Class 5 at bedroom volume secret

Marshall Class 5

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AndyK
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Re: Class 5 at bedroom volume secret

Postby AndyK » 17 Nov 2009, 13:58

Interesting! So, if you crank the volume to halfway, or over, and run the headphone jack to external speakers, you wouldn't harm the amp or tubes in any way (above the normal wear and tear)? Is the built in load that lets you use headphones like a mini Power Brake, with the headphone volume control being a level of attenuation indicator?

Can you actually get that cranked up Plexi tone at bedroom levels (minus the speaker break up or air movement, etc)?? :scared2
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Re: Class 5 at bedroom volume secret

Postby SteveD » 17 Nov 2009, 15:47

No you wouldn't harm the amp, just normal wear and tear.

You can get great cranked tone at bedroom level this way.
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Re: Class 5 at bedroom volume secret

Postby AndyK » 17 Nov 2009, 16:57

Wow, I wonder if that's the technology that Fargen uses in his "power scaling" feature? Seems too good to be true to be able to crank the power tubes, then attenuate with the headphone circuit!

Any chance of you (Marshall) making a Class 5 head?? :yea
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Re: Class 5 at bedroom volume secret

Postby ClubAndCountry » 18 Nov 2009, 00:54

Power scaling is different, and involves controlling the power supply voltages in the amp so the actual power developed is lowered, rather than generating the same amount and turning some of it into heat rather than sound. It's more sophisticated and reduces valve wear (and potential stress on other components including the output transformer) as well, whereas attenuating either doesn't change it or actually increases it, if you then run the amp harder than you would have otherwise.

In an amp as low-powered as the Class 5 and cathode-biased, you could do it just with a large variable resistor (rheostat) in the power supply. In bigger amps it's done with a solid-state control circuit, a little like a much higher quality lighting dimmer. It's not quite the same sound as attenuating, since the power stage is still being pushed less hard and you don't get as much sag - it's more like a perfect master volume that retains the output valve tone.

It's hard to tell what method low-power amps use without seeing inside though. For example the little Vox that's labeled as having three different power outputs down to 1/4W is just done with attenuation resistors, so it's not really power output control at all.


But you still can't get that cranked up Plexi tone at bedroom volume... it's physically impossible, there are too many differences, not just the speaker breakup and air movement. I honestly think people should stop chasing this particular mirage and just work on how to get a *good* tone at low volume, because otherwise they tend to end up disappointed and blame the tools (eg attenuators) for not working.

The closest I've ever got is to use a full-size Plexi, run into a dummy load, and then re-amplified through another Plexi set very low, into a normal full-size cabinet. And even then it didn't have the directness and punch that you get from a single amp turned up loud.

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Re: Class 5 at bedroom volume secret

Postby AndyK » 18 Nov 2009, 08:44

I hear ya. But if you check the Fargen mini plexi amp demo videos, it comes pretty close to sounding like a good Marshall Plexi at conversation volumes.

I also love the sound of my VM 2266 at low volume, getting mostly preamp gain.

I'm a low volume player, in my basement with kids sleeping mostly! So I need good low volume tones!
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Re: Class 5 at bedroom volume secret

Postby Lowdown » 16 Dec 2009, 18:14

SteveD wrote:Yes C&C pretty much tells it like it is. The internal speaker lead is indeed on push fit spade connectors both to speaker and to PCB so is easily removed.

You could actually make a speaker lead that had a stereo 1/4" jack plug on one end and terminated with spade connectors for the speaker on the other (if you didn't want to solder anything). Connect the signal to the 'tip' and the ground to the 'sleeve'. Leave the 'ring' disconnected. This way you can plug the jack all the way in for either situation. The new speaker lead can reach through the rear panel opening and just needs to be long enough to plug into either socket.

Note however that if you plug into the headphone out but have the switch in the 'extension speaker' position, the output is unloaded. Now as I said, I have carried out extensive tests on the output being unloaded with no negative results, but I would still encourage people to check and make sure everything is plugged in and switched correctly! It's good practise to get into the habit of doing that anyway. :winking
Hi Steve. Thanx for making this amp available to us. I'm loving it!
A couple of questions -

1. I did the mod as above,but when I wired up the TRS jack the way you described,it still has to be backed off half way in. If I plug the jack in all the way(headphone only)there is no sound? I have wired it the way you suggested but nothing,unless I back it out as you would a standard 1/4 jack. Any idea?...I will add,I disconnected the original wiring from the speaker terminal but left the wiring spade connectors connected to the amp chassis itself. Would this make any difference?I taped them up so they wouldn't short anything out.

2. My speaker has double terminals for each + and - and I was wondering if I could also leave the existing internal wiring on as well as adding the mod on the other 2 terminals?

Thanx mate... :Thumbs

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Re: Class 5 at bedroom volume secret

Postby SteveD » 17 Dec 2009, 05:43

Welcome to the forum Lowdown. :Thumbs

It sounds like you have grounded the 'ring' part of the jack socket (the middle section). Only the 'tip' should be connected to signal and the sleeve should be grounded. Connecting the 'ring' to the 'tip' would also be OK but not the 'sleeve'. It's easiest to leave the ring disconnected.

It's better to leave the internal wires disconnected and use one common speaker lead (with TRS jack) to go between the two outputs as required.
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Re: Class 5 at bedroom volume secret

Postby Lowdown » 17 Dec 2009, 23:26

Well of course I did Steve :Embaresed

All done now. Thanx heaps for your help mate. :ntworth

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Re: Class 5 at bedroom volume secret

Postby Max » 06 Jan 2010, 00:13

First, let me just say that at this point I don't own a class 5 but as soon as this rattle issue is put to bed I'll be bagging one. This idea of using the head phone socket for an even lower volume output is appealing but having a lead hanging out the back of the amp attached to the internal speaker is not. Would it be possible to have the internal speaker attached to the ext/headphone switch so that it works the same in both positions? What I mean is that when the switch is set to the head phone position you still have the internal speaker working but at the lower volume until you plug in a set of headphones. Another question: will the class 5 cope with an extension 8 ohm speaker load?

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Re: Class 5 at bedroom volume secret

Postby LivewireBlanco » 06 Jan 2010, 12:32

I asked Steve about the 8 ohm question and the answer was no. The Class 5 has an external 16ohm jack but is not switchable to 8 ohms. :nope
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Re: Class 5 at bedroom volume secret

Postby ilovedonna » 07 Jan 2010, 00:48

Does the speaker impedance matter when we connect it through speaker jack?

Will i have any problem if i connect it with a 4ohm speaker that way?

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Re: Class 5 at bedroom volume secret

Postby Lowdown » 07 Jan 2010, 00:53

ilovedonna wrote:Does the speaker impedance matter when we connect it through speaker jack?

Will i have any problem if i connect it with a 4ohm speaker that way?
YES. It must be a 16 ohm speaker/cab.

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Re: Class 5 at bedroom volume secret

Postby ilovedonna » 07 Jan 2010, 01:01

Sorry i meant through the headphone jack..
Does the impedance matter for the headphone jack?

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Re: Class 5 at bedroom volume secret

Postby SteveD » 08 Jan 2010, 03:02

ilovedonna wrote:Sorry i meant through the headphone jack..
Does the impedance matter for the headphone jack?
No it makes virtually no difference because there is 100 ohms in series anyway.
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