Taboo cheapness: Harrison Labs attenuators & crossovers

[differenceclouds]

I bought a pair of Harrison Labs 12dB in-line RCA attenuators to solve a hiss in an old Hafler preamp. It works beautifully, as the hiss was independent of the volume control. To my ear, these little magic RCA adapters are transparent, but I would love for someone around here to see how they measure. I've never tried their inline passive crossovers, but I am VERY curious. The only word I've seen from online audio people is that these products are "for car audio, avoid," which is unconvincing. While it might appear they haven't updated their website since 1998, don't be afraid to order direct from them, they ship quickly. Anyone up for the challenge?

Attenuators:
https://www.hlabs.com/products/attenuators/

Crossovers:
https://www.hlabs.com/products/crossovers/

 

[Willem]

I use their attenuators because my Quad power amps have a now uncommonly high input sensitivity of 0.5 Volt. They work very well. You cannot order them from Europe I think but RME recommend EU alternatives. I have no experience with their inline filters but they may be a cheap and easy way to add a high pass filter.

 

[JeffS7444]

Passive line-level crossovers have been available for many years: Magnepan was offering them in the 1980s. Theirs was a small box with RCA jacks and a couple of film capacitors acting as high-pass filters, and much of the actual work was still being done by the passive crossover components built into the speaker panel. Not an ideal setup, but it worked. No such thing as inexpensive electronic crossovers or measurement tools back in those days!

 

[win]

While it might appear they haven't updated their website since 1998

wow, that site is aggressively 90s internet. Love it.

 

[Martin]

I use passive attenuators to balance the tube top / solid state bottom biamp setup on my speakers. I found Harrison Labs attentuators in my search but I needed balanced XLR attentuators. I tried some pro audio attenuators but they introduced strange effects into the signal. I tried Sescom and Procraft balanced attenuators. Neither were suitable for my purpose. I used a passive preamp for a while but I did not like the additional box and cables in the audio chain, that and I only needed a 20dB set attenution. I finally found attenuators that worked. They're pricier than Harrison Labs but Rothwell Inline Attenuators work perfectly. I find them completely transparent.

Martin

 

[ElNino]

The Harrison Labs attenuators are solid, but the passive crossovers have some drawbacks. The crossover frequency actually varies depending on the input impedance of your power amp, and they don't give enough info on their website to help you predict in advance what it'll be. Also, given the filter slope, you're not going to be able to create an LR2 crossover with a powered sub (i.e., with a flat sum) with these.

If you're looking for cheap crossover solutions, a cheap active crossover box like the Rolls SX45 or some of the no-name brand ones floating around is probably a better solution than buying a pair of Harrison Labs crossovers. Elliott Sound Products also sells a popular active PCB that you can configure as LR2 or LR4 if DIY is more your thing.

 

[AnalogSteph]

I tried some pro audio attenuators but they introduced strange effects into the signal. I tried Sescom and Procraft balanced attenuators. Neither were suitable for my purpose.

Procraft:

WTF?

This looks like someone literally looked up "attenuator" on the interwebs, but with zero understanding of how balanced audio connections work.

This kind of T-type attenuator is what you use for unbalanced signals in impedance matched systems. Balanced audio connections are neither.

EDIT: Here's what ought to be inside:

For a line-level 20 dB, one could use e.g. R1 = R3 = 4k7, R2 = R4 = 510R.
The same for microphone use might employ R1 = R3 = 1k5, R2 = R4 = 180R.

 

[Martin]

Procraft:

WTF?

This looks like someone literally looked up "attenuator" on the interwebs, but with zero understanding of how balanced audio connections work.

This kind of T-type attenuator is what you use for unbalanced signals in impedance matched systems. Balanced audio connections are neither.

EDIT: Here's what ought to be inside:
View attachment 85928
For a line-level 20 dB, one could use e.g. R1 = R3 = 4k7, R2 = R4 = 510R.
The same for microphone use might employ R1 = R3 = 1k5, R2 = R4 = 180R.

Nice to know why they did not work. The Procraft attenuators were 1/4 the price of the Sescom units but both were equally bad in my system. I wonder what Sescom's circuit looks like. In any case the Rothwells work perfectly.

Martin

 

[EJ3]

I bought a pair of Harrison Labs 12dB in-line RCA attenuators to solve a hiss in an old Hafler preamp. It works beautifully, as the hiss was independent of the volume control. To my ear, these little magic RCA adapters are transparent, but I would love for someone around here to see how they measure. I've never tried their inline passive crossovers, but I am VERY curious. The only word I've seen from online audio people is that these products are "for car audio, avoid," which is unconvincing. While it might appear they haven't updated their website since 1998, don't be afraid to order direct from them, they ship quickly. Anyone up for the challenge?

Attenuators:
https://www.hlabs.com/products/attenuators/

Crossovers:
https://www.hlabs.com/products/crossovers/

I have had great success using the HARRISON LABRORATORY'S PFMOD for running under 80 Hz to my stereo NAD 2200 SUB AMP running into 2 dual 4 ohm voice coil 12" woofers operating each one as a 2 ohm circuit.

 

[Head_Unit]

The Harrison Labs attenuators are solid, but the passive crossovers have some drawbacks. The crossover frequency actually varies depending on the input impedance of your power amp...Also...the filter slope

I once measured a pair of "100 Hz" units, and they were about -6 dB at 100 and -3 around 155. I'm pretty sure inside is a stacked set of 1st order RC filters. Someone posted that one of the small Rolls was pretty transparent, but if one doesn't want electronics in the chain the Harrisons can be effective. I'd spend a bit more and get the parametric to be more flexible https://www.hlabs.com/products/crossovers/index_files/Page384.htm

 

[Speedskater]

Note that neither of the above balanced attenuator schematics is correct.

 

[LTig]

EDIT: Here's what ought to be inside:
View attachment 85928
For a line-level 20 dB, one could use e.g. R1 = R3 = 4k7, R2 = R4 = 510R.
The same for microphone use might employ R1 = R3 = 1k5, R2 = R4 = 180R.

This circuit would be correct if you would skip the connection to the shield. Then you can replace R2 and R4 by a single resistor having twice the value of R2/R4.

 

[Matias]

but Rothwell Inline Attenuators work perfectly. I find them completely transparent.

I bought a pair of Rothwell RCA attenuators and they were severely mismatched, one was stronger than the other, had to return them for a refund...

 

[AnalogSteph]

This circuit would be correct if you would skip the connection to the shield. Then you can replace R2 and R4 by a single resistor having twice the value of R2/R4.

You could. The crux of the matter is that while a floating attenuator has fewer potential issues with resistor matching, it also has a common-mode attenuation of zero. (If I can find the article discussing the pros and cons of both again, I'll link it here. I was originally convinced that the floating one was better, too...)

At substantial attenuation, this can become a major issue, straining input CMRR at the very least as the differential mode signal is being attenuated while nothing happens to common-mode. Imagine you're using an attenuator like this to connect an audio interface microphone input to an unbalanced power amplifier output. Unbalanced output means that the common-mode signal is half the output amplitude. An input that can take like +9 dBu max (little over 2 Vrms) is not going to be happy when subjected to 20 Vrms of common-mode out of a 200 wpc amplifier.

You do have to watch out for resistor matching, but that's not a super big issue these days (if you're too cheap for 0,1% resistors, just buy a bunch of 1% and match them yourself - it's not like you need better than 0.1 dB accuracy in terms of attenuation anyway, it's the relative matching between any two resistors of the same value that counts).

 

[Martin]

I bought a pair of Rothwell RCA attenuators and they were severely mismatched, one was stronger than the other, had to return them for a refund...

They only make 10 and 20dB versions so the must have mixed one of each together in the package.

Martin

 

[Matias]

They only make 10 and 20dB versions so the must have mixed one of each together in the package.

Martin

It was not that severe, and I did not measure them, but surely 1 or 2 dBs different enough to ruin the balance.

 

[AnalogSteph]

That may have been a bad solder joint in one of them. Resistor tolerances would not normally account for any difference that big.

 

[flowcharts]

I would encourage anyone who's considering buying a Harrison product to take a moment and read through their website before making a purchase.

 

[Willem]

I could do without some of it indeed. Creepy.

 

[hege]

Had good success with Naiant, ordered many times, there's proper line-level options too:

https://naiant.com/studio-electronics-products/inline-devices/mpd-inline-attenuator/