NAD: It's here! AFD100 in the house!

[Twinfan]

Home levels.  Power on 0, Master around 7-8.

In rehearsal it's been fine too - power around 5-6.

[HairyChris]

Intermittant amp glitches are the worst, especially on something that new.  :(

3 strikes & out?

[purpleplexi]

How are you finding the #34 mode - any use for it?

[Twinfan]

Nope.  I find it cr@p to be honest.  Too thin and not enough gain.  I can't believe a JCM800 sounds like that????

[Brow]

Nope.  I find it cr@p to be honest.  Too thin and not enough gain.  I can't believe a JCM800 sounds like that????

The real 1s don't, but they have to be cranked up real loud for them to get their balls

[Twinfan]

I get that, but with the power scaling it should sound good at low volumes?

It's the same at rehearsal too, around half power  :?

[HTH AMPS]

the #34 mods add even more treble to an already trebley amp - not surprised you've found it to sound that way Dave.

[Dmoney]

I get that, but with the power scaling it should sound good at low volumes?

It's the same at rehearsal too, around half power  :?

Do any of the low power tricks work and sound good? I've never played any amp with power scaling or anything, the closest thing I have is an attenuator.

I found that... using a lot of attenuation sounds pretty bad... that's different to using power reduction techniques (which all sound different according to design and implementation) but if you're playing through a normal rig, using low power, you're speakers are not getting driven much at all... I think that plays a part... also, when I've played with PPIMV, I find using a low PPIMV setting with a really high level setting on an average pre-PIMV creates a harsh sound which is probably the phase inverter getting smashed to bits by the preamp signal. I wouldn't be surprised if you could get that tone using power scaling.

This has led me to the conclusion that using a lot of attenuation or indeed anything to reduce volume to a low (loudish speaking level maybe) volume is never ever going to sound that good. All the power reduction tricks have their downsides from what I've read so the quieter you try to make a powerful amp, the more you have to compromise on tone.

I don't think "power scaling", and we need to remember that term applies to a specific circuit NOT found in the AFD, and similar things are the complete solution to this need for less volume while retaining tone.  It just seems to be addressing 1 factor of many in what makes your tone up.

that said... it may well be the best technique anyone has come up with so far.

[Twinfan]

Power Scaling works.  My MJW Orion had it, and sounded great, and the AFD100 in AFD mode sounds great too.  Very, very good.

The PPIMV issue is that it affects the Presence circuit and at low volumes you have full presence - very trebly and harsh.  The more volume you give, the lesser the effect, so it's a compromise.

the #34 mods add even more treble to an already trebley amp - not surprised you've found it to sound that way Dave.

Is that what the mods are?  I didn't know that.  No wonder it's not my cup of tea!  I *think* there are only 2-3 changes from a standard JCM800 in the mod, so do you know what they are?

[HTH AMPS]

Power Scaling works.  My MJW Orion had it, and sounded great, and the AFD100 in AFD mode sounds great too.  Very, very good.

The PPIMV issue is that it affects the Presence circuit and at low volumes you have full presence - very trebly and harsh.  The more volume you give, the lesser the effect, so it's a compromise.

the #34 mods add even more treble to an already trebley amp - not surprised you've found it to sound that way Dave.

Is that what the mods are?  I didn't know that.  No wonder it's not my cup of tea!  I *think* there are only 2-3 changes from a standard JCM800 in the mod, so do you know what they are?

yes, I know the circuit changes for the #34 mods.

[Twinfan]

Secret then are they?  ;)

I found the schematic online and it seems pretty simple - just some bypass stuff.  That would explain the extra hiss and noise too...

[Dmoney]

Power Scaling works.  My MJW Orion had it, and sounded great, and the AFD100 in AFD mode sounds great too.  Very, very good.

The PPIMV issue is that it affects the Presence circuit and at low volumes you have full presence - very trebly and harsh.  The more volume you give, the lesser the effect, so it's a compromise.

I think it could sound good... but is it honestly as good as the amp cranked up with your cab getting a healthy dose of voltage? How low is too low is what I'm interested in. I'm sure there is a point where the speakers just don't get that much drive to them and the response of your speakers/cab is less than ideal.

I understand that as you decrease the output level you get less and less negative feedback into (usually into) the phase inverter. However I find that when using a typical high gain master volume amp for example, once I get down to a certain volume I need to crank the presence control more (decreasing high f in the nfb further) to increase the high end again, otherwise I get a really wooly 'duvet over the cab' sound. That's with a normal master volume setup... that sounds kind of fizzy if you put too much presence on. Having the depth control at low volumes is good too. Thats all without scaling or a PPIMV. The point being that the relationship of the MV/PI/Output/NFB is a constant.

Different PPIMV's give you different results. The one i used was a potential divider on the output of the PI using a dual 1M pot. You're right, the more I turned it down the less the pres and depth controls worked... but if I then (just for the sake of an experiment) turned the pre-PIMV up, I found I got some pretty horrid distortion in addition to fizz from what you describe as the almost maxed out presence (not that all amps without NFB sound fizzy). I put the noise down to overdrive characteristics of the long tail pair phase inverter taking a full preamp signal and with NFB working against the PPIMV.

I did this in a JCM800. Standard master volume on max, and the PPIMV REALLY low. Now you could say that turning down the MV and turning up the PPIMV would solve it... and it does. It isn't power scaling however I have read that Kevin O'Conner has at some point recommended the use of a Master Volume in conjunction with particular power scaling circuits of his to act as a 'drive compensator'. When using negative feedback & scaling in the same power section, I think the PI needs to be scaled also to maintain the PI/Output/NFB relationship to a normal MV or PPIMV, otherwise you'd run into this PPIMV Presence-on-max/distortion issue again. The point here is that these power scaling ideas can vary and may not all work as well as one another.


I want to try an Egnater Rebel 20. The 'watts' controls aren't power scaling controls like the London Power circuits at all. I want to hear how well that works.

[Twinfan]

I think it could sound good... but is it honestly as good as the amp cranked up with your cab getting a healthy dose of voltage?

It's just different.  You don't get the speakers pumping of course, but then who actually plays at that volume regularly anyway?  And does everyone actaully want speakers flapping?

[Dmoney]

I think it could sound good... but is it honestly as good as the amp cranked up with your cab getting a healthy dose of voltage?

It's just different.  You don't get the speakers pumping of course, but then who actually plays at that volume regularly anyway?  And does everyone actaully want speakers flapping?

No I agree with you... but I think the sales jargon with power scaling and similar features is more often than not about obtaining 'that cranked tone and bedroom level' which to me means cranked amps pushing speakers, but that sales speak is really just a bunch of cool words that sounds good in a magazine... but isn't it always?

I think if people set out to get 'that cranked tone' at really low sound levels it's just inevitable that it won't be the same... though it could still be good. You and me know this, as does most of the forum probably. The marketing of the ideas is what I can't always stomach. Before power scaling similar phrases were probably used when discussing PPIMV's or Attenuators, and we know neither of those are ideal solutions to playing quietly in your bedroom but sounding cranked ("quietly" isn't really quantitative or a recognized reference level).

I'm not really talking about blasting the speakers out, compared to really quiet levels either. I'm only talking about the range from where your speakers start to sound good compared to not really driven. Still loud, but not '75% output from a 100watt head loud'. Resistance of the speakers varying at different frequencies and all, stands to reason there is going to be a point where the speaker response isn't that good in relation to how they are driven, and that doesn't need to mean driven to loud gig volumes...but more than likely loud for 'in your flat' volumes.

Playing really quietly into 4x12 doesn't have to sound bad... even without power scaling, PPIMVs or attenuators. It doesn't have to sound bad even when using a 100watt amp to do it either. Though it's not very convenient.

I should probably say, that all this probably varies with the style of amp. High gain master volume 100watts are probably going to produce different results in conjunction with the low output ideas compared with non-master volume amps with lots of headroom.

still... if anyone has tried the Rebel 20 and wants to let me know if the Watts pot works well, or if it sounds scratchy, I'd like to know.

[HTH AMPS]

Secret then are they?  ;)

I found the schematic online and it seems pretty simple - just some bypass stuff.  That would explain the extra hiss and noise too...

nah, not a secret, they're freely available online if you search for them.  they're just tweaks to a JCM800, nowt flash.