Ampmaker 'Double Six' Boost TOO MUCH.............

Neckwringer

This 12w Double Six is'nt very loud,which is great for home use but the boost switch provides way too much volume.
Looking at the scematic does C8 have anything to do with the amount of level?
Don't know how to fix this so any feedback...would be grateful.

Oldbramwell

No, nothing to do with C8. The boost switch is nothing more than a tone stack 'lift'. You'll notice the bass/treble controls don't work with the boost switched in. You can turn it into a 'partial TS lift' by adding a resistor across the boost switch terminals. Something in the region 47k-100k should do the trick.

Modulus_Amps

Or add a 50k to 100k pot across the boost switch so you can set the boost level to your desired level

Oldbramwell

@Neckwringer  Do you have a schematic for the Double Six. If not, here's a link: https://i.imgur.com/w9qKrpA.jpg

Oldbramwell

I have a Double Six, bought on an impulse in lockdown! The James tonestack & the twin-T notch conspire to eat up a great deal of potential gain which meant it was never going to get loud enough for use with a band. So I ditched both & replaced them with a more conventional FMV tonestack. But I retained the boost (aka tone stack lift).

Neckwringer

Modulus_Amps said:

Or add a 50k to 100k pot across the boost switch so you can set the boost level to your desired level

There is a 470 ohm pot already fitted on the back and also a stereo input socket for switching the boost and/or fat.
I'm probably around the 5th owner and there are various degree's of workmanship inside,from flux splatter to evidence of
a too hot iron being used.
What I would like to achieve is to be able to dial in the boost to taste,add the footswitch capability and replace the cheap
oval 15" speaker with a better one,could just do with a bit of guidance.........

Oldbramwell

Hi @Neckwringer.

That pot looks more like 470Kohm. That value is rather high for a meaningful variable boost control - but it might be a useful place to start! You would quickly find the resistance range you really wanted and then you could swap the pot to something more useful.

Do I take it the stereo jack is mounted but not wired...?

Can we assume you're handy with a soldering iron?

Are you ok reading schematics like the one I posted above? If so, a really useful exercise would be to go over the whole amp & check out what's been modified & what hasn't!!

Modulus_Amps

Really for this you should use an internally mounted relay rather than just switch it with a foot pedal switch
A simple solid state relay would work well and be small or you can get relay boards to mount a larger one.
You can probably get a DC power source from the heaters.

470k will act like a on off switch and not give you the range you want, but you could put a 120k resistor in parallel with it to make it more useful

Neckwringer

Thankyou gents,I do have some soldering skills......


But seriously I have bought a different speaker to try so I would like to just add a resistor on the boost switch.
Which terminals do I add it to and any particular way around?
I'll then button it up and see how the speaker is before I check out the schematic for future upgrades.

Oldbramwell

Hi @Neckwringer  In the schematic I linked above, you can see the boost switch is a simple single pole switch with the common terminal connected to ground. You want to add the additional resistor between the other two (non-common) terminals. Resistors have no sense of polarity so it can be added either way round.

Neckwringer

So the boost switch has 6 terminals,one to ground the other to the board so where exactly should I connect the zister?
Thanks

Oldbramwell

Ah, that sounds like a double pole switch with one pole completely unused...? Each row of 3 terminals will be one pole of the switch with the centre terminal being switched by the toggle between the two end terminals. So... for the side of the switched already being used, I think you need to attach the resistor between the two end terminals.

Neckwringer

Oldbramwell said:

Ah, that sounds like a double pole switch with one pole completely unused...? Each row of 3 terminals will be one pole of the switch with the centre terminal being switched by the toggle between the two end terminals. So... for the side of the switched already being used, I think you need to attach the resistor between the two end terminals.

Thanks but just to clarify,if you look at the diagram in the above post it shows the 6 terminals
L upper L centre L lower etc;
At present the ground wire is to L upper and the wire to the board is L centre.
Can you state using this method of id where the zist goes,sorry for the game show approach but I want to get it right.
Also which value zister will remove the most boost.....4.7K or 10K.
Thanks for your patience......

Oldbramwell

Righto... the additional resistor needs to be added between L upper & L lower.

Both 4.7k & 10k are too small values. I suspect the 'boost' will be negligible. Almost certainly need something more like 47k or 100k. Lower value resistor = less boost (currently a pure short (very low resistance) is no boost & open circuit (infinite resistance) is the full boost). Hope this helps.

Neckwringer

Thats fantastic,thanks again.........

Oldbramwell

You may need to experiment with the resistor value. I'm much more familiar with 'FMV' tone control circuit than James tone control circuit. It's possible you may need to go up to 220k, for instance. What I'm trying to say is that your first choice may well not prove to be optrimal... Enjoy!

Neckwringer

Just fitted the new 15" Celestion in place of the Pop speaker and added a couple of flying leads so I can see which value resistor will suit my needs.............

Neckwringer

Tried a 120k,100k and a 75k but settled on a 47k as it gives the best result for me.........

Oldbramwell

Excellent!! Glad it worked out!

Neckwringer

Oldbramwell said:

Excellent!! Glad it worked out!

Yeah,thanks for your advice....................

Oldbramwell

My pleasure.