ROG Thunderchief HUGE volume issue

[ElectricDruid]

I wonder if adding the tonestack would lower the volume enought to a normal level.

A Big Muff style tonestack would lower the volume to about -12dB..
There is much more road till -86dB..

Why do you say -86db? Isnt 2m2 in series to de 100k pot producing a -10db attenutation?

Yes, I was wrong. I dropped a "K" somewhere, somehow. Still, I don't agree with -10dB. 100K / (2200K + 100K) = 0.0435 = -27.23dB
Incidentally, I would have corrected this in the original post when I noticed it, but the "modify" button disappears after a short while, so I wasn't able to, so I'm kind of glad it came up.

[Rob Strand]

Why do you say -86db? Isnt 2m2 in series to de 100k pot producing a -10db attenutation?

You need to be clear where you put the 2M2.

In your first post you say:

"I had to put a 2M2 in series wich the ouput which sounds crazy but actually made it."

So it is:

1) I'm assuming you placed the 2M2 between the *pot wiper* and the *output jack*.   That forms a divider with amplifier input impedance.   If the amp is 1M input impedance then the divider is 1M / (1M + 2M2) = 0.3125 or -10.1dB.
[FWIW, the 1M input impedance is an estimate.  I don't know what the input impedance of your amp really is.]

or

2) Many people in the thread are assuming you put the 2M2 between the last 15k & 2n2 cap and the *clockwise terminal* of the 100k pot.   That's going to give you a divider of 100k / (100k + 2M2) = 0.04348 or -27.2dB.

Only you can confirm what you did.

I'm reading it as case 1.    The fact the hiss has gone up supports that as the 2M2 in case 2 would add a lot less hiss than case 1.

All we are doing here is determining what attenuation you actually got in your experiment.

The suggestion to use the L-pad is a way of getting the desired attenuation without affecting the circuit's behaviour *at all*.  (and without adding hiss).

[Atodovax]

Why do you say -86db? Isnt 2m2 in series to de 100k pot producing a -10db attenutation?

You need to be clear where you put the 2M2.

In your first post you say:

"I had to put a 2M2 in series wich the ouput which sounds crazy but actually made it."

So it is:

1) I'm assuming you placed the 2M2 between the *pot wiper* and the *output jack*.   That forms a divider with amplifier input impedance.   If the amp is 1M input impedance then the divider is 1M / (1M + 2M2) = 0.3125 or -10.1dB.
[FWIW, the 1M input impedance is an estimate.  I don't know what the input impedance of your amp really is.]

or

2) Many people in the thread are assuming you put the 2M2 between the last 15k & 2n2 cap and the *clockwise terminal* of the 100k pot.   That's going to give you a divider of 100k / (100k + 2M2) = 0.04348 or -27.2dB.

Only you can confirm what you did.

I'm reading it as case 1.    The fact the hiss has gone up supports that as the 2M2 in case 2 would add a lot less hiss than case 1.

All we are doing here is determining what attenuation you actually got in your experiment.

The suggestion to use the L-pad is a way of getting the desired attenuation without affecting the circuit's behaviour *at all*.  (and without adding hiss).

Thanks Rob! Sorry everyone. I wrote "at the output" and that is totally misleading and incorrect. What i did add in fact is a 2M2 resistor in series before the pot .  THat would be. From the junction of 15k and 2n2 ---------- 2M2 ----------- pin 3 of the 100k pot. I didnt have the oportunity to solder the L pad yet but i do want to emphasize that the pedal is in fact working now and sounds pretty good, but the 2M2 series resistor did add some hiss. Its just that without the 2M2 resistor, the pedal was insanely loud. I mean, really really loud. i checked the feedback path and everything seems fine. Im really curious if someone had the same impression before. I've seen videos on Youtube and even though there are very few the pedals do not seem to sound so loud there.

[Rob Strand]

Thanks Rob! Sorry everyone. I wrote "at the output" and that is totally misleading and incorrect. What i did add in fact is a 2M2 resistor in series before the pot .

OK cool, that clears that up! 

So you are attenuating by about 27dB.

I'm surprised the hiss went up so much.   It will go up just the same.

If you use an L-pad with R1=100k and R2=4.7k that will give you 27dB attenuation.  You can see if the hiss drops.  (In theory the noise should be lower by a factor of *at least* 2).

Just for comparison with other pedals:  many diode-based pedals output +/-0.6V and the Fuzz-face outputs about +/- 0.22V to +/- 0.35V (depending on specific resistors).  If we assume the JFET output swings +/- 4.5V then  27dB attenuation will drop that to +/- 0.2V.   So you might be able to use a little less attenuation.

[anotherjim]

But doesn't this pedal include a speaker sim filter in the output? In which case it ought to work driving a full-range power amp input, not a normal amp input channel with all of its signal gain and a real guitar speaker.

I think a better attenuation is 100k series into a 4k7 log pot for less resistor hiss. That's closer to the 100k output load with just the 100k pot.

[Rob Strand]

I think a better attenuation is 100k series into a 4k7 log pot for less resistor hiss. That's closer to the 100k output load with just the 100k pot.

I was thinking the same thing but you need to buy a new pot.   As far as noise goes it would be more like the original 100k dialed back to low volume.

The noise resistance of the 100k pot + LPAD will be about 25k which is getting down towards guitar pickup noise levels.

[antonis]

Have we any info about the power amp used..??

[duck_arse]

.... can you measure the resistance to ground at the 2M2//pot junction, please?

.... The resistance to ground is essentially de 100k pot. ....

in theory, and on paper [the circuit diagram], and in a 100% problem free working build with happy volume, yes, 100k. but if the CCW leg connection to ground is bad, odd things will occur. so, measure from the 2M2 resistor and CW pot lug junction to a ground point - not to a pot lug. this will prove the pot connections are good. make sure the resistance to ground does not vary when you up/down the volume knob.

[anotherjim]

IMO, the output stages of these amp-in-a-box pedals need some work. If it's meant to drive an existing guitar amp in the usual way, it doesn't need a speaker sim but does need some attenuation. Used like this, I think you're expected to use a clean channel, not a high-gain one. If you want to use it as an "add" to an already high-gain sound it probably will be too loud. This isn't necessarily the wrong thing to do in search of a sound but I've heard of Alembic F2b used like this and their volume setting too is touchy -  close to off in many cases.

If it's meant to work as a DI feed to any line input device, it needs the speaker sim and not so much attenuation and pot alone should be enough.

There's another in-between situation. Driving the power amp input or FX return of a guitar amp. I don't think many players like that idea since it renders their amps' existing preamp channels inoperable - but it's probably the best way to use an amp sim  -  IMHO.

I think it's possible to have output option switching to serve the different needs. Personally, I'd add a buffer to the speaker sim output on its own jack for DI and attenuate the output to a "normal" out jack.

[Atodovax]

IMO, the output stages of these amp-in-a-box pedals need some work. If it's meant to drive an existing guitar amp in the usual way, it doesn't need a speaker sim but does need some attenuation. Used like this, I think you're expected to use a clean channel, not a high-gain one. If you want to use it as an "add" to an already high-gain sound it probably will be too loud. This isn't necessarily the wrong thing to do in search of a sound but I've heard of Alembic F2b used like this and their volume setting too is touchy -  close to off in many cases.

If it's meant to work as a DI feed to any line input device, it needs the speaker sim and not so much attenuation and pot alone should be enough.

There's another in-between situation. Driving the power amp input or FX return of a guitar amp. I don't think many players like that idea since it renders their amps' existing preamp channels inoperable - but it's probably the best way to use an amp sim  -  IMHO.

I think it's possible to have output option switching to serve the different needs. Personally, I'd add a buffer to the speaker sim output on its own jack for DI and attenuate the output to a "normal" out jack.

WOuld you also remove both low pass filters and attenuate to use on a normal amp? I just want to use this pedal with a guitar amp. I dont intend to use it as a preamp + a power amp section or DI. Even though the two low pass filters act as the "speaker simulator" , they reduce some of the harshing highs. I like it with both filters on. Or is the speaker simulation inside the feedback loop on Q 3 / 4?

[Atodovax]

OK, never mind, the "speaker simulation" is aproached by the final dual low pass filter.

[Rob Strand]

OK, never mind, the "speaker simulation" is aproached by the final dual low pass filter.

I don't really see it as a "speaker sim" it's just a low pass filter which removes the high frequency rubbish.   How much HF filtering you add is a choice, it's part of the sound.

Blues Breaker
http://www.generalguitargadgets.com/pdf/ggg_mbb_sc.pdf

Fancy Lime Posted One the other day,
https://www.diystompboxes.com/smfforum/index.php?topic=129605.msg1253265#msg1253265

Incidentally, both use 100k output pots but they are fed with low impedances.  The signal levels means the pot will be set backed off which lowers the impedances feeding the amp and also lowers the noise.

As far as the noise goes I can't help but think your amp has got something to do with it.  Normally you noise isn't so obvious.   Maybe the input stage of the amp has a problem or uses bipolar technology opamps. 
What is it?

[Atodovax]

There's a way you can add an output attenuator without affecting the impedances in the circuit, and in fact without affecting them for any pot setting.




Notice that R1 + (R2 // 100k pot) = 100k

You can use this L-pad attenuator calculator:

http://www.sengpielaudio.com/calculator-Lpad.htm

Speaker Impedance Z:      Enter 100 ohms (enter 100 for 100k, entering 100000 is just making things messy)
Enter attenuation as a positive number (eg 10 for 10dB)
Read off R1 and R2 as if they are in k ohms.

An L-pad attenuator provides attenuation without changing the input impedance.

Thanks Rob and everyone!
I finally settled with the L-pad attenuator using 100k for R1 and 10k for R2 just before the 100k pot. That gave me something around 20db attenuation which worked really well. Now the volume control is a little bit more usable although the pedal is still pretty loud even with the 20db attenuation. So thanks everyone . Sorry for the delay but i wanted to share that this ended up working really well.
I wonder if without the attenuation, this pedal could be used as a preamp just before a power amp stage?