Ceriatone Forum

Hello tonelovers,

At last here are my tweaks on the OTS layout.
Those mods work for MY TASTE and not necessarily for other players taste and style.

WORNING !!! PLEASE DO NOT MESS WITH TUBE AMPS  if you don’t know how to. You can damage it or worse - IT CAN KILL YOU !!! Better take it to good amp technician !!!

I tried to make OTS bigger, fatter, bit more compressed, even on cleans. Actually get closer to “Bluesmaster” mod. Some of this tweaks can apply to HRM model too, especially removing a negative feedback NFB from V1 (just removing 0.05mF cap) which adds fat to the amp. Actually it would be better if one drills a hall near V1 and installs mini toggle switch for switching 0.05uF cap ON (for humbucker guitar) or OF(for strat and tele).
I hope everything is clear on the diagram.
Note that JAZZ/ROCK switch is three position switch and changes DRIVE CHANNEL gain only – Hi/Dumb/Plexi. Amp itself is always on ROCK setting.
BRIGHT switch is also 3 position for more flexibility.
As you noticed I removed FET board and there is boost gain pot in the FET input hall.
PAB is disconnected and gain boost happens with simply increasing a CLEAN VOLUME via PAB footswitch. With this you can have regulated (via boost pot) volume (gain) boost on both channels without changing the TONE. It allows to get nice crunch on clean channel and awesome drive boost.
Three way switch near V2 adjusts drive’s high cut, so you can go as smooth as you want without affecting clean channel.
Added International power switch (in the ground lift hall) for the travelling musician.

Best wishes to all

(http://www.drika.biz/OTSIKA.JPG)

Great post.

By the way, the amp name is spelled wrong :D ;) :P

Sorry! Shame on me. I’ll correct it soon. It was there originally BTW, we have to tell Nick.

Nice work!
That must be a big fat monster on the clean side with 100k slope.  :D
Some things I don't understand:
-Increasing the coupling cap on v2b, doesnt it make your drive channel  muddy?
-What is the effect on decreasing the resistor to 27k (after V2a coupling cap)?
-The size of the snubber on v2B; did you have something to tame here? ; its a huge value for its application.

Grtz Erwin

Hi Erwin,

I love sweet mud and dirt :-[ ;D, well it does a little bit but 27K (one can put 12K as well) resistor opens up the tone and together it is magic (FOR MY TASTE)!.
Because of the bright 47pF cap on the volume is always ON - I’ve milded drive with 770pF - really Robben’s drive tone.
With experiments I've noticed that better to  keep V2A snabber low and increase V2B’s value – better chirp definition and waterier tone.

Excellent. Very well explained and documented. Thank you very much indeed.

I really do feel the need for another OTS to try all the mods on!

Just a couple of questions about the Rock/Jazz replacement switch. Seems like a good idea to me
as I never use the Jazz setting.

You mention that the switching is Hi/Dumble/Plexi.
Am I correct in assuming that in the Dumble position, ie OFF, the trimmer controls the level of drive?

The two caps connected to the switch via the purple wire seem to be connected to wire X shielding.
Should they be connected to the signal wire of wire X? and what is their purpose since they don't appear to be connected
to anything at the switch?

Many thanks

Hywel Harris

You are absolutely right – in the middle OFF position a trimmer works, for other positions – the switch. One can put little trimmers instead of resistors to adjust desired gain settings on Hi gain and Plexi.
Well spotted Hywel, I’ve just corrected it! Caps cut highs – when gain increases highs increase too so to compensate!
One can chose caps value according to their taste.
Caps are connected to HOT not to shield (ground).

Thanks for the clarification. I think I'm going to do the mods one at a time to get a feel for
what effect they have. First will be Rock/Jazz since that will be of greatest use for me.
The Boost control will also be very useful. PAB has always been a little too much
of a volume step with my TMB settings plus I have never had a use for the FET input.

Hi Ika,

Thanks for explaining!
Interesting thing about the snubbers, I'm gonna try that.

Grtz Erwin

I've added a 500k trimmer with a 1 nF cap across the overdrive master to reduce the lead highs, which works fine. I use 270p snubbers on V2a + V2b so I need a little extra to trim off some highs.

I was really looking forward to this.   ;)


Thanks

Hello,

This is central scrutiniser again!
Some folks complained that removing the 0.05mF cap from V1’s NFB makes amp TOO FAT!  ::)
So here is more flexible solution – three way switch with 470pF/OFF/0.05mF.
Drill little hall for the switch near V1  and chose the desired setting.
I’ve added this to the layout. :P
Cheers.

Are there caps with variable values that i could use and adjust for the V2 snubber caps? Sortof like the OD trimmers but this adjusts the V2 cap values

Hi Pick Master, while the ots is not on my immediate to build list as i am building a couple of other smaller amps at the moment , I may attemp to tackle it in the future. I have quickly glanced over the layouts of both the 100 and 50 watt versions, and forgive me if I am totally wrong as i didn't spend too much time comparing , but they appear similar except for the extra power tubes etc , now your layout shows a 50 watt version . Can your mods also be applied to a 100 watt version , Thanks.

Just want to ask something...

IKA do you have any pics of your amp, pics with all the switches and pots... I just want to see how does this look in person.
 ;)

Good thinking my friend!
Yes ! one can get variable trim-cap 250-1180pF, but I’m not sure about voltage though. Usually they are 100v max.  Made by Sprague-Goodman (US) and Murata (Japan).


Hi telecaster,

Yes you are correct! OTS 100 and 50 are identical and all mods apply to both of them.
100w already got 200mF filter caps so no change there.
Cheers

Hi Mcinku,

I have some pics and I'll try now, but soon I have to open my amp (again >:() and I'll take more pics.

Be cool ;)

Mcinku ma man,

Some pics for you:

Boost gain pot inside and treble 47pF cap on vol pot.
(http://www.drika.biz/TWEAK2.JPG)

and outside
(http://www.drika.biz/TWEAK5.JPG)

OD trimmer and switch
(http://www.drika.biz/TWEAK1.JPG)

filter caps
(http://www.drika.biz/TWEAK4.JPG)

Internationall power reg. switch (left) and master pot cap selector (three way in half/full power hall)
(http://www.drika.biz/TWEAK3.JPG)

 :o  :o

That was FAST.

thanks man

Good thinking my friend!
Yes ! one can get variable trim-cap 250-1180pF, but I’m not sure about voltage though. Usually they are 100v max.  Made by Sprague-Goodman (US) and Murata (Japan).

well keep an eye out for some, i've been looking and had no luck

Just done the V1 and V2 mods today, leaving FET/Boost and Rock/Jazz switch mod for another day. Finished off a new footswitch with a 5 pin XLR socket on the switch so I will be able to swap cables easily.

Very impressed with the mod to V1 caps. Like it best with no cap in place of the .047. Much fuller sound.

V2 mods are a big help with treble on OD channel.

Anyone in the UK know where I can get 5 core flexible (and I don't just mean flexible like lighting flex!) cable for footswitches?. I'm currently using 7 core automotive cable but its a little too rigid, could do with something better.

Hi Hywel,

You need overall lapped scree 4 core cabel ! fifth will be the earth.
get in Maplin http://www.maplin.co.uk/Module.aspx?ModuleNo=137

Thanks Pickmaster. I just wonder if that cable has large enough cores for a 5m cable or whether I'm going to get too large a voltage drop. I've since found this

http://www.evelcables.co.uk/epages/Store2_Shop1476.sf/en_GB/?ObjectPath=/Shops/Store2.Shop1476/Products/SY5C0.75 (http://www.evelcables.co.uk/epages/Store2_Shop1476.sf/en_GB/?ObjectPath=/Shops/Store2.Shop1476/Products/SY5C0.75)

but they want £10 for delivery for  approx £5 worth of goods!


By the way, when I did my mods I had to substitute some cap values since I couldn't get the exact same ones, but I guess thats not necessarily a problem, but with resistors I'm never sure of the voltage/wattage rating required. Nik uses three types the standard colour ring versions , Dale and another brown bodied one with writing on. Where would I get these in small quantities? RS won't do less than 25 a time of most stuff of this value. I got most of my caps from Hotrox as they are local but his stock of resistors amounts to 4 differing values!

Thanks again for posting those mods.

sound clips please! :)

For sounds scroll down on the pages here:
http://www.guitarampcab.com/overtone.html

and here:
http://www.guitarampcab.com/fatty.html

Cheers

Another source of muliticore audio cables

http://www.studiospares.com/Cables+Connectors/Cable-Multicore-/icat/cabmulticore

Has anyone tried mic cables for the footswitch?. I wonder if the small conductors will drop the voltage too much and prevent the relay working reliably.

That’s what I’m using. 8)
Van dam microphone cable. I don’t use 4 or 5 core, switching is fine with just two core and ground. No problems at all.
And also! G-major needs two core for switching.

I did wonder whether 3 conductors would do the trick only my electronics knowledge is not sufficient to have worked it out. I'm pretty much toed to 5 pin XLR's now since I've built the new footswitch, bought all the connectors to convert the original, my pedal board etc etc. And to think I could have got away with mic cable and a stereo jack socket.

Would you be so good as to show us how you wire the footswitch for this?

Many thanks

Hywel Harris

Hi Hywel,

Here we go: I’m using ultra bright LEDs they use little current and with 2,7k resistors work well. All parts are in Maplin.
(http://www.drika.biz/OTSPEDAL.JPG)

Thats brilliant thanks! I would bet many kit builders would prefer this to the 5 core with DIN or XLR connectors, its so much easier to use a simple stereo jack/mic cable arrangement. I think I might have to mod the amp to a Neutrik locking jack socket (the hole is too big now for standard jack socket). I think this should also be posted in the Mods and Tweaks forum and indeed Nik should have it available on his Mods page.

Hi

Cool!

Yeah this works great i bet!

Thanks Hywel!

Nik

Don't thank me Nik, it was Pickmaster who did this layout.!!

Hi Dr Ika, I'm just about to convert one of my footswitches to three coonductor wiring, one question.

Wires P and Q, did you just snip them? or indeed just not use them?

Many thanks

Hywel Harris

Hi Hywel,

No I did not snip them.
Just using 3 conections.

Cheers

Great, thanks. That means I can use either footswitch without changing the amp

Many thanks

Hywel Harris

Dr Ika, I've just finished making the footswitch mods and it appears I have a problem with the LED's. I used the LED's of the original footswitch which were 12v LED's so I didn't put the resistor in series. Now it appears that they are drawing too much current since if I disconnect them the switching works fine.

So could you tell me the spec of those you used. I'd assume that a 5volt LED with a suitable resistor in series will draw a lot less current than the 12v.

Thanks for your help.

BTW I've just changed the mid cap to 50nF and the treble cap to 1nF with the intention of making it have a little more mid scoop when turning the mid pot down. Not had chance to try it yet, will report back later.

Hi Hywel,
You can use lo current LEds from maplin
http://www.maplin.co.uk/module.aspx?moduleno=35736

or superbright LEDs
http://www.maplin.co.uk/Search.aspx?menuno=12369

Good luck

Thanks for the info, DrIka, I bought both types just to be sure just aswell really as the 'low current' types still drew too much. In fact the 2.7k was borderline for the high power LED's, the PAB relay would trip but the OD wouldn't. I ended up using 12k and now both work fine and the LED are plenty bright enough, in fact the green I'm using is still too bright.

Only problem is the way the switches are wired up, I get the PAB led light up when the PAB is OFF. I seem to recall a discussion a while back that suggested that the switch was wired wrong in the original. I'd think it was just a matter of switching a couple of wires at the relay but I'm not confident enough to know which.

Dr. Ika,
   Thanks for posting your mods. I still have a few questions.
   I have a new OTS with 100uf filter caps. What does making them 150uf do?
I have a 100K volume pot. What difference does the 250K pot do? I play
humbucking guitars, and love great clean tones. What's the best mod for best clean tones? Sure appreciate your help.

150uf filters will make your bass tighter at higher volumes.

Quote from erwin_ve about the 100k-250k pot
"Od level pot 100K makes a smoother transition from light overdrive to a heavy overdrive. When the level pot is 250K the transition is less subtle."
...and also with 100K you will have smaller volume jump from clean to OD


something like that
 ;)

Hi Docmh,

Mcinku is correct,
loud bass notes will be tighter with 150uF caps and 100k will work better for drive.

To get great clean sound (especially with LesPaul) permanently solder 68pF cap to the clean volume pot’s terminals and use 100k 3W slop resistor instead of  150k on the first tube. This will give you bigger, more open clean sound.

Good luck

mcinku, pickmaster, thanks. I'm not sure which 150K resistor to change.
It looks like one is right behind a 0.1uF cap, and the other is linked with a 220K resistor behind a 0.05uFcap. Thanks! 

One right behind a 0.1uF cap, near lower bord bolt.
marked in GREEN 100k on my layout.
Cheers

Pickmaster,
    Thanks.

I'm hoping to buy the parts necessary for this mod and have a tech install it but I have a few questions:

1) In the original post, are those the only mods present in the diagram? I don't want to permanently change the sound of the amp, only add the options with all the switches and maybe do the PAB mod.

2) The tech I know is one of those guys that uses the cheapest parts says "Why are you using that? I can buy that part for 25 cents and save you a dollar," but I don't want to go cheap on this amp's mods so I'd like to buy the parts somewhere and bring them to him. Could someone make a list of the parts needed for this noob?

Thanks for everything,

Alex

Hi Alex,

You can drill the chassis from the back and install additional switches and pots.

Don’t go for cheaper parts, you don’t need much, just couple of switches, pot and capacitors. Good luck.

Yeah I don't want cheaper parts, but since I don't know anything about this, I was hoping to get a list of parts. This way, I can avoid my tech getting his own cheap parts.