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Ashdown Dual-Band Compressor problem

#21
There seems to be some confusion brewing on this issue. It appears that only some early generation models of theses pedals came with stickers that said "passive basses only". I have both the Dual Band Compressor and the Drive Plus, and neither came with such a sticker. I ordered mine from music123.com. I have used both pedals with a Fender Jag in active mode and I have not experienced any problems. However, when I use the compressor with my Ibanez RKB900 (which is passive) I have to watch the input level. Too hot and I get some distortion when I try to compress the LF even though the VU meter is not hitting red. I can hit red with the Jag and there's no distortion. It's weird. In any event as long as I keep the input level down a bit, or keep the LF compression under 1 o'clock the compressor is still useful with the RKB and it still adds a nice bit of punch and clarity to the tone.

The only thing I can figure is that each bass is going to behave differently with the compressor, and the VU meter is probably more for show than anything else. The input knob allows you to dial in the right amount of input, but you might need to use your ears more than the VU meter to determine what is the right amount of input. Another huge factor is going to be your playing dynamics. Once you get the input dial solved, you can balance things out with the the output knob.

Overall, these are very good pedals -- well made, rugged and useful, with loads of thick, juicy and useful tone. (And true bypass.)
 
#22
Well, once again it's 10 out of 10 to Ashdown's technical service people!

I've just phoned them and described the problem. They admitted that this over-sensitivity was a known issue with the earlier units (as you pointed out, cmhgreg - hence the stickers).

They then rang me back with full instructions for how to modify the input stage in order to bring the unit up to current spec!

I am going to publish the mod here for anyone else who's been having a similar problem. Naturally, this information comes with the usual riders:

1) You should only do this if you know how to solder onto a PCB board properly. If you screw it up, don't come moaning to me or Ashdown - any loss or damage incurred is your problem.

2) Doing this mod yourself will completely invalidate the warranty.

All understood? OK. Here goes:

Basicly, it consists of replacing four resistors, all of which are labelled on the circuit board.

1) R7 - originally 22k - replace with 220k
2) R16 - originally 47k - replace with 22k
3) R44 - originally 33k - replace with 68k
4) R47 - originally 10k - replace with 1k

I'll report back as soon as I've done the mod myself. I'll also be reporting back to Ashdown - they asked me to let them know how I got on.

That's what I call customer service.:D
 
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#26
cmhgreg said:
Epsidog:

Nice work. Thanks for your persistence on this issue. Question: is there any way to determine if a certain compressor has the bad resistors in it or not? In other words, can you ID the resistors by just looking at them? Thanks.
Click to expand...
I wouldn't go so far as to characterise them as "bad" exactly - they're just the values that were chosen for the original design, and it tends to make the input stage quite sensitive.

Yes, if you're familiar with the modern 5-band resistor colour code, they're easily identified. The first four colour bands show the resistance value. For our purposes we can ignore the fifth band - it tells us the component's tolerance figure. These days it's usually brown, indicating 1% tolerance.

Here are the codes for the 'passive only' version:
R7 (22k) = Red / Red / Black / Red (2 / 2 / 0 / 00)
R16 (47k) = Yellow / Purple / Black / Red (4 / 7 / 0 / 00)
R44 (33k) = Orange / Orange / Black / Red (3 / 3 / 0 / 00)
R47 (10k) = Brown / Black / Black / Red (1 / 0 / 0 / 00)

and these are the current codes:
R7 (220k) = Red / Red / Black / Orange (2 / 2 / 0 / 000)
R16 (22k) = Red / Red / Black / Red (2 / 2 / 0 / 00)
R44 (68k) = Blue / Grey / Black / Red (6 / 8 / 0 / 00)
R47 (1k) = Brown / Black / Black / Brown (1 / 0 / 0 / 0)

Here's a link to a useful webpage that has a javascript device you can play with to demonstrate what the various different values look like: [Invalid or Expired Link Removed]

Note: One annoying fact with most standard resistors nowadays is that the body of the resistor is bright blue. This makes some of the coloured bands look really dark and difficult to identify. I find it's especially easy to confuse red, brown and orange. You get used to it with experience, but I've never understood why they do this! In them thar olden days, resistors were beige or dark brown, and the colour bands were a lot easier to see.

Finally, before anybody goes looking inside their compressor, there are a few of things you should be aware of:
1) If your unit hasn't got the "passive only" sticker on the box, you're OK - you've got one of the newer models.
2) Even if it has got the sticker, that doesn't make it bad. If you haven't been experiencing a problem like mine, DON'T TINKER.
3) In order to see the components, you have to take out the whole circuit board. This involves removing the eight side screws, prising the case open (it's a tight fit), then undoing all five control knobs and both jack sockets before very carefully levering the circuit board out. It's not a job I'd recommend to anyone who hasn't got endless patience, the right tools and a steady hand (two hands are even better).

MY NEWS:
I've done the modification to my unit, and it has reduced the input sensitivity. However, I'm still getting the same distortion, so it's clear that my compressor is faulty. Consequently, the technical service guy at Ashdown has given me some further suggestions. I'm going to do some signal-tracing on the Op-Amp chips to try and isolate the problem. If that doesn't prove conclusive, he has offered to examine the unit himself.

Can't say fairer than that. Many other companies wouldn't even have bothered to speak to me!
 
#28
vindy500 said:
it depends what sort of resistors there using, i.e what materials are used
Click to expand...

Hi Vindy500,

I'm guessing that you're talking about the bright blue colouring, yes? Quite right: the blue ones are the basic metal film type you see everywhere these days. I just think bright blue was a really stupid colour to choose. As modern components are so tiny, the colour bands are very thin and they seem dark against the blue background. :D
 
#30
I HAD the same problem (and the sticker), but i replaced the resistors today. Guess what: The pedal works just fine now. The vu-meter is now doing what it should, and even in the very low end there is no distortion at all. I'd sent a mail to Ashdown last week but they said that this wasn't a known problem.
Ah well, for those who has the same problem: this is a good resolution.

p.s. sorry for my bad english (dutch-guy)
 
#31
Sasquatch said:
I HAD the same problem (and the sticker), but i replaced the resistors today. Guess what: The pedal works just fine now. The vu-meter is now doing what it should, and even in the very low end there is no distortion at all. I'd sent a mail to Ashdown last week but they said that this wasn't a known problem.
Ah well, for those who has the same problem: this is a good resolution.

p.s. sorry for my bad english (dutch-guy)
Click to expand...
Your english is fine, mate - better, indeed, than the garbled stuff some of us native speakers manage to scribble!

The kind of distortion I've been experiencing is definitely NOT a known problem. It's a fault with the particular unit I happen to own.

I hope that this is now clear to everyone. The last thing I want is for the usual chain of Chinese whispers to start, resulting in some totally wrong but widely believed myth that "Ashdown Pedals distort". They don't. Mine does.
 

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