Marshall JTM30/JTM60
Moderator: jingle_jangle
Marshall JTM30/JTM60
In the mid 1990s, Marshall released a range of valve amps called the JTM series (nothing to do with the old JTM45s!). The JTM30 was supposedly 30watts, and the JTM60 was 60 watts. They both, however used 2 EL34s (or 5881s) in the output stage. How can one be rated twice the power of the other?
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soundmasterg
- RRF Consultant
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- Joined: Tue Oct 01, 2002 1:06 pm
The lower power one has to have a lower voltage on the power tubes, and a smaller output transformer. The power level out is a function of the capabilities of the output transformer, and the B+ voltage on the pwoer tubes, not necessarily the type of tube used. They also probably have the screen voltage lower on the lower power amp, which limits how much power it will put out overall, and also makes the sound colder and less alive.
This is an interesting topic. I suspect that most people think that buying an amp that produces more watts means it will have more volume.
In other words an amplifier with 100 Watts per channel is twice as loud as 50 Watts per channel. Can you expand on this misperception and tell us what we really should know when buying an amp for our on stage or in home needs. Thanks.
In other words an amplifier with 100 Watts per channel is twice as loud as 50 Watts per channel. Can you expand on this misperception and tell us what we really should know when buying an amp for our on stage or in home needs. Thanks.
“We can't solve problems by using the same kind of thinking we used when we created them.” - Albert Einstein
"You do not really understand something unless you can explain it to your grandmother" - Albert Einstein
"You do not really understand something unless you can explain it to your grandmother" - Albert Einstein
Brian,
an output power doubling make an amp (only) 3 decibels louder. If you have 2 identical speakers
instead of one connected to your amp, it is 3 dB louder, too.
So an AC30 with 2 speakers is 6 dB louder than an AC15 with one speaker. An AC50 is about 2.5dB louder than an AC30.
3 db isn't that much more volume, it is just noticeable. If you want to get it 10dB louder
you need ten times more output power!
btw: loudspeaker chassis sensitivity varies easily more than 3dB from model to model, so a 60Watt amp
with a cheap speaker can have less sound pressure than a 20Watt amp with a speaker of higher sensitivity.
an output power doubling make an amp (only) 3 decibels louder. If you have 2 identical speakers
instead of one connected to your amp, it is 3 dB louder, too.
So an AC30 with 2 speakers is 6 dB louder than an AC15 with one speaker. An AC50 is about 2.5dB louder than an AC30.
3 db isn't that much more volume, it is just noticeable. If you want to get it 10dB louder
you need ten times more output power!
btw: loudspeaker chassis sensitivity varies easily more than 3dB from model to model, so a 60Watt amp
with a cheap speaker can have less sound pressure than a 20Watt amp with a speaker of higher sensitivity.
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soundmasterg
- RRF Consultant
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- Joined: Tue Oct 01, 2002 1:06 pm
Speakers are one of the biggest things that determine volume. A really efficient speaker like a JBL (100db or so) will have a lot more volume than some vintage Jensens (87db or so). Speaker/cabinet choice can make an amp too loud or just right for a venue with the same tubes being used. Play a gig at a small club with a 25 watt amp and a single 12 that has around 90db efficiency. Play a larger venue, and that same amp can suddenly be plenty loud with a 2x10 or 4x12 or something along those lines if the speakers are the same or more efficient.
If you take a look at the data sheets for various tubes, you can see how the power level changes depending on what voltages are on the tube, what load the tubes are driving, and how they are biased. This will give you a clue as to the capabilities of the power output of an amp using a given tube type, but the speaker(s) used will determine the volume from there.
If you take a look at the data sheets for various tubes, you can see how the power level changes depending on what voltages are on the tube, what load the tubes are driving, and how they are biased. This will give you a clue as to the capabilities of the power output of an amp using a given tube type, but the speaker(s) used will determine the volume from there.
Wolfgang,
Your reply mentioned the importance of sound pressure. Perhaps either you or Greg can expand on that aspect of producing pleasing tone with lots of volume. In other words explain the difference between a cheap speaker and a good speaker and how that relates to sound pressure and tone.
Many thanks. As I said this is a very interesting topic.
Your reply mentioned the importance of sound pressure. Perhaps either you or Greg can expand on that aspect of producing pleasing tone with lots of volume. In other words explain the difference between a cheap speaker and a good speaker and how that relates to sound pressure and tone.
Many thanks. As I said this is a very interesting topic.
“We can't solve problems by using the same kind of thinking we used when we created them.” - Albert Einstein
"You do not really understand something unless you can explain it to your grandmother" - Albert Einstein
"You do not really understand something unless you can explain it to your grandmother" - Albert Einstein
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soundmasterg
- RRF Consultant
- Posts: 1923
- Joined: Tue Oct 01, 2002 1:06 pm
Hmm...well I don't completely understand all the dynamics of speaker construction and what makes something sound better or have more or less volume or not. That said, I do have some knowledge about it. The best source for questions about speakers and what affects or doesn't affect the sound would be Ted Weber and his website at www.tedweber.com. He has a whole FAQ section that talks about speakers and what makes them tick, and he also has a bbs section devoted to speakers. He could answer any questions you have in greater detail and more clarity than just about anyone else alive. Plus, he makes GREAT speakers!
Most cheaper speakers are not very efficient, and may sound ok, but won't have as much volume as a good efficient speaker. Most of the older Jensens sound very nice, but aren't as efficient as Celestiona. The new Jensen reissues can handle more power than the older ones because they changed some materials, but as a consequence, they don't sound as good and are brighter. You don't get something for nothing, but Jensen hasn't learned that yet. JBL's are very efficient, but are often too bright for some people, partially due to the efficiency and partially due to the materials. Many old JBL's use an aluminium dome over the voice coil, which makes the top end really bright. JBL's are probably one of the most clinical and articulate speakers out there, but if your playing is sloppy, then you wouldn't like them because they magnify any mistakes.
Different magnets, different glues, different dopes, (and amount and location of dopes and glues) and different materials used in the cone all change the sound. Also the gap in the voice coil determines how efficient the speaker will be, and the magnet strength determine how powerful and efficient the speaker will be. Personally I like different brands and types of speakers for different applications, but I generally stay away from cheap quality speakers like Radio Shack for example. Good modern brands are Webervst, Tone tubby, Eminence, Celestion, Fane. Older ones that were good include Celestion, Fane, Jensen, Oxford, JBL, CTS, EV.
Most cheaper speakers are not very efficient, and may sound ok, but won't have as much volume as a good efficient speaker. Most of the older Jensens sound very nice, but aren't as efficient as Celestiona. The new Jensen reissues can handle more power than the older ones because they changed some materials, but as a consequence, they don't sound as good and are brighter. You don't get something for nothing, but Jensen hasn't learned that yet. JBL's are very efficient, but are often too bright for some people, partially due to the efficiency and partially due to the materials. Many old JBL's use an aluminium dome over the voice coil, which makes the top end really bright. JBL's are probably one of the most clinical and articulate speakers out there, but if your playing is sloppy, then you wouldn't like them because they magnify any mistakes.
Different magnets, different glues, different dopes, (and amount and location of dopes and glues) and different materials used in the cone all change the sound. Also the gap in the voice coil determines how efficient the speaker will be, and the magnet strength determine how powerful and efficient the speaker will be. Personally I like different brands and types of speakers for different applications, but I generally stay away from cheap quality speakers like Radio Shack for example. Good modern brands are Webervst, Tone tubby, Eminence, Celestion, Fane. Older ones that were good include Celestion, Fane, Jensen, Oxford, JBL, CTS, EV.
I have always liked JBL's for bass.
The way I was taught was in laymen's terms if you want twice the volume you need ten times the amount of watts. I had a double SVT set up one night and tried a 50 watt Fender Bassman head with it and the 300 watt SVT head absolutely killed it which is six times the amount of watts. It sounded much more than twice as loud. The Fender sounded good and had decent volume for most of the bass range but when you went down it absolutely krapped out which shows that usually we don't use all that power, only for certain notes and/or loud peaks. This is called head room and is very necessary playing bass in a live band. I've been asked why I always bring the big Ampegs with either two 15's or at least one 8 X 10 which I prefer. It's because pre-Ampeg when I was using Fenders, Sunns, even Marshals, there were many times when I got drowned out by guitar players which does not happen to me anymore no matter what the situation or room acoustics, I always have enough juice to hear myself clearly and none of my notes drop off.
I do know that the human ear can "hear" a midrange tone such as a trumpet approximately ten times easier also which is why you can hear a trumpet a mile away and is why a tuba is so much bigger besides the fact that the wavelength is much longer. This is also why basses need much more power than guitars to keep up with them especially if you like to play with a lot of clear bottom like I do.
The way I was taught was in laymen's terms if you want twice the volume you need ten times the amount of watts. I had a double SVT set up one night and tried a 50 watt Fender Bassman head with it and the 300 watt SVT head absolutely killed it which is six times the amount of watts. It sounded much more than twice as loud. The Fender sounded good and had decent volume for most of the bass range but when you went down it absolutely krapped out which shows that usually we don't use all that power, only for certain notes and/or loud peaks. This is called head room and is very necessary playing bass in a live band. I've been asked why I always bring the big Ampegs with either two 15's or at least one 8 X 10 which I prefer. It's because pre-Ampeg when I was using Fenders, Sunns, even Marshals, there were many times when I got drowned out by guitar players which does not happen to me anymore no matter what the situation or room acoustics, I always have enough juice to hear myself clearly and none of my notes drop off.
I do know that the human ear can "hear" a midrange tone such as a trumpet approximately ten times easier also which is why you can hear a trumpet a mile away and is why a tuba is so much bigger besides the fact that the wavelength is much longer. This is also why basses need much more power than guitars to keep up with them especially if you like to play with a lot of clear bottom like I do.