Laney L5T tone control

[slowmichael]

Hello,

My first post here. I attached the schematics of this amp. There is a tone control just before the powervalve. It shows on the schematics on page 2, there is a grid the tone control is on c2 of the schematic grid.

I recently bought this amp and for the price it is an excellent studio or practice amp. The tone control acts as a treble cut, on 10 there is no treble cut, between 9 and 10 no treble cut. On 9 the tone control cuts the highs and also the overal volume. The difference between 9 and 10 is well, it is like playing an other amplifier, or like the amp is covered in a layer of wet towels it sounds muffled. Well it states so in the manual "tone is a brightcut at the end of the amplification circuit, enabling rolling of upper harmonics".

I love the sound of the amp with the tone on 10 but sometimes when using bright single coils and for certain songs there is to much upper end harmonic content, so it would be nice to have the ability to roll this off a little. Unfortenatly the tone control goes from nothing on 10 to cutting almost all content on 9.

As far as i can tell the tone circuit is a lowpassfilter with a no load potentiometer. I used to have a american standard strat with a no load tone control and it also behaved this way, sounding great at 10 and muffled at 9.

Could this circuit be altered so that i could gently roll off the upper harmonics preferably without losing volume or as little as possible.

Thanks for any suggestions, advice.

Regards.

Michel

[J M Fahey]

From what I see itīs a mixed active/passive tone control; with the wiper "up" (as shown in the schematic), it kills all treble by straight dumping it into ground.
With the wiper down , highs in the feedback loop get dumped to ground through C36 and R54, so it acts somewhat similar to a presence control.
I think the problem lies in the Pot curve.
They used a cheaper and easier to find Linear (B) one, which does what you notice, most of the effect in a very small rotation, not easy to adjust to taste.
I *guess* youīll need to replace that B220K pot by an expensive and harder to find "C" or "anti log" 220K pot, same size and everything else, of course, to fit in that PCB and accept that knob.
Personally I would leave it always in 10 (considering what you say) and use the more normal acting regular treble control as a "fine tuning" pot.
It will certainly be more controllable.
Or try to get the correct Pot.
EDIT: or lift C29, since you donīt seem to like muffled, wet towel in front of the speakers sound anyway, , and replace VR8 by a B 5K (linear) pot, turning it into a conventional presence control.
Just donīt tell them I suggested that

[slowmichael]

Thanks for your help. Leaving the tone on 10 and using the regular treble control to fine tune, well i have tried that but the regular treble control seems to play in a lower frequencie spectrum than this tone control. The tone control adjusts upper harmonics.

I also tried this, plugged my strat in on the neck pickup so no noisecancelling. Turning volume at 10, tone at 10, of course there is a lot of hum a kind of static noise, reducing the tone setting 9,7 9,5.........9,1 same volume of hum.......... 9 bang the hum is massively reduced and from that point i can reduce it linear by turning the tone control to 8, 7,....... . This leads me to think that VR8 is a no load pot, when the wiper is fully up it does not make contact anymore with the resistor in the pot. Or when the wiper is fully up it breaks the tonechain by breaking the link between c29 and vr8, this would totaly disable the bleeding away of highfrequencie harmonics trough this part of the circuit.

Michel

[J M Fahey]

Well, it definitely is not a "no load pot", in fact I donīt know what you mean by that and even more, the wiper is grounded .... but you might have a point here : the pot might be defective, even having a cracked track.
That would sure explain the "jump".

[slowmichael]

Thank you for your replies. Will not experiment on this myself since i have only a theoretical knowledge of electronics and no experience with working on a guitar amplifier, for safety reasons i will go to a profesionel to check this out.

However no load tone pots do exist, actualy if you go to
http://music-electronics-forum.com/t26831/

then you will find a thread about this item in this forum, there is also a simple diagram.

Best regards.

Michel

[andrius]

From what I see itīs a mixed active/passive tone control; with the wiper "up" (as shown in the schematic), it kills all treble by straight dumping it into ground. With the wiper down , highs in the feedback loop get dumped to ground through C36 and R54, so it acts somewhat similar to a presence control.

I understand almost nothing about electronics - could you please explain me what are the wipers? How are why made "up" and "down"?
You said that when the wipers are up, they kill treble, and when they're down, they kill highs. What is the difference between treble and highs?

[J M Fahey]

You must have some basic electronics terminology knowledge, otherwise itīs impossible to explain anything.
That said, the "wiper" is the sliding contact in a potentiometer, which "wipes" the carbon track and can go from one end to the other.
Itīs usually connected to the center leg.
In this case, itīs not a "no contact" pot (which are *extremely* rare) nor a cracked/broken one but a very poorly specified one.
They want it to make 2 jobs, which would need 2 separate pots: a 220K one (as is) for the treble cut part (the upper half) and a , say, 5K one for the presence circuit (the lower half).
As you see, the pot is 40X over the correct value.
For better results, do the Mod I suggested (lift C29 and replace R8 with a B5K one).
Good luck.

PS: and I said

, highs in the feedback loop get dumped to ground

, the net effect is a highs *boost* , a.k.a. Presence.

[andrius]

You must have some basic electronics terminology knowledge, otherwise itīs impossible to explain anything.
That said, the "wiper" is the sliding contact in a potentiometer, which "wipes" the carbon track and can go from one end to the other.
Itīs usually connected to the center leg.

Thanks the reply!
So the wiper, in this picture ( http://interactiondesign.sva.edu/cla...er_diagram.jpg ) would be that sliding contact (called "Rotating Dial" in the picture), that travels over the arc (the red "Resistive Element"), - is that right?
And which is the position of the wiper that you call "up" and the one that you call "down"? What is the "lower half" and "upper half"?

[J M Fahey]

Good ! You got it !!!
Usually (sigh!) I have no way of knowing what they call "10" and what they call "0" in a schematic.
Sometimes I can guess, sometimes not.
I donīt know whether your knob "fully to the right" means "trebley" or "bassey"
So I say "upper or lower" *as drawn* (not necessarily "as on the PCB" ... which I don't see).
In your schematic "up" should mean "bassy" and "down" should mean "trebly".
Or to be more precise: "up" (as drawn) is when the wiper touches the leg connected to C29 and "down" to C36.
You should be able to follow the tracks and confirm.

[andrius]

Good ! You got it !!!
Usually (sigh!) I have no way of knowing what they call "10" and what they call "0" in a schematic.
Sometimes I can guess, sometimes not.
I donīt know whether your knob "fully to the right" means "trebley" or "bassey"
So I say "upper or lower" *as drawn* (not necessarily "as on the PCB" ... which I don't see).
In your schematic "up" should mean "bassy" and "down" should mean "trebly".
Or to be more precise: "up" (as drawn) is when the wiper touches the leg connected to C29 and "down" to C36.
You should be able to follow the tracks and confirm.

In this case fully to the right the knob means "trebly".
So basically all that means that when I turn the knob all the way to the right, it both gets "trebly" and also more "presense-y"?
Does this all happen at the same time - like turning the knob from 0 to 10 it is gradually adding back the cut truble AND adds presense? Or is it like it restores the cut treble up to some point (let's say, 8 or 9), and after that point it adds the presense?

For better results, do the Mod I suggested (lift C29 and replace R8 with a B5K one).

What does "lifting" C29 mean, if it's possible to explain to a newbie like me?
And I found R8 in the schematic, but did not find B5K, so I assume that B5K maybe is a potentiometer that you suggest to put instead of R8 (also a potentiometer?)?

[J M Fahey]

So basically all that means that when I turn the knob all the way to the right, it both gets "trebly" and also more "presense-y"?
Does this all happen at the same time - like turning the knob from 0 to 10 it is gradually adding back the cut truble AND adds presense? Or is it like it restores the cut treble up to some point (let's say, 8 or 9), and after that point it adds the presense?

They try to do too much with too little.
I'd say that it cuts treble with the knob on 0 , restores it from 0 to 5 or 6 and adds presence from 9 to 9.5 or so it seems.

For better results, do the Mod I suggested (lift C29 and replace R8 with a B5K one).
What does "lifting" C29 mean, if it's possible to explain to a newbie like me?
And I found R8 in the schematic, but did not find B5K, so I assume that B5K maybe is a potentiometer that you suggest to put instead of R8 (also a potentiometer?)?

Lifting C29 means desoldering and pulling it from the PCB.
I also suggest pulling R8 which now is a Linear 220K (B220K) and placing there a Linear 5K (B5K).
I strongly suggest you get somebody with some experience to do this, either a proper serviceman or an aficionado which has already (successfully) built , say, a couple pedals or an amplifier.
Otherwise, the potential for damage is important.
If you donīt, learn to live with the small inconvenience you have today, as certainly thousands of Lionhart users do, until somebody can help you.
Otherwise you risk getting some damage, NOT COVERED BY WARRANTY , which will probably cost more than a new amp.
And you will be ampless until then.
Good luck.

[andrius]

I strongly suggest you get somebody with some experience to do this, either a proper serviceman or an aficionado which has already (successfully) built , say, a couple pedals or an amplifier.

I understand that - I'm not going to be touching that thing, but I wanted to know these things so that I knew what to ask for when I find someone who can do this . Thank you for the explanations

Otherwise you risk getting some damage, NOT COVERED BY WARRANTY , which will probably cost more than a new amp.

You mean, to repair an amp would cost more than to buy a new one?

Unfortunately, the warranty becomes void if someone does modifications to the amp...

[andrius]

By the way, I found a comment about Laney amps:

However, most Laneys have a "design-flaw" that you should be aware of: They have an Opamp between the pre and power amplifier. Not a problem by itself, but they've been paranoid about oscillation prevention. There is a lowpass filer built inside the circuit that goes into the hearable range.
Something similar is right in front of the phase-inverter tube btw. Any Laney user should get that thing removed or at least the corner frequency raised. The sound will open up a lot and will sound a lot more alive.
For a qualified tech this is a 10 minutes job.

Does this apply to the Lionheart too? What part is this in the Lionheart schematic?

[J M Fahey]

Donīt worry about vague threats posted in Forums by people who repeats what "happened to a friend of a friend of a friend" without details.
The signal path in your amp is all tube except in the reverb circuit (like in most "tube" amps today).
Signal level there is low, and the RF filtering cap that worries said poster has a cutoff frequency of 16KHz and above, absolutely inaudible through guitar speakers.
As of repairs, bench cost in the USA goes from U$50/60 an hour in a smaller city to U$120 an hour in an established Shop in N.Y.
So any repair that takes more than a couple hours in a cheap amp: do the Math.
Even simpler: *most* (almost all) "cheap" Fender amplifiers , up to the 100W 2x12" FM212R , the Passport PA amps, all SWR below 120W and many more, are in an official "do not repair " list.
If within warranty, they ship you another ; if not, may God help you !!.

[andrius]

Could you please explain to me what the Bright switch does in that Lionheart according to this schematic? Does it affect both channels?