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So far, I've made quite a bit of progress as I've studied a few electronics books, got some components and tools from Bitsbox and put together some basic circuits on a breadboard. Heck, I even made a power capacitor discharge cable, some flashing traffic light LEDs, and I know what a 555 and decade counter chip does, and ohm's law! And now I'm learning about op amps.
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So, I've decided to build a Timmy clone based on the schematic I found online. The initial aim is to put this together on a breadboard, with the simplest of offboard components - i.e no footswitch, no LED, in and out jacks wired loosely, and trim pots for the 4 pots because I can't be arsed to have dangling wires. Initially, that is. I want to be able to experiment with different value components and types of capacitor and understand what each thing does, rather than just blindly cobbling it together. Actually, it might be interesting to also try something else for the dual op-amp IC, the JRC4559. Any suggestions?
Later today I'll order some components from Bitsbox. Still not sure what type of non-polarised caps to use - I understand the use of electrolytics, but for the decoupling caps there's polyester film, multilayer ceramic, polybox, polypropylene...not sure which to use.
As for the caps at pedal voltages if they’re good quality you’re unlikely to hear much difference between them if they’re the same value. Some cheaper ceramics will just introduce noise so make sure you use NPO ceramics. Most pedal builders tend to use poly box or NPO/COG MLCC caps because they sound good, are quiet and they’re the right size.
When I was starting out and ordering caps based on the right value without paying attention to size or power rating I accidentally ordered some massive buggers which I wasn’t able to use.
Now i order 5% poly box film caps with a 5mm pitch for all nf values, NPO/cog ceramics/mlcc with a 2.5mm pitch for pf and mini electrolytics for uf with a height of 5 or 7mm to give me as much room to fit everything in an enclosure as possible. Electrolytics can get very tall if you’re not paying attention when ordering them and fitting anything over 11mm in a 1590b enclosure is a real challenge.
Good luck with your exploration it’s a very addictive but fun hobby.
As for caps, I'm a bit confused why there's a mixture of different types used in a project. I'm ordering my components from Bitsbox and they have a Timmy kit - https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=280_281&products_id=2046 but the caps they specify are mixed:
- 1x 47nF Polyester Film
- 1x 10nF Polyester Film
- 1x 39nF Polyester Film
- 2x 1uF Multilayer Ceramic
Why not all Polyester Film? Or all Multilayer Ceramic?Cheers!
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_76_77&products_id=361
I’d also use one of these instead of the 100pf ceramic disc in that kit. It will have a tighter tolerance and less noise.
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_75_318&products_id=2218
Multilayer Ceramic Kit https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_286&products_id=1992
Polyester Polybox Kit https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_286&products_id=1994
I replaced the ceramics in my early bitsbox builds with NPO ceramic caps and the difference was huge they had a lot less noise and sounded much better definitely less harsh.
Electrolytic are typically polarised (I.e. they have a + and -, get them wrong they'll most likely leak or go bang), but they get used because they give you the most capacitance per volume, however they're not the most efficient type capacitor. They're typically used where you need lots of capacitance, and if you need lots of smoothing, you'd pair them with a ceramic capacitor (Electrolytic will handle low frequency voltage ripple, whereas the ceramic will handle any higher frequency ripple).
Polyester are probably the most bulky in terms of capacitance per volume, but they are non-polarised, and very good at handling varying frequencies.
Ceramic again usually fall in between polyester and electrolytic, but there are different types.
The only time I've used ceramic, is for filtering on SMD PCBs, as they're nice and durable for reflow soldering, compared with other types.
It's probably worth having a read of this discussion - https://electronics.stackexchange.com/questions/69919/ceramic-vs-film-capacitor-which-one-is-preferred-in-audio-circuits
I've played with LTspice in the past - http://www.linear.com/designtools/software/ but a quick search has turned up an online simulator - http://www.partsim.com/simulator#
What they let you do, is take the likes of that timmy circuit, create a model of it, and the see how it reacts to different signals. Although aimed at testing circuits before you make them, it is actually a very good learning tool, as it lets you see what's going on, and how changing components affects the output.
http://tagboardeffects.blogspot.co.uk/2013/03/vemuram-jan-ray.html?m=1
Thanks @m_c I’ve never seen that before thanks for sharing I’ll have a play with this later.
I'm on it! Cheers.
Almost every overdrive I've ever seen is basically an opamp with clipping diodes in the negative feedback loop so if you build a basic non inverting config and run 2 wires from pin 7 and pin 2 (on dual opamp as used in most pedals) you can experiment with different diodes and the gain without having to solder things in and out of the circuit board just by connecting the diodes and gain pot \ fixed resistor between these 2 wires
It's just to do with neatness. If you look at the Timmy diagram, the Vref output from the bias circuit is used in 3 different places.
If you didn't draw it separate, then you'd have a few extra wires linking things, which would make it look cluttered. Plus by keeping it separate, it clearly identifies where the Vref actually is, and where it is being used.