Clipping from the master volume?

[agedhorse]

2 hours ago, BassmanPaul said:

@Downunderwonder I hope you're keeping your feet dry my brother. 

Yeah, and I thought we got some rain... nothing like you guys!

[BassmanPaul]

We just got snow and piles of it!! Biggest snow storm in decades! Some of the neighbours got together with our snow shovels and Ice picks and cleared the snow from driveways and walkways.  it's not work when you're with a bunch of friends just fun!  

Edited February 2, 2023 by BassmanPaul

[BassmanPaul]

@Jaybeevee sorry for the derail but weird weathera ffects us all!! LOL

 

[Jaybeevee]

On 02/02/2023 at 06:05, agedhorse said:

Knob position has nothing to do with how much power is being delivered. This misunderstanding may be part of the problem.

I think in this case it does. it is apparently a different approach to that used in most amps. This is a point made by the builder leading me to understand that the pot position does relate to the power being delivered. 

On 01/02/2023 at 22:12, Downunderwonder said:

Put bass into one amp and take the preamp out to the other amp's return, and on to the cabs. Play with gains to see if it's still impossible to get volume.

Good idea, but I have returned it now. I wait and see what comes back

On 01/02/2023 at 21:54, Bill Fitzmaurice said:

Seems like a good idea, but our hearing isn't linear with respect to power. It's logarithmic, requiring ten times the power to sound twice as loud.

This is knowledge above my pay grade, but in terms of the pot used on the master, the builder specifically talks about this aspect and that the power delivery from the amp is via a linear (not sure of the technical terms) pot, and the user can expect to run the master at a higher setting than would be normally expected.

[warwickhunt]

1 hour ago, Jaybeevee said:

This is knowledge above my pay grade, but in terms of the pot used on the master, the builder specifically talks about this aspect and that the power delivery from the amp is via a linear (not sure of the technical terms) pot, and the user can expect to run the master at a higher setting than would be normally expected.

 

What @Bill Fitzmaurice was saying is that 'scientifically' (not made up stuff by musicians or amp builders), for an amp to register as twice as loud as another amp you would need to multiply the power output of the lower amp x10 to be twice as loud; a 1000w amp is twice as loud as a 100w amp (all other factors being equal).

 

Just an observation but maybe if you are getting unwanted clipping out of a 400w amp and the output attenuation was less than 50% of it's possible travel/rotation (you said it was on 11 which I assume to mean viewing it as a clockface), then maybe the amp designer needs to rethink things.  Unless of course there is a fault with the amp.  

[Bill Fitzmaurice]

1 hour ago, Jaybeevee said:

I think in this case it does. 

Most assuredly it does not. Power output depends on a number of factors, starting with the voltage output and frequency response of the bass, ending with the actual impedance of the speakers, which isn't a constant. It varies with frequency. This is a plot of the power output of an amp across the frequency spectrum into a typical 8 ohm twelve in a ported enclosure, driven with 28.3v, which is nominally 100 watts. There's nothing linear about it. This, BTW, is why loudspeaker engineers don't deal in watts. We deal in volts, which are a constant into any impedance load.

 

 

 

 

Edited February 3, 2023 by Bill Fitzmaurice

[Jaybeevee]

2 hours ago, warwickhunt said:

Just an observation but maybe if you are getting unwanted clipping out of a 400w amp and the output attenuation was less than 50% of it's possible travel/rotation (you said it was on 11 which I assume to mean viewing it as a clockface), then maybe the amp designer needs to rethink things.  Unless of course there is a fault with the amp

Thanks, yep.. when i posted the thread this is exactly what I was wrestling in my mind as this is what I was seeing. The builder didn't answer me dirctly on this point. I will ask him directly again. 

 

1 hour ago, Bill Fitzmaurice said:

Most assuredly it does not. Power output depends on a number of factors, starting with the voltage output and frequency response of the bass, ending with the actual impedance of the speakers, which isn't a constant. It varies with frequency. This is a plot of the power output of an amp across the frequency spectrum into a typical 8 ohm twelve in a ported enclosure, driven with 28.3v, which is nominally 100 watts. There's nothing linear about it. This, BTW, is why loudspeaker engineers don't deal in watts. We deal in volts, which are a constant into any impedance load.

 

 

 

 

Wow, great info, really insightful. So am i understanding..? the driver input power in watts (same as the amp output power going into the speaker) varies considerably with regards to the frequency of the signal, the signal being volts. But what difference will a linear volume pot Vs a Log volume pot have on the user? based on my original query that volume at 11o'clock causing the amp to clip was both new and suspect to me? I was given the understanding that as a user, i can expect to set the master volume higher in it's range than i would normally expect to.. er go this is normal for this amp. Playing my Stingray wide open, with the pre amp (of the amp) set to it *crunch* position (on the gain dial) and the 6db drive button engaged (within the design intent of the pre-amp and without clipping at lower volumes) and then not getting past 11 o'clock  on the master without clipping seemed like an issue, especially as it was (although quite loud) not loud enough to keep up a loud drummer.

[warwickhunt]

I'm going to have a punt that this is a Handbox product!  

[Bill Fitzmaurice]

1 hour ago, Jaybeevee said:

not getting past 11 o'clock  on the master without clipping seemed like an issue, especially as it was (although quite loud) not loud enough to keep up a loud drummer.

It's an issue, but not one necessarily caused by the pot. The total voltage gain from pickup to speaker starts with the pre in your bass and ends with the output stage of the amp, with every gain and EQ stage in the chain making its own contribution. Google 'gain staging'.

That said, you've got the effect of the pot backwards. Assuming you have a linear pot wide open versus at half the attenuation at the halfway point is -3dB. That's audible, but just. It's not half volume, which is -10dB. A log taper pot at half is -10dB compared to at full. Therefore the linear pot goes louder earlier in its rotation, not later. Some amps did so on purpose, so that someone trying one in a shop would be impressed at how loud it got at, say, a setting of 3. They wouldn't have been able to realize in a shop that anything past 4 didn't get any louder. 🙄

Edited February 3, 2023 by Bill Fitzmaurice

[2pods]

Why not just tell us what the amp is ?

[Mottlefeeder]

With regard to the use of a linear volume pot, the manufacturer may have taken the option recommended by Rod Elliott and others, and used a resistor between the pot wiper and pot ground to convert the linear effect into a logarithmic one with a smoother characteristic than a cheap log pot would give you.

David

[2pods]

I remember my old Trace Elliot manuals saying don't put the master any higher than 4, which I think was

about 10 o'clock. The rest of the control was only if you were using it as a pre-amp into another amp.

 

Possibly something like this ?

[Jaybeevee]

4 hours ago, 2pods said:

Why not just tell us what the amp is ?

Shucks, the point of my asking the initial question was just to help me understand something I haven't seen before. to try to figure out if I have an issue or not. I´m not sure naming the product is appropriate is all. I wouldn't like to suggest an issue that I am mistaken about (and it seems I am to some degree). The guys are really service minded and I don't want to betray that. It's no biggie, just being respectful

Edited February 3, 2023 by Jaybeevee
typo

[Jaybeevee]

2 hours ago, 2pods said:

I remember my old Trace Elliot manuals saying don't put the master any higher than 4, which I think was

about 10 o'clock. The rest of the control was only if you were using it as a pre-amp into another amp.

 

Possibly something like this ?

wow, never heard anything like that before. I can ask the question

[DGBass]

I've been reading this thread with interest and it reminded me of a similar sounding setup used on an old Warwick ProFet 3.2 amplifier that I used for a time which had linear volume pots by design. I initially thought there was something wrong with it as the pre-amp and master knobs didn't behave the same as just about every other amp I had ever used. The ProFet had a clip led on the input and as long as I kept input position just so the clip led would flash intermittently or not at all everything was fine. That was usually around 2 or three oclock. The master was unusual as well and I'm pretty sure it was booming out all its power around one or two oclock but very quiet around nine or ten oclock when most other amps are getting noisy. These were notched pots as well so it was difficult to use the amp at low volume, one notch up was literally the difference between medium loud and full power. 

Changing the pots to smooth ones did help but I read that Warwick themselves sorted the issue in the Profet 3.3 with log pots. The older 3.2's never got much love but they were great amps once you understood them imho. If you've ever been servicing an amplifier and fitted a linear pot where a log pot once was or vice versa, you will realise how quickly a change like that can make an amplifier almost unuseable. For the OP I guess if you have a clip led, dont make it flash no matter what o'clock that is and I'm wondering if there is a manual for your amp with guidance on how to set the input and output knobs for best results? Fingers crossed the builder hadn't got linear pots mixed in with his log pots parts tray when the amp was built. 🤔

[agedhorse]

14 hours ago, Bill Fitzmaurice said:

It's an issue, but not one necessarily caused by the pot. The total voltage gain from pickup to speaker starts with the pre in your bass and ends with the output stage of the amp, with every gain and EQ stage in the chain making its own contribution. Google 'gain staging'.

That said, you've got the effect of the pot backwards. Assuming you have a linear pot wide open versus at half the attenuation at the halfway point is -3dB. That's audible, but just. It's not half volume, which is -10dB. A log taper pot at half is -10dB compared to at full. Therefore the linear pot goes louder earlier in its rotation, not later. Some amps did so on purpose, so that someone trying one in a shop would be impressed at how loud it got at, say, a setting of 3. They wouldn't have been able to realize in a shop that anything past 4 didn't get any louder. 🙄

For clarification, a linear pot at 1/2 rotation is 1/2 the input voltage or 6dB of voltage attenuation which is 1/4 the power. 
 

Log pots are available in various taper rates or laws, this affects the output versus rotation curve and is part of the “user interface experience” (for lack of a better term).

[agedhorse]

19 hours ago, Jaybeevee said:

I think in this case it does. it is apparently a different approach to that used in most amps. This is a point made by the builder leading me to understand that the pot position does relate to the power being delivered. 

Good idea, but I have returned it now. I wait and see what comes back

This is knowledge above my pay grade, but in terms of the pot used on the master, the builder specifically talks about this aspect and that the power delivery from the amp is via a linear (not sure of the technical terms) pot, and the user can expect to run the master at a higher setting than would be normally expected.

The position of the control is only one factor in the output power an amp delivers, but is interactive with everything else in the signal path.
 

If you turn the bass volume down by 6dB and increase the amp’s master volume by 6dB, the amp delivers exactly the same power that it did before. This is an example of the position of the master not dictating the power that the amp delivers.