ROLLS HV6 Headphone Volume Control

[amirm]

This is a review and measurements of the ROLLS HV6 passive volume control. It was kindly sent to me by a member and is discontinued. It cost $65 when it was sold.

The box is quite solid and the volume has a nice, fluid feel to it. Note that the XLR input is stereo and not for balanced connections.

ROLLS HV6 Headphone Volume Control Measurements
Let's feed the HV6 4 volts and see what it outputs into high impedance at max volume:

While there is some loss, noise and performance are essentially as good as the source (the audio analyzer). I adjusted the volume down and performance remained proportional.

As noted, input impedance is constant at around 520 ohm. Output impedance changes from that value down to 5 ohm. That obviously interacts with the impedance of the headphone. And that interaction will be variable depending on where the volume control is at.

I tested for channel balanced and it was quite disappointing:

As you see, it starts to drift almost immediately. I have a target of less than 0.5 dB which the HV6 reaches at just 5 dB of attenuation. After that, it keeps getting worse and worse. I have never seen the pot in an headphone amplifier be this bad.

Conclusions
Passive volume controls are quick hacks to solve a problem for which you don't have another option. The problem with them is variability of the impedance. Here, you have poor channel balance to go with it as well.

I can't recommend the ROLLS HV6 headphone volume control. Seek out a different solution at the source.

Manufacturer Specifications:

• Stereo(Male XLR jack) and 1/4" TRS Inputs
• 3.5mm and 1/4" TRS Stereo Outputs
• Stereo signal Level adjustment

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As always, questions, comments, recommendations, etc. are welcome.

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[ROOSKIE]

Bummer. I am not seeing a lot to like within the Rolls brand in general.
Oh well, thankfully have no need of one of these though it seems others do.

 

[xema]

passive headphone volume…… not a good idea

 

[JSmith]

Well this is a real Rolls Canardly!

Thanks for checking it anyway @amirm.


JSmith

 

[wwenze]

Headphone volume pot? Yet no mention of rated power or voltage in the product webpage or manual?

 

[ocinn]

Genuine question - what is the purpose of this/who is the target market. Can’t figure it out, but maybe I’m missing something.

 

[Multicore]

Genuine question - what is the purpose of this/who is the target market. Can’t figure it out, but maybe I’m missing something.

I would guess it's a quick hack to give a musician or singer a personal volume control for their monitoring cans in a recording studio.

 

[BadAudioAdvice]

Genuine question - what is the purpose of this/who is the target market. Can’t figure it out, but maybe I’m missing something.

I bought it to use with my Akai GXC-570D cassette deck that has a fixed volume level on the headphone output.

I sent it in for review because I thought it was a decent unit, made in the USA, smooth control, rugged - too bad the performance didn't match up to the build quality.

I also use another inline volume control (not the ROLLS) as @Multicore says, to control the levels on monitoring headphones for a videoconferencing setup. Its a matter of convenience since where the audio interface is located is out of arms reach, and having an inline control close-by is nice.

 

[Michael Fidler]

Personally, I really don't like the concept of a passive volume control for headphones as...

1. There will always be some compromise in output impedance which will inevitably change the headphone frequency response as the control is rotated and the Thevenin resistance of the wiper rises and falls (due to the non-flat frequency/impedance response of headphones), making it a poor choice for monitoring.
2. The wiper contact resistance itself can vary considerably at headphone impedance, exacerbating point 1 even further. Ideally, potentiometer wipers should feed into a high-impedance node for best tracking performance.
3. There will be much greater loading on the headphone amplifier, so you're going to get more distortion/early clipping.
4. Extremely inexpensive headphone amplifiers (with multiple controlled outputs) are readily available for a very low price on sites such as Aliexpress that will perform much better given the two points above, for $20 or less. I've seen inside these and they're not too bad at all, SMT NJM4556 output amplifiers on 10V positive and negative rails can do about 100mW into 300 ohms.

Having said that, this could be forgiven if it managed to achieve decent channel matching... Unfortunately it doesn't manage even this. I've seen this type of attenuator a few times before in in-line volume controls from Pound Shop headphones in the late 2000s.

Something much better might be just a simple attenuator/rotary switch with 6 levels that would allow you to control output impedance a lot better (Thevenin + series resistance to keep things even).

 

[Eldus]

I wonder how an in line cable with volume control would fare.
Something like this. https://koss.com/products/vc20

 

[BadAudioAdvice]

The other unit I use that goes between a MixPre3-II and Apple 3.5mm Headphones (to listen to the other party in a videoconference and to provide simple monitoring to make sure the microphone isn't clipping or there isn't problematic background noise) is this one https://www.amazon.com/Volbox-inline-audio-control-attenuator/dp/B00XDKKQ9E

I selected it over the Koss one as I can pick my own cable length for the input. Also supposedly hand-made made in Canada.

I wish I had sent it in for review - fidelity is not important with this unit, but seeing how poor the ROLLS was, would have been interesting to see how this stacked up.

Extremely inexpensive headphone amplifiers (with multiple controlled outputs) are readily available for a very low price on sites such as Aliexpress that will perform much better given the two points above, for $20 or less. I've seen inside these and they're not too bad at all, SMT NJM4556 output amplifiers on 10V positive and negative rails can do about 100mW into 300 ohms.

Agreed that there are better solutions for fidelity and performance (either a powered solution, or the simple 6-level control), in both situations I was trying to keep cable clutter to a minimum and have fine-grained control. Also in my case with the AKAI, the quality of the source is limited, that's why its a shame about the channel-imbalance, since that will definitely impact the listening experience.

 

[Michael Fidler]

Agreed that there are better solutions for fidelity and performance (either a powered solution, or the simple 6-level control), in both situations I was trying to keep cable clutter to a minimum and have fine-grained control. Also in my case with the AKAI, the quality of the source is limited, that's why its a shame about the channel-imbalance, since that will definitely impact the listening experience.

I think a tapped autotransformer might be a better idea for this product... I remember AKAI used to use output transformers in some of their reel-to-reel recorders (4000DS etc.) for the headphone output. No idea if you can get these but it could be an interesting product.

 

[BadAudioAdvice]

Looking at the schematic, the 570D uses:
Headphone Transformer
N19-349S
Primary 160 ohms ±15%
Secondary 0.64 ohms ±15%

And from a previous discussion here on ASR, solderdude said given how they implemented the headphone output, it might not be worth trying to do too much with it:
"The headphone output is an afterthought.

It is the line output run through a very low power emitter follower which is connected via a small audio transformer as used in portable radios of that day. They used that same signal for the meters and just tapped it off for the headphone out.
Measured performance will not be great."

 

[lc6]

As noted, input impedance is constant at around 520 ohm. Output impedance changes from that value down to 5 ohm.

If this is a 520-Ohm "pot-in-the-box," then what else electrically could be expected?

 

[amirm]

Well, it could have had better channel matching.

 

[milosz]

Use of an L-Pad can maintain constant impedance.

 

[ocinn]

I would guess it's a quick hack to give a musician or singer a personal volume control for their monitoring cans in a recording studio.

Every time I’ve worked in professional studio settings, headphone level is adjusted by a simple verbal command to the engineer.

Most importantly; almost all, if not actually all of monitoring change requests I’ve ever seen in studio settings, are to adjust their relative level in context of the full mix (which this product cannot do) , not overall loudness.

I don’t see how this product would solve any of the real world issues for those use cases.

@BadAudioAdvice explained how they use a similar device for general convenience in videoconfeeencing scenarios, but I honestly see no point for this product to be used in a hi-fi context, poor measurements or not.

 

[Multicore]

I don’t see how this product would solve any of the real world issues for those use cases.

Yes, a proper studio wouldn't need this. I used the word "hack" and properly set up studios don't need hacks.

@BadAudioAdvice explained how they use a similar device for general convenience in videoconfeeencing scenarios, but I honestly see no point for this product to be used in a hi-fi context, poor measurements or not.

Like Amir said in the review, get a proper volume control upstream.

 

[Svperstar]

Genuine question - what is the purpose of this/who is the target market. Can’t figure it out, but maybe I’m missing something.

I am using a passive volume control on my Koss electrostats. The reason is the volume knob is terrible on the energizer and controls the balance as well as volume, its hard to explain unless you have tried the knob yourself. I found a passive volume control meant for subwoofers in cars that don't have a separate volume knob. I like it because it does not have to be plugged in. Just stuck in the middle of the RCA cables.

Anyway, it works pretty well for being like $9

 

[Bacchusoo7]

Rolls products aren't about high fidelity. They're typically tools for solving niche problems, often in live sound applications or similar applications, where you need it to "just work" rather than be of the utmost quality. These products were far more relevant 20-30 years ago before computer integration and high tech Chinese manufacturing. But in the days of quick and dirty PAs or 4-track cassette recorders their products could offer options/features to those on a limited budget that might foreclosed to them. Most of the products they offer today are the same as 30 years ago. On-Stage, Whirlwind, Gator, etc. offer similar types of products.