# JDS Labs C5/C5D (pg96) portable amp/amp+DAC

Discussion in 'Portable Headphone Amps' started by ostewart, Jan 24, 2013.
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1. Looking at picking one of these up, Anyone have any problems with the volume controls? Never used a portable amp but it looks like the volume control has a chance of rubbing up against something and getting cranked up to deafening levels(say if i had it loose in a backpack). Is there any type of hold feature or is this a non-issue

2. It really isn't likely to move when in a backpack, I wouldn't worry about it, I prefer it to the analogue one of the C421

3. Quote:
Agree with randomkid.  I've only had it for a week.  Wrapping up my 4 flight travel week and haven't had a single instance of an incidental volume change.  I put it in my slacks pocket, my snugger jean pockets, shirt pocket, and laptop bag.  All good!

4. Quote:

Because it can be calculated in two different ways from the available data, and the results do not agree (that is not necessarily a problem with the specs, because the total open loop output impedance - which also includes internal components of the op amp, the power supply, and the virtual ground, if there is one - is likely non-linear). The first method uses the known unloaded output voltage, and one of the voltages with a load, by solving the equation
Code:
` v150 = vUnld * 150 / (150 + rOut)`
for rOut. This way, the output voltage calculated for the 600 Ω load would be slightly higher than the specified value. Alternatively, the two loaded voltages can be used, and solving these equations
Code:
` v150 = vUnld * 150 / (150 + rOut) v600 = vUnld * 600 / (600 + rOut)`
for vUnld and rOut gives parameters with which the results are correct for both the 150 and 600 Ω loads, but this time the maximum unloaded voltage does not agree with the specifications (it is 12.8 Vpp instead of 14). The formula for rOut actually simply divides the voltage difference by the current difference. Initially, I chose the first approach, but then added lines 11 and 12 to modify the script to use the second one. With those lines removed, the results are:
Code:
`  16 ohms: V = 0.509 Vrms, Ipeak = 45.0 mA, P = 16.2 mW  32 ohms: V = 1.018 Vrms, Ipeak = 45.0 mA, P = 32.4 mW  50 ohms: V = 1.591 Vrms, Ipeak = 45.0 mA, P = 50.6 mW  62 ohms: V = 1.973 Vrms, Ipeak = 45.0 mA, P = 62.8 mW 150 ohms: V = 3.337 Vrms, Ipeak = 31.5 mA, P = 74.2 mW 300 ohms: V = 3.986 Vrms, Ipeak = 18.8 mA, P = 53.0 mW 600 ohms: V = 4.416 Vrms, Ipeak = 10.4 mA, P = 32.5 mW`
The difference is not major, but with all the low impedance loads, the maximum power is determined by the (not necessarily correct) current limit.
Ultimately, it is only possible to get reliable and accurate values by actually measuring the amplifier with the various loads, especially in the case of the lower impedance ones.

5. Guys all these maths and calculations is giving me a headache .

Remember guys amplifiers are rated using a sine wave signal.
Because amplifiers are rated this way, their peak power output will be twice the RMS rating.
Most amplifiers cannot sustain output at their peak capability for too long (and the
characteristic of most music signals is such that this is not necessary anyway).

As you are probably aware, audio amplifiers put out a voltage (to phones) that is constantly changing. A music signal can be called AC (alternating current), but it is not the same as a sine wave(unless you happen to be playing test tones through your system...but who listen to tones right),and it is not DC... however a sine wave is more representative of a music signal than DC is. So, the standard practice in use today is for manufacturers to rate amplifiers in "watts RMS". Be aware that watts are watts, there is technically no such thing as watts RMS.

To make matters more complicated these ratings are taken using a resistive load which phones or speakers are reactance in nature meaning you also have inductance and capacitance to account for.

So my point is as long as the amp can drive your phones with minimal distortion and clipping than
lets just leave the numbers in the spec sheets and get back to your normal disscussion on the C5.

PS: You guys can open another thread to discuss the theories/formulas/methodlogy on amp power ratings .

6. Quote:
I haven't had any problems with the volume control getting too loud. On the contrary though, I often listen at "volume 1", so sometimes I accidentally press volume down and I don't hear anything.

The volume control is almost flush with the metal surface, so the chances of accidentally moving it are pretty slim, and even more so when you have the source/headphone jacks sticking out. The volume level takes 3.5 seconds to go from 0 volume to max, so there shouldn't be a problem about it reaching deafening levels. There's no hold feature.

7. Um...well then, a real-world test for the battery life. It literally just died for me on the bus right now and I've been timing the battery life with my iPhone.

Testing specs:
iPhone 4S (playing Ottmar Liebert's "Up Close" album at 256 kbps V0 LAME MP3) -> FiiO L3 -> C5 (high gain, volume step 4, no bass boost) -> V-MODA Crossfade M-100

This wasn't a straight-on 11-hour listening session, but I turned on/off the iPhone's timer whenever I turned on/off the C5. It's not quite the 14-hour claimed battery life with this test, but still ample for my purposes. I did this test over a course of 2 days with plenty of opportunities to charge the C5 if I wanted to.

The flashing green LED indicating 20 minutes of remaining battery life was pretty accurate though because the bus arrived at my stop at around 20:48 and the LED was flashing at the end of the last listening session (the battery later died at 21:05).

8. Plus you used high gain, that might make a difference. With IEMs on volume 1, low gain, it might last longer. Volume one if sufficiently loud for my CIEM

9. Quote:
Does a higher gain suck-up more battery life?
I figured volume level was probably the biggest factor, and if the volume level is the same regardless of the gain, then the battery drains at the same rate.

In any case, the higher gain on volume step 4 of 63 should be plenty of volume for louder music instead of the quiet music I was playing (which I found to be the bare minimum volume to use while riding in a noisy public bus with the fairly sensitive V-MODA M-100's).

10. anyone tried them with the MDR-1R, SRH840 or XBA3?????

11. Quote:
I don't have a SRH840, but I have the SRH940 and it sounds pretty good with the C5 to me. The bass boost also does wonders for that headphone.

12. Thanks.....

13. Quote:

Run-time depends on the source signal level, headphone impedance, and output listening level.

I observed 14+ hours during actual listening at high gain from an iPod Nano, driving 250 ohm Beyerdynamic DT-880's (also measured by iPhone's stopwatch, by the way). Your M-100's and listening style consume more power. Some people will see more than 14 hours; some will see less.

14. Thanks for that John.

I'm really enjoying mine, thank you.

15. Wait so DT880 250ohm consumes less power than the M-100?
I obviously have a lot to learn about amping