Amp Guru's..some questions

BFT Gibson

BFT Gibson

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I get what they do but i kinda want to know why, maybe in layman terms.

Can anyone explain the Fender Bassman & then what the JTM 45, what was done as it was taken from the bassman. I Understand the value & parts difference in the equation But, man i would really appreciate an explanation. I can grasp of what is going on., as far as what the pre circuits are doing & how the dif values get added in or added at dif places in the circuit to influence the amps tone shaping,

That marshall roar , how can i say it..is it the mid & high being enhanced & the bass response being cut or tightened in the jtm 45 & in the Bassman more bass is allowed to pass through & therefore that sorta sloppy bottom. Sorry i dont understand & realy want to learn cause i love these amps. Thanks
 
This may help

reverb.com

A History Of Marshall Amps: The Early Years

How well do you know your Marshall history? Take a look back from the early days in 1962 to the end of hand-wired circuitry in 1973.
reverb.com reverb.com

A few more points Fender 5F6A Bassman used Triad transformers and Marshall used Radio Spares transformers and of course different speakers.
Fender used Astron capacitors and Marshall used Mullard and Radio Spares capacitors they do sound different. The devil's in the details.
 
67plexi said:
This may help

reverb.com

A History Of Marshall Amps: The Early Years

How well do you know your Marshall history? Take a look back from the early days in 1962 to the end of hand-wired circuitry in 1973.
reverb.com reverb.com

A few more points Fender 5F6A Bassman used Triad transformers and Marshall used Radio Spares transformers and of course different speakers.
Fender used Astron capacitors and Marshall used Mullard and Radio Spares capacitors they do sound different. The devil's in the details.
Click to expand...
Thank you so much ! When my phones stop ringing tonite. Going to really take that in !
 
BFT Gibson said:
I get what they do but i kinda want to know why, maybe in layman terms.

Can anyone explain the Fender Bassman & then what the JTM 45, what was done as it was taken from the bassman. I Understand the value & parts difference in the equation But, man i would really appreciate an explanation. I can grasp of what is going on., as far as what the pre circuits are doing & how the dif values get added in or added at dif places in the circuit to influence the amps tone shaping,

That marshall roar , how can i say it..is it the mid & high being enhanced & the bass response being cut or tightened in the jtm 45 & in the Bassman more bass is allowed to pass through & therefore that sorta sloppy bottom. Sorry i dont understand & realy want to learn cause i love these amps. Thanks
Click to expand...

The 5AF6 circuit was duplicated, but then some changes were made.
The finished JTM45 is not exactly the same as a Bassman.

First Bassman Lesson:

A. The Marshall circuit basically changes the frequency response, when compared to a bass amp 5AF6.
The Marshall is set up in a way the allows high frequency to pass.
But at the same time, the low frequency is reduced, or attenuated.

B. The higher the frequency is, the more passes through. Like this: /
The lower the frequency is, the less of it is allowed to pass. The lower the frequency, the more attenuation to the lows.

C. The result is: that high frequencies distort first, and lower frequencies remain essentially clean.
The lows are not allowed to distort, or distort much less than the highs.

= The British Sound
The highs are crunchy and compressed, the lows are clean.
The lows are not supposed to distort, (lows distort much less) which can result in a muddy sound.

The typical guitar amp will break up === too much in the bass frequencies. This results in the "stinker" sound or the "muddy sound."
The Marshall was intentionally avoiding that muddy result in the low frequencies. It did this by attenuating the lower frequencies.

There are now about 2-3 things more to learn about Marshall VS Bassman...
 
Amp Mad Scientist said:
The 5AF6 circuit was duplicated, but then some changes were made.
The finished JTM45 is not exactly the same as a Bassman.

First Bassman Lesson:

A. The Marshall circuit basically changes the frequency response, when compared to a bass amp 5AF6.
The Marshall is set up in a way the allows high frequency to pass.
But at the same time, the low frequency is reduced, or attenuated.

B. The higher the frequency is, the more passes through. Like this: /
The lower the frequency is, the less of it is allowed to pass. The lower the frequency, the more attenuation to the lows.

C. The result is: that high frequencies distort first, and lower frequencies remain essentially clean.
The lows are not allowed to distort, or distort much less than the highs.

= The British Sound
The highs are crunchy and compressed, the lows are clean.
The lows are not supposed to distort, (lows distort much less) which can result in a muddy sound.

The typical guitar amp will break up === too much in the bass frequencies. This results in the "stinker" sound or the "muddy sound."
The Marshall was intentionally avoiding that muddy result in the low frequencies. It did this by attenuating the lower frequencies.

There are now about 2-3 things more to learn about Marshall VS Bassman...
Click to expand...
Ahh..on the Bassman the bass frequencies are breaking with everything else ?

Marshall passed the low & it tightened up, thats makes sense..then with closed back celestions... now i am grasping whats happeneing

I play em side by side & even use same cabs & those differences really come to play

What got me noticing, by mistake left Boss SD1 on & it was set to basically treble boost..the bassman got darn near nasty without the flub.

Thanks AMS, appreciated the terminology
 
The JTM45 was pretty much a direct knockoff of the 5F6A Bassman. The only circuit difference was the use of a 500pf "treble peaking" capacitor across the bright channel's 270k "mixer" resistor into the 2nd gain stage (V2a). This accentuates the upper mids & highs on the bright channel. All the rest of the circuit is identical. The 5F6A Bassman called for a 12AY7 in V1 whereas the JTM45 an ECC83, so the JTM45 had a little more gain (could overdrive more easily). Otherwise, as Mr Plexi said, the devil's in the details.
Different capacitor types colour the tone differently & even resistor types can affect tone (especially where they get a large voltage swing across them). The Triad OT played a large part in the magic of 5F6A. Different speaker types & cab configuration also account for sonic differences. Cheers
 
ivan H said:
The JTM45 was pretty much a direct knockoff of the 5F6A Bassman. The only circuit difference was the use of a 500pf "treble peaking" capacitor across the bright channel's 270k "mixer" resistor into the 2nd gain stage (V2a). This accentuates the upper mids & highs on the bright channel. All the rest of the circuit is identical. The 5F6A Bassman called for a 12AY7 in V1 whereas the JTM45 an ECC83, so the JTM45 had a little more gain (could overdrive more easily). Otherwise, as Mr Plexi said, the devil's in the details.
Different capacitor types colour the tone differently & even resistor types can affect tone (especially where they get a large voltage swing across them). The Triad OT played a large part in the magic of 5F6A. Different speaker types & cab configuration also account for sonic differences. Cheers
Click to expand...
Thanks
I am having a blast last few days comparing. The 1960bx cab & Fender bassman closed back & a 2x12 semi open.

I have JTM 45 Cl that my tech put Fender Bassman 1965-67 power in it. Its a beast,

a have a bone stock 1968 Fender Bassman drip edge my tech made 100% back to stock but grounded it better,,it has no noise at all. Kind of interesting on an American voiced cab & the British cab . they close but i am noticing the full bottom on the Fender & the Cut on the 45..together in a mix monstrous !

I have mucho respect for these 2 amps & how they lead to the future of amps we all love
 
BFT Gibson said:
I get what they do but i kinda want to know why, maybe in layman terms.

Can anyone explain the Fender Bassman & then what the JTM 45, what was done as it was taken from the bassman. I Understand the value & parts difference in the equation But, man i would really appreciate an explanation. I can grasp of what is going on., as far as what the pre circuits are doing & how the dif values get added in or added at dif places in the circuit to influence the amps tone shaping,

That marshall roar , how can i say it..is it the mid & high being enhanced & the bass response being cut or tightened in the jtm 45 & in the Bassman more bass is allowed to pass through & therefore that sorta sloppy bottom. Sorry i dont understand & realy want to learn cause i love these amps. Thanks
Click to expand...

The bassman output transformer was different in that it had extra low frequency response, compared to other output transformers.
It will hit 10Hz no problem. Leo Fender probably wanted it to have extra deep subsonic bass response.
Normal output will roll off below 40 Hz in a Marshall guitar amp.
The Marshall doesn't pass the subsonic low frequencies the same way as a Bassman does.
 
Amp Mad Scientist said:
The bassman output transformer was different in that it had extra low frequency response, compared to other output transformers.
It will hit 10Hz no problem. Leo Fender probably wanted it to have extra deep subsonic bass response.
Normal output will roll off below 40 Hz in a Marshall guitar amp.
The Marshall doesn't pass the subsonic low frequencies the same way as a Bassman does.
Click to expand...
Yesterday i did a weird thing. Played a Bassman into a bass cab with a bass. lol

Lil flubby but the old school sound into a 15 is really nice. Then plugged a jtm45 in & then a jmp50. 45 was a bit tighter. Then the jmp..talk abput an interesting sound..what can i say ,immediate in the response maybe?
 
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