Vox ac15tb > ok with a 16ohm spkr?

[vintagekiki]

I stand corrected. It is the solid state newer amplifiers that I stay away from.

If you still stand that it is a solid state amp, please upload schematic.

[Jon Snell]

I am merley stating that the newer VOX amps were Chinese, made by Korg, nothing else.

[Sea Chief]

I am merley stating that the newer VOX amps were Chinese, made by Korg, nothing else.

Its just that your post was ambiguous Jon thats all. It confused me for a while too.

[Chuck H]

The big opposition to attenuators seems to be that they wear out power tubes. Well... If you're running an amp cranked then you're running an amp cranked. Attenuators allow you to do this at lower volume. But players seem to equate volume with use/wear. Since they're not getting volume the assumption seems to be that there should be less wear. Not at all so. If you run an amp cranked into an attenuator for three hours a day a hundred days in a row it's just the same as if you ran the amp cranked three hours a day for a hundred days at full volume without the attenuator. When an attenuator is in use the WHOLE amp is working just the same as it would if no attenuator were used, but the volume would be much higher. (<period) I like attenuators for their honesty of tone. I run cranked when I can, but when I can't I use an attenuator. Wear on the power tubes (and by the same virtues the whole amp) is the same either way.

The other reason attenuators get a bad rep is that when players are more frequently unplugging and plugging into various loads there's a greater likelihood of an error or open load on the amp. That's user error, not a fault in the attenuator or their functionality.

As for EL84's... Perhaps my favorite tube for guitar amps. Not as cheap as they use to be, but still a great value and almost strangely durable. So, as I've said here before, smoke 'em if you got 'em.

[Jon Snell]

Its just that your post was ambiguous Jon thats all. It confused me for a while too.

The joys of my dyslexia. A lifelong issue we have.
Sorry for any confusion.

[Sea Chief]

The joys of my dyslexia. A lifelong issue we have.
Sorry for any confusion.

Dont worry- I got what you meant on reading 2nd time just fine. thx

[Sea Chief]

The big opposition to attenuators seems to be that they wear out power tubes. Well... If you're running an amp cranked then you're running an amp cranked. Attenuators allow you to do this at lower volume. But players seem to equate volume with use/wear. Since they're not getting volume the assumption seems to be that there should be less wear. Not at all so. If you run an amp cranked into an attenuator for three hours a day a hundred days in a row it's just the same as if you ran the amp cranked three hours a day for a hundred days at full volume without the attenuator. When an attenuator is in use the WHOLE amp is working just the same as it would if no attenuator were used, but the volume would be much higher. (<period) I like attenuators for their honesty of tone. I run cranked when I can, but when I can't I use an attenuator. Wear on the power tubes (and by the same virtues the whole amp) is the same either way.

The other reason attenuators get a bad rep is that when players are more frequently unplugging and plugging into various loads there's a greater likelihood of an error or open load on the amp. That's user error, not a fault in the attenuator or their functionality.

As for EL84's... Perhaps my favorite tube for guitar amps. Not as cheap as they use to be, but still a great value and almost strangely durable. So, as I've said here before, smoke 'em if you got 'em.

Hi Chuck- great info as always thanks. I'm inclined to maybe dip my toe into attenuators then, if the reviews of my amp are 'sag/ compression galore' then it'll be a shame to never having heard kit. Like owning a lotus but not being able ever to throw it round some bends properly, selling it having just pootled about in it.

I get the idea of wear is same amp cranked with or wothout attenuator- I always knew this. I dont play a huge ammount so my tubes might well last better than most folks, I use a taylor acoustic 90% of time now I find in a rural cottage (near bron-y-aur in fact..so you can maybe picture the setting).

Only thing i can't perceive is how -well- an attenuator can actually attenuate. Buit I guess this boils down to makes. What one do you have? I'd always go along with your recommendation, as per your very helpful replies.

thx SC

[Chuck H]

An attenuator attenuates by sharing the actual speaker load (Which converts some of the amps energy into sound and some into heat.) with a "dummy load" (Which converts the amps energy into heat only. No sound). Some attenuators are partly resistive and partly inductive. Some are entirely resistive. Whereas a speaker load is more inductive. It's generally believed that including inductive elements in a dummy load makes the amp react more like it would when playing into a speaker. The increase of the ratio of restive loading opposed to inductive loading when using an attenuator is said to change the way an amp performs. Which it does, but no system is perfect. In my experience the difference in tone using an attenuator is certainly less than any master volume circuit.

[vintagekiki]

A matter of taste
There are various attenuators, dummy loads, but if you want a real experience, the sound as on stage, the amplifier is set to 12, natural distortion, and in the room the sound is room power 0.5W and up (neighbors sleep peacefully)

Marshall Power Brake PB100
or
Palmer Speaker Simulator PDI-03

The only drawback is that all attenuators, dummy loads devour the output tubes, because tubes work at full power.
But everything has a price ...

[Chuck H]

The only drawback is that all attenuators, dummy loads devour the output tubes, because tubes work at full power.
But everything has a price ...

And just to be clear, the attenuator doesn't make the tubes run at full power, players are just more likely to run the amp at full power when using an attenuator because they finally can. The only drawback to an attenuator vs. a full speaker load would be a decrease in volume. Which is the point if you're using an attenuator And that's an excellent point about the sheer volume and how sound pressure acts in a given room being a part of "tone" that does get lost with an attenuator. As does any sustain (fundamental or harmonic) that would be relative to acoustic feedback at full volume. Playing at full volume is definitely the preferred situation.

But on the notion of getting cranked amp tone and still preserving the power tubes relative to work in watts... We haven't brought up power scaling yet. And maybe we shouldn't.?.

[Sea Chief]

And just to be clear, the attenuator doesn't make the tubes run at full power, players are just more likely to run the amp at full power when using an attenuator because they finally can. The only drawback to an attenuator vs. a full speaker load would be a decrease in volume. Which is the point if you're using an attenuator And that's an excellent point about the sheer volume and how sound pressure acts in a given room being a part of "tone" that does get lost with an attenuator. As does any sustain (fundamental or harmonic) that would be relative to acoustic feedback at full volume. Playing at full volume is definitely the preferred situation.

But on the notion of getting cranked amp tone and still preserving the power tubes relative to work in watts... We haven't brought up power scaling yet. And maybe we shouldn't.?.

Sometimes it seems to me I need a physics degree to play my bloody electric guitar.. for something relatively simple in terms of components, as I know having made a 5E3 & 5F1, the complexity of underrstanding how you can actually play the damn things often puts me off, & i just pick up an acoustic. But I keep coming back. Probably cos I once played a silverface Champ dimed (no idea aged 17 that it wasn't broken cos it distorted, I needed it at vol 10 to keep up with the drums).. & it felt 'kinda touchy feely' in a good way IE I played soft & it was clean/ dug in & it distorted. I thought 'hey its cool, but must be a fluke if its broke'.. so I surmised.

I have made an attenuator too.. just a tiny device with huge resistors & a stepped vol pot thing, but rarely used as it doesn't seem to 'release the goodies' too well. Its not very good. Y|ou see Ive no idea if I fork out £180 on a 'powerbrake' if it will be exactly the same as this contraption.

So Chuck, what attenuator do you use? if someone can recommend one, a really strong recommendation, then I might be tempted..

[Chuck H]

Well, as you might guess, I designed and built my own attenuator. When I looked at what schematics I could find for existing designs and analyzed them I figured I could do better. I think I did, but I can't really say because I haven't played through any other than my own enough for a fair comparison. As for a strong recommendation I can say that the Weber MASS and mini MASS are generally loved. They're expensive though. And in looking at the schematics it seems to me that there's a pretty wide variation in impedance load to the amp that is setting dependent.

If you're feeling ambitious, here's a schematic for my design. Good for 50W @ 8ohms. The note on the .5mH inductor came about as a solution for feedback I was getting when using single coil pickups. I had to make an inductor sandwich as a sort of built in humbucker. It's easy enough to make other than fabricating the copper plate. Any copper sheet thicker than foil will do and it does need to be just a little wider than the inductors themselves to minimize "mutual inductance" (tech babble, don't worry about it). I bought the inductors from Parts Express. The 12mH inductor I used is no longer made, but this one would be fine:

https://www.parts-express.com/12mH-2...uctor-269-2126

The two .25mH air core inductors for making the .5mH inductor are these:

https://www.parts-express.com/Jantze...ductor-255-214

Build the thing in an aluminum box with those chassis mount resistors and thermal paste. Here ya go:

[Chuck H]

For something a lot simpler here is the purely resistive version (with easy read diagram included!) that I've recommended here many times. I don't think it sounds as good as the more complicated version with the inductors and capacitor, but most people here that have built it seem to like it well enough.

[Sea Chief]

Well, as you might guess, I designed and built my own attenuator. When I looked at what schematics I could find for existing designs and analyzed them I figured I could do better. I think I did, but I can't really say because I haven't played through any other than my own enough for a fair comparison. As for a strong recommendation I can say that the Weber MASS and mini MASS are generally loved. They're expensive though. And in looking at the schematics it seems to me that there's a pretty wide variation in impedance load to the amp that is setting dependent.

If you're feeling ambitious, here's a schematic for my design. Good for 50W @ 8ohms. The note on the .5mH inductor came about as a solution for feedback I was getting when using single coil pickups. I had to make an inductor sandwich as a sort of built in humbucker. It's easy enough to make other than fabricating the copper plate. Any copper sheet thicker than foil will do and it does need to be just a little wider than the inductors themselves to minimize "mutual inductance" (tech babble, don't worry about it). I bought the inductors from Parts Express. The 12mH inductor I used is no longer made, but this one would be fine:

https://www.parts-express.com/12mH-2...uctor-269-2126

The two .25mH air core inductors for making the .5mH inductor are these:

https://www.parts-express.com/Jantze...ductor-255-214

Build the thing in an aluminum box with those chassis mount resistors and thermal paste. Here ya go:

Hi there Chuck- only recently saw these posts of yours.. really appreciated. I did in fact build a simple attenuator version, i think it might resemble your 2nd post affair, but I found it only 1/2 useable.. I'm not entirely sure why, but seems to work only mediocre at best so it's left unused. I'd love to try building the 'better' version, but alas I cannot re-interpret schematics into physical layouts, I'm just not that advanced. I dont suppose you had an inside pic of your creation?

thanks alot for these- it's food for thought.

[Sea Chief]

Does running the amp flat out put as much strain on the PT, as I know it does the tubes? Ive read mine is possibly its achilles heel/ some info history of failures on this vox model.. tho seems perfectly ok to me.. just wondering if the idea of attenuation is a good one considering this aspect.

thx SC