Wrong ohm setting

[Harlequin tusk]

Adwex, I have that same power amp, you need a gorilla to lift it! And Gorgeous Les Paul you have there, that and that Jubilee....must be a deadly combo!!!!

 

[Joey Voltage]

I did not mean feedback affects the loading, but works hand in hand with it. Yes, feedback must be used correctly with phasing kept in mind.

To me as plate load decreases so does power, but with an increase in total harmonic distortion. The introduction of feedback will decrease power as well as total harmonic distortion. So, if one increases plate load, the need for feedback decreases. And therefore, if she weighs less than a duck, she is a witch!

well here check it out, and don't think I'm just gearing this towards you mickey, even though I quoted you, as I think two different things are getting convoluded here. ignoring the speaker load for a second, and just thinking about the DC operation, usually as the a-a plate load decreases (so long as you are not too crazy) peak output power may Increase some (note this does not mean the maximum dissipation rating of the device, or power transfer), but yes at the expense of more THD, this is the case with all amplifiers whether they are transformer loaded constant drive amplifiers like an output stage, or they are resistively loaded voltage amplifiers like a typical preamp stage.

now negative feedback - The indroduction of -FB wether it be current, or voltage feedback, wont so much reduce the output power, as much as it will reduce the gain of the stage or block it is applied to, this will as you mentioned increase the linearity, but voltage feedback also serves another very important function in that it also reduces the impedance of the stage or block it is applied to.

so Joey where the hell are you going with this???? well here it is, I think that was a bit of a blanket statement, although I'm sure you meant it as an all things equal statement. it is not necessarily true that the inclusion of a higher a-a load (a reasonable one) decreases the need for -FB (perhaps just not as much of it), because although a higher plate load may reduce THD/increase linearity, (if linearity is your prime goal with the feedback, or prime goal at all) it does not mean that it will reduce the output impedance of the output stage enough to adequtely dive all the crazy peaks and dips of the reactive load, and how much it does or doesn't depends on the plate impedance of the valves you use as well, and of course as you said the properties of the load too(nominal impdeance, and how crazy they get) so again more factors, YIKES. IMHO the most important thing -fb is doing in this scenario, especially since we are hooking up to a horribly reactive load is reducing impedance, so a tighter leash can be kept on the damping of the load. screw the linearity.

Smaller, cheaper OT's will heat up more and as characteristics approach maximum ratings, distortion increases = some degree of saturation.

Oh no, I agree there, I just didn't necesarily agree that this was a desireable thing. Incedentally The only OT I ever had blow on me, was undersized for the job, and this OT was actually purposely sized this way as part of the amplifiers design, and selling point.

Your are right, guitar amplifiers are not designed to be perfect, hince the distortion and the less than ideal power transfer.

would you have it any other way?

 

[Marshall Mann]

Does this mean Joey is back????

 

[mickeydg5]

Yes, agreed. And this is for everyone to read, not directed to anyone.

When I say decrease plate load, I mean using a lower resistance OT. Like say dropping from a 6400ct primary to that of a 3400ct. A tube that will give higher power at 6400Rpp will give a little less power with a 3400Rpp but have an increase in good harmonics. The difference in power is only a slight decrease in perceived volume.

I look at negative feedback as affecting the stage in which it is introduced along with every stage following. As you said feedback affects that stage by reducing impedance, its gain plus its distortion and other stuff. The lower gain in this stage will consequently reduce output in the power stage. Again, this is only a slight decrease in perceived volume. Yes to damping is important. We gots to keep this thing controllable, stable and sounding good.

As far as guitar amplifiers go, low plate to plate load on the power tubes and less feedback both within reason is what we desire. It provides a nice dose of even harmonics with a good amount of power.

ADD: All this can be affected by using the wrong ohms setting.

 

[Joey Voltage]

Yes, agreed. And this is for everyone to read, not directed to anyone.

Yet I'm starting to get the feeling this is turning into one of those things where two people are talking, and nobody is listening

When I say decrease plate load, I mean using a lower resistance OT. Like say dropping from a 6400ct primary to that of a 3400ct. A tube that will give higher power at 6400Rpp will give a little less power with a 3400Rpp but have an increase in good harmonics. The difference in power is only a slight decrease in perceived volume.

Well sorta, and it depends on how close or far both the 6.4K, and 3.4K are to the load that would theoretically yield maximum power transfer. too light of a load and too heavy of a load will BOTH reduce power, and result in shitty transfer.

Tonally yeah they sound very different. Marshalls tend to be a little more heavily loaded (lower reflected primary). Generally speaking I find a higher reflected impedance tends to "Smooth" and compress the sound a little, very similar to the sound you get when installing a pseudo Triode mode switch. where as lower reflected primary impedance tends to be a bit bolder and brighter.

I look at negative feedback as affecting the stage in which it is introduced along with every stage following. As you said feedback affects that stage by reducing impedance, its gain plus its distortion and other stuff.

Technically speaking it only really reduces the gain of the stage it is introduced to, and every subsequent stage enclosed in the loop is affected because of the new closed loop gain, and because they are now part of the block, and partly work to keep the open loop gain high enough to keep the feedback loop intact. In other words if you have three stages and apply 6db worth of feedback from the last stage to the first, you reduce the gain of the first stage by half, not every stage by half. this affects everything else because you now need double the input voltage to the first stage to get the same output voltage out of it as you would have if you had no negative feedback, however the gain of every other stage with in the feedback loop stays the same regardless. here I'll illustrate for anybody who is interested. say each stage in the example above have a gain of 10, and you input 1V. 1*10*10*10, you get a gain of 1000. Now if you reduce the gain of the first stage by 6db (half) it now becomes 5*10*10, not 5*5*5, and now you need double the input voltage to get you 1000 out of it.

The lower gain in this stage will consequently reduce output in the power stage. Again, this is only a slight decrease in perceived volume. Yes to damping is important. We gots to keep this thing controllable, stable and sounding good.

The only thing I really had exception to is that -fb doesn't *Technically* lower output power, but yes it does lower the perceived volume due to lower gain of the output stage. It's an example a perceived change versus whats electrically happening, and also sort of an example that watts doesn't necessarily equal loudness. you can have a 100W output section, and apply 20db of -feedback. It may sound quieter than a 100W amp with 2db of -fb, but it doesn't mean it is no longer 100W

 

[RickyLee]

Yet I'm starting to get the feeling this is turning into one of those things where two people are talking, and nobody is listening

I'm here . . . And I'm All Ears.


And Eyes!








Good stuff fellas. Carry On.

 

[mickeydg5]

Hey Joey, I am listening.

Now that's what I am talking about.

Good to have you back. Psssst, I do not believe you ever left.

 

[tresmarshallz]

I'm listening! Love this stuff....

 

[mickeydg5]

RickyLee
You have to be the hardest working man on the forum. From what I see in your post you probably work 8 hours a day and pull amps apart the other 16. There is no way you can sleep with all the stuff you do!

 

[hbach]

Very much listening.

 

[RickyLee]

RickyLee
You have to be the hardest working man on the forum. From what I see in your post you probably work 8 hours a day and pull amps apart the other 16. There is no way you can sleep with all the stuff you do!

LOL

Yeah, you are close there. With my commute time my work days are 11 to 12 hours long. But I am fortunate to have a 9/80 schedule so that I have Friday, Saturday, Sunday off every two weeks and Saturday, Sunday off the other in between week discounting any overtime worked of course. Gives me a three day weekend every two weeks then you mix in some Holidays and it's not too bad.

As for constantly working on my amps? That has become somewhat of my therapy I would say. I have some health issues going on now that has me a bit worried. And then the band has not been gigging much less even rehearsing so there is no outlet there at the moment.

Then this year, some unexpected family financial stuff ruined my plans and dreams of finally getting my studio built. I really need to get back to being the song writer I once was. I have loads of recording stuff piled up here with no place to set it up.




I guess it was good to get that off my chest - thanks for listening . . .

 

[mickeydg5]

LOL

I guess it was good to get that off my chest - thanks for listening . . .

Well, chin up, be positive.