Way Huge Green Rhino MK2 TRACED

[Ciaran Haslett]

One of our students had this in today and allowed me to take it apart and see what's going on for a few hours.  And sure enough it's YATS (as we knew from MK1) with a few mods and something I'm hoping someone can enlighten me on.

Some pics for whoever wants to cross reference the schematic with.



I missed the 10u>10K>GND trace on this pic but it's all fine on the schematic AND apologies for not lining up the front/reverse pics better before I started.  I had little time.

The Schematic (massively overcomplicated relay switching omitted)and hi res here



So my question...what is the point of 4 BJT in parallel at the input buffer?  This wrecked my head for way longer than it should!  I initially thought there was some kind of design error....or I missed some traces but nope...4 transistors in parallel acting as nothing more than a buffer.  Anyone know why they couldn't just use 1 like any other TS?

Anyone want to tackle a breadboard/layout and make an eejit out of me? 

I should point out that another forum member also had a go at tracing this here but I'm very confident there are a few errors.  Still...it's good for referencing anyhow.

Cheers folks...hope all turns out well

[notnews]

wow great effort! thanks a bunch!

I've always liked the GR.. so much more than the Ibanez- made TS.

Analogman does a few different mods to the TS808/TS9.. has anyone played with any of these? I've seen the "Brown" mod, the "Silver" mod, and a few others. When I was really into the band Phish in college I read up on Trey Anastasio's rig and read that he used two Analogman-modded Silver tube screamers, one more mild/soft OD sounds and another for more aggressive, cutting distortion sounds. After I read that I listened more closely to Trey's sounds and could definitely hear when he kicked on one or the other or both. It costs about 150 to get a silver-modded TS on eBay.. just wondering if anyones had experience with these units.

Love this circuit... the 100hz knob is money.

[Frank_NH]

Thanks for this Ciaran!  

I think those BJT "buffers" at the input are what is known as a "current mirror".  This idea is maintain a stable current but why it's used here (versus a standard BJT or op amp buffer) I'm not sure.

The Drive and Tone circuits are conventional tube screamer, with a Timmy-style bass control ("Curve").

The later sections are a buffer and additional filtering prior to volume control and BJT output buffer a la tube screamer.

So, all in all, it is YATS but with a few interesting quirks to keep the pedal DIYers on their toes .

[Sphere80]

Thank you!  I'd like to eventually build this in the same enclosure with a Red Llama.  

 The 100Hz boost seems to be like on the MXR badass (Dunlop, like this one). I guess it has active and passive bass controls  in the signal path.

[Alex]

Cool job Ciaran!
Hope this would work.
I've used one LF347 instead of 2 LF353s for space reason.
Can anyone double check?

[IvIark]

Great job Ciaran, and Alex on the layout

[notnews]

Alex, thanks for sharing all your work!

[Alex]

Thanks guys!
I think it matches the schematic.
If you could confirm that, I'll move it to the main page.

[Ciaran Haslett]

Fantastic job Alex!!!!  The pot grouping is pure class!

If it matches the schematic...apologies lol.  The output cap should be 10uF electro...not 1u.  I even mentioned it under the dot trace but didn't correct it on the schem!  Sorry about that.

Sent from my iPhone

On 28 May 2016, at 15:36, Alex [via Guitar FX Layouts] <[hidden email]> wrote:

Thanks guys!
I think it matches the schematic.
If you could confirm that, I'll move it to the main page.

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[Alex]

No problem.
I've updated it.
Let me know if you think it's good to go!

[Ciaran Haslett]

Sorry Alex...just back from a long studio job.  Layout matches the schematic perfectly.  Really amazing...as always.  I hope the schematic doesn't let you down

EDIT:  Schematic and hi res link updated!

[Frank_NH]

Hi all,

I just did an LTSpice simulation of the 4 transistor input "buffer" and saw no real difference between that configuration and a single transistor.  Don't know if the four transistors provide any other "mojo" or not, but you could probably save three transistors by simplifying the input buffer.

[EBRAddict]

I've seen parallel transistors used for lower noise before, but I'm not sure what the point is for a guitar pedal. This isn't a lab instrument. 4 parallel transistors would lower the noise by 1/2X but there's probably more noise on the power rail than the input jack.

Oh, and I found this from The Art of Electronics (3rd ed) page 113:

[balazs.bencs]

Did you guys had any luck building this?

[Battery Acid]

Hi there! I've made two of those Green Rhinos following the stripboard, but now I have a real unit in my hands, and the output from both my clones aren't nowhere near the real one. Where should I start tweaking?

[Battery Acid]

Well I got around it placing trimpots on the 10k from base to ground on the output buffer and before the 10uF capacitor. Used 100k trimpots and tweaked by ear

[Ciaran Haslett]

Do you mean volume?  I only had this for a few hours so it's possible I got a resistor value wrong....and in fact I did.  The pulldown resistor on the output should be 1M, not 10K.  Sorry about that folks.

On the layout its the 10K on OUT, between the 1u and 10u caps.

Just went over the rest and they check out.  Hopefully that does it for you.

[Ciaran Haslett]

You posted when I was in response so I missed your comment sorry.  There's no need for the trimpot.  A swap to 1 meg will do it.  Sorry for the hassle

[Battery Acid]

Damn, now I feel really dumb! I was so pissed I didn't realized I was messing with pulldown resistors HAHAHAHA, thanks heaps!

[Frank_NH]

For those who have built it - how does it sound compared to a tube screamer???