(Nearly) Complete LXH2 Full PCB

[rody82]

Morocotopo, today i tried a 300mA tranny with the same results. Under load, usually i get strange voltages at the + output (around 0,8V, sometimes even negative voltages!), without load, everything seems fine. I've checked everything a thousand times, and replaced every part, its going on my nerves 

[AJS]

rody,

About the reported gating at op-amp6. Did you find the explanation or was it really a resistor value all the way down in the cab sim that caused the gating?

I'm experiencing gating at 6:op and have tried several power solutions including batteries. Gating get pronounced at high presence settings, did you see this as well?

What voltages dou you read at op 6?

Regards

[rody82]

AJS: Try the SIM section alone, if it sounds fine (very dirty, but no gating) then the problem is somewhere else.
The only problem i had at the SIM section was using the ggg bipolar power supply. Use 2 fresh batteries to be sure its not the ps!

There was a missing 1k resistor at the cabsim, and a value mistake at one of the filters, but the SIM section was fine from the
start.

[Morocotopo]

Rody, I finished my Fender simulator. I built the Anderton bipolar power supply, and that works great. I had the same issues as you with the GGG power supply. I think that the GGG one is not a good design, I think. The Anderton one uses a center tapped secondary transformer,(nV - 0V - nV), uses (I think) a full wave rectifier instead of a half wave one, and adds some diodes that prevent the regulators to fail, and most importantly, prevent latchup, I think that´s what´s happening with the GGG one. Also, there´s some parts that have to be removed because it uses a 8V regulator instead of a 9V one. If you need help I´ll post a drawing.

EDIT: I had some biasing problems with the circuit, when for some reason the bias is not right it starts gating. Caused by the (bad) power supply, since I used the new one no more biasing problems. Something to take into account.
Well, since this is a bipolar schem it´s not actually biasing, it´s... too much difference between +V and -V?

[rody82]

Morocotopo: Can you send me a layout / schem? Or did you buy a kit?
I dont fully understand your biasing problem. You mean the GGG ps had this problem
or your new ps?

[Morocotopo]

Here:


Yes, the GGG one had this problem, the new one works OK.

EDIT: both power supplies gave me around +8,97V and around -9,23V, don´t know why the difference between +V and -V, but the more or less 0,25V difference between them doesn´t seem to matter... a quirk of the negative supply chips maybe?

[rody82]

Thanks Morocotopo! Hope this'll work finally

By the way, i have a tranny with 2 x 12V secondaries, do you
think i can simulate a CT tranny with it, by connecting the 2 secondaries
together?

[Morocotopo]

How many wires at the tranny secondaries?: if three, one is the center (ground, usually different color wire, check the transformer instructions), and the others are the 12V outs. I used this type of tranny. If four, you have two independent secondaries. I think that the latter type you can connect it to work as the first type...not really sure how, I´m not too sharp on transformers, so better ask people with more knowledge than me.

Hope it works better!

Morocotopo

[rody82]

It works with the new ps! Strange though, that usually it doesnt work for the first try, (squeaky noises)
i have to unplug and replug the ps (the primary side).  This must be cap related right? I suppose
the problem is that there's  an instant load at the ps output. It could have been the same problem
with the GGG ps, except it was more serious because of the half-wave rectifier? Or am i completely wrong?

My tranny had 2 independent 12V secondaries (4 output legs), i just connected the 2 inner
legs together, and that works fine. Its just a more flexible CT transformer with 2 CT legs

[Morocotopo]

Great! So far, my unit works OK, starts every time. That happened to me with the GGG PS... Don´t know why you have that problem at startup, I´m not really expert on PS.

Morocotopo

[km-r]

i bumped this old post because of some problems/doubt experienced by some of the constructors of the marshall sim [Rafa!  ]

heres a modified presence control and a cap replacement before the clipper stage

[Yazoo]

I built the Fender version of the LXH2 a while ago and tried to solve a few problems of my own creation, all in the preamp section I think. I thought I had got it fully working, but now what I get is it works initially but gradually gets more and more distorted. I am using the GGG bipolar power supply design as well. Could this be the same problem? Is this what is described as gating?

I built the Marshall LXH2 as well and it seems happy with the GGG power supply!

[km-r]

i cant imagine how powersupply-related problems cause gating... but mostly, gating occurs when there is poor biasing.
the problem with the marshall sim is that the presence does not really work as intended. it acts more like a "gain" control than a "presence" control.
also, ive experienced gating with my marshall sim but as i replaced the cap before the clipper stage, everything seemed to work fine.

my powersupply is a standard dual 12volt transformer, rectified and filtered and then regulated by 7809 and 7909...
i have my own layout since ive built my sim before this layout came out. ive also used dual opamps! 

[Yazoo]

I went ahead and updated the power supply to a full-wave version - it didn't cost me anything so I thought it was worth a try. I originally had the power going into the preamp section and out into the cab section on a separate stripboard. I've now rerouted it into the cab section then on to the preamp section because I had a lot of wires very close together, power and signal. Now the power wires are the only wires on one end of the board. I also wondered whether the pots might have been shorting out because they were close together. I put insulating tape on the ones that looked as though they might have done this. And I am pleased to say it is working at the moment (I'm being cautious here after past experience ) - no build up of distortion as before, and it does sound good, with a range from clean sounds through to distortion, definitely different to the Marshall version which is also good. 

[rody82]

Hi! 
I needed a long rest before housing my LXH2, but its finally complete
I just wanted to share some pictures with you  sorry for the quality,
i had only my phone right now...







And thank you again for your help building it!

[DougH]

That's a nice chassis. Good job.

One of the things that caught my eye is the photos on the LXH2 site indicate he did the proto in perfboard. I'm thinking, hmmm, I -like- perfboard. I could do that. I've got a 19" rackmount chassis that was going to be used for an amp at one time that would be perfect for this...

[rody82]

thanks I'd never do this on perf... It'd be a debugging nightmare 
But good luck, and keep us informed on your build!

[mike_a]

Hi,

That's a great looking build!

I would love to hear those sounclips, but the links are all dead.
any chance you could upload them again?

Thanks!

[rody82]

Sound samples: http://www.4shared.com/dir/5225037/fbbac11d/diystompboxeslhx2share.html

[DougH]

Is that direct using the speaker sim? How did you set the controls? What kind of guitar did you use?