohm load :-( i thange it to the right side and 8ohm on the head, they told me that it hasen`t played loud, so my q are will it blow op now ? seem to work fine at the moment

11-04-2009, 11:34 AM	#66 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Being played loud is really inconsequential to having the impedance mismatched. You should refer back to the first post. If both cabinets are plugged into the right side input with the cabinet set to Mono and the head at 8ohms you should be in good shape. As long as the amp plays fine it should be alright for the future. Being mismatched in the store was definitely not good for it, but it seems as it has survived. Transformers won't necessarily go bad immediately, but if the mismatch was continued damage will have taken place. It should be all good. __________________ -I'd rather be a good liver than have one...

11-05-2009, 04:56 AM	#67 (permalink)
nielsdaugaard Junior Member Join Date: Nov 2009 Posts: 2	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Hi are there anyway to messure the trafo to see if it is ok ??

11-05-2009, 08:53 PM	#69 (permalink)
Aerostar2005 Junior Member Join Date: Aug 2007 Location: Chicago,Illinois Posts: 25	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Here's my question: I have a MF350 head (The Infamous Mode Four). I want to run a second 1960B cab using it. The amp is at 16oms, the cabs are set to 16 as well. Can I do this safely? (I've been waiting 2 months for an answer from Marshall Support)

11-18-2009, 07:45 PM	#72 (permalink)
BluesDisciple Junior Member Join Date: Oct 2009 Posts: 18	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! O.K., new guy question here... My new JCM 2000 TSL 60w head has, on the back, a switch for 16 ohm or 8 ohm. It also has two jacks for cabinet leads. The 1960 cabinet has a switch on the plate for stereo (8ohms) or mono(16ohms). I will ignore the 4ohm designation over the left hand jack for now. The switch on the cab, right now, is set to the right for mono at 16 ohms. The switch on the back of the head is set at 16 ohms. I have one lead running from one of two output jacks down to the cab. The question: To run stereo out of one cabinet, would I be doing any damage to run two leads out of the two jacks on the back of the JCM 2000 TSL 60w head, into the two jacks on the back of the 1960 cab, if I have both switches set at 8 ohms? Your thoughts please...

11-19-2009, 10:02 AM	#75 (permalink)
movo Junior Member Join Date: Jul 2009 Location: Netherlands Posts: 13	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Hmm I'm currently running a JCM800 set on 16ohm trough two 8ohm Valvestate speakers. Is that correct?

11-19-2009, 01:22 PM	#80 (permalink)
BluesDisciple Junior Member Join Date: Oct 2009 Posts: 18	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Aha! Thanks for the clarification. I scoured the Marshall lit. that is downloadable, but could not find a reasonable answer. Yours makes the most sense. I appreciate your time on this. BD

11-19-2009, 03:45 PM	#83 (permalink)
Rev-al Junior Member Join Date: Nov 2009 Location: South Coast. England Posts: 2	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Hello and Thank You for great info - Hope this isn't a duplication of an earlier post - but - How do I connect both my 16 ohm 4x12 AND my 1936 2x12 cab to my '72 super lead 100 ? Think the 1936 would have to be on the 4 ohm mono setting, ?? So what do I set the head output to please ?? Many thanks al __________________ 1972 1959 Super Lead 100w. 1973 1985 PA 50w. 4 x 12" Celestion Vintage 30s 1979 Les Paul Custom 1998 '58 Historic Collection

11-19-2009, 04:42 PM	#89 (permalink)
movo Junior Member Join Date: Jul 2009 Location: Netherlands Posts: 13	Re: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! Thanks for the answers Adwex and Wilder. And sorry for being stupid :P Never dealth with this before.. http://img43.imageshack.us/img43/7495/dsc00363lb.jpg http://img684.imageshack.us/img684/9291/dsc00364d.jpg

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