DBX 120

[leigh]

[quote author="clintrubber"]In case anyone has more specifics w.r.t. Ashdown please tell.[/quote]

For $60 you could gut and/or mod their pedal version:

http://www.musiciansfriend.com/product/Ashdown-SubOctave-Plus-Bass-FX-Pedal?sku=155164

Or track down some of those "Sub-Hormonic" ICs that we were discussing in the other Ashdown thread....

Leigh

 

[wiz1der]

so you're the lowender dude? Great work! i've heard it on a friends mac.

I'm a pc guy tho, which is why i've been screaming for a hardware 900 series of this.

any word on when the pc version will be out?


is anyone working on the 920? (120 on a 900 size card) :grin:

 

[leigh]

[quote author="wiz1der"]so you're the lowender dude? Great work! i've heard it on a friends mac.

I'm a pc guy tho, which is why i've been screaming for a hardware 900 series of this.

any word on when the pc version will be out?[/quote]

Yep, that's me. Thank you! The PC version will be out soonish... by the end of the year if all goes well.

I've been poking around on the diystompboxes.com forum, and found this link to some scans of a newsletter called Stompboxology:

http://moosapotamus.net/IDEAS/stompboxology/stompboxology.html

If you're trying to wrap your head around how the dbx 120 and similar boxes work, the Stompboxology issue "Frequency Division & Subharmonic Synthesis" is required reading. I've read all kinds of literature, patents, etc, and this issue lays out the workings more clearly than I've seen anywhere else. It also has layouts and plans for four different variations on subharmonic effects.

cheers,
Leigh

 

[leigh]

[quote author="mediatechnology"]Here is the User manual for the 204. No schematics but we might troll the patent list. I'm going to Google Patents to see what's there.

http://www.aphex.com/pdf/204/Aphex_204_user_man.pdf

...

EDIT: From a quick read of the patent it appears that "Big Bottom" does not generate sub-harmonics. Block 1 in the patent is called a divider, but it appears only to be a signal splitter and does not do frequency division.[/quote]

I'm taking a look at the Aphex Exciter / Big Bottom manual this morning. Check out page 32, column 2. They are definitely distancing themselves from subharmonic generators - according to them, such boxes are problematic for causing an "increase in overload problems".

Instead, their inventor discovered that "by making a copy of incoming low frequency information, delaying it by a set amount, and adding it back as a constant-level enhancement signal, he was able to achieve a dramatic increase in the perception of the bass without a corresponding increase in peak output. " (p. 33)

So the process is low-pass, delay, compress, mix back in. The delay is apparently very short - if the block diagram on page 10 accurate, the bass sidechain is delayed using only a phase network. No digital lines or BBD's necessary here.

Food for thought... now back to work on that Lowender for Windows port...

Leigh

 

[barclaycon]

Anyone have a schematic for the Aphex Big Bottom unit ?

 

[clintrubber]

[quote author="leigh"]So the process is low-pass, delay, compress, mix back in. [/quote]
Hmm, interesting... the first thought is that this would cost instead of yield muscle (something like LF-combfiltering), but obviously there's more to it...

 

[SSLtech]

Here's another video of a tune which features the classic sub-octave synthetic generation: this time using a Roland/Boss octaver, this time on the (fretless) bass.

http://youtube.com/watch?v=MZ7vX7xX0G8

I was looking for a link to this tune when I posted the above link, but it wasn't available at the time, I believe.

This was recorded at the studio where I worked, Mike Howlett was the producer. -The drum sequencing/sampling was an oddball BBC computer based affair called a 'Motion' I seem to recall, and the bass was played to tape through a brown Boss Octave pedal. I worked with this band on and off from 1980 to 1989.

Keith

 

[tv]

I had good experience with dod fx35 octaver for bass.

It had to be modded, though: input/output caps and input biasing resistor - to work as I wanted. Luckilly, dod makes mod-friendly boxes (I hate their potis otoh).

 

[SSLtech]

(I hate their potis otoh).
_________________
If you sprinkle when you tinkle, please be neat and wipe the seat.

You hate their "Potties"?

-It would certainly match your signature if you did!!!

:green:

Keith

 

[thermionic]

[quote author=SSLtech]
they just use a zero-crossing detector and mute every alternate half-cycle. (which mis-tracks occasionally and randomly flips the polarity, but that's all part of the charm...)

snip...

Keith
[/quote]

My experience repairing a dbx 505 in the last few days would support this exactly. I can't show it flipping the phase as I'm too lazy to post a video, but you can observe it doing this.

I've attached a few shots to show how it boosts every alternate cycle, as described. When fed with a generator the 'boost' LED only comes on below 100hz. If you send in a 100hz sine, once you increase the boost above a certain amount, the frequency detection on the 'scope changes from '100' to '50hz' - as can be seen here.

Slight boost:

 

[thermionic]

Higher boost:

 

[thermionic]

Here's a schematic for a dbx 500:

http://i646.photobucket.com/albums/uu186/Justin-G-2009/dbx500.jpg?t=1244114606



Justin

 

[giro1991]

I can testify that the LF output drifts in and out of polarity depending on the input level or the settings...

Keith

Does anyone know if this is true for the Normal outputs aswell? I remember reading somewhere that the LF outs could potentially be made to stay inverted, is this correct?

Thanks

 

[abbey road d enfer]

"I can testify that the LF output drifts in and out of polarity depending on the input level or the settings... "
Does anyone know if this is true for the Normal outputs aswell? 

No, the normal outputs are not phase or polarity shifted. The VLF output polarity changes every half-cycle; that's the principle of operation.

I remember reading somewhere that the LF outs could potentially be made to stay inverted, is this correct?

No.

 

[giro1991]

2 in one!


Thanks

Edit: the manual for the original dbx100 is packed with info about processes and underlying theory. Its safe to assume little has changed in its re-incarnations, the 120 models. For instance, an initial doubt was whether it was stereo or not; the manual states it blends L&R inputs. processes this, then routes the result equally to L&R outs, information which clarifies this.
Heres a link: http://vintagedbx.free.fr/owner%20manual/DBX100.pdf

And here are some pictures of 120x:
https://imgbox.fr/images/HqB.jpg
https://imgbox.fr/images/Hq8.jpg