Clipping wireless.

[ecc83]

Great info and interesting.
There are indeed a load of mods. Love experimenting. Though can't do them myself except changing and biasing tubes.

fact stays that some wireless systems are not having enough headroom making them almost unusable.

That's fine friend, we can't be good at everything*. You don't do circuits, I can no longer play guitar worth a damn!

Biasing valves? Ha! There's an area of guitar amplification mired in BS and myth. The company I worked for biased all 25W valves the same, 25mA per valve. EL34, 6L6, even the (not so now) mighty KT88, they all got 25 mils and in the 3 years I was there I never had a customer or band member ask me to bias their amp any hotter or colder. That was 20 years ago and I am willing to bet no one ever has since!

*You do come across individuals now and again who can...and don't yer just hate 'em!? (don't mean it Cliff if you ever look in!)

 

[TalismanRich]

Dave,
There is a natural treble roll off with most guitar wiring schemes. Some time back there was a program put together that would graph the response curve for the circuit if you knew the resistance, inductance and capacitance inside a pickup, and the specific tone cap and potentiometer values. You could see a significant peak around 5-6kHz, if I remember correctly. As you lowered the volume pot, that peak would droop as the overall level fell until it was more of a smooth roll off.

The treble bleed circuit counteracted that droop in the higher frequencies, letting some of it back in so that the approximate response curve stayed more constant with volume roll off. It had nothing to do with cable capacitance.

--

So far, all of my guitars have worked well with the Joyo/Legato units, but I don't have any high gain pickups. All of mine are more traditional passive units, so they are well below the clipping point. I just used it a week ago with Lollar P90s and SD Alnico Pro IIs. A fellow in a local band used the Joyo with his Les Paul Std and a Supro with Gold Foil pickups. It all depends on the pickups you're using as to whether the wireless system has sufficient headroom (AND Output... can't forget about the receiver!!!). If you are trying to slam the front of your amp and your pickup puts out 8V p-p, but the receiver can only put out 2v p-p, you just lost all your drive, even in the transmitter can handle 20V! It may not be just a "pad" issue of the receiver.

But as I said earlier, NOBODY publishes output figures for their pickups that I have seen. All you ever see is Ohm readings, which mean ZERO. You can calculate that if you know the wire gauge and length. It doesn't tell you the number of turns, the magnet strength, and how hard you're banging the strings.

 

[ecc83]

Yes Rich, the guitar circuit with its lumped L,C&R is a very " middly", an inverted "smile" curve if you will but I have just gone through 1/2 doz each of single coil and humbucker diagrams grabbed at random and not one has the bleed cap. I can only conclude therefore that most players are happy with the intrinsic response of their pups?

But my point really was that the "bright up cap" in a guitar and the cap in the circuit I attached are doing the same thing. Boosting treble as the VC is turned down. Partly in the case of the guitar to compensate for cable capacitance but also to offset the psychological effect that as things get quieter we hear less treble and to a greater extent less bass.

I agree that some standard data on pickup output voltages would be handy but then microphone speccs' are often badly reported and don't get me started about headphones!

Dave/

 

[FrankD77]

Do you mean that bias is not necessary or changing the original values ?

Pre amp tubes yes
Powertubes are important to bias. If you don't your amp will not run the way it supposed to or burn through the power tubes.

I bought a system where I can bias the tubes while in the amp. I'm not experimenting with it, but with that system it's pretty easy to do you yourself. I just follow the service manual when i replace the tubes i don't change anything

 

[ecc83]

You misread!! Of course OP* stage bias is important in that you need to avoid over dissipation on one hand and grating crossover distortion on the other but between those extremes there is plenty of leeway. I have read of people biasing very hot, up to 50mA with Va at around 450V. That gives an anode dissipation of 22.5W and that is very close to design max of 25W for the EL34. Remember, mains voltage wanders up and down so a margin of safety is prudent.
Also, the hotter the bias, the less headroom you have.

*Pre amp stages are of course cathode biased so, so long as the maker got it right, all is kushty but don't assume they ALL did all the time!

Dave.

 

[FrankD77]

You misread!! Of course OP* stage bias is important in that you need to avoid over dissipation on one hand and grating crossover distortion on the other but between those extremes there is plenty of leeway. I have read of people biasing very hot, up to 50mA with Va at around 450V. That gives an anode dissipation of 22.5W and that is very close to design max of 25W for the EL34. Remember, mains voltage wanders up and down so a margin of safety is prudent.
Also, the hotter the bias, the less headroom you have.

*Pre amp stages are of course cathode biased so, so long as the maker got it right, all is kushty but don't assume they ALL did all the time!

Dave.

Agreed. Maybe if you know the design you can adjust it differently. For normal users follow the service manual.

The guy that services my amps if he would make adjustments i trust him myself not

 

[ecc83]

Agreed. Maybe if you know the design you can adjust it differently. For normal users follow the service manual.

The guy that services my amps if he would make adjustments i trust him myself not

Yes indeed, follow service data instructions. What I mean though is that there is a "movement" if you like, to bias guitar amps very hot. Close to, sometimes above valve max specifications. There is no valid evidence that I have ever seen that this has much if any tonal benefit. OP valves are expensive and will only get more so. They are not as tough as the original makes either in many cases, do not run KT88s above 600V for example! Therefore, cooking the buggery off them for no good purpose is daft IMO.

Bias setting is quite easy if the amp has a sense 1R in the cathode circuit, mVs equate to mA and then measure Va. Simple 'rithmetic to find the anode dissipation. Always worth checking the voltage either side of G2 stoppers as well That gives you the G2 dissipation. I always fitted 1K 1W MF resistors as the screen grid is the first line of failure if a valve arcs over...and they all do eventually!

If the amp does not have a sense R then you can use the "OP transformer resistance method" bit hairy mind!

Dave.

 

[FrankD77]

Maybe it's also because I have a deep respect for my tube amps, I know they can kill me

But I know what you mean, sometimes it's forgotten that those stories often have a background in studio setups where they burned through the tubes in a few hours for the "perfect" recording. And those techs probably knew they systems by heart or designed them.

I highly recommend people listening to Tone Talk with Dave Friedman, there is an insane amount of information about tube amps and adjusting them in between the lines. And it just strengthens my confidence, they are designed that way for a reason. Maybe they can be a bit hotter, but if it would make a huge difference they probably would have designed it differently, and tubes are fricking expensive. So just keep it as they tell you. And if you miss something, add a pedal or get a different amp

I just wish I could repair or mod my gear myself, the service for tube amps is dying out here slowly.
And I would never dare to do it the way you probably do. The "dumb click" system should work fine for me I hope, I got the version for the most used guitar tubes. So for the coming years I hope I can do that myself, if I can still get tubes after I'm out

 

[ecc83]

"
I just wish I could repair or mod my gear myself, the service for tube amps is dying out here slowly.
And I would never dare to do it the way you probably do." Did mate, did! I could still do the soldering etc but lifting a 100W chassis onto the bench would be a trial! "The way I did" WAS carefully, there are no Old, Bold valve amp techs!
You have the advantage that you are not under time pressure. You can hook meters up 'cold', stand back, switch on and read. Switch off, dump the caps and move on to the next test.
"Valve amp techs dying out? Has been so for over 20 years here. I was in my 60s when I went for my interview with a local amp company and sat waiting with 3 'young bloods'. Nobody was more surprised than I when I was called back the next week! I asked why, how? "Just wannabies said my then boss. You were the only one who really knew valve circuitry".
I went to day release and night tech to get my electronics ticket. You can still get a degree of course but do they teach valves? I bloody doubt it.

Dave.

 

[FrankD77]

"
I just wish I could repair or mod my gear myself, the service for tube amps is dying out here slowly.
And I would never dare to do it the way you probably do." Did mate, did! I could still do the soldering etc but lifting a 100W chassis onto the bench would be a trial! "The way I did" WAS carefully, there are no Old, Bold valve amp techs!
You have the advantage that you are not under time pressure. You can hook meters up 'cold', stand back, switch on and read. Switch off, dump the caps and move on to the next test.
"Valve amp techs dying out? Has been so for over 20 years here. I was in my 60s when I went for my interview with a local amp company and sat waiting with 3 'young bloods'. Nobody was more surprised than I when I was called back the next week! I asked why, how? "Just wannabies said my then boss. You were the only one who really knew valve circuitry".
I went to day release and night tech to get my electronics ticket. You can still get a degree of course but do they teach valves? I bloody doubt it.

Dave.

Our local audio repair Company has a real expert. He did my engl 920/100. But he is a pensioener and can take a long time.

The amp Tech is about my age but lives too far away. And i love to do it myself it its easy.

I like modellers but nothing beats tube Amps. For me.