Ceriatone Forum

Hi guys! I've been breaking in my OTS now for about a month and continue to be impressed by the variety of tones it can achieve. Today I found something that I hope I can correct. The low end sounds a little loose when playing at anything above moderately loud volumes. The OTS is stock as received from Nik, no mods done yet.

Speaker cabinet details:
I'm using a repro Fender Bandmaster piggyback style 2 x 12 cab that is loaded with Celestions...one Vintage 30 and one G12H Heritage. They are both 8 ohms and are wired to operate at 4 ohms...this is because I have a 64 Fender Bandmaster that pairs up with the cab which, as you all already probably know, runs at 4. The combination of these two speakers sounds fantastic with both the Fender and the OTS. I know the problem is not the speakers because the Bandmaster sounds very tight and focused when cranked. 

OTS settings are as follows:
Volume: 5
Bright: Down
Deep: Down
Rock/Jazz: Rock
Treble: 5
Mid: 5
Bass: 3
OD Channel Level: 5
Ratio: 3
Master: 3
Presence: 5

Just for a frame of reference...these setting nailed Robben Ford's 'Rugged Road' sound....

I noticed that when I switched to the Jazz setting, the low end kind of tightened up but the overall tone wasn't the same. I tried to adjust some settings but it lost some sustain which makes sense after reading some of the posts on that subject. Anyway, the overall sound is great but it would be nice to have the low end tightened up a bit. 

Do you guys think if I install 2 X additional 47uF, 350V caps in parallel to the 2 X 100uF, 450V from factory (Zucker Mod) that it would solve this problem? 

Maybe a mod to the Rock/Jazz circuit????

Adding more smoothing to the power supply should firm the bass a little- my OTS does mush out a little too at times, especially with a Les Paul. You might try lowering the OD circuit trim pot a little, or changing the value of the snubber caps on V2- I upped mine to 330pf as per the Zucker mod sheet- this certainly smoothed out the top end with overdrive engaged. Check your values- you may want to re-install 270pf or lower to brighten the OD.  Also- re-check your bias- raising it to 70% dissipation will certainly firm up low end response.

Good luck!

if you bass weakness is a problem in BOTH clean and OD - then look a the powersupply caps as you've suggested.

If it only happens in OD, then you should try the "Ayan Gil mod" from ampgarage.com.
....install a 10m resistor (input to ground)/ 47 nF (input to on the input of the OD just before the 220k resistor) this will trim off a little low end and make the tone less wobblely in OD

With the master on 3 the power supply is barely breathing hard, so I would not look at the filter caps as a solution to your problem.

More than likely, if this is one of the newer amps with the 4.7uF cathode bypass caps, your problem can be solved by going back closer to the original design values of 1.0 and 2.2uF. Increased low end response is what happens as you increase the cathode bypass caps.

Try 2.2 or 3.3 in one or both spots and see if it solves your problem. I think 4.7 may be a bit too much in my personal opinion, based on the results I've had with my own amp. (I'm also now getting a bit too much low end with 4.7's.)

Just for info, the amp has the folloving values

3,3k / 5uf is 10hz cut off frequency
2,2k / 5uf is 14 Hz cut off frequency

You are suggesting

3,3k / 2,2 uF is 22 hz cut off freq
2,2 / 2,2 uF is 33 hz cut off freq

OR

3,3k / 1 uF is 48 hz cut off freq
2,2 / 1 uF is 72 hz cut off freq

Just to get the record straight, what Fullerplast is suggesting has the exact same effect as the suggested Gill Ayan mod.

Anyway
If the problem is both in clean and OD mode try recuding the cathode values on V1.
If only in OD mode then do it only on V2

First of all...please bear in mind that I am a novice and will probably ask some stupid questions so i apologize in advance! I really appreciate all your help

Just to confirm...the cathode bypass caps are connected to V1 and V2 via pins 8 correct? My OTS should be the newer version with the Zucker mods so they both should be 4.7uF caps. I will check that tonight.

By "2,2k and 3,3k" are you referring to the resistors installed in parallel with the  bypass caps on both V1 and V2?

Here are the part numbers I found in the Mouser site for the caps:
140-XAL63V2.2-RC = 2.2uF Axial Electrolytic Capacitors 63V 20%
75-516D105M050-E3 = 1uF Axial Aluminum Electrolytic Capacitors 50volts 20%
594-2222-021-38338 =  3.3uF Miniature Axial Electrolytic Capacitors 63volts 20%

Do these look like the right part numbers I need for this mod? I figure I would get all 3 values and see which ones work best.

thanks again for the help!

[quote/]
Just to confirm...the cathode bypass caps are connected to V1 and V2 via pins 8 correct? My OTS should be the newer version with the Zucker mods so they both should be 4.7uF caps. I will check that tonight. [/quote]

yes, pin8 and pin3
[quote/]
By "2,2k and 3,3k" are you referring to the resistors installed in parallel with the  bypass caps on both V1 and V2? [/quote]

yes, pin3 and pin 8 on V1 AND pin3 and pin 8 on V2

The parts you have listed are all fine, but you still need to answer the basic question: Is your bass issue evident in both clean and OD mode ??

I suppose you could say that as a general description....i.e. decreased low end response....but I would not go as far as saying you would not hear a difference.

As you mentioned, the cathode bypass caps affect one or both stages and are located at different points in the circuit so depending on what you wanted to do WRT to clean/OD alterations and what value caps you use, they will almost certainly sound different. YMMV of course and the truly curious would be best off trying both. :D

(FWIW, Gil actually uses 4.7M in his version, the 10M is a non-Gil variation of the theme...)

yes, pin8 and pin3

[/quote]
By "2,2k and 3,3k" are you referring to the resistors installed in parallel with the  bypass caps on both V1 and V2?
[/quote]

yes, pin3 and pin 8 on V1 AND pin3 and pin 8 on V2

The parts you have listed are all fine, but you still need to answer the basic question: Is your bass issue evident in both clean and OD mode ??
[/quote]

I will check that out tonight if my wife and kids give me a chance...LOL!

I did not test the clean channel but will and will update this post.

Thanks again!

Agree with you, but we should suggest the simplest solution for archelo  to use, who describe himself as a newb. ;-), which is why i suggest the Gill Ayan mod. However,a s always each to his own  ;D

I am definitely a newb....no shame in admitting it...

I tried looking for the details on the Gil Ayan mod in ampgarage.com but am not having much luck...a lot of posts to read through. I will keep looking...

Thanks again guys!

Difficulty should not be an issue at all with either approach. Both are about as simple as it gets. ;) The cathode cap method does offer a bit more flexibilty.

Here Ya go: http://ampgarage.com/forum/viewtopic.php?t=5888   :D it's quite easy

Just tried the clean channel and it sounds fine to me. Sounds like it is only happening on the OD channel....or...thats how I am  perceiving it. I also confirmed that I do have the mods...5uF caps which replaced the 1uF in the OD channel and 2.2uF in the clean.

So, I should lower the value of that same 5uF cap next to the 2K2 resistor in V2 until I find the value that solves the problem correct?

That's it....

Cool...Thanks fullerplast! I will go get the caps tomorrow and try this out.



Thank you bluesfendermanblues...of course, this generates more stupid questions by me....

Ayan rights...."my mod is .0047uF (4.7 nF) // 4.7Meg. I don't use it in the amp(s) with 100K plate loads, but I did use it in the amps with 220K/150K plate loads."

Questions:
1. Does the OTS use 220K/150K plate loads? Are these the 2 resistors in the latest OTS layout (May08) which are connected to pins 1 and 6 of V2?
2. Do I replace one of the caps on V2 or simply add the .0047uF cap?
3. Do I remove either the 2K2 or the 3K3 resistors in V2 and if so, which one goes....or....do I add the 4.7M resistor and if so where?
4. You could send me to hell whenever you like?  ;D

Sorry guys...I hope to speak your language one day but for now, I may need a little hand holding so i don't destroy my amp.

thanks again!

I was finally able to mess a little more with the OTS last night. Based on the information in this forum related to the proper orientation to use when adjusting the OD Trimmer (should be looking from the input side of chassis towards the trany) mine came from factory set at 2 o'clock.  ??? 

I never messed with it because looking in the opposite direction it looked like it was at 10. I backed it off to about 10-11 and the low end issue I was having improved. It's still there but much more manageable than before. I tried to go a little lower but felt that 10-11 is where i like it best. I'm inclined not to change a thing with the cathode bypass cap but am curious about the frequency cut off detailed by bluesfendermanblues. I am going to lower one the caps a bit and see what happens...stay tuned...

ad 1: yes, 220k/150k
ad.2 : dont change anything just add the 47nf cap
ad. 3 no dont change those either, the 4,7m goes to input ground before the 220k, which goes into the 100k input trimmer and the 47nf is connected between the other end ogf the 4,7M and the 220k. The trimmer goes to the 68k input grid connection 2 on V2.
add4: I don't wan't you to get into trouble with these mods, if you're insecure don't touch anything. The amp contains lethal voltages. Its a great toy for a guitarist, but dangerous to poke around in.

Just turn the trim to 09:00 and let it stay these for at couple of days and try out different settings on input volume and OD gains-  you'll be surprised - godd luck

Great...Thank you bluesfendermanblues! This is awesome information. I will definitely watch myself inside the amp...no doubt. At least you have cleared up some doubts as to what I was looking at in the layout which is extremely helpful.

For right now...I will take your advise and mess around with the settings before getting in there and changing stuff. I have definitely noticed the range of tones available by just adjusting the input, volume and OD gains. Reminds me of my MKIIc+....

Anyway...thanks again for all the advice.

Anytime..

And don't forget the "Patch Cord" mod which does some similar things and is not permanent. Just a 6foot to 2foot patch cord across the send/return jacks sending the signal through a 250pf cap and 220k resistor in parallel.

I didn't mount those to components in my amp - what does it sound like??

http://soundclick.com/share?songid=6575515

After testing with various length cords, it seems the cord length may have as much effect as the resistor/cap network.
That clip is with a particular 6ft cable that sounds good in the loop.

A cable in the loop makes a *huge* difference in the high end smoothness and response. Different length, different construction are all worth trying. At about 30pF/ft of cable, you are adding a fair amount of capacitance to the signal path.

It's the easiest way to smooth out a D amp without a mod.

I was able to get in touch with Gil Ayan and he responded with the exact placement of his mod...heres are his comments in case anyone wants to know exactly where he placed the components in the circuit:

"The resistor and cap are in parallel to one another. Interrupt the connection between the wire that comes from the relay board and the 220K resistor at the input of the overdrive, and insert the pair (4.7M//.0047uF) in series with that. So, relay to 4.7M//.0047uF, to 220K resistor. "

After playing the amp for a few days, it seems that the problem still exists even messing with the OD trimmer. Because of this, I actually removed the trimmer and placed a 100K pot where the unused ground switch was and wired it accordingly. Now I can adjust it on the fly which has really helped in dialing it in. I also lowered one of the caps in the OD channel but still seems a little funky when playing single notes in the lower registers. Since I like tinkering with this stuff,  I'm going to try Ayan's mod and cross my fingers.