another Express type build

[norburybrook]

I like doing the PPIMV like this. My express have a cut control, and it is useful for adjusting treble at low PPIMV settings. See in the link I posted above. 0.002u cap and 250k pot.

thanks Martin, that looks like I had in mind I'll wire up tomorrow and fire her up
If I want to bypass the cut control I imagine I just need to break the 'send' from one side of the PI nodes. will that have a different effect from having the cut control on full?

i.e is it worth doing?

M

[martin manning]

If I want to bypass the cut control I imagine I just need to break the 'send' from one side of the PI nodes. will that have a different effect from having the cut control on full?

i.e is it worth doing?

Yes, disconnecting one end will eliminate the cut control completely. The 250k pot blocks the cap out pretty well, but not 100% of course. You can demo that for yourself. I think the control is useful for trimming HF at high vs. low volume settings. The most convenient place to put it is right next to the MV, since it is wired across the CW lugs.

[Roe]

I'm using a no load pot for a cut control on my ac30 and k60 - works well

[norburybrook]

finished off the wiring today and fired her up. OT primaries wrong way round but caught it before it reached full feedback scream


Got it biased at 44mA with 360 on the plates.


Fitted the bypass switch for the cut and used the linear Pot fro master volume. I'm not sure if the Log POT would be better though as not much seems to happen until halfway down, would the Log pot work better? I don't want to change it if I don't have to as it's a PIA with the mixer pots i have as they just have tabs.

Express 4.jpg

express 4-2.jpg

I'd forgotten how bonkers the express is.

Now, everything is working fine, the fast /Slow switch with the 4M7 no longer pops I think the fast setting though has too much bass. This is strange because the slow setting has a 0.1uF which you would think would have more bottom end than the fast which has a 0.005uF but the fast is definitely carrying more low end.

can someone explain why? it should be the other way round surely?




m

[martin manning]

Can you mark up the standard Express schematic with the fast-slow switch as you you have it?

[sluckey]

Maybe the switch just needs to be rotated 180°?

[martin manning]

Could be... the bat position is opposite to the lugs that are connected internally. Slide switches connect the lugs on the same end as the slide position.

[norburybrook]

Maybe the switch just needs to be rotated 180°?

you guys!!

here's what i've got

phils Komet.gif

I have a 0.05uF instead of the 0.002 on the drawing.
so the gradual(Slow) has the 0.1uF going to the node between the 82/22k and the fast has a 0.05uf going to the bottom of the 82k straight to the plate. this is giving the desired effect i.e less gain so it's all wired and working as expected, I'm just getting more bass on the fast side than I expected.
and I've a 4m7 across the two outer switch terminals so they're always connected to stop the pop.



M

[martin manning]

Which points are you calling the outer two switch terminals?

[sluckey]

So use a .002 rather than a .05. Are the results more like you think they should be?

Why did you decide to use a .05? That's not much different than using a .1.

[martin manning]

Why did you decide to use a .05? That's not much different than using a .1.

True. Both combinations are less than 20Hz.

[norburybrook]

So use a .002 rather than a .05. Are the results more like you think they should be?

Why did you decide to use a .05? That's not much different than using a .1.

Steve,

i used a 0.002 and a 0.1uF on the last build I did and there was a marked difference between fast and slow in the bottom end, I wanted to reduce the tonal difference so used a cap that was nearer the 0.1 but perhaps still had a slight effect. Perhaps the extra gain is making me think there's more bottom end than there is, you know the old Fletcher Munson curves and all that.

@Martin. I've removed the 4M7


I'll leave it as is and see what my friend thinks, if he wan't less bass I can fit the original 0.002 on there. He's been using the other amp only in Slow mode so I was trying to tailor the fast mode to be similar tonally on this build just to see how it is.

It might work as he plays a single bridge pickup firebird .

I'm building a ported 1x12 cab that he wants to put a Classic lead 80 in so it should be a punchy rig.

I need to get on with the wood work now...not my favourite part of the process but I enjoy the tolexing and finishing off



M

[norburybrook]

let the amp burn in all day yesterday, sounding great


Started work on the cabinets. Going to cover amp head in cream tolex and I've got a lovely piece of African Walnut for the front panel.

The 1x12 cab is the same dimensions of the peavey combo I made into a Bliuesmaster combo, which then became a separate head and cab. I made the combo into a speaker cab and used the amp opening as a port and made a new solid back panel. It sounded great so I'm reproducing it again.

Letting it all dry tonight then sessions in the studio tomorrow and hopefully tolexing on Thursday.

wreck 5-1.jpg

WRECK 5-2.jpg

WRECK5-3.jpg

M

[sluckey]

Love that workshop. I had one that looked similar. May want to trim that grass!

[andresound]

Wish we had grass like that!! Nice build Marcus