Anybody know whats in the orange microcrush cr3

[wormfooduk]

I was thinking of making a ruby or noisy cricket and i was just wonder how they got the sound of an orange into such a small box. ok so its not a lm386 so what is it because it still runs off a 9v battery? it doesn't have such a starved sound if that makes any sense. I know its a long shot but i thought someone here may have taken one to bits.

[Axe-audio]

Hi
I'm a freshman in college so take it with a grain of salt.

I tore up a broken Micro Crush from Musician's Friend and drew up half a schematic. Totally avoided the in-built tuner.
Didn't have the heart to tear it up so I've made some assumtions, please notify me if you see anything amiss.
I'm converting the overdrive channel into an effect pedal.
Will try to draw it up on the computer though. Haven't heard the amp yet, I suspect its just a dead battery.(and yes I can't find a single 9v
on campus. I'm having them shipped to me from HI!)
I bought a condition 4 Vox AC4 for $100. It just had a burned out tube! Ten bucks and it's 100%.

Back to Micro Crush. Three ICs: two TL072's and one TDA7267A (amplifier IC).
First TL072 does all the good stuff as far as I concerned, reminded me of an MXR distortion +. Clean channel
is first op-amp, overdrive channel adds the second op-amp.
Next in series with the first op-amp is the second TL072. It seems to just prepare the signal for the tuner. Don't have any experience in digital though.
The TDA is wired just like in its datasheet. Its between the speaker and the rest of the circuit.

Sorry if the info isn't as relevant, becuase your interested in the amp itself. Here are some bad pics of
my schematic found at my blog, which I'm still working on> http://3rebelutionaries.blogspot.com/2010/09/orange-micro-crush-3w.html

[wormfooduk]

Thanks that just what i wanted to know, i wouldn't have thought the batteries would last very long with all that going. Thanks for the quick responce 

[Axe-audio]

My pleasure, glad to help.
I will be completing a PEDAL based on the orange micro amp later in the month. So I hope to post a verified schematic in two weeks of so, maybe longer
because I'm having all my equipment shipped to me from home.
One Orange Emulator coming soon!- if possible.

[wormfooduk]

Cool 

Orange has been so far overlooked by the emulation pedals, I love the sound of my orange amps. i use the tiny terror all the time. Sounds great with a fet booster giving the front end a good kicking. 

[jewellworks]

total newbie here...
regarding the overdrive circuit on the microcrush...  i recently got one as a gift, and although i like the clean sound, the overdrive is very harsh.  it sounds like its clipping and has an awful lot of high end as a result.  so im wondering if it can be modified?  maybe a little more drive, but less highs.  even if i turn down the tone knob, it still sounds "clippy".  and switching from clean to overdrive and having to adjust the tone knob as a result is a lot of work. 

yes its a micro amp, and yes i shouldnt expect it to sound like a "real" amp, but i guess i DO.  its not like its my only amp, but i dont see anything wrong with wanting ALL my amps to sound good!  even the toys.

i have several micro amps.  my fav being the Vox Amplug, with the mini extension cab.  it actually sounds like a Vox!  and with very useful controls.  i also love my Fender Mini Tonemaster, but it has a serious high end roll off.  very warm.  the Danelctro Hodad sounds like dog poo.  buts also the smallest, with 2, 1" speakers.  its all mids.  it honks, but it has echo and tremolo!  so its cool for what it is.

so i downloaded your hand written schematic, and i see the clean and overdrive channels are sharring the same IC.  does that mean iif i want to get a tad more gain id have to swap that chip with something else?  like what?  (i know nothing about IC chips)  -and what about a roll off for the highs on the OD channel?  where would i do that?  i know its a cap to ground (like in a guitar tone knob) , but any idea for a value??  maybe if i just added a high roll off cap it'd be better and i wouldnt need more gain?

the Fender Mini Tonemaster has a great distortion channel.  if i could get that kind of overdrive on the Microcrush, it'd be a useable amp! 

thanx.  ive modded wah wah pedals before and im an A/V tech, so i know a thing or two, but this kinds of thing is fun.  and the circuit looks like something i could work on.  (unlike the Hodad, which is all micro circuits and impossible for me to understand whats what in there)

thanx again     

[Axe-audio]

Hey All,
First time back in here in a month, just in time I see.
Sorry I'm not expert, but here's what I can offer.
The overdrive channel puts the second op-amp stage in series with the first and cranks the gain on the first op-amp by shorting the 1M feedback resistor to ground.
Form what I could see there is only one clipping diode after the second op-amp, so you may want to add a second for symetrical clipping or two of asymetrical. Check up the configurations.
The first op-amp gain isstage is interesting, I've never encountered two feedback resistors set up with filtering like that (probably because I've never studied the RAT or MUFF circuits).
Maybe you could lower the gain of the first op-amp by increasing the 2.2K resistor, but this will also affect the clean channel.
Or try increasing the first feedback resistor(6.9 K) to I-have-no-clue-just-increase-it, 10 - 15K.
Filtering actually maybe what you need though rather than decreasing gain. Try replacing the original diode with a simple symetrical combination first, since that's probably easiest.
Hey you pros help out! - please.
I haven't had any time to work on my Micro-Crush, so I still don't know how it even sounds. Good Luck man!
Nathan

[jewellworks]

thanx for such a quick response. 
like i said, im a newbie to modding electronics, but ive studdied your schematic, and i can follow what your saying with the two feedback circuits with filtering. increasing the resistor will reduce the gain, and conversely, reducing the feedback resistor should increase gain, but on the clean channel as well.  -dont want that.  im fine with the clean as-is.
but im lost on a few things.  the clipping diode on the 2nd op-amp... so the 2nd op-amp is the overdrive circuit?  and im not seeing the diode at all??  you say to try adding a second diode, then say to replace it with symetrical combination diode.  it sounds like 2 different things.  couldnt i just decrease the feedback resistors?  (1M and R39 on IC2?) then add a filter cap to ground to smooth things out? 
a second diode or a symetrical diode (a "dual" diode im guessing?) will get me more overdrive?  wouldnt i need to add an inline resistor to tame the output before the volume control?
sorry, im confused.  im a newbie.  maybe im overthinking.  maybe i dont know anything at all...  (most likely)

[Axe-audio]

Sorry I confused you!
When I was talking about the first and second op-amp I was only referring to IC1. IC2 prepares the signal for the digital tuner and possibly the headphone output, can't exactly remember.
Make sure to understand the channel switching, which is hard with my schematic.
So just referring to IC1, the first dual(2) op-amp, the second part of that op-amp is actaully a buffer with gain of aproximately 2.
After the signal exits the second op-amp, IC1 pin7, we see the single diode(that how it was in my Micro-Crush). The reason I say make it a symetrical pair, instead of just a single diode, I that pure IC distortion is usually termed 'harsh' and that's been my experience too. By having a pair of clipping diodes, the signal becomes more natural, tame, and pleasing(maybe).
There are two common areas to put clipping diodes: in the feedback loop (TS style), or after the op-amp's output (not as popular, example the MXR Dist III).
So this circiut takes after the MXR Dist III, but the major difference is the MXR III has two clipping diodes after the first op-amp. The Micro-Crush has the clipping diode(s) after the second op-amp (IC1 pin 7).
Well I hope you're not more confused. Lets move on to feedback of the first op-amp(pins 1, 2, and 3 of IC1).
Understanding the switching here is critical. On the clean channel, switch pin 3 is not connected to anything so the 1M resistor is the feedback to ground resistor.
Read the basic rules for calculating gain of op-amps (this how I know anything analog, EE classes have me on digital for now):  http://www.allaboutcircuits.com/vol_3/chpt_8/4.html

Short summary: Op-Amp Gain = feedback-resistor (divided by) feedback-resistor-to-ground
Example in second op-amp: 2.2K / 1K = gain of 2.2

My computer's acting strange so I'll wrap up(finally!). Increasing the  2.2K feedback-to-ground-resistor to  5-7K will have almost zero affect on the clean channel, but will significanly change gain when in overdrive channel.

[jewellworks]

ok so...  taking another look at your schematic, i can see your "link" to the chip at the top of the page.  (going to pins 6 and 1) what threw me is if you follow the output of pin 7, and the links, i see 3 diodes.  but because you also drew the resistor (r23) i can see its actually 1.

so, in laymans terms, if i add a second diode to ground, parallell to the first, (after r23) and increase the feedback to ground resistor from 1k to 5-7K, (we ARE talking about the resistor after the .1uf cap, right??)  then ill have more gain, and itll sound smoother and less harsh.  and if its still too harsh and i want to tone it down a bit, i can add a cap to ground (also after the diode).  -or should i uncrease the .1uf to something else? 

ill add another diode first and see what happens.  it may be a few days till i get to it tho.

this has been great!  this is the only place on the web where ive been able to get any info on this circuit, and especially how to modify it.  most people just look at these lil amps as toys, but they can actually sound pretty good.

[jewellworks]

well..  i read your post again and im still confused about 1 thing.

the 2.2k feedback resistor to ground.  
isnt the 1k the feedback resistor TO GROUND?  the 2.2k is the feedback resistor.  increasing it will DEcrease the feedback into the op-amp, wouldnt it?  INcreasing the 1k TO GROUND will force more signal to the 2.2k feedback resistor, (and back into the op-amp) and INcrease gain?  wouldnt it??
  
according to your math formula: (Short summary: Op-Amp Gain = feedback-resistor (divided by) feedback-resistor-to-ground
Example in second op-amp: 2.2K / 1K = gain of 2.2) increasing the feedback resistor to 3k, 5,k, 7k, will result in 3 to 7 times gain, which is ALOT!   

im also guessing that ill need the same value diode.  (symetrical pair?)  im still going to try that first before messing with the feedback resistor.

i cant wait to try this over the holiday.  of course, i still need to find the components on the circuit board itself!  a schematic is one thing, a layout is another.

thanx for all your help.  this has been great!  

[jewellworks]

i finally got around to messing with this circuit.  your drawing is slightly wrong.  the clipping diode is allready a symetrical pair, so i didnt need to add a second diode.  but what i did do was replace the 2.2k feedback resistor with a 3k, which slightly improved the gain.  not over-the-top crazy, but just enough that it sounds great with a single coil guitar, like a tele.  
BUT, i still think its waaaaayy too bright, so i wanted to add a tone cap to roll off the top end a bit, but JUST on the overdrive channel.  i tried to add a tone cap to ground, on pin 6 of the overdrive switch, and it didnt work.  then i tried it both before and after the feedback resistor, and it still doesnt do anything.    i used a pretty heavy cap too.  .047uf.  the same in a guitar (.022, .033 and .047 were all tried.)

what could i possibly be doing wrong???

[jewellworks]

btw...  i strapped the tone cap across pin 6 and pin 2 (to ground) of the switch.  if thats any help at all...