[6BQ5]

Given the RM-5 has two outputs, from a technical standpoint, could one of the outputs be converted to a headphone jack?

And ....  if it can be made to work, how good would an RM-5 be to the task relative to a dedicated headphone amplifier?

One issue I see is being able to drive both low (below 50 Ohm) and high (300 to 600 Ohm) headphones properly. Being able to drive both high and low z phones tends to separate the wheat from the chaff.

A good example is the latest Musical Fidelity X-CAN V8 (not the older V3) headphone amp. This uses a 6Dj8 tube with a some type of a solid-state output buffer that results in a low output impedance (1 Ohm). Specs also say 1W output.

Can the RM-5 be made to do the same with some rewiring or is it easier to just get a dedicated headphone amp?

[Roger A. Modjeski]

I hear people pay crazy money for headphone amps, doesn't make sense to me. A headphone amp is a simple thing. The EM7 does just fine.  The RM-5 could run a 600 ohm phone and lower impedance with a transformer.

[Scottdazzle]

Roger,

Have you considered bringing back the RM-5 with remote and a headphone jack?  I'll buy the first one!

Scott

[mateo]

I hear people pay crazy money for headphone amps, doesn't make sense to me. A headphone amp is a simple thing. The EM7 does just fine.  The RM-5 could run a 600 ohm phone and lower impedance with a transformer.

There's a lot of overpriced, questionable-at-best gear in the headphone world, but not all of it is crazy in my opinion. For example, I'd completely be willing to pay ~$2k for an Eddie Current Zana Deux.

An EM7 headphone amp as a standard offering would do pretty well, I think.

[K.C.]

I've always wondered what it would take to use my RM-10 with a pair of Senn HD-650s.

With any amp isn't it just a matter of matching the correct impedance with the HPs ?

[Roger A. Modjeski]

Actually headphones are rarely "matched" to an amplifier impedance. Most headphone jacks have a 100-300 ohm resistor in series with the phone. This resistor protects the phones from getting the full power of the amplifier and going up in smoke. They also attenuate the noise that would be bothersome from most amps.

Connecting phones to any amplifier can be as simple as making a jack with a pair of 100-300 ohm resistors in series with the hot L and R. The shell goes to ground.

I have made headphone amps where the output impedance is quite low which results in an entirely different sound. This is probably the best way to go. I bought my first 500 6EM7 tubes to make such an amp but the level of interest was not what it is today. Should I resurrect it?

Another way to reduce the output impedance and noise is a transformer. If there is interest I can wind some nice transformers, put them in our standard plastic box for something around $250. Turning the speakers off is always a bit of a problem dealing with heavy speaker cables and switches that can be trusted to be of good audio quality.

For those who do not listen very loud I can make a transformer that would allow the RM-5 to run the phones.

[cryoparts]

I have made headphone amps where the output impedance is quite low which results in an entirely different sound. This is probably the best way to go. I bought my first 500 6EM7 tubes to make such an amp but the level of interest was not what it is today. Should I resurrect it?

Yes! 

Peace,

Lee

[Roger A. Modjeski]

I hear people pay crazy money for headphone amps, doesn't make sense to me. A headphone amp is a simple thing. The EM7 does just fine.  The RM-5 could run a 600 ohm phone and lower impedance with a transformer.

There's a lot of overpriced, questionable-at-best gear in the headphone world, but not all of it is crazy in my opinion. For example, I'd completely be willing to pay ~$2k for an Eddie Current Zana Deux.

An EM7 headphone amp as a standard offering would do pretty well, I think.

I had a look at that amp and the price is a fair one but I can't go along with the choice of tubes. It takes 80 watts just to light up the 6C33s unless he is just lighting one half of each. Add in the tube rectifiers for another 40 watts, then add the B+ watts. I could find nothing in the specs about power consumption but I would expect it to be 100-200 watts. That's a lot of input watts for a max output of 0.25 watts.

For those curious about this Russian Cold War Surplus tube here is a very good data sheet. http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf.  Note the following in the opening paragraph.  "These triodes are intended to work as regulating valve in electric stabilizers of voltage" These are the wrong tubes for audio as it is very difficult to set and hold the bias level. In a voltage regulator there is no bias to stabilize and all the tube parameters we care so much for go right out the window. The data sheet speaks of a maximum of 1.5 meg ohms for the grid resistor when directly connected to the servo (foot note #8). It is no wonder that amps using this tube are troublesome. In its proper application the tube can do its job perfectly under widely drifting parameters because there is a high gain error amp, usually a pentode, that is constantly adjusting the grid over a very large range.

We offer a headphone jack as a option on the EM-7.

[6BQ5]

Here are some of the things to consider in designing a headphone amp.

1. Low amp output impedance, same reasons as to why this is desirable for driving speakers, remain with headphones. Near zero as possible is what some aim for.

2. Able to drive both high and low impedance cans adequately. While there are a a handful of headphones out there that are in the 300-400 Ohm range, the majority are now less than 70 Ohms. Driving each type presents different challenges, which explains perhaps why some headphone amps now come with a hi/lo switch which toggles the output buffer.

3. Wattage and current. While your typical headphone amp is fine at .25W output, some of the best headphones (such as my AKG K340s) are very power hungry. 1 - 2W is ideal. However, this would be far too much for low impedance headphones, which typically need high current but not high voltage to sound best. Some form of gain control is needed.

In retrospect, adding a headphone option to an RM-5 may turn out to be costly if addressed via adding a transformer (such as a Sowther). Once labor is factored in, probably cheaper buying a headphone amp.