I was going for a "rounder" sound at lower volume. The addition of the Tone Tubby speaker, and the way the original Celestion has mellowed over the last year or so has certainly helped.

Apart from the triode/pentode switch, the mods are fairly minor and are geared towards giving me a little more versatility depending on the gig. I usually run the amp in pentode mode, half power. If I need more clean sound I switch to full power. Triode mode is useful for quieter gigs where I need a little mellow crunch at low volume.

And - hey! - it's fun to fiddle around and see what happens!

Yes, she's loud all right!

But the secret to this kind of amp is that in a live situation, beyond a certain volume the amp doesn't get louder, it gets grindier and grubbier.

For many years I used a Fender Twin, which stays clean and just gets LOUDER as you turn it up. If you want overdrive with a Twin you need a pedal. The DC30 is very different and took a while for me to get used to.

You can crank the DC30 up, turn your guitar volume down, and use the guitar volume to adjust the amount of overdrive you get. Use the 30W setting if you want louder clean tone, and the 15W setting if you need more dirt. The VOLUME doesn't really change, just the overdrive. I've thrown all my pedals away!

Not with this particular master volume implementation - it's post phase inverter so affects the overall mixed signal right before the power tubes.

Probably best if you Google it to get the general theory. It's a very simple mod that switches the pentode EL84 valves to run in triode mode, thereby producing less power and a rounder tone. Some say it's great, some say it's a heap of old toss.

Hard to say about the SOZOs. I just wanted to try them to see what the fuss was about, plus I was in a tinkering mood and they weren't overly expensive. Perhaps if you were building an amp from scratch and went SOZO all the way there would be a more appreciable benefit.

You're right about wanting to tame the top end. That's partly because my playing style is very bright, and I got sick of the top-end fizz of so many amps in the 80s and 90s. Now that the speakers have mellowed things are much more balanced, and I may even reinstall the bright caps, though maybe a lower value.

Because of this mellowing - and maybe because of the power tube screen resistor change - the last few gigs I've done have all been HI power, pentode mode. Whereas previously the amp seemed screamingly loud before I got any breakup, now it's just right - roll back the guitar volume, or pick softer and you're clean; pick harder or turn up and you're dirty. It takes discipline but it's worth it.

The Pentode/Triode switch is a great mod for low-volume gigs. A much rounder tone and distortion at lower volumes. Only drawback is an increase in hum. Make sure you turn the standby on when you flick the switch!

Kevin O'Connor suggests increasing the EL84 screen resistors to protect the tubes. They also tend to make the amp exhibit its "loud" characteristics at quieter volumes. I may actually change these back to something lower, perhaps 330K or 470K.

The mod to the "Cut" control capacitor is pretty necessary, IMHO.

The mods to the EF86 plate resistor, and to the resistor  directly before the effects insert on the 12ax7 channel were done to bring the two channels more into line volume-wise. Increasing that 12ax7 resistor also has the effect of increasing headroom in the 12ax7 channel, as the 2nd stage does not have to be driven so hard for the same perceived loudness. I may change the EF86 plate resistor back to its original value now that the 12ax7 channel is louder.

The EF86 is an RFT, which sounds good and has low microphonics, even though The Tube Store doesn't recommend them for Matchless. I tried a NOS Mullard but it was noisy - maybe I'll try to find another.

When I first got the amp, while I loved the tone, it was very bright and tight. While these mods have had some impact on the tone, I've also changed one of the speakers for a Tone Tubby, and both the TT and the original Celestion have mellowed nicely over the last year or so. It took a while to get to know the amp's capabilities. I'm now using it without any pedals whatsoever, just use the guitar's volume control to go from clean to overdrive with the appropriate combination of HI/LO and Pentode/Triode settings to suit the gig.

ian@igmusic.co.nz

Greetings!

I'm a Muchle$$ DC30 owner and have drawn up some schematics. They include a few mods I have done. I'm happy to share them but take no responsibility for their accuracy:

http://www.igmusic.co.nz/graphics/DC30_PI&PowerAmp.pdf
http://www.igmusic.co.nz/graphics/DC30_PowerSupply.pdf
http://www.igmusic.co.nz/graphics/DC30_Preamps.pdf

DISCLAIMER: These schematics were drawn for my own use. I am not in any way responsible for any misuse or misadventure arising from their use by any other person.

Chur!


ian@igmusic.co.nz