[KeithEmo]

With the jumpers in, the headphone output on the A-100 is connected directly to the same place as the speaker terminals.
(The speaker outputs have slightly lower impedance because they use fatter wires.... but that is not going to matter with headphones.)

@bequietjk I actually got a detailed email from Jeremy from Garage1217 about his idea for the custom power adapter box too. Somehow I managed to overlook it in my inbox.

Sounds like he’s thinking about a box with speaker cable terminals and a 6.3mm input and output. He thinks it will be about 4”x4” in size. He said output impedance should be about 3.5ohm, so all in all it sounds pretty perfect for our needs.

I’m on the fence about whether or not the speaker cable terminals are necessary. Those with the older A100 model already have adapters to connect straight to the terminals on the amp, so I think maybe we could keep the device smaller and perhaps cheaper to produce by not including the speaker terminals inputs. I’d like to get others opinions on this though.

I told Jeremy I’d try to gauge the level of interest in a custom product like this. I also invited him to join our discussion in this thread to answer technical questions. If he doesn’t join us here, I can relay questions to him.

 

[ckhirnigs113]

With the jumpers in, the headphone output on the A-100 is connected directly to the same place as the speaker terminals.
(The speaker outputs have slightly lower impedance because they use fatter wires.... but that is not going to matter with headphones.)

Thanks @KeithEmo. that was my understanding as well. I think what Jeremy (at Garage1217) was thinking was that it may be helpful to have speaker terminal inputs on the power adapter box (aka attenuator) so those with a speaker amp and no headphone out (like on the original A-100) could connect more efficient phones to their amp.

I personally think the speaker terminals are unnecessary for most here because we either have the BasX A-100 that already has a headphone out or we have the original A-100 and have already acquired an adapter to connect directly to the speaker terminals. I think all we need is some robust resistors in a box that allows adequate cooling (as @KeithEmo thoroughly described in his previous post) and keeps the output impedance relatively low. The question becomes: what is the most universally applicable resistor combination that will benefit the most diverse collection of headphones.

All I want to accomplish in my particular situation is to remove the background hiss with my HD58X (150ohm, 104 dB at 1V, 1 kHz) and get a little more useable range on the volume knob. Not sure if inline attenuators like those Harrison Labs -12dB ones you linked to earlier will be necessary as well as an output side attenuator. I would hope the output side attenuator will be enough, but we'll see. The little Garage1217 unit is still in the design phase at the moment.

Is anyone else interested in one of these? I'm not sure how many units are needed to make it a viable build for Jeremy.

 

[KeithEmo]

Here would be my suggestions......

First off, if you're using the output attenuator, then you probably don't need the input attenuator.
(Unless your source itself has a very high fixed noise floor.)

The values that would make sense are probably going to depend on the headphones themselves.
You also need to remember that damping factor is a ratio between the impedances of the source and load.
(If you're looking for a certain damping factor, the lower the impedance of your headphones, the lower the output impedance you'll need to drive them with.)
I would assume (this is something of a guess) that relatively low impedance headphones are going to act more like loudspeakers.
And so they would see a larger improvement with better damping.

Here are the values I might consider as a starting point.....

For low impedance phones I would go with 7.5 Ohms and 0.5 Ohms.
That will give you a nice low drive impedance with plenty of damping.
The size of the resistors you need will depend on the efficiency of your phones.
More efficient phones mean you'll be running the volume lower so you can get by with smaller resistors.
(And, if your phones are very efficient, you might end up adding those input attenuators after all.)

Doubling those resistor values (15 Ohm and 1 Ohm) will give you the same attenuation with a slightly lower damping factor.
That should also be plenty for most low impedance phones, and you'll be able to get by with smaller resistors.

Your HD58x phones are both high impedance and high efficiency.
I suspect you could get by with much higher values....
Perhaps 47 Ohms on the top resistor.... and 4.7 Ohms, or even 2.2 Ohms, on the bottom one.
That will give you a 2 Ohm output impedance (which will still provide a damping factor of around 75 with your 150 Ohm phones.)
And you will probably be able to use much smaller resistors.

Remember that, when you're discussing this with someone who manufactures a product, they're going to want to make a product that works well with the widest variety of headphones and amps.
So, connecting to the speaker terminals makes sense, because very few amps are going to give you a high-power output from their headphone jack (the A-100 is the only one I know off hand).

For a product, I might also consider adding a few resistors and switches.
Make the top resistor 33 Ohms.... and add a switch that lets you parallel a second 33 Ohm resistor (for a choice of 33 Ohms or about 16 Ohms).
Make the bottom resistor a 3.3 Ohm one.... and add a switch that lets you parallel a 1.2 Ohm one (for a choice of 3.3 Ohms or about 0.8 Ohms.).
Now, by changing switch settings, you're going to be able to achieve several different attenuation and impedance settings...
This should give you a better chance of finding one that works well with many different headphones.
(As a commercial product, the box and construction are going to cost more than the parts inside, and this would offer good performance with a much wider variety of headphones. Feel free to pass this on if you like.)

Thanks @KeithEmo. that was my understanding as well. I think what Jeremy (at Garage1217) was thinking was that it may be helpful to have speaker terminal inputs on the power adapter box (aka attenuator) so those with a speaker amp and no headphone out (like on the original A-100) could connect more efficient phones to their amp.

I personally think the speaker terminals are unnecessary for most here because we either have the BasX A-100 that already has a headphone out or we have the original A-100 and have already acquired an adapter to connect directly to the speaker terminals. I think all we need is some robust resistors in a box that allows adequate cooling (as @KeithEmo thoroughly described in his previous post) and keeps the output impedance relatively low. The question becomes: what is the most universally applicable resistor combination that will benefit the most diverse collection of headphones.

All I want to accomplish in my particular situation is to remove the background hiss with my HD58X (150ohm, 104 dB at 1V, 1 kHz) and get a little more useable range on the volume knob. Not sure if inline attenuators like those Harrison Labs -12dB ones you linked to earlier will be necessary as well as an output side attenuator. I would hope the output side attenuator will be enough, but we'll see. The little Garage1217 unit is still in the design phase at the moment.

Is anyone else interested in one of these? I'm not sure how many units are needed to make it a viable build for Jeremy.

 

[KeithEmo]

I should also point out another interesting option.

You (or Jeremy) could design a nice little "semi DIY" unit.
It could be a nice little box, with the proper connectors on the outside, and a small PCB with spring clips inside.
Each user could then select the perfect combination of resistors for the particular headphones they want to use it with.

If I was doing it, as a company, I would ask the user what headphones they have, and provide the unit with the appropriate set of resistors.
Alternately, if spring clips were used, the user could experiment with different values.

Thanks @KeithEmo. that was my understanding as well. I think what Jeremy (at Garage1217) was thinking was that it may be helpful to have speaker terminal inputs on the power adapter box (aka attenuator) so those with a speaker amp and no headphone out (like on the original A-100) could connect more efficient phones to their amp.

I personally think the speaker terminals are unnecessary for most here because we either have the BasX A-100 that already has a headphone out or we have the original A-100 and have already acquired an adapter to connect directly to the speaker terminals. I think all we need is some robust resistors in a box that allows adequate cooling (as @KeithEmo thoroughly described in his previous post) and keeps the output impedance relatively low. The question becomes: what is the most universally applicable resistor combination that will benefit the most diverse collection of headphones.

All I want to accomplish in my particular situation is to remove the background hiss with my HD58X (150ohm, 104 dB at 1V, 1 kHz) and get a little more useable range on the volume knob. Not sure if inline attenuators like those Harrison Labs -12dB ones you linked to earlier will be necessary as well as an output side attenuator. I would hope the output side attenuator will be enough, but we'll see. The little Garage1217 unit is still in the design phase at the moment.

Is anyone else interested in one of these? I'm not sure how many units are needed to make it a viable build for Jeremy.

 

[ckhirnigs113]

I should also point out another interesting option.

You (or Jeremy) could design a nice little "semi DIY" unit.
It could be a nice little box, with the proper connectors on the outside, and a small PCB with spring clips inside.
Each user could then select the perfect combination of resistors for the particular headphones they want to use it with.

If I was doing it, as a company, I would ask the user what headphones they have, and provide the unit with the appropriate set of resistors.
Alternately, if spring clips were used, the user could experiment with different values.

Come on Keith, I know you can get this little niche product produced at Emotiva. Then we can have a complete Emotiva solution!

 

[bequietjk]

The complete Emotiva solution is the release of the HP-1 >

 

[ckhirnigs113]

The complete Emotiva solution is the release of the HP-1 >

Very true, but I’m hoping to stop buying amps! Easier said than done when I spend so much time on these forums.

“Welcome to Head-fi, sorry about your wallet.” That’s so true. I’ve been here since 2005! My wallet is most definitely lighter because of this place.

 

[ckhirnigs113]

@KeithEmo Jeremy from Garage1217 got back with me and basically said you and he are of one mind about offering options on the attenuation based on the headphones being used. He plans to offer two settings on the attenuator box, one with -20dB and one with -10db. Here are his own words describing his design:

“The size resistors needed for this are very large and require custom cooling. I could use cheapy 5-10% tolerance ceramics with heatsink on them but will use much better, high power SMD resistors with a custom cooling implementation. Enough to handle 100W of dynamic power from an amplifier. A little overkill for most situations. The unit will have a -10 and -20dB setting select-able via a switch. Have other values in stock will not be a problem.
Tailoring resistor sets to each headphone, I cannot see real value in it to be honest since the actual output is variable from the amplifier. A couple of set values will more than do the trick. The goal is to attenuate the signal to the point you have a usable volume range from the amplifier and also make it safe for the headphones in use.”

To me it sounds like an iEMatch with the capability of handling the power output of a 100w/channel speaker amp. Should be perfect for the A-100 assuming he is able to keep the output impedance low, which I believe he will. Before discussing the switch on the unit he was aiming for just under 3.5ohm output impedance. I’ve asked him what the -10dB and -20dB switches’ respective output impedances will be. I’ll report back when he responds.

This thing sounds like it will be great for all of us that want to safely use the A-100 or any other moderately-powered speaker amp with more efficient headphones that don’t soak up power like planars.

 

[vormhat]

The Garage guys have any idea what this would cost? I'd love to keep my a100 and have the ability to drive more efficient cans without the high output impedence we have today. I'd prefer to keep this a100 over getting a JDS Atom.

 

[ckhirnigs113]

The Garage guys have any idea what this would cost?

Jeremy's initial estimate was about $75 for the adapter. He's out of town this week, but he's going to get back to me once he's got more concrete details.

 

[HiFiRebel]

Jeremy's initial estimate was about $75 for the adapter. He's out of town this week, but he's going to get back to me once he's got more concrete details.

Would Shiit SYS not do the same thing for less money?

 

[ckhirnigs113]

Would Shiit SYS not do the same thing for less money?

I thought the same thing until it was explained to me that all a passive preamp like the SYS would do is give more useable range on the A-100 volume knob. Inline attenuators on the RCA inputs of the amp, like these that @KeithEmo suggested, would effectively do the same thing except at a fixed value like -12dB.

Neither solution does anything about the noise floor of the A-100 itself. I hear the hiss even with no source plugged in. This hiss/noise floor doesn’t noticeably increase when turning up the volume on the amp. The only way to get rid of a noise like this is to put something on the headphone output of the amp.

The resistors Emotiva have in place when the jumpers are removed effectively remove the hiss but also drastically increase the output impedance to 220ohm. This may work with some headphones, but with my HD58X for example, the bass loses a lot of control and sounds bloated and a lot muddier.

The solution is to have resistors in place that remove the audible noise floor and give more useable range on the A-100 volume knob while still keeping output impedance relatively low, thus keeping a high damping factor for our headphones. Things like the iFi iEMatch and Garage1217’s own attenuator cable seem like the perfect products in theory for this issue, but unfortunately, they aren't suitable.

The stumbling block is these products were not designed to handle the huge amounts of wattage put out by a speaker amp like the A-100. iFi and Garage1217 both confirmed they don’t recommend using their products with speaker amps. This is why I’m talking to Jeremy at Garage1217 about this custom solution for people like us that want to use our A-100 with jumpers installed with headphones other than just our power-hungry planars (Hifiman, Fostex etc.).

 

[HiFiRebel]

I thought the same thing until it was explained to me that all a passive preamp like the SYS would do is give more useable range on the A-100 volume knob. Inline attenuators on the RCA inputs of the amp, like these that @KeithEmo suggested, would effectively do the same thing except at a fixed value like -12dB.

Neither solution does anything about the noise floor of the A-100 itself. I hear the hiss even with no source plugged in. This hiss/noise floor doesn’t noticeably increase when turning up the volume on the amp. The only way to get rid of a noise like this is to put something on the headphone output of the amp.

The resistors Emotiva have in place when the jumpers are removed effectively remove the hiss but also drastically increase the output impedance to 220ohm. This may work with some headphones, but with my HD58X for example, the bass loses a lot of control and sounds bloated and a lot muddier.

The solution is to have resistors in place that remove the audible noise floor and give more useable range on the A-100 volume knob while still keeping output impedance relatively low, thus keeping a high damping factor for our headphones. Things like the iFi iEMatch and Garage1217’s own attenuator cable seem like the perfect products in theory for this issue, but unfortunately, they aren't suitable.

The stumbling block is these products were not designed to handle the huge amounts of wattage put out by a speaker amp like the A-100. iFi and Garage1217 both confirmed they don’t recommend using their products with speaker amps. This is why I’m talking to Jeremy at Garage1217 about this custom solution for people like us that want to use our A-100 with jumpers installed with headphones other than just our power-hungry planars (Hifiman, Fostex etc.).

Thank you for detailed explanation.

I don't experience any noise from my A-100. However, I have not installed the jumpers yet. At the moment I only use Philips Fidelio X2 headphones connected to A-100. They are very easy to drive and even with jumpers out, I am at the low end of volume knob scale and have very little play in the knob between when the initial volume imbalance ends and where it gets very loud. I therefore can't install the jumpers until I get my Argons, because it would limit the volume knob even further to the point where I won't have any play in it at all.

That's the reason why I have also not invested in Shiit SYS yet (this was top of my list), because I simply don't yet know what I need. When I get Argons and install jumpers and hear a lot of noise, then I would need to find something to solve the issue, but if I don't, I only need some kind of volume pre-amp for when I want to use my X2's with A-100 to increase the volume knob range. At the moment with the X2's, at 9 o'clock it is already quite loud. 10 o'clock is where it is already very loud for my ears, and that is with the jumpers out. I don't have any noise floor at all, dead quiet.

 

[ckhirnigs113]

@HiFiRebel I also didn’t have any hiss with my HD58X when I took the jumpers out. I just find the sound better with jumpers installed even with these sensitive cans. The hiss is not even noticeable when music starts playing.

To be honest, I didn’t find I had much more play on the volume knob when I took the jumpers out. This surprised me. I assumed I’d be able to get to 11-12:00 but probably didn’t get past 8:30-9:00. With the jumpers installed, I can get past the point of channel imbalance with my HD58X, but it obviously gets really loud really fast with a small turn on the knob.

One thing I don’t know, and maybe @KeithEmo could educate us, is how much attenuation is possible with a passive preamp like the Schiit SYS or JDS Labs OL Switcher versus the fixed -12dB inline attenuators from Harrison Labs. Is -24dB or -30dB attenuation possible with a passive preamp before you run into channel imbalance?

I’d like to know if I can get more useable range on the volume knob of the A-100 using those preamps or are the simpler inline attenuators going to get me plenty of useful travel on the volume knob without having to add another box to my desk? I’d prefer to get to around 12:00-3:00 on the A-100 if possible, so I’m just not sure which option is going to get me there.

 

[ckhirnigs113]

I just learned something that might be useful to some A100 users here. I was considering getting some of those Harrison Labs -12dB in-line attenuators, but I was afraid they would not give me enough attenuation to really increase useable range on the A100 volume knob using my HD58X.

I asked John at JDS Labs how many decibels attenuation should be possible using his passive OL Switcher preamp before channel imbalance becomes an issue. He thinks -40dB should be possible, so this might be a much better option for those of us using relatively sensitive headphones with the A100 with jumpers installed.