Reverse engineering vintage Haz Labs pre

[AgingEngineer]

Well, I finally got a little time this weekend to do some testing on the Legacy preamp to see if I could figure out what was going on. A little backstory: I'd had several clients reach out over the last few months saying the Legacy felt a little darker than their old Hazlabs preamp. That didn't make sense as the Legacy is allegedly a clone of the Haz just like the LHZ.

After one client replaced his Legacy preamp, he sent it to me to test.

To everyone who felt like the Legacy is a little darker than the LHZ or the Hazlabs, you're not crazy!
Not too many people can hear the difference, but for those who can, this might explain why.

 

[fourstringbliss]

As the LHZ started life here in this forum, TB always will get the scoop on news.

RETIRING SOON: The LHZ-03 preamp is down to about a dozen units left in our shop. Once these are gone, the LHZ-04 will be the successor. The LHZ-04 is the same circuit, same components, and same tone. It's just a physical redesign to a smaller and a VERY low-profile board that makes installation much easier for those challenging spots and limited spaces. While the LHZ Shop will run out soon, Bass Direct in the UL and Ties Store in Japan still has stock.

COMING SOON: The LBCA-02 is an Active Blend control designed for the LHZ preamp. While we've been offering limited sales, we'll have full inventory listed within a week including versions for BOTH Active and Passive pickups.

ON THE DESIGN DESK: We've been working on a mid saturation control as a side project in response to inquiries from a client. This isn't a midrange EQ, this dials in a little saturation to a select range of mids to give a bit of drive that works really nice for solos and higher register work. I do not expect this to be a retail product as it is a very niche thing. I will be building a few prototype boards in the next month so if anyone is interested and wants to play with something a little... different... let me know.

Is the currently available mid control this same mid saturation idea or does it function more like a regular mid control?

 

[fourstringbliss]

That is almost exactly my own experience with the X series pickups in my Zebrawood Rebop. I've got two other Rebops that are all within +/- 2 years of each other, each with different woods. The Zebrawood definitely has a VERY different tone than the other two.

Because I love experimenting, I tried the X series in my Zebrawood Rebop but they didn't stay there for a month before I went back to my tried and true 40P5 and 40J set. Like you, I found it too bright and clean sounding. I ended up putting them on one of my frankenbasses that has a duller tone, and they sounded great on that instrument.

How do you like the 40P5 and 40J setup? I have two 40DC's in my Spector Pulse, but I had thought about switching to a P/J setup for more of the "Spector Sound".

 

[AgingEngineer]

Is the currently available mid control this same mid saturation idea or does it function more like a regular mid control?

The the MID-03 control behaves exactly like the mid control on the 18V Haz preamp. It uses the same opamp and same circuit design. The interesting thing about this design is that it is placed after the bass and treble portion of the circuit. This means that it is easy to push this midrange into saturation when running at 9 volts, particularly if you have the bass and treble boosted.

That ease of saturation is likely why Hazlabs only offers the midrange on their 18volt model. On the LHZ, you can easily run it either way.

How do you like the 40P5 and 40J setup? I have two 40DC's in my Spector Pulse, but I had thought about switching to a P/J setup for more of the "Spector Sound".

I absolutely LOVE the 40P5 and 40J combination on my Rebop and Euros! I started with humbuckers, moved to the DC's, did the 40P5 and 40DC combo, and finally landed on the 40P5 and 40J combo. Let me qualify this however...

The Rebop and Euro models I play have that "narrow" pickup spacing: the neck pickup is a LOT closer to the bridge pickup than other models. I think this makes a difference when it comes to which pickup pairing works best. On my basses, the P pickup does not overshadow the volume of the J pickup. On a bass with traditional pickup spacing (where the neck pickup is closer to the neck), you get a LOT more volume from the P pickup just because it's seeing a lot more string travel.

The closer to the midpoint of the string, the more string motion it sees. This equates to more volume and a "rounder" tone with less overtones in it.

I tried doing the P/J combo on my Omen Extreme. Since it has the same scale length and same outstanding complex body tone when played unplugged, I assumed it'd sound like the Rebop and Euro basses. Nope! Different beast entirely! The P/J with LHZ sound GREAT in that bass, but I was having the same problem people in the forums noted where --in center blend-- it feels like it's mostly P pickup and is missing those . On that bass, a 40P5 in the neck and a 40DC in the bridge neatly solves that.

All that to say this... If you're thinking about a pickup swap, maybe go halfway at first? Try just replacing the neck with a 40P5 and leave the 40DC in the bridge. You'll be spending half the $$ and might find yourself exactly where you wanted to be.

 

[Hillie]

Have you tried adjusting pickup height to balance the neck & bridge pickups in the middle blend setting?

 

[fourstringbliss]

The the MID-03 control behaves exactly like the mid control on the 18V Haz preamp. It uses the same opamp and same circuit design. The interesting thing about this design is that it is placed after the bass and treble portion of the circuit. This means that it is easy to push this midrange into saturation when running at 9 volts, particularly if you have the bass and treble boosted.

That ease of saturation is likely why Hazlabs only offers the midrange on their 18volt model. On the LHZ, you can easily run it either way.


I absolutely LOVE the 40P5 and 40J combination on my Rebop and Euros! I started with humbuckers, moved to the DC's, did the 40P5 and 40DC combo, and finally landed on the 40P5 and 40J combo. Let me qualify this however...

The Rebop and Euro models I play have that "narrow" pickup spacing: the neck pickup is a LOT closer to the bridge pickup than other models. I think this makes a difference when it comes to which pickup pairing works best. On my basses, the P pickup does not overshadow the volume of the J pickup. On a bass with traditional pickup spacing (where the neck pickup is closer to the neck), you get a LOT more volume from the P pickup just because it's seeing a lot more string travel.

The closer to the midpoint of the string, the more string motion it sees. This equates to more volume and a "rounder" tone with less overtones in it.

I tried doing the P/J combo on my Omen Extreme. Since it has the same scale length and same outstanding complex body tone when played unplugged, I assumed it'd sound like the Rebop and Euro basses. Nope! Different beast entirely! The P/J with LHZ sound GREAT in that bass, but I was having the same problem people in the forums noted where --in center blend-- it feels like it's mostly P pickup and is missing those . On that bass, a 40P5 in the neck and a 40DC in the bridge neatly solves that.

All that to say this... If you're thinking about a pickup swap, maybe go halfway at first? Try just replacing the neck with a 40P5 and leave the 40DC in the bridge. You'll be spending half the $$ and might find yourself exactly where you wanted to be.

Thanks! Yeah, my Spector is one of these:

So the neck pickup is farther forward. I've read about the idea of replacing the the neck 40DC with a 40P5, so I'll probably go with that. As it is, the J part of the 40J is in the rear, so closer to the bridge. The 40P5 would overshadow that for sure, just like the neck 40DC overshadows the bridge 40DC in the bass as it is now.

This beast has been a work in progress. I traded a bass I wasn't going to play for this only to find that the truss rod is frozen and four of the tuners didn't work well. Thankfully the truss rod stuck almost exactly where I need it with the strings I'm using on this bass and my hope is that seasonal weather changes don't mess with that. After replacing all of the tuners I'm on toward replacing the preamp.

I'm struggling with the stock Tonepump Jr's output. I played at church this morning and even after I used an amp modeling patch with much lower volume that I use on either of my other basses I still needed to turn it down to avoid distortion in my in-ear monitors.

Is this pulse in need of the midrange control or would the 2-band LHZ work just fine? What would mids saturation sound like?

I'm not a fan of stacked controls, so if I didn't need the mid control that would be good.

 

[fourstringbliss]

Have you tried adjusting pickup height to balance the neck & bridge pickups in the middle blend setting?

I did that and it sounds more balanced, thanks!

 

[AgingEngineer]

This weekend I was working on a wiring diagram that uses the EMG's Push/Pull Pot (B136rE) for a unique purpose: acting as a push-pull bypass for the LHZ preamp and master volume control. This was a tricky one as the B136rE is specifically designed for use with the TW pickups. While it has modular connectors that make this a VERY attractive control for the modding community, the layout of the connections were optimized for the TW pickup connectors and configuration.

This task was made more complicated because the schematic for the B136rE (as published in EMG's PDF document) DOES NOT MATCH the wiring! The document that ships with the control omits the schematic entirely to focus on how to use the control with TW pickups.

So, to the bench I went to see how this thing is wired!

For anyone wanting to use this unit for custom work, it's more than capable: you have an independent DPDT push-pull switch and 25K audio taper pot, all routed to modular pin headers Here's how it's wired internally:

 

[Bonjareno]

Well it only took me 3 months to sit down and install this the way I wanted without excessive cable lengths all over the place. Even though it doesn't really matter, I have an Ibanez with a packed cavity that is just annoying to work in if needed.

I haven't had much time with it but I'm happy to have a mid control back on my main bass.

 

[AgingEngineer]

Well it only took me 3 months to sit down and install this the way I wanted without excessive cable lengths all over the place. Even though it doesn't really matter, I have an Ibanez with a packed cavity that is just annoying to work in if needed.
View attachment 7352617View attachment 7352618

I haven't had much time with it but I'm happy to have a mid control back on my main bass.

Nicely done!!!

I am still guilty of "rats nest" cavity wiring myself. While I spend a LOT of time when it comes to wire routing and ergonomics when designing PC boards, when it comes to doing installs I am not that patient. I get caught in that "let me hear it right now, and I'll clean it up later" mindset, but later never comes.

Looking good!

 

[musicmax]

Well it only took me 3 months to sit down and install this the way I wanted without excessive cable lengths all over the place. Even though it doesn't really matter, I have an Ibanez with a packed cavity that is just annoying to work in if needed.
View attachment 7352617View attachment 7352618

I haven't had much time with it but I'm happy to have a mid control back on my main bass.

Wow that's as smooth as a Yacht Rock concert!

 

[crazycloud]

I asked in the Spector thread a few days ago about these preamps, but didn't realise there was a thread on them.

Post Christmas, I'm going to order a 2 and 3 band for a couple of projects I have. I need to wait until then as I special ordered a bass, and bought another via a chance sale, so the pocket money fund is zero until then.
I'll spend some time reading the thread front to back in the mean time too.

 

[AgingEngineer]

I asked in the Spector thread a few days ago about these preamps, but didn't realise there was a thread on them.

Post Christmas, I'm going to order a 2 and 3 band for a couple of projects I have. I need to wait until then as I special ordered a bass, and bought another via a chance sale, so the pocket money fund is zero until then.
I'll spend some time reading the thread front to back in the mean time too.

Hey @crazycloud! This is the thread where LHZ Preamps was originally born! This all started from a post-COVID project to see if I could save my 2008 Rebop from being sold. I'd bought it brand new, loved the look and feel and playability, but had struggled getting that classic Spector tone out of it. I knew, of course, that the tones I was chasing (Eddie Jackson, Mike Starr) came from USA NS2 basses, and I had the Rebop. However... it had excellent construction, the pickups had the same NS2 spacing, and unplugged it growled like a beast. I knew it had the body tone. It seemed logical to me that if I had the same electronics that I'd be able to get really close to that NS2 tone.

I'd spent years swapping out pickups and preamps and had settled on active EMG P/J pickups (40P5 and 40J because this was a 5 stringer) and EMG preamp, but it still just wasn't there. I was planning on selling it when I thought "well, the only thing missing is the Hazlabs preamp," so I went on a search to get one. No way I'm going to spend $400+ on a 40 year old board, and SNC stopped making clones, so I thought I'd just make my own. I posted here looking for info and sharing my progress, but never planned on anything more than being a one-time project.

Truly, it was the TalkBass community here that kept driving me forward. I tend to squirrel and get off onto other tracks, but folks kept chiming in with information and help, and eventually requests to buy one. So, this is where the history of LHZ starts! If you want more info about the product line (we've got everything now, volume pots, active blends controls, midrange modules, jacks, parts, and pedals), check out the LHZ Preamps website.

Cheers!

 

[AgingEngineer]

We've finally got the TonePump vs LHZ Preamp comparison video finished a posted!

 

[crazycloud]

^^ That's how you perform a proper comparison. Same signal from file, not an attempt to play the same way twice and level matched in a consistent manner. The tech analysis was great too - I understood it and I thought it was pretty clear and most non technical people should still get something out of it

Kudos from another old (electrical) engineer.

PS: I'll still be ordering a 2 and 3 band next year, once the recently ordered bass has arrived. There's a hard stop on any new gear until then.

 

[AgingEngineer]

^^ That's how you perform a proper comparison. Same signal from file, not an attempt to play the same way twice and level matched in a consistent manner. The tech analysis was great too - I understood it and I thought it was pretty clear and most non technical people should still get something out of it

Kudos from another old (electrical) engineer.

PS: I'll still be ordering a 2 and 3 band next year, once the recently ordered bass has arrived. There's a hard stop on any new gear until then.

Thank you! I always find myself second-guessing myself when I work on these. Social media in general has gotten a lot of people addicted to dumbed-down 1 minute soundbites, so I keep thinking no-one is going to have the patience to watch these. But I'm finding the modding community is different: we want to know as much as we can before we start digging into the guts of our own equipment.

It's a balancing act that I am still trying to figure out. How do I give enough detail without rambling on? Coupled with the fact that I am not at all comfortable being the guy in front of the camera (my happy place is being the guy behind the curtain, pulling the levers to make the great Oz do his thing) so that's been a learning curve too.

All that to say your encouragement means a lot! Cheers!

 

[clickclack]

Having built many preamps including several HAZ clones, some with slight mods, I like the early saturation and compression of TonePump more. Not just TP I guess, I like the discrete jfet designs more overall despite the extra work you have to put in not just in design stage but also as a player later on.

I have the TP in a full maple hunk 6 string Legend Classic.

I wish we could have a schematic for TP as well. It's probably a 2 stage Jfet design but the way the pots respond makes me question if it's a regular tone stack in between or something more enthusiastic like adjusting first fet's source cap to ground for bass control and for treble, a simple cap-to-ground tone pot on output, after a huge boost, like the HAZ's first stage.
Either way, TP's treble cut is not enough sometimes so I simply added a regular passive tone pot before the pre and used a stack pot for pickup volumes.

Thanks for the comparison video!

 

[AgingEngineer]

Having built many preamps including several HAZ clones, some with slight mods, I like the early saturation and compression of TonePump more. Not just TP I guess, I like the discrete jfet designs more overall despite the extra work you have to put in not just in design stage but also as a player later on.

I hear you! I was really into JFET based pedals back in the day. Forrest M. Mims Engineers Notebooks from the late 70's got me hooked on electronics, but it was Craig Andertons "Electronic Projects for Musicians" book (maybe 1980 or so?) that inspired me to try building circuits to emulate that glorious tube amp tone.

I remember being both inspired and frustrated with JFET circuits. For a "build it first, then figure it out" guy, they require a much larger grounding in theory than I'd had at the time. I spent several years experimenting with discrete designs, then fell into the opamp world and never left.

Like you, I am really curious what's inside the TonePump. Not enough to try to tear one open, but just to understand the design.

Cheers!

 

[clickclack]

I hear you! I was really into JFET based pedals back in the day.

When working with fets, it's almost certain that you will continue biasing and thinking about what different models will respond like in your dreams. When you're finally happy that you got a beautiful balance and tone and then it all gets f***ed up in the mix by someone who thinks(doesn't know any better) bass should only do bass frequencies and it ends up sounding the same so much that it almost doesn't even matter what bass, pickups and strings you got. lol

Talking about frustrations, there's this amazing software called LiveSpice, designed by a few very clever people. I think you'd find that useful. You won't see realistic saturation but it does a great job of simulating filters and simple circuits like the preamps we like to tinker with in real time so you don't have to solder parts or jiggle breadboards to hear how it would sound like, mostly EQ-wise. Gets close enough except the real-world complex harmonics. I'd say it requires a newish, above average CPU model no older than 5 years old to be fast enough. Works as a VST plugin too.

 

[AgingEngineer]

This is the forum where LHZ was born, so TBer's always get the scoop on what's new. This is a prototype of what the 2026 LHZ platform will look like. This particular unit is a 3 band LHZ. It combines the current LHZ-04 and MID-03 modules into one unit that is the same physical size as the current LHZ-04, and uses miniature JST connections for the pots and output.

This design allows users to easily swap out pots, change from a righthand to lefthand configuration, or assign a concentric pot to any EQ control. Want the mid & bass on the concentric pot instead of the usual bass & treble? Yep, you can do that. Don't need the mids and just want 2-band control? No problem. Broke a pot? It's now a no-solder replacement.

We have many clients putting the LHZ into Fenders and basses with tight control cavities. This configuration makes those installations a lot easier as it eliminates the MID module and the extra wiring. We've got a few other accessories and variations in the works that will make many of the custom modifications (bypass circuits, tone controls, switchable 9v/18v operation) a plug-and-play process.

Got something on your wish list? Let us know! Our "concept engineers" are our clients. Every update to LHZ preamps started with players going "this is great, but I'd LOVE it if I could do this..."

We've got a few prototypes going out this month for beta testing (it's going to be a fun Christmas for a few folks). Assuming all goes well and there are no major revisions needed, they'll be available for sale around the end of January or February.