Reverse engineering vintage Haz Labs pre

[VeryTallBassist]

No, if there was some treble "overdrive" baken in, you'd notice it very clearly as nasty distortion.
That's the way how it is, no myth involved.

There is another thread here on TB regarding this "overload" myth and that clearly demonstrates that there is no treble overload present to the HAZ schematic nothing at all.

If any then at least the (old school) LF442 OP-Amp may have some coloring influence to the total sound. Once the LF442 was swapped for a TL072 (for example), then the magical HAZ sound is widely gone.

I've read those arguments as well and there are several people who build well regarded HAZ clones that don't believe you're looking at the full picture of what is happening within the circuit using only an LT splice simulation. I'm not an electrical engineer, but I've had a career as an AV integrator for over 30 years with a particular focus in audio reinforcement. I have a trained ear. I know what I'm hearing. That said, I have an LF442 in one of my basses and I agree there is a noticeable difference between the older op amp and the new.

I have a back to back recording of a Queensryche tune somewhere - the first with the BTS and the second with the SNC clone. The input levels were identical as was the signal chain. The distortion is (quite ironically) clear as day. If I can find them both, I'll post them.

 

[ThisBass]

As far as I can tell from my own experience with LF442 OP-amp, the LF442 provides some kind of mellow basic sound texture. With the LF422 its possible to gain rather highish treble content, while to the contrary TL072 may produce some sizzle sounding treble at the same amount of treble boost.
Furthermore the LF442 in total might soundwise tolerate more of overload.
With both bass and treble knobs all the way up, the headroom that a 9V battery provides might be maxed out. The LF442 might tolerate exceeding of headroom limits in a more musical way than OP-amps such as TL072.

 

[ThisBass]

I've read those arguments as well and there are several people who build well regarded HAZ clones that don't believe you're looking at the full picture of what is happening within the circuit using only an LT splice simulation.

I have got a master degree in electronics (RF).
Actually I do not need LT spice just to prove and evaluate schematics. But it makes it way more easier to demonstrate the principle of working of "schematics" on forum discussions.

Addressed to all of those who intend to search for mystical things, I don't feel responsible for incomprehension of signal theory.

I'm not an electrical engineer, but I've had a career as an AV integrator for over 30 years with a particular focus in audio reinforcement.

Most of amateurs and hobbyists try to evaluate a schematic with sinusoidal waveform, yet the real practice is way more complex than it looks like with an idealized signal waveform.

I have a trained ear.

Congrats!
Yet in first instance, I try to trust in my own ones.
At the other hand side, at the age of 62 I have to admit that hearing was better at the age of 40, yet more experience at the age of 50.

I know what I'm hearing.

Personally I almost always think I do know what I'm hearing. Yet sometimes the ears can be very tricky. At least I'm aware they can be very tricky at some time.

That said, I have an LF442 in one of my basses and I agree there is a noticeable difference between the older op amp and the new.

Agreed.
And that's the reason what I always tried to to tell in previous threads. The NS2-O (see my avatar) does sound more "organic" due to its different OP-amp, rather than because the oil finish and where there is no varnish that might lock the tone/vibration of the wood

 

[AgingEngineer]

@VeryTallBassist, it's probably best not to engage as they tend to jump into every conversation about HazLabs, claim everyone else is wrong, spew misdirection and folklore based on cherry-picked (or possibly not fully understood) data, and keep banging on until the last word is had. It's not worth it. Some people either believe what they believe, or have an agenda, and neither one is worth wasting time on!

 

[VeryTallBassist]

Agreed.

 

[ThisBass]

@VeryTallBassist
just keep in mind, there are plenty of folks out there who want to sell you snake oil.
Television is full of selling shows, even is internet full of it, and even in forum discussion every DIY guy want's to be the best expert who (sometimes) pretends to be more experienced than professionals.

 

[straightup]

@VeryTallBassist, it's probably best not to engage as they tend to jump into every conversation about HazLabs, claim everyone else is wrong, spew misdirection and folklore based on cherry-picked (or possibly not fully understood) data, and keep banging on until the last word is had. It's not worth it. Some people either believe what they believe, or have an agenda, and neither one is worth wasting time on!

Is it possible to purchase a Haz Clone LHZ-01 shipped to UK?

 

[AgingEngineer]

@straightup: Yes, but it'll be a little while before I am prepared to actively sell.

This started personal project with a goal to get that elusive tone I was looking for and to also share what I've learned with other enthusiasts. I've gotten several inquiries in the last few weeks, so I am building a QA test station to test and document that the preamps are functioning to spec. When that is done, I will be able to sell with assurance that the buyer is receiving a fully functional preamp.

PM me and I will follow up with you when I have units ready to sell.

 

[bowthing]

@straightup: Yes, but it'll be a little while before I am prepared to actively sell.

This started personal project with a goal to get that elusive tone I was looking for and to also share what I've learned with other enthusiasts. I've gotten several inquiries in the last few weeks, so I am building a QA test station to test and document that the preamps are functioning to spec. When that is done, I will be able to sell with assurance that the buyer is receiving a fully functional preamp.

PM me and I will follow up with you when I have units ready to sell.

The test station sounds like an interesting post in itself!

 

[avi]

Agreed.View attachment 5067059

Wow. For what it's worth I'm with VTB and the OP on this. (Especially as he and I both used the same op-amp for our Khaz's.) From a layman's perspective of a guy who has been playing for 40 years, to me the LF442 op-amp does sound like it has a slight compression sound and while I wouldn't say the haz pres have distortion it does clearly "break up" a bit in the mids when compared to the EMG. And truthfully I don't care why. I'm an end user. The word sizzle I use for the high end and niether have that annoyance thankfully. I prefer the clean BT pre's myself but see the allure and enjoy the results on a crap ton (technical word btw) of recordings. I also believe oil caps and cloth wire have magic along with Lucky Charms and babies on Christmas morning so take that as you will. As with all of this everybody has an opinion.... No need to call/imply people are amateurs. Enjoy what you like!

 

[avi]

Also I appreciate and greatly respect the OP's work on recreating this and explaining his efforts. Pretty cool labor of love.

 

[AgingEngineer]

@bowthing: For the true electronic geek, absolutely! Basically, I am making a rig using spring-loaded pogo test pins that I can clamp the finished PCB into. The pins will make contact with the connection pads on the board so I can run controlled, repeatable signals through the board and capture output for analysis. Right now I am planning on running the following tests to give me baseline metrics to make a pass/fail determination:

• Current draw
• Frequency response curve (using sine wave sweep) with Bass & Treble at minimum
• Frequency response curve (using sine wave sweep) with Bass & Treble at midpoint
• Frequency response curve (using sine wave sweep) with Bass & Treble at maximum
• Input vs Output response (using recorded signals direct from pickups at same level as original pickup signal)
• Noise floor

I'm also wondering what a subtractive comparison might look like if I record the raw pickup input signal and the LHZ output into my DAW. I'd then normalize the two of them and subtract the input from the output: the result should just the noise floor plus the harmonic overtones the preamp creates when pushed hard.

 

[ThisYouCanTrust]

I'm also wondering what a subtractive comparison might look like if I record the raw pickup input signal and the LHZ output into my DAW. I'd then normalize the two of them and subtract the input from the output: the result should just the noise floor plus the harmonic overtones the preamp creates when pushed hard.

That would be fantastic !

 

[bowthing]

@bowthing: For the true electronic geek, absolutely! Basically, I am making a rig using spring-loaded pogo test pins that I can clamp the finished PCB into. The pins will make contact with the connection pads on the board so I can run controlled, repeatable signals through the board and capture output for analysis. Right now I am planning on running the following tests to give me baseline metrics to make a pass/fail determination:

• Current draw
• Frequency response curve (using sine wave sweep) with Bass & Treble at minimum
• Frequency response curve (using sine wave sweep) with Bass & Treble at midpoint
• Frequency response curve (using sine wave sweep) with Bass & Treble at maximum
• Input vs Output response (using recorded signals direct from pickups at same level as original pickup signal)
• Noise floor

I'm also wondering what a subtractive comparison might look like if I record the raw pickup input signal and the LHZ output into my DAW. I'd then normalize the two of them and subtract the input from the output: the result should just the noise floor plus the harmonic overtones the preamp creates when pushed hard.

Awesome! The fixtures will be so nice. The longest part of testing for me is hooking everything up, I really need to make some. I do all the sweeps at limits/centers, and noise/distortion, and I've been meaning to add a recorded signal too. Is that something you would listen to and "play around" with the controls, or use instrumentation?

That last idea is great! What fun! It would be eerie to hear what the preamp is "saying" (hopefully not "Paul is dead"!!)

 

[AgingEngineer]

I want to do instrumentation. My intention is to run the sweeps and actual bass signal through the test PCB in three sets: EQ min, EQ flat, EQ Max (automating that if I can). Then take the results into Audition for FFT analysis and to generate frequency response curves. What I'd like is a set of strictly objective pass/fail metrics that tell me the board operates as expected.

Listening is good for a quick "yeah, it works" but hearing is temporal and subjective.

Yes, I'd like to have some hard data to once and for all settle the question of what the preamp itself is adding (or taking away from) the original signal.

 

[Arthur U. Poon]

I want to do instrumentation. My intention is to run the sweeps and actual bass signal through the test PCB in three sets: EQ min, EQ flat, EQ Max (automating that if I can). Then take the results into Audition for FFT analysis and to generate frequency response curves. What I'd like is a set of strictly objective pass/fail metrics that tell me the board operates as expected.

Listening is good for a quick "yeah, it works" but hearing is temporal and subjective.

Yes, I'd like to have some hard data to once and for all settle the question of what the preamp itself is adding (or taking away from) the original signal.

I’m very interested in the finished product that you come up with. One thing I’ve also thought that would be really cool is a foot pedal version. Is this a possibility?

 

[AgingEngineer]

A foot pedal version was on my radar last year, actually! My very first prototype lived in a stompbox enclosure box where I could tinker with it without having to constantly open a bass to try things.

The more I learned about how it works, the more intrigued I was. As the original design goes, the effect is very subtle. HOWEVER, if we were to change the first stage gain, or add a buffer gain stage ahead of it so the signal is pushed very close to the 9volt supply limit (=/- 4.5v swing) when it gets into the 2nd stage, this design might be an very interesting stompbox indeed!

 

[ThisBass]

The more I learned about how it works, the more intrigued I was. As the original design goes, the effect is very subtle. HOWEVER, if we were to change the first stage gain, or add a buffer gain stage ahead of it so the signal is pushed very close to the 9volt supply limit (=/- 4.5v swing) when it gets into the 2nd stage, this design might be an very interesting stompbox indeed!

As long as you don't try you'll never know.
In first instance I'd expect a quite nasty sound timbre once only treble content was hard driven into overload territory.
That's what my scientifically verifiable experience does tell all about this. But hey, as long as you don't try it on your own, you'll never know!

 

[AgingEngineer]

My most recent side-quest lately has been to find the perfect blend potentiometer for my setup. My challenge is that I am running EMG 40P5 with an EMG 40J (both active) and was never happy with any blend potentiometer. Whether it was Linear, M/N, or A/C taper I always had a combination of:

1. Volume dropping off slightly at midpoint when both pickups are one, and
2. Small range of control around the middle.

I tried a lot of different value ranges, with no real difference. I even tried the ungrounded blend. Close, but still no cigar.

The holy grail of blend pots for me is the EMG ABCX (B118), but at $80 that's steep for just a single potentiometer. For those who are curious, here's how to get a smooth blend across the entire span of rotation and none of that annoying volume loss due to impedance loading when in the middle.

 

[fibz]

Looks like you gotta add a blend pot to your preamp, thus making it a LHZ system package :-D