Dissecting a Chinese Knockoff Guitar Pedal | Hacker News Reader

Dissecting a Chinese Knockoff Guitar Pedal

cushychicken.github.io

81 pointscushychicken37 comments

This is an ad in disguise. First up the pitch: it's the same but much cheaper. Then the teardown and the continuous harping on how fantastic the quality is. Finally, an affiliate link to get you to go and buy it.

Hey Jacques, author here. In a way, you're sort of right - I hacked the affiliate program a little bit, mostly to be compensated for my work in ripping apart the pedal and ohming out the PCB. But mostly, I wanted people to know that there's a cheaper alternative to "boutique" electronics that are sold at an outrageous markup. The fact that these are easy to modify is a plus.

Also, I kind of liked the idea of showing off the workings of a Chinese product that's so clearly a ripoff of an American product. (Boss BD-2 Blues Driver, if you're curious.) Granted, that was also a ripoff of the TS808. And, I'll admit that something is lost in the spirit of the effort, since no one in China gets hung up when you take their design, improve it, and resell it.

I appreciate the critique; thanks for reading - I'm a fan of your blog!

Maybe you could include a bit on what it actually sounds like, that would make it a lot more informative. It's not as if people buy these as sources for parts, they buy them to give them a specific sound.

That's the plan, once my noise-sensitive neighbor is gone for the weekend. :)

Here's an example of what the stock one sounds like if you're curious. https://www.youtube.com/watch?v=cqPaL0vfVwU

The problem with promoting the product that you review is that your review skews towards the superlative approval. If you reviewed it without the affiliate link you might have added more balance to the article. That's a real risk when you're trying to make money of the things that you review and I don't know of a good way to both 'maximize your take' and 'be objective' at the same time. If I ever reviewed a product I would definitely not try to make money of that particular product.

That's fair. I have some experience in manufacturing engineering; in retrospect, I got a little too excited about how it was designed to be put together in mass quantities. After rolling it around in my hands for a few weeks, I've noticed a few warts in the circuit board - extra flux around the solder pads, a PCB throughhole that was a little too close to the board edge, and got a little shorn when the PCB was milled out, other little things like that. In all honesty, there's nothing really superlative about the electronics themselves. The JRC4558 is a really, really old opamp. It was brand new around the time The Who were getting airlifted to Woodstock.

I shot you an email about some of the other aspects of the article that I didn't want to write about in open air. Check your inbox!

Hm, I did and there is nothing in it, let me dig into spamassassin and see if it got dumped for some reason.

Ok, checked the spam. Nothing. Did you spell it right? jacques@mattheij.com

This apparently got stuck in my "Outbox" folder, so it never got sent. I'll pass it along tonight - this is turning into one of those workdays that became really busy all of a sudden.

Email sent! Talk to you soon.

Haha... I have that _exact_ pedal on my board. Overall, not bad if you want something cheap... Couple of complaints: Things get muddy fast, you really have to pair it with a compressor to control your input volume for things to be any good. Next, there's a massive volume difference between the hot and warm modes. You can't flip between them without need to adjust the volume knob. Finally, there's a distinct lack of bass in the "hot" mode. Other than that, it's not terrible, just don't expect a ton and it's not too bad!

The kind of problems you've mentioned are typical of thoughtless "what a cool mod!" changes to a design; these often ignore practical issues such as the volume change you've mentioned. However, 'fixing' these issues would require a bit more work and a few more parts, attributes that seem commonly not to be important in low-end pedals.

But, yeah, good for starting players (although even then I'd recommend a cheap multi-fx unit); beginners often don't even know what certain effects are, and once you know enough to feel you need a 'proper' version of effect you're better off getting something this is a step or two up from the cheapest available.

(disclosure - part owner of Prophecysound Systems)

Yeah, I suppose if you wanted to do the extra bass mod right so that your volume level is mostly the same when going "hot", you'd also need to tweak the series resistor value as well to get the gain of the snubber to match up. Guessing you'd probably also want to drop down that parallel 470k as well.

Does the original have the same issues?

Not exactly... It might be my hum buckers causing the muddy sounds well then volume gets too hot. I don't have a TS808 I can compare apples to apples with.

The volume change problem and the lack of bass aren't problems for the TS808 because it was hardwired for the "warm" mode with no selector switch. Google is telling me the Boss BD2 doesn't have the toggle switch either.

Reduced gain in the lower frequencies is a feature, not a bug, of the original TS808 circuit. It was meant to keep the distortion from getting muddy. The original clipping stage includes a little resistor/capacitor snubber that rolls off frequencies below ~720Hz.

> Next, there's a massive volume difference between the hot and warm modes.

If I read the text and schematics correctly, that's because one uses 0.7V silicon diodes and the other 1.7V LEDs in the opamp feedback loop. (At least red LEDs used to be 1.7V when I was messing with them.)

So that should clip the voltage in that branch to +/- 0.7 or +/- 1.7 volts, hence the power difference if nothing else is moderating it.

The turn on levels I measured were much smaller in discrepancy than that; the silicon diodes were clipping at 0.55 V, while the LEDs were only slightly higher, at about 0.8 V. Made me wonder if I was measuring them incorrectly.

That sounds OK, if a bit low. Perhaps the resistors are large, or you might be diverting some current through a low(ish) impedance voltmeter, but those should be rare nowadays.

The trick with diodes is that the curve is exponential - so for a "0.7V" diode, and pulling numbers out of the air, you can get 0.3V for nanoamp currents, or 1.0V for power-station currents (for the brief moment before it melts ;-)

The real equation is very simple, if anyone wants to play. For instance, it's well explained here, midway down the page: http://www.allaboutcircuits.com/textbook/semiconductors/chpt...

That's a good point; the DMM I used could have just been extrapolating "turnon" to a certain current. I'll have to check the DMM's specs.

That actually looks really well made for a Chinese clone. I know the no-SMD and no-switches-on-the-board zealots won't agree, but the design is clean and solid. I was expecting a rats nest.

Also, I used these sources for my work on a digital emulation of the device:

http://www.geofex.com/article_folders/tstech/tsxtech.htm http://www.bteaudio.com/articles/TSS/TSS.html

Geofex was a huge inspiration for my first article on the TS808.

Have you seen Electrosmash's rundown? That's some next level guitar pedal analysis. http://www.electrosmash.com/tube-screamer-analysis

The biggest unanswered question is how does it sound?

You should resize the pictures before uploading - I was wondering why they took so long to download, and realised each one was >4MB! The full-resolution version is not that much clearer, they are 15MP but look as though there was a watercolour-like effect applied to them.

The telltale sign of a small sensor. A great example of how a larger file (in MPs) can look worse - taken on even a 10mp DSLR the pic would look substantially better.

EXIF says it was taken by a Galaxy S5.

A small sensor and not enough light hitting it.

Good question! I haven't had the chance to really let rip with the modified circuit yet, as I have a very noise-sensitive neighbor. The bass mod worked out pretty well for me, however.

The stock version sounds like this, if you're curious: https://www.youtube.com/watch?v=cqPaL0vfVwU

Should we even call these "knockoffs" anymore. By now, the tubescreamer circuit is practically mythological in guitar hacker circles. There are thousands of builds from one-off basement projects to commercial runs like this. It's more like a retelling of a favorite story.

My favorite part:

> Just for completeness's sake, I included a quick ohm out of the [EOL]

It's like an existential statement of some kind.

That's what I get for pushing these out at half past midnight. Even thought it made for a really nice meta statement, I updated the post to finish my thought.

Thanks for pointing it out. :)

Nice, hadn't heard of Donner before.

I've got a bunch of chinese pedals (by Mooer, Joyo, Moen) based on Boss etc classic pedals of yesteryear - they have been solid performers so far.

Wish the Chinese brands got into repro analog synths next :)

> Nice, hadn't heard of Donner before.

Mission completed.

As it turns out, Joyo and Mooer are produced by the same company as Donner.

I think the Joyo Tremolo is going to be my next subject for experimental surgery. https://www.geartree.com/p/joyo-jf-09-tremolo-effect-pedal-u...

Is this one sold by Monoprice similar/same as well?

https://www.monoprice.com/product?c_id=115&cp_id=11501&cs_id...

>...just some simple emitter followers with half-rail bias to maximize dynamic range of the buffer, and cap isolation to stop any nasty clicking or popping from circuit switching.

Yeah, I don't think that's what the caps are for...

On the input side? Absolutely! That 2.2M/330nF combo is a really low value highpass filter to keep any DC adjustment transients from a level mismatch out of the audio chain, which would result in one of those nasty loud "pops" you hear when you unplug a circuit. It's also serving to set the DC bias point of the input transistor without loading it down from the 2.2M pulldown.

On the latter part we agree.

Well, what am I missing here? Don't leave me in suspense! :)

Weirdly, he does not compare its sound to that of the cloned pedal her refers to (Tube Screamer and its close relatives).

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