"I have done a preliminary circuit tracing of most of the Bass Bot and compared its function and signals with those of the TB-303.
The Bass Bot is not claimed to be a replica of the TB-303 - it just looks that way. Please note that what I wrote relates to a single machine from the December production batch. There is a new batch just about to be made and I understand that there are some hardware and firmware changes - but I don't know what they are. What I wrote here may be updated in the future, may not be complete or accurate, and may not reflect the behavior of all Bass Bots: http://www.firstpr.com.au/rwi/dfish/TT-303/#diffs (Update: see the link for additional assessments added after this post)
It does not receive Roland/DIN Sync.
Although the right-most button is labeled "Tap" as part of replicating the design of the TB-303's front panel, there is no Tap entry mode in the TT-303's sequencer.
The synthesiser circuitry is functionally identical to that of a TB-303 except (based on our experience with one unit sent to us in December 2012):
Maximum Env Mod is about 37% stronger.
Accent Sweep via the Resonance Pot is about 33% stronger.
The VCA is a BA6110, which is a modern, enhanced, version of the original and now unobtainable BA662. The BA6110 has linearizing diodes, which are not used, so it behaves much like a BA662. The control current to the VCA is approximately doubled and the load resistor for the VCA is approximately halved. The signal level is about the same, but these changes reduce the VCA's background noise significantly.
The CV Out range is 1.333 volts for lowest C to 5.333 volts for the highest C in a Pattern's 3 octave range, when the Pattern is transposed up 1 octave. In the TB-303, this 4 octave range is 1.0 to 5.0 volts.
The exact response curve of the Resonance Pot is a 'log' curve at both the anti-clockwise and the clockwise ends. This is the same as with the replacement Resonance pots we have been installing in the Devil Fish for several years. The TB-303's Resonance pot has a "log" (AKA "audio taper") response curve. This difference only affects what knob position produces a given sound, not the range of sounds which are available.
The circuitry is in general identical - except of course that different transistor and IC types are used. I didn't find any evidence that these differences result in a different sound.
I will await a machine from the new production batch before I do the detailed work for the forthcoming Devil Fish modifications. Although the modifications will be identical or similar in principle to those for the TB-303, the new machine has totally different component numbering, different layout, and almost all the components are surface mount. It will be a while before I finalize the modifications.
I have added the Swedish distributor Jam.se to the above page."
Update: you'll find updates to Robin's assessments on his TT-303 page here.
I really hope a later revision adds in the missing tap mode, thats one of my favourite 303 features.
ReplyDeletethanks for the info!
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