Biyang OTD-100 more drive mode

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Biyang OTD-100 more drive mode

Postby nenic » 18 Feb 2009, 23:02

:D Hello from Croatia,
BE CAREFUL INSIDE THIS PEDAL THERE IS 240VDC. Unplug it and leave it 5min before opening.
First thanks to Bajaman for his post about VT911 and Baja real tube driver. :applause:
That inspired me to write this post. On eBay or on Alibaba you can by OTD-100.
I bought it for 64 GBP with delivery from Hong Kong. Maybe for some of you it will look expensive but it has 12AX7 inside and 240V on plate. Similar pedals have price 400 USD or more.
It is quality built with quality components. Look at the picture of PCB.
From factory, without mod it sounds good. Very nice sound with my Fender Stratocaster 1978 and Fender Bassman 100W. The Box is from Spider Croatia with Eminence Texas heat inside.
However for my taste, this distortion needs more gain. It was good for riffs and chords but not for solo and Gilmour sound.
I couldn't find the schematic on web so I contacted Biyang by MSN messenger and they were kind but they didn't give me the schematic. Probably they want to protect it. :(
So I decided to reverse it and track the schematic. :evil:
Now I have schematic for complete audio path without output tone stack but I will track it too. I measured capacitors because there is no mark on SMD.
If you are interested I will post schematic in next few days. I am very busy man and I can't post all right now.
Also I have simulation in LTspice with graphs.
Take a look on PCB pictures.
http://www.box.net/shared/vvyxr0x2ob
There is small PCB with SMD and 4558C OP amp.
http://www.box.net/shared/u85dqsb787
http://www.box.net/shared/mafbxfa3lq
The mod is to change cathode resistor on first triode. It is 10k and should be 2.2k or 1.5k.
You can add resistor in parallel with existing 10K like on picture
http://www.box.net/shared/7lad5zt8qu
After this mod there is lot of gain and the sound is like Gilmours. Real tube driver sound. However I have in plan to put pot 10K in series with this resistor. This is because the sound without this mod is interesting. With mod it is good for solo but for riff and chord the sound without mod is better (more direct). I think that this pot will be something like bias on chandler tube driver. The pedal will be more versatile with this pot.
Schematic and more about this in next few days.
It will be more clear then.
Buy.
Nenad Mihajlovic, Krizevci Croatia
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Re: Biyang OTD-100 more drive mode

Postby IvIark » 19 Feb 2009, 00:37

Excellent post, I'll be really interested in that schematic when you've done it. I agree with you that for the price these are a bargain compared to some of the fashionable alternatives. :thumbsup
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Re: Biyang OTD-100 more drive mode

Postby nenic » 21 Feb 2009, 00:35

:wink: Schematic is here.
http://www.box.net/shared/oy8qgsgnft
I didn't draw bypass relay, relay logic IC, power supply etc.
But here is complete audio path and that is the most important part for me.
I checked the tone stack on
http://www.duncanamps.com/tsc/
and OTD-100 has James tone stack. Interesting :D
On SMD PCB, components have numeration marks and I tried to follow this in my schematic.
R25 is cathode resistor from first triode. It is placed on bottom of SMD PCB.
http://www.box.net/shared/mafbxfa3lq
But you have direct connection to this resistor from above pins.
http://www.box.net/shared/7lad5zt8qu
It is third pin on left and second pin on right side.
Solder 2.2K or maybe 1.5K here. I will solder POT 10K with 1.5K in series.
I think that it is not smart idea to go with lower value than 1.5K because in LTspice simulation I see that grid voltage on second triode will go lower then -50V in that case. In 12AX7 data sheet there is written that grid voltage is -50V.
I will try to post some additional info tomorrow.
Neno
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Re: Biyang OTD-100 more drive mode

Postby borislavgajic » 21 Feb 2009, 17:15

did you try to put electrolytic capacitor 22mF/100V
in paralell with cathode resistor?.....more gain

boris

P.S. pozdrav iz Sombora :thumbsup
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Re: Biyang OTD-100 more drive mode

Postby nenic » 22 Feb 2009, 00:18

borislavgajic wrote:did you try to put electrolytic capacitor 22mF/100V
in paralell with cathode resistor?.....more gain

boris

P.S. pozdrav iz Sombora :thumbsup


Now I tried with capacitor but the tube is squealing.
It is too much gain with capacitor.

:wink: Pozdrav iz Križevca
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Re: Biyang OTD-100 more drive mode

Postby Fuzzer » 22 Feb 2009, 00:42

Then, split the cathode resistor, so the series value remains the same for DC, but bypass one of the series resistors with the Capacitor.
The Freestompboxes Forum search function is soo great, use the search function..., the S E A R C H function.
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Re: Biyang OTD-100 more drive mode

Postby borislavgajic » 23 Feb 2009, 13:25

nenic wrote:
borislavgajic wrote:did you try to put electrolytic capacitor 22mF/100V
in paralell with cathode resistor?.....more gain

boris

P.S. pozdrav iz Sombora :thumbsup


Now I tried with capacitor but the tube is squealing.
It is too much gain with capacitor.

:wink: Pozdrav iz Križevca


Try to change R6-1K for something bigger.........and some clipping diodes after tubes....( from signal path to ground) :blackeye

boris
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Re: Biyang OTD-100 more drive mode

Postby electric larry » 07 May 2009, 00:26

Hi,

I'm larry. I purchased an OTD-100 Pro and when I got it...it didn't work. I am having a hard time with the dealer returning it.They told me to put a fresh battery in it. Anyway my friend is a tech and looked at it. He said the transformer's not working. Does anyone have a full schematic or at least a power supply schematic? I would be very greatful to anyone who could help me.

Thank so much
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 12 Nov 2009, 18:18

Hi i'm new in this forum, i'm from Portugal
I have purchased the Collins OTD100 from http://www.musikproduktiv.de is't a re-branded Biyang

http://www.musik-produktiv.de/collins-otd100-tube-overdrive-distortion.aspx
49 Euros is about 73 dollars... cheap for a tube pedal!! and it comes with transformer..

Yesterday i've open it

Swapping the 6AX7 to 12AX7 is very simple, just change the jumper on the base of tube PCB.. i've done that and it works...
Next step:
I've found that the pedal is to trebly... very harsh treble frequencies... i have to put the bass on max and treble pot on min to have a decent nice fat overdrive...

i'm gonna do some mods tonight.. i have tested (on TSC) some options to remove those horrible frequencies... and i will try some other tweaks on tube resistors and bypass capacitors... i will post my results here after.

PS: I have the X-Overdrive and the Metal-End from Biyang and I love those pedals!!! The X-Overdrive is maybe the most tried by many people and it's a good sounding pedal... and the Metal-end is far away better than the well knowed by DIYers Dr.Boogie.
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Re: Biyang OTD-100 more drive mode

Postby himister » 12 Nov 2009, 19:04

More guts shots would be nice. Looks like interesting pedal to do. :D
Maybe someone else would be also interested in building this one.
Cheers and welcome to forum. :thumbsup
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 13 Nov 2009, 11:23

After some mods here i am to post my mods

ATENTION: IN MY OTD100 THE RESISTORS AND CAPS ARE LABELED WITH DIFERENT NUMBERS THAN IN THE SCHEMATIC POSTED HERE BEFORE!!!! (I FORGOT THE FILE IN MY HOME COMPUTER WITH CORRECT NUMBER ON MY PEDAL), SO BEFORE DO MODS... RE-CHECK THE LAYOUT IN YOUR PEDAL AND THE SCHEMATIC

the mods that i've made:
Image

It reduces the high frequencies and scoop the mids.. if you want mids roll off the tone pots and the mids appears ;)

Image

The mod posted her before, pin 2 (cathode resistor on V1A) do pin 3 (ground) adds more gain (it reduce the 10k resistor to an overall 5k resistance.
The second mod on tube that i've made is from pin3 (cathode resistor on V1B) to pin3 (ground) adds a little more bass add little more gain.
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 13 Nov 2009, 12:21

First... how i edit a post?

here is an explanation of what i'm talking about (all credits for photos and schematics for NENIC)

Image
Image

TIP: you can put a switch to the "more gain and bass" mode! ;)
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 13 Nov 2009, 15:32

Here i come again

if you want more tonal options try this:
Image

this change the center frequency response of the tonestack. with an on-off-on mini-switch you can paralel the resistors

this weekend i'm gonna try it.
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Re: Biyang OTD-100 more drive mode

Postby valvelover27 » 11 Jan 2010, 18:35

I want to shed the harsh treble and add more bass, but don't want to scoop out the mids. Which mods, just to be clear, should I perform?

Also, in making this pedal able to accept a dual-triode, 12v tube like a 12AX7 or 12AT7, what do I do, specifically, with the jumper. I was a little unclear on that point.

Thanks!
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 15 Jan 2010, 11:46

hi, to take away the harsh treble and add bass you have to perform the mods showed here (the last one i didn't tried it yet)... it transform this pedal to an amazing sounding peace of gear..

those mods don't take away the mids... only reduce harsh and add bass... if you need more mids is just to roll off the treble and bass pots and beautiful warm mids jumps out...


Image
at the base of tube PCB there is 3 points at the center... with original 6AX7 tube the lower and middle one are shunted... to swap to 12AX7 you have to UN-shunt those ones and shunt the upper one and the middle like explained on this picture.

The jumper thing is very easy to perform... if needed i'm gonna take another photo to explain it better to you...
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Re: Biyang OTD-100 more drive mode

Postby dcustom » 17 Mar 2010, 13:06

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Re: Biyang OTD-100 more drive mode

Postby rawd » 24 Aug 2010, 19:46

Hi everyone,

I just purchased one of these Biyang OTD-100 pedals and am interested in modding to make it
as warm, and fat as possible...without any harsness. I plan to use it for Pink Floyd covers...

Can anyone recommend someone to perform the mods for me?

I'm in the U.S., Oregon...

Thx,

= Rawd =
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Re: Biyang OTD-100 more drive mode

Postby deeaa » 26 Oct 2010, 12:30

Whoa, weird that the OTD-100 seems lacking drive for you guys. I have its gain nearly at zero and it has huge drive. Around halfway mark it's got so much drive it's just useless woosh to me. Maybe it has something to do with me using EMG 85's and it's also in front of an already slightly driven p-t-p tube amp...but anyways, it has like ten times the distortion level of any other stomp I ever had, including stuff like The Weapon, HM-2, WarpFactor and such.

Here's a short clip of my Biyang demoing...only to my home amp, not the all-tube one:

http://www.youtube.com/watch?v=lokoa5ztFkE

Also here the drive is nearly in off-position but I can't think of ever using more drive really...but there would be planty available if I wanted.
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Re: Biyang OTD-100 more drive mode

Postby KHELSTROM » 14 Jun 2011, 00:41

Hey guys. I just bought an OTD-100 STA brand new for $40. I'm really excited to dig in and get this thing sounding amazing. I was looking around on the web to get some info on the 3 versions (val, sta & pro) and came across this pic of the guts of the pro. It looks like there is a bit more going on in this one than just a 12AX7 instead of the 6AX7. FWIW I've also found that the VAL version is the only one that comes with the 6AX7, the STA & PRO have the 12AX7. I'm curious to see what else is different in the PRO. If anyone has one and is willing to share I'd really appreciate it.

Image
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Re: Biyang OTD-100 more drive mode

Postby KHELSTROM » 14 Jun 2011, 18:02

Has anyone tried different tubes in their OTD?
I've got a NOS GE 5751 and a NOS Sylvania 12AU7 I'm gonna try when I get home tonight.
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