LJ20 Help Please!

ruoma

@Lebarque Thanks, so cleaner with vac@4 watts (quiet) and hairier @20 watts (loud)? The terminology is misleading here, one man's vac on full is another man's vac out of the circuit...

Lebarque

Lol, sorry @ruoma ! No. Hairier when Vac is up full (quieter). It's more compressed. When you take the vac out of the circuit (louder), it's much more open sounding.

Wazmeister

@JerkMoans  -  so how are your u getting on with the Lazy J now its all sorted mate ?

hotpickups

Yeah that makes sense. Meaning the j20 is driving more but at quieter volumes. I think it sound better when not having the vac in full operation. Damn loud though when volume on 4 and the vac off. I don't find it gets much dirtier though when turning the vac off etc but that's only my ears lol

JerkMoans

Wazmeister said:

@JerkMoans  -  so how are your u getting on with the Lazy J now its all sorted mate ?

I’m still undergoing the sweet agony of anticipation: it’s still in the hands of the zen master Jesse Hoff for fettling.

Wazmeister

JerkMoans said:

Wazmeister said:

@JerkMoans  -  so how are your u getting on with the Lazy J now its all sorted mate ?

I’m still undergoing the sweet agony of anticipation: it’s still in the hands of the zen master Jesse Hoff for fettling.

Cool. Keep us posted mate.

ruoma

Lebarque said:

Lol, sorry @ruoma ! No. Hairier when Vac is up full (quieter). It's more compressed. When you take the vac out of the circuit (louder), it's much more open sounding.

Yeah that’s what I thought. Anybody know what could be the issue here? It being the other way around with me, aka dirtier on full volume and cleaner on low wattage? The first preamp tube, power tubes and rectifier have just been replaced. Any of the amp guys in the neighborhood? @ICBM ? I started to notice it when hooking the amp up to a load box with speaker sim. Then I thought, now I finally crank her up to record and get mega dynamic tones! Turned out I had more distortion when turning her up. Double checked it with its own speaker and same thing. 

JerkMoans

ruoma said:

Lebarque said:

Lol, sorry @ruoma ! No. Hairier when Vac is up full (quieter). It's more compressed. When you take the vac out of the circuit (louder), it's much more open sounding.

Yeah that’s what I thought. Anybody know what could be the issue here? It being the other way around with me, aka dirtier on full volume and cleaner on low wattage? The first preamp tube, power tubes and rectifier have just been replaced. Any of the amp guys in the neighborhood? @ICBM ? I started to notice it when hooking the amp up to a load box with speaker sim. Then I thought, now I finally crank her up to record and get mega dynamic tones! Turned out I had more distortion when turning her up. Double checked it with its own speaker and same thing. 

Are you on Facebook? Jesse Hoff regularly responds to queries like this when posted on the Lazy J amps group page. Just a thought.

SunDevil

Non-expert ‘unhelpful chip in ahead’ >>

The VAC is assumedly lowering the voltage going to the power valves and therefore lowering their ability to amplify?

If that’s the case and you’ve changed all the glassy bits, then I suspect you are looking at one of the components that controls the power valve bias, the output transformer or the VAC chip?

ruoma

Thanks guys. Just talked to Jesse and he said the speaker and tubes are working harder at higher volume so a bit more gain is normal and I just needed to compensate with the volume knob. Guess my mind was playing tricks on me!

SunDevil

No expert (as ever) but I'm not sure that makes sense?

Whilst you'll get more speaker distortion at high volumes, increasing the voltage in the power valves should allow you more clean headroom before you get distortion - you're effectively increasing the window of 'clean' amplification by feeding the valve more voltage and current to play with 

I guess the thing to do is to try and and see if there's a window where you get more headroom before it starts to go into power valve distortion and speaker break-up territory

hotpickups

The thing is tgese teeed amps break up very early indeed. Past 4-5 it won't get louder but more compressed 

ruoma

SunDevil said:

No expert (as ever) but I'm not sure that makes sense?

Whilst you'll get more speaker distortion at high volumes, increasing the voltage in the power valves should allow you more clean headroom before you get distortion - you're effectively increasing the window of 'clean' amplification by feeding the valve more voltage and current to play with 

I guess the thing to do is to try and and see if there's a window where you get more headroom before it starts to go into power valve distortion and speaker break-up territory

The thing that still puzzles me is that it even occurs when I use a load box and speaker sim, so the speaker is out of the equation then. So then it really comes down to the power tube distortion I guess. Amp sounds wicked though with new tubes!

SunDevil

@rouma, going back to you're original post, as I understand it, with the vol on 3 (ie below the point where the amp should be breaking up, you get a clean sound with the VAC reducing the voltage to the power valves and as as you allow more power to the power valves, the amp starts to break up (even though it's still on 3)? ..that being the case, I don't think that's how it should be ..you'd expect the VAC reducing power to the valves to reduce the headroom and give you more breakup for a given amp volume setting

Can you take the VAC out of the circuit on the J20? ..if so, it might be worth trying that and seeing if you still get the same issue  or it goes away? ..you can get some unpleasant sound artifacts with any form of attenuation and without hearing it, I'm wondering if that might be what you are describing as distortion, but taking the VAC out of the circuit would answer that

Running a load box is just another form of attenuation, so whilst it takes the speaker out of the mix, it doesn't say whether it's attenuation related

ruoma

@SunDevil, I just had a breakthrough! Bear in mind, all this is done through headphones with universal audio Ox box load box and speaker sim, but it does apply to the real thing as I checked it out too with earplugs in my little room

With the volume of the amp set at edge of breakup and VAC@20watts, the sound is what it is. When I turn the VAC down to 4watts there's a big volume drop and the sound gets cleaner. I compensate the volume loss with the OX's headphone volume so it matches. I can definitely hear the sound is cleaner. A LOT cleaner, and rather nice tbh!

Now for the breakthrough. Tonight I unplugged the reverb jack next to the extension cab out, removing the (whole?) reverb from the circuit? The VAC@20watts is about the same volume as before, but now when I attenuate down to VAC@4watts, the volume loss isn't as huge and the sound remains the same, probably how most of you guys hear it. Perhaps even a bit gainier.

Jesse mentioned something about this little screw on the reverb unit feeding more clean signal into the reverb or something, to match the 'bypassed' signal. I don't know what it technically does but I might have to experiment... Maybe it's set very low, and it only affects the VAC@4watt setting, feeding it with very little clean signal, and thus being a very weak/clean signal?? It puzzles me though, that unplugging the reverb unit resulted in louder vac@4watt settings.

SunDevil

I think you’ll need the listen to the amp for real rather than through the load box to determine if there’s a problem.

The load box and headphones add many elements which could manifest the problem you’re trying to solve and adds a lot of potential problem areas where you can he getting distortion

The relative signal going to Reverb )vs clean) would change if you turned up the Reverb via the control panel and should not be impacted by the VAC

if you are always using the load box, why not turn off the VAC?

hotpickups

Turn the VAC up all the way I.e. Clockwise until the knob clicks. Then the VAC is totally out of use. It is on mine anyway 

ruoma

I'm using the load box at night times to record, not to attenuate, it cuts the speaker off completely. No sound, only in the computer. But talk of the loadbox is derailing the issue I think. It's a quality piece costing half the amp so it does no harm. 

But anyways, I just double checked it with the actual Tayden 25 speaker and measured with my phone's db meter, playing the same open E chord with same force and turning the vac from 4watts to 20watts:

Without reverb plugged in: 92db - 104db (minor difference in tone between these extremes)
With      reverb plugged in: 82db - 104db (82db sounds cleaner, 104db sounds the same)

I bet there's a logical reason for this that probably has something to do with the screw?

SunDevil

The loadbox is an attenuator. It doesn’t matter how expensive it is, it’s still absorbing the energy of the amp by one of two variations on the same method.

If you want to know if the amp has a fault, play it without the load box in the circuit

ruoma

@SunDevil check my previous comment, I did check it without the loadbox and measured in dB. I don't think there's a fault with the amp, probably just the setting of the screw.