Ashdown Superfly Mods

Ashdown labs' Superfly bass amp is a pretty interesting little unit. For me it's become the one that rides around in the back of the GTI along with a 2x10 cab for whatever happens to come up. It's not the amp that I don't mind leaving somewhere (The GK RB400), or the one that only leaves the house when something important is happening (A MarkBass F1), but it's small, relatively light, and sounds good.

This amp does have a couple of odd characteristics that must be kept in mind, though. The first is that, though it's rated 500 watts, this is obtained by having two separate 250 digital watt power amps, each feeding one of the speakon output connectors.

The second oddity is that the input, after going though a buffering preamp, goes directly into a DSP. The DSP is where all the interesting compression and EQ happens. From the DSP, the signal is off to the effects loop and finally to the input of each power amp.

I found 2 BagEnd D-10X 4ohm, 2x10 cabinets to use with this. They provided optimal loading for the two power amps and sounded great.

The problem I had with this unit was that I could never get the output signal to drive very hard. My guess is that Ashdown was trying to balance the need to control the input level to the DSP (it has, of course, a pretty hard limit on how much input signal it can digitize), and the variability of levels coming from whatever bass is plugged into it. The amp has no input level control.

My Zon Sonus (active) curiously has a fairly low output level, while the Pbass is fairly normal. The Superfly has a multi-segment LED showing the drive level to the power amps, but in no case could I get it to show much level. When any kind of gain was put in the effects loop, it would drive things pretty well. This showed the problem was in the preamp area and there just wasn't enough signal available.

Mod 1

Ashdown was kind enough to send me a schematic for the Superfly when I asked them, and I quickly determined the first mod – make the input gain adjustable. This would allow me to adjust the signal going to the DSP so it could process an optimal signal. The original gain was .8 (a signal reduction, probably to anticipate pretty high input levels from the bass). This was made adjustable from .8 to 5 giving quite a range.

And how do I know the optimal signal level? Well, when you get clipping on serious peak signals, you've go too much gain.

It was pretty easy to identify on the schematic how to do this, so I put a potentiometer on the back panel (all the analog circuitry is at the back of the amp) to make the gain adjustable. This worked great. I could adjust the input drive for each instrument and got more drive to the power amps without affecting the DSP processing – and likely optimizing the processing since it had a more optimal input signal level.

Here's the back panel with the new control (in red). Things are pretty tight behind that panel, so there wasn't a lot of choice about where it goes.

Mod 2

After Mod 1, I still couldn't get the level indicator to show much drive to the power amps, even when the front panel input level control (which is actually used in the DSP) was at full drive, even with red indications on its own multi-segment LED.

This indicated there wasn't enough gain between the DSP and the power amps, and inserting gain in the effects loop confirmed there was plenty of headroom.

In the case of the GK, it has a gain control before the power amp labeled Boost. The MarkBass is better balanced and just has an input gain control and master volume.

The solution to this was found in the output buffer between the DSP and effects loop output (which goes directly to the power amps when nothing is plugged into it). Another advantage to increasing the gain here is that it's applied to the effects and DI outputs.

The original gain here was 8 (offsetting the input gain of .8). The gain here was increased – well, to 20 to tell the truth …

Together with mod1, this mod, the Superfly changed from an amp deserving the faint praise it gets in most discussions of it into something really quite useful.

This amp is now something I'm very happy with. It can accommodate a range of input levels from different instruments and provide very loud output from any of them. Be sure to look at the discussion of how to deal with the two output amps.(Dual Impedance Cabinet)