treble bleed?

[Seemoore]

Most interesting thing I'm finding is in this thread, is rolling off treble.
Correct me if I'm wrong. Doesn't the entrance bass roll off that affects the OD tone more, are we heading toward the "tube screamer" approach for od issues.

I have the Ceriatone and find treble side of the amp under control with all my guitars, it's the massive bass boost that the rock mode provides that screws with the overall balance of the clean/od parts of this amp.

I have to keep the bass around 3 or it gets out of hand. Of course I'm using a cheap cab, but with a decent speaker, Emi Govner', I was hoping it was the cab, now I don't know.

[Structo]

Sounds like he got his description from Wikipedia... I like the no words can describe the tone


Tony VVT

Yeah I kind of wonder if it is a scam.
Don't they usually list the seral number?

[pine]

Thought I'd bump this question before it got lost:

"I have installed the treble bleed at the Ratio pot on my Ceriatone OTS (non-hrm), and it works well, yet it seems to be taking out a larger portion of the frequency spectrum than I would like. I am currently using a 1000pF to 45K ohms to ground arrangement. If I wanted to knock out just the very highest, harsh frequencies, how would I change the components?

Am I right in saying that the value of the resistor changes how much of the highs you remove and the value of the cap changes which specific frequencies you remove? Would lowering the value of the cap to 470pF target higher frequencies than the 1000pF or lower frequencys? "

[Structo]

Yes just try a lower valued cap.

[ayan]

I have installed the treble bleed at the Ratio pot on my Ceriatone OTS (non-hrm), and it works well, yet it seems to be taking out a larger portion of the frequency spectrum than I would like. I am currently using a 1000pF to 45K ohms to ground arrangement. If I wanted to knock out just the very highest, harsh frequencies, how would I change the components?

Am I right in saying that the value of the resistor changes how much of the highs you remove and the value of the cap changes which specific frequencies you remove? Would lowering the value of the cap to 470pF target higher frequencies than the 1000pF or lower frequencys? Sorry to be such a noob, and many thanks as always.

Charlie

Charlie,

I believe your resistor values is too small. If you try a 1,000 pF cap with a 120K resistor, I suspect you''ll like the effect. "My" thing is a 250K pot and the cap, you can dial it to taste... As to who came up with this, it is the simplest of tone controls, which have been featured on guitars since 1950....

Gil

[Structo]

Thought I'd bump this question before it got lost:

"I have installed the treble bleed at the Ratio pot on my Ceriatone OTS (non-hrm), and it works well, yet it seems to be taking out a larger portion of the frequency spectrum than I would like. I am currently using a 1000pF to 45K ohms to ground arrangement. If I wanted to knock out just the very highest, harsh frequencies, how would I change the components?

Am I right in saying that the value of the resistor changes how much of the highs you remove and the value of the cap changes which specific frequencies you remove? Would lowering the value of the cap to 470pF target higher frequencies than the 1000pF or lower frequencies? "

At 45K with a .001uf cap your cutoff freq is 3536.78 Hz

At 45K with a .00047uf cap your cutoff is 7528.9 Hz

Here is a handy calculator that you can plug values into.

http://www.muzique.com/schem/filter.htm


I installed the 250K with a .001uf cap.

Doesn't seem to do a whole lot, a very subtle difference as I roll through the rotation of the trimmer.

I still have some very high frequency hash that I thought could have been my speakers but now I have two EVM 12L's so I think I can rule that out.

[pine]

Thanks very much for this information, this all is making more sense to me now

[martin manning]

I think Pine had it right. The way this is wired you have a low pass filter made up of the 150K resistor coming from the V2B coupling cap and the treble bleed cap. The signal is taken from the junction of the 150K and the cap, and the trimmer basically lifts the cap from ground to a varying degree.

The -3dB frequency, as in 1/2PiRC, is therefore really determined by the cap value, and the trimmer then controls the amount of bleed. Using a 0.001u cap, the cut-off will be 1062 Hz. 470pf raises it to 2259Hz.

[Structo]

I thought that a low pass filter had the cap to ground and a high pass filter has the resistor to ground.

[img:223:174]http://hyperphysics.phy-astr.gsu.edu/HB ... e/rclo.gif[/img]

Attached is how Gil has the treble bleed circuit in one of his amps.

You can't see the 150K resistor but it is directly below the eyelet on the top right of the daughter board.

The cap is grounded to the ground connection between the two bypass R/C of V2.

So what we have here is a low pass or high cut filter right?

[martin manning]

Right, so you have a node connecting the 150K, the trimmer/cap to ground, and the lead to the Ratio pot.

The signal (Vout in your schematic) comes from the junction of the 150K and the trimmer and goes to the Ratio pot, so the R in your schematic is the 150K.

The order of the cap and the trimmer could be switched, and it probably wouldn't matter. Think of those two as the lower leg of a voltage divider that has a pure resistance (the trimmer) and a frequency dependent resistance (the cap) in series.

MPM

Edit:

After more thought, and a little math, I'm pretty sure the order of the cap and trimmer doesn't matter, but the trimmer resistance does change the -3dB frequency.

The Z of the cap has to be lower (need a higher Frequency) to reach -3dB with increasing trimmer resistance. In any case, it is a low pass filter, and the 150K is the series resistance, but you can't use the 1/(2PiRC) to get the turnover frequency.

[talbany]

Thought this was kind of interesting... A back shot of the rare 150w ODSR w/trem...Notice the Taper and Trigger...Anyone know what the trigger is?... My guess would be the OD entrance... If that's the case I wonder if he is bleeding high's right there at the OD entrance... If he is bleeding highs @ the Level/OD Master as discussed here that would be a fairly long run to the opposite side of the chassis to reach the level pot..Also keeping in mind your coming off the last gain stage so you would most likely need to shield that run..One would think if you were to put a taper control it would be on the front or inside...Things that make you go HMMM!! I've built a few with a switch on the back (no room on the front) bleeding highs right off the OD entrance ...One side of the switch is a 150k the other is a 220k...Worked fine



Tony VVT

[jelle]

Trigger is OD entrance. For some reason, HAD removed it.
Taper is High Frequency Taper.

Jelle

[ElectronAvalanche]

Hi Jelle,

Dumble did not remove the Taper and Trigger on the 150W ODS but moved the controls to the front using dual-concentric pots for the OD-Content and Volume. So there is OD content and Trigger, Volume and Taper on two pots on the front. Trigger is the timmer setting the amount of signal INTO the OD and Taper is a HF bleed or simple Tonecontrol.

Cheers,

Electron

[martin manning]

Am I right in saying that the value of the resistor changes how much of the highs you remove and the value of the cap changes which specific frequencies you remove? Would lowering the value of the cap to 470pF target higher frequencies than the 1000pF or lower frequencys? "

After a little more thought and a little more math, I think I have this figured out. The thing has a shelving response (trebble cut) with the min and max attenuation above the cut frequency set by the 150K series resistor and the trimmer setting. The -3dB turnover frequency defies a nice tidy formula, but you can get pretty close using 1/(2*Pi*R*C), where R is the series resistor. The attached plot shows the response for the proposed 0.001u and 250K trimmer.

This was an interesting exercise, but maybe I'm easily amused.


MPM

[Structo]

Well it looks good on paper or should I say on my monitor.

I just don't "hear" that kind of attenuation in my amp.