Has anyone built the LXH2?

[Kevin Mitchell]

I've been toying around with the idea of building a headphone amplifier but haven't settled on a design yet as with many of today's options there is much to be desired IMO. However, the other day I had stumbled upon the now discontinued LHX2 designs for both Marshall and Fender amp & cab simulation circuits which are solid state circuits designed to emulate the frequency response of the traditional tube combo amps - circuits for both the preamp and cabinet/speaker. While I've pondered on this approach in the passed, it's quite interesting to see someone's take on such a challenge.

So I thought I'd ask, has anyone here tinkered/built either the LXH2 Marshall or Fender amp & cab simulators?
What did you think? Did it come out as expected and comparable to the original equipment it's aimed to emulate?

I'm fixing to breadboard these monsters and add some extra goodies like reverb and a headphone driver.

[Ice-9]

I have owned the Marshall JMP1 with the cabsim that is documented in your link. It is a simple multi pole filter design and in my opinion was one of the best I have used when recording guitar into a DAW so should be suitable for headphone use as well. There are possibly better now using DSP but for simple easy to build I would say give the JMP1 speaker simulator a try as it is only a handful of components.

[Kevin Mitchell]

I'm an analog snob - where I can help it 
No DSP for me!

That's a nifty circuit! Much more simple in comparison. I'll add it to my breadboard to-do list.

The link I had posted contains a bunch of cabsims. But I'm specifically talking about the solid-state Marshall and Fender projects. They refer to a wayback link. I know the Marshall design had gotten decent attention at the time.

But I'll share the Fender schematics here as it's the one I'm most interested in. Mostly because my go-to amp is a home-brew Deluxe Reverb.
Since it's a dead project I hope I'm not stepping on any toes posting em' (please let me know otherwise).
Wayback link: https://web.archive.org/web/20100114235423/http://home3.netcarrier.com/~lxh2/distampt.html

*there are two image links below this text*

[Ice-9]

Hi Kevin,
That wayback link wouldn't open for me.
I'm a bit sad today as I have just sold my JMP1 preamp on Ebay. I have recorded so many guitar parts using the output emulator direct to tape or DAW setup. End of an era I guess.

I think most of the old hardware speaker/output emulator circuits are based on multistage Sallen key type filters and gyrators.

[PRR]

That wayback link wouldn't open for me.

Archive.org, the WayBack Machine, has a crisis going on. It is off-line for most people most of the last day and apparently ongoing. DDoS attack and 31 million user accounts exposed.

Put a tickle on your calendar to try next week.

https://arstechnica.com/information-technology/2024/10/archive-org-a-repository-storing-the-entire-history-of-the-internet-has-been-hacked/
https://cybernews.com/news/internet-archive-down-ddos-cyberattack-users-breached/

_I_ had an Archive.org account, and password. Who knew? Why? I've changed that password.

[Kevin Mitchell]

Thanks, PRR. I was going to say that it's been acting up since I've found the link. Yesterday it was a hit or miss.

Looking into the JMP1 further, I can see how it will be missed. That thing is packed! Even had what looks to be a couple of dual triodes stuffed in there.

Thanks for naming the filter. I knew I was looking at a load of identical filters in the speaker simulator portion but wasn't aware of the topology. Another for the list 

I'm currently pondering on how one would substitute all of those germanium diodes - there's 9 inverse pairs in series for what I believe to be just compression. Seems a bit excessive instead of using more appropriate parts or design?

[Ice-9]

Looking into the JMP1 further, I can see how it will be missed. That thing is packed! Even had what looks to be a couple of dual triodes stuffed in there.

Thanks for naming the filter. I knew I was looking at a load of identical filters in the speaker simulator portion but wasn't aware of the topology. Another for the list 

I'm currently pondering on how one would substitute all of those germanium diodes - there's 9 inverse pairs in series for what I believe to be just compression. Seems a bit excessive instead of using more appropriate parts or design?

The JMP1 12ax7's really do nothing for the overdrive, it is mostly diode clipping. The part I was referring to was just the Speaker output emulation, it works very well and would be a useful with any preamp or drive pedal, but I will miss my JMP1. Many of the other speaker output emulators you will see are based on pretty much the same type of topology.
I would also say have a look at the AMT legend2 series pedal speaker out emulator sections, it has a different approach but does also sound very good. I worked on dissecting these with Bajaman some years ago and you can find the schematics on another forum that we shall not name.

[Rob Strand]

The problem with cab sims is they all promise to match Fender amps or Marshall 4x12" but when you look at the response they are all over the place.   The underlying mic'ing position obviously has a big effect.

I found a schematic for a MARcus 2400 Guitar preamp which claims to emulate a 4x12" cabinet.



It has some notches to emulate the 4x12" sound.   Fairly economical compared to the LHX design and as I recall it does add some 4x12" character.

At some point I played around tweaking it, kind of an unfinished project.   I also remember grafting some of the low pass filters which are based on notch filters at the high end from those Russian designs, like the Lart design.    You can tweak the low-pass filters to make it brighter or darker.  The notches on the MARcus are at 1.5kHz and 7.5kHz, the upper notch changes the slope of the low-pass filter (and makes it along the lines of the Russian designs.)   I have a feeling I played with adding another notch at a lower frequency as well.

IMHO there's three types of cab sims depending on the source signal:
Speaker out w reactive load ->  cab sim only emulates speaker
Preamp  ->  cab sim emulates speaker and power amp + speaker interaction (treble & bass boost)
            = cab sim + partial amp sim
Guitar  ->  cab sim needs to include whole amp chain including shaping from amp's tone control.
            = cab sim + amp sim

The target EQ curve is quite different in each case.
EDIT: clarified a small point after jogging my memory.

[Rob Strand]

Here's a quick comparison of a few contenders:

marcus2400
marshall jmp1
marshall jtm
lart2 (simple)

[Ice-9]

It could be interesting to add a pot control to some of the LXH2 eq filter stages to adjust the level of cut/boost of each frequency.

[PRR]

try next week.

Spooky. It came back Monday morning.

https://www.theverge.com/2024/10/14/24269741/internet-archive-online-read-only-data-breach-outage

"The Internet Archive is back online in a read-only state after a cyberattack brought down the digital library and Wayback Machine last week. ...... back online in a "provisional, read-only manner," according to founder Brewster Kahle. "Safe to resume but might need further maintenance, in which case it will be suspended again."
Internet Archive wobbles back online, with limited functionality
"Kahle and the Archive have not yet detailed the incident, or any steps taken to harden the site against future heists. Fair enough – they've been busy getting back online."

[Morocotopo]

Yup.
I built the LHX2 Fender amp and cab sim. Quite a few years ago. Put it all in a yellow painted box with a 3 band EQ and the power supply.
But I think  it was someone´s mod to the amp part, some changes in the diode strings as I recall.
How does it sound? Not like a real tube Fender amp, no. But it makes some useful sounds.
Haven´t plugged it in in quite a few years, maybe I´ll take it out and see if I like it now.