Tuesday, April 9, 2019
EHX Bassballs
Not sure I missed doing this one ages ago, but better late than never. The Bassballs is a classic envelope filter that's been a staple of Electro Harmonix's line up for a long time. Designed for bass, but works great on guitar as well. Trimmers are very dynamic and might be fun as external pots. Also if it's super loud, adding a volume pot at the output is super easy—remove the 47k resistor off the Out pad, wire the Out pad to lug 3 of an A100k pot, lug 1 to ground, and lug 2 becomes the new circuit output. Here's the schematic for reference. Should fit in a 1590B, though it'll be a tight squeeze.
Verified. Used 4558 & tl 062,72,82, every working. But i couldnt get distortion, its like a fuzz sound. David that caps: c7,c11 on that schem = 560p, yours=56p.
ReplyDeleteA typo that got copied and pasted. Thanks for verifying!
Deletethat 470nf it's tantaluim? can i substitute for a ceramic too?
ReplyDeleteYou're probably right. Ceramic should be fine.
DeleteI've built the circuit many times over, and will make the following mod recommendations:
ReplyDelete1) The trimmer for the *upper* filter can be profitably converted to a panel-mount control. The lower filter can simply be set optimally with the trimmer, and left there. That will let you easily "stagger" the filters, as well as get back to the stock sound.
2) With simple half-wave rectifiers, there is often audible envelope ripple as notes decay, producing unpleasant sounds. The decay rate of the BB is fixed. To change it, you would change R7 (330k). Higher values prolong the decay, while lower values shorten it. Shorter decay times sound more "synth-ey", and funkier, and are better suited to bass use. As well, short decays close the filter before the ripple gets bad. Instead of a pot, I'd recommend using 510k for R7, and a 3-position toggle to reduce the decay time to faster rates with 470k and 100k switched in parallel to get effective R7 values of 510k (slowest), 245k (a bit faster than stock), and 84k (fastest). If you want a faster attack, drop R6 down to 47R or so.
3)The mix between upper and lower filter can provide some useful variation. Varying the mix is pretty simple. R11 and R16 behave like a 5.4K pot set exactly in the middle. You can replace them with a 5k linear pot, connecting the outside lugs of the pot to the outputs of each filter section.
4) Finally, the "fuzz" setting is simply the misbehaviour of the 1458 op-amp (you MUST use a 1458 for IC1a/b; 4558 types are fine for the filter sections). The downside is that, when you set the sensitivity of the envelope-follower higher, you also increase the output volume of the pedal (something which does not occur in the "clean" setting). As was noted on this site, you can always install a volume pot to compensate. That works, however I found that I didn't particularly like the "sick parrot" sound that passed for fuzz, even if it was a freebie. What I did was replace R8 with a 10k resistor, and R9 with a pair of back-to-back diodes. One silicon and one germanium gets the level-balance between clean and fuzz about right, though feel free to experiment. This produces a more pleasing "fuzz" and also holds the output volume constant, despite variations in sensitivity-setting.
Mark. Would U help me with this mod? It’s kinda exactly what I need. This additional control u mentioned. But in your description I’m a bit confused about the back to back diodes and the parallel switchable resistance. Don’t know exactly how to differ the sections in the schematics as you tell us to do for grabbing those additions
DeleteHi Mark !
DeleteIf you have time, and for my own education, would you mind elaborating on that misbehavior ?
More specifically, I understand that the first half of the 1458 acts as a simple buffer, but I can't quite get my head around the next part :-)
I understand the purpose, but not the circuit. It looks a bit like a negative feedback amp configuration but with no input resistance...
What about Ehx Pog, do you have any might to make it? Or any clean octave effect for bass.
ReplyDeleteI am not getting the wah wah effect and when I change the position of the spdt switch the sound is muted there is no fuzz what should I do?
ReplyDeleteHi Lincoln,
DeleteI realise this is old, so you might have sorted it, but I've just built this on an isolation-milled board and had the same problem with the SPDT switch. In my case it was a solder-bridge between the signal line and ground at the SW1 pad. I'm fortunate that it was so early in the signal path, but if the switch is causing cut-out, it must be before that point.
I found on the veroboard website that the 02 ceramic capacitors are 560p and not 56p. the scheme also identifies 560p. are these values correct in the layout? just one question, thank you for the work you do !!!
ReplyDeleteWhat type of 1458 is that? LM or MC? In my layout with MC1458, pin5 must not be grounded, otherwise its not working..
ReplyDeleteLM/MC are just manufacturer indicators. Either should work.
DeleteBeen following this blog for years and can't thank you enough for your work. Absolutely stellar resource.
ReplyDeleteMaybe a dumb question but would two tl072s work in place of the 1458 and 4558? Why must a 1458 be used for IC1 a/b? Thanks in advance!
Hi!, is that a 470nF ELECTROLYTIC cap?, I don't know much about these and I'm struggling with finding the components, thanks c:
ReplyDeleteIt is electrolytic. If you can't find them you can use a film or ceramic cap, or put two electrolytic 1uF in series to create a 470nF.
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