Amps with gain and master volume ..wattage

Barney

just thinking tonight about amps with gain and master volume ...if its a 40 watt amp to get the full volume do both the gain and the master need to be on full...or can we get the same volume by having gain on maybe 3 and master on full..?

ICBM

You'll probably find it reaches full volume with the master somewhat below full, even on a clean sound - and definitely on an overdriven one. With the gain up far enough that the preamp is into distortion it will probably reach full output power well below full, and just get more distorted above that as the power stage starts to overdrive as well.

When I test amps for maximum clean power I put the MV up all the way, and it's common for a guitar-level signal to push the power amp to full clean power with the gain only at 9 o'clock, or even less.

This also means you can't make any deduction about the power the amp is putting out based on the control settings - it could easily be on full power with both under half. The EQ setting often makes a big difference too.

samzadgan

i always thought the gain (assuming its pre amp gain) can be left at a lower level and with the master volume being cranked. The way i think about it is that master volume will make use of your power tubes, which may still distort at high volumes, but will sound different to the distortion you get from the pre-amp by cranking the pre-amp volume/gain.

then again…i could be completely off!

Barney

thanks ...its just something i was thinking about tonight ...as in how much gain do i need to get maximum volume .....i would like to think the volume is the overall out put and the gain alters how much distortion is added without adding or taking away from the volume..

ICBM

The only way to get power valve distortion is to crank the master *and* have the preamp gain up high enough to push the whole amp into distortion. It has to be loud - unless you use an attenuator. It does sound different, but not as much as is usually though - certainly not "preamp bad, power amp good".

Actually, many classic non-MV amps don't even produce pure power valve distortion, contrary to popular myth. Usually other stages distort first or very shortly afterwards, producing a mixture of preamp and power valve distortion. (Also including phase inverter distortion, which is a "preamp valve", but usually thought of as part of the "power amp".)

A good example is the classic Marshall non-MV circuit. The tone stack driver and the phase inverter produce a lot of the distortion even though the amp has no MV. And an amp with fairly pure power valve distortion - at least until it's really cranked - is a Silverface Fender Twin… not most people's idea of a good overdriven tone.

Barney

ICBM said:

The only way to get power valve distortion is to crank the master *and* have the preamp gain up high enough to push the whole amp into distortion. It has to be loud - unless you use an attenuator. It does sound different, but not as much as is usually though - certainly not "preamp bad, power amp good".

Actually, many classic non-MV amps don't even produce pure power valve distortion, contrary to popular myth. Usually other stages distort first or very shortly afterwards, producing a mixture of preamp and power valve distortion. (Also including phase inverter distortion, which is a "preamp valve", but usually thought of as part of the "power amp".)

A good example is the classic Marshall non-MV circuit. The tone stack driver and the phase inverter produce a lot of the distortion even though the amp has no MV. And an amp with fairly pure power valve distortion - at least until it's really cranked - is a Silverface Fender Twin… not most people's idea of a good overdriven tone.

so maybe the best way to set a amp would be setting the master first to the volume needed then add the gain to the desired amount and go from there ?...just a lot of times i do it the other way round but maybe not the best way thinking about it...
BTW im talking about loud live band playing ....

richardhomer

Barney;160558" said:

so maybe the best way to set a amp would be setting the master first to the volume needed then add the gain to the desired amount and go from there ?...just a lot of times i do it the other way round but maybe not the best way thinking about it...

BTW im talking about loud live band playing ....

Not really. On a none MV amp, the volume control determines the amp's overall level, from a given input - assuming the amp is working within its clean headroom, a higher output guitar will be louder than a lower output one.

With an MV amp, the MV determines the MAXIMUM output level (again assuming the amp is operating within its clean headroom). The volume will however be dependent on the gain/drive control's setting. Set low, the amp will become quieter, set high, it will be louder....

The aim is to balance the two controls in such a way that they give you the gain characteristics that work best with your playing dynamics, at the right level to fit in with a band's mix.

Many players perceive very high levels of gain fail to 'cut through' at higher stage levels - presumably because the dynamics of their playing are heavily compressed under hi gain - therefore 'digging' doesn't get you 'heard' more.

As I said, the trick is balance. You might find less gain and more MV works best for you in a live situation.

koss59

@ICBM any chance you could give us a more detailed explanation of Badcats new Kmaster? They aren't explaining it very well but say that you can control pre and power amp overdrive separately.

Thanks!

ICBM

koss59 said:

@ICBM any chance you could give us a more detailed explanation of Badcats new Kmaster? They aren't explaining it very well but say that you can control pre and power amp overdrive separately.

Thanks!

No idea, sorry. Not familiar with it.

To control preamp and power amp overdrive separately you only need gain controls at different points in the circuit anyway - any master volume amp can do that. If you want to control power amp overdrive independent of final volume you need either an attenuator or power scaling… nothing much new to be done there.

Does "not explaining it very well" correspond to "obfuscation and re-packaging a standard concept for marketing purposes", perhaps?

ecc83

The only "fair" and consistent test of a guitar amplifier IMO is with all controls at max and injecting a specified input voltage (which will be VERY wee in many cases and getting clean, i.e. noise free results needs care.

Of course, slamming everything to max will probably cause some amps to go instable, but I only dealt with them as didn't!

I shall not go any deeper into the test procedures I used, not mine to tell but if other amp makers would like to weigh in?

On the subject of pre versus power amp gain. Remember, not all OP valves have the same sensitivity, by a long way! A pair of 6V6s will demand a much greater drive from the PI than EL84s for instance. Then, the application (or not) of negative feedback will muddy the waters!

Dave.

Barney

thanks for the input everybody....just something i was thinking about last night...i remember a couple of years ago i had a HRD on full volume ..it was quite a big place no backline ..i had the gain up as well but was getting far to much distortion ...but by backing the Gain off i didnt really use any volume just got increased clarity...i know if i backed it right off i would lose volume but backing of so far i didnt loose any at all..

ecc83

Barney said:

thanks for the input everybody....just something i was thinking about last night...i remember a couple of years ago i had a HRD on full volume ..it was quite a big place no backline ..i had the gain up as well but was getting far to much distortion ...but by backing the Gain off i didnt really use any volume just got increased clarity...i know if i backed it right off i would lose volume but backing of so far i didnt loose any at all..

This: http://www.google.co.uk/imgres?imgurl=http://www.audioholics.com/audio-amplifier/product-managing-receiver-platforms-power-ratings/distortion.jpg/image_preview&imgrefurl=http://www.audioholics.com/audio-amplifier/product-managing-receiver-platforms-power-ratings/product-managing-receiver-platforms-power-ratings-page-2&h=245&w=400&sz=16&tbnid=jxN7nbno4RWtcM:&tbnh=90&tbnw=147&zoom=1&usg=__2Ospe6bOmEPsBuRHzbrVXXqcykI%3D&docid=zyGm_FcRwrf9eM&sa=X&ei=im_8UvaYEY6QhQfimYG4Dw&ved=0CDEQ9QEwAg

is hopelessly out of scale (HTF do we post attachments?!!) but it shows the principle.

Once you reach the power amp's limit you do not increase output, merely produce more distortions. Then, "gain" controls on guitar amps almost never are, they are simply interstage volume controls.

The above curve also shows why simple "solo boosts" hardly ever work, once you have got close to the power limit you have had it all!

Dave.

ICBM

Exactly. When you had it full up the amp was so far into power amp distortion it just produced mush - when you backed off the gain, for quite a long way there was still enough gain to overdrive the power amp so the volume didn't go down, but because it was less distorted it became clearer. It would probably have sounded perceptively louder - in fact, it might even have been slightly louder, since an overloaded power amp causes more sag in the power supply (even in an amp without a valve rectifier) which reduces the maximum power a bit.

What a lot of people forget about amps like these is that the controls are not at all 'linear'* - in fact this is one of the major complaints about them - the volumes take you to full output power much too soon, normally below halfway on the numbers, and then the amp just gets more and more distorted and saturated. This makes it impressively loud at low settings ("see how loud it is, and it's only on 3!" - probably deliberately, to make it win in a shop shoot-out… not realising that it won't get any louder beyond 4) but makes the controls too touchy at low settings and means that you have no idea how little headroom you really have if you're used to amps with a more sensible range.

(*Technically, the problem is that the control *is* linear! The human ear doesn't respond that way, and you actually need a Logarithmic taper to produce a natural-sounding sweep. Since Log pots are standard for gain and volume controls - they're often called 'Audio Taper' exactly for this reason - it must have been a deliberate decision for Fender to use a Lin one.)

ChrisMusic

Lets see if I can get that graph up, it is well worth a look @ecc83.

http://www.audioholics.com/images/powerdistortion.jpg

Just use the image URL i.e. http:// www.audioholics.com/images/powerdistortion.jpg

without the space between // and www - which I had to put in so it will show as text on here

The pic above is same without that space, oh and you may need to refresh your browser to see it - hope that helps  

ecc83

ChrisMusic said:

Lets see if I can get that graph up, it is well worth a look @ecc83.

http://www.audioholics.com/images/powerdistortion.jpg

Just use the image URL i.e. http:// www.audioholics.com/images/powerdistortion.jpg

without the space between // and www - which I had to put in so it will show as text on here

The pic above is same without that space, oh and you may need to refresh your browser to see it - hope that helps  

Thanks Chris.

No didn't help! This PC numpty does not get it. Why can't we just send attachments as per Home Recording.com?

Dave.