Altering Attenuator Advice

[sirdavy]

I have a 4w Vox AC4TV, which I'm trying to bring further down in volume than it already is by patching an attenuator in between the amp and its speaker. I mistakenly bought a 8ohm/15w TubeJuice Attenuator (which I think have been discontinued) when I should have got something rated for the amp's 16ohms. It actually works ok but I've got hold of a 16ohm/100w L-Pad and I'm planning to put it inside the TubeJuice enclosure.

I thought it would be a straight swap for the L-Pad in the TubeJuice but it having opened it up it looks to me like it operates on a different set of components.

Instead of an L-Pad I think it has a potentiometer (its part number comes up as the component in the screengrab) attached to two (4ohm?) resistors. Is that correct? Is that another definition of 'L-Pad'? Is this a 'better' attentuator than an L-Pad?

Can you have a look and tell me if all I need to do is swap in the L-Pad and detach the resistors?

 

[Printer2]

I pulled the OT, checked its reflective load on the primary and found that with a 16 ohm load on the secondary there was about a 10k impedance on the primary. With an 8 ohm load on the secondary there was about a 5k impedance shown on the primary.



Also for 4TV8 owners you might have found that the 1/10W setting is not as useful as you may like it to be. You can replace the 3.3 ohm resistor @ R14 with a 5.6 ohm 2W (or better 5W and replace them all) power resistor to get the 1/4W mode found on the other series. Besides speaker and cabinet configurations that one resistor is the only thing I could see that sets the 4TV8 apart from the rest in the series.

Not saying the above is valid. From the schematic it does look like there is a tap on the secondary. For an 8 ohm?



http://dealers.korgusa.com/svcfiles/AC4TVH_SManual.pdf


If you want you could put a 8 ohm resistor in series with your attenuation and the amp will see 16 ohms if all is kosher. Don't have the time to really look at things, just finished my coffee and time to get stuff done.

 

[sirdavy]

Thanks, Printer2. Yes, I had read in forums that the AC4TV is safe with an 8ohm load, I just wanted to find out if the tone achieved with an attenuator might be improved if it was correctly rated. (With an 8ohm speaker the AC4TV is apparently, louder with more headroom).

Yesterday I went ahead and swapped the pot, which was attached to two (ceramic?) 4ohm resistors for an L-Pad along with a bright switch (2.2uf & 6.8uf).

I've only tested it so far with a 6.5"/16ohm speaker I made (using a speaker from a vox ac4tv mini) and it sounds GREAT, really good and the difference between both settings on the bright switch is clearly audible to me. This is the bedroom volume tube amp I've been trying to achieve.