Marshall Class 5 Cranked at bedroom volume mod

Kalcium

Sigh...How did I manage to post this in the wrong place? Wish there was a way to move it myself ?
So I don't even know how I came across this since I had no intention of looking for mods for my amp. Its my first valve amp and I've had it for 2 days and I have no idea about building amps or anything about the circuits. I just know that I came across a SUPER simple mod that is SUPER for me ?

The first ideas for making the class 5 quieter when crank were to plug a cab into the headphone jack but only halfway in, that way it becomes a lot quieter, I however don't have a cab...The other ideas were to wire a 1/4 inch jack to the speaker and plug it into the headphone jack halfway to get it at the lower volume and then plug it into the ext. speaker when you want it at normal volume (if i understood correctly...)

But there is a much more convenient way of getting the internal speaker to function at the lower volume. The awesome thing about this is it is really easy to do and once done makes it simple to switch between the settings (regular/bedroom).

Originally Posted by Ad_02Std

I wonder if it's possible to re-wire the output to the headphone socket to the internal speaker, so that when the switch is on "headphone" it just switches to 1/4 Watt. Anybody tried that?

I just did this mod myself and it works perfectly. It doesn't interfere with any of the other functions of the amp (if you plug headphones in it still switches the speaker off) but when the headphones are not plugged in just switching to "headphones" runs the amp at 1/4 watt through the internal speaker.

The mod looks like this:

Enjoy

Adam

I have done this mod tonight and it works wonders! I get that awesome cranked distortion sounds from the amp at 10 but its at a volume that doesn't hurt my ears or disturb my parents ? its awesome!

Heres the link to the forum I found the mod on http://marshallvintagemodern.com/viewtopic.php?f=31&t=6532
The people discuss it there and the SteveD guy seems to be an expert (possibly the designer from what I've seen..) on the Class 5 and he says its basically wiring to do the same thing as the bedroom trick (plugging a cab halfway into the headphone jack...)

Heres pics of my amp:

I am SUPER stoked with this mod ? Though Im not sure if it would void the warranty by opening up the amp or not, probably would...

G-Man

Congrats, you are a braver soul than I! I'm no fundi when it comes to electronics so I don't know if what you did is good or bad for your amp, but I see what the result is, well done. ?
(I think your warranty may be kaput though...)

Kalcium

Well I bought it secondhand anyway, so no warranty...but the guys on the forum i found the mod on were worried about doing it at first but then the guy SteveD said its fine, its the equivalent of wiring a jack to your speaker and pluging the speaker halfway into the headphone jack.

I wont lie though, despite all the people saying they did it and it was awesome I was worried...When I plugged it in again I was like please please please please please please be ok!!! And it was 100 % fine and the mod did exactly what it was supposed to ? Plus it sounded better than I expected, I know my ears aren't entirely tuned in to great tone or not so great tone as much as many people on this forum, but it sounds like theres no tone loss (or at least very little), just a decrease in volume when switch to the headphone out without having headphones plugged in ?

Mo-Facta

Hi Kalcium,

I'm having trouble understanding the goal of what you are asking or attempting to do. My first concern is that if you're trying to get a "cranked" sound out of a Marshall Class 5 tube combo, no mod short of some sort of load attenuator (like the Marshall Powerbrake or the THD Hotplate) is going to accomplish it. Simply soldering a wire between two points on a small circuit like the one in the picture is not going to accomplish this. After all, it is very dangerous for a tube amp to be cranked up high without a load (speakers) attached or said load attenuator. You are almost certain to blow your output transformer at very least. I see the Class 5 has a headphone out but I have not been able to find any documentation on this to explain how the load is maintained while switching to headphones. It may, in fact, be speaker compensated but I wouldn't do anything to your amp until I know if it is or not. Your mod may work but slowly unbalance the output transformer and eventually blow it. This may take some time, too.

The idea of a cranked sound comes from the fact that tubes generate pleasing amounts of even harmonic distortion when they are pushed to their limits. In the case of preamp tubes (the ecc83's in the Class 5), this is where you get your preamp gain. Output tubes (one EL84 in the Class 5) have to be driven really hard in order to achieve pleasing results - thus at a loud volume - which, for example, is why an old Marshall JMP sounds so great when you turn everything to 10. Or 11, as Nigel Tuffnel's amps do!.

Sorry if I'm insulting your intelligence because you might know all that already. No offense intended.

So, what I'm saying is that cranking a solid state amp will not get you a better or drastically different sound at bedroom level because it's electronics are not as non-linear as a tube design and do not break up in a pleasing manner at the output section. In other words, you do not get that rich, even harmonic distortion that you would from a tube amp like the Class 5. What the load attenuator does is enable the output tubes to work really hard and supplement the preamp overdrive with their flavour of harmonic distortion without the excessive volume levels. However, there is a lot of debate about whether this really accomplishes a "better" sound because one thing that also contributes to a good tube distortion sound is the how the speakers break up in conjunction with the amp. This is the one part of the amplifier that can not be attenuated.

These are a list of load attenuators you may find:

Scholz Power Soak
Marshall Power Brake
Groove Tubes Speaker Emulator II
Harry Kolbe Soundsmith - The Attenuator
ADA MicroCAB
Hughes & Kettner - Red Box Mk III
THD Hot Plate[/li][/list]

And here's a link to the Marshall Powerbrake:

http://www.amptone.com/marshallpowerbrake.htm

Hope that helps.

Cheers ?

Kalcium

The headphone out jack is wired to be at 1/4W as far as I can tell from the people on the forum that I found this mod on (the link is in the OP). The headphone out jack is wired with a dummy load, not sure how much, but its there, and the guy who designed/the official marshall expert on class 5s says its fine to plug any ohm cab into the headphone jack as the added resistance is negligible compared to the dummy load (i don't really know all the details, but looking around that forum at all the posts of SteveD (the official marshall expert) he says its fine to plug any load into the headphone jack. What the mod i described above does, basically plugs the on-board speaker into the headphone jack. but its the equivalent of only plugging it halfway into the headphone jack, which is a thing known as the bedroom trick. The bedroom trick, as decribed by steveD is to plug a cab halfway into the headphone jack, and that way the output is reduced (i think to 1/4W) which makes the breakup occur at a lower volume, so even when turned to 10 you get the breakup but its not as loud as before. This mod is a hardwired equivalent of plugging the on-board speaker halfway into the headphone jack, its just simpler than wiring a jack to the speaker and plugging it halfway into the headphone jack.

In essence i think it can be summed up as using the attenuation built into the headphone jack to lower the output voume for internal speaker.

Mo-Facta

Hmm, yes after a bit more googling I did come across this information.

In any case, I would strongly suggest doing more research before making any mods to your amp yourself because even though it may work, there's no telling whether it will damage your amp over time.

Cheers ?

Kalcium

Yeah definitely a good point ? thanks hey ?

Jayhell

Kicking a dead horse here, but instead of starting a new topic, I'll keep going, if no one replies I'll start a new one. anyway...

So my Class 5 is out of warranty and I want to do this mod, thou it scares me. A couple of things I need to know;

What Kind of wire should I use? Can I just strip a piece of kettle chord and use that or should I use a specific type of wire?

Can I just solder this wire on top of the others or should one unsolder what is there, clean it up and resolder it?

Should I rather get a professional to do this for me?

Kalcium

Hey Jayhell, it should be fine to use a wire from a stripped kettle cord. I don't think you should remove any wires though, just add the new wire to what is there already. I did find that when set to this mode that it wasn't quite as good as the normal tone but it doesn't cost you anything and it allows you to play the amp driven but at a lower volume without the need for pedals. Just make absolute sure you're joining the right connections by googling it for detailed pics. At the time I did this I had no experience with electronics so I was literally just doing exactly what I saw in the pictures and it worked first time.

Jayhell

Thanks, I came right with a little help from a friend. Uber cool mod, going to start a new thread.