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

[ClieOS]

The new site looks great btw.

 

[d marc0]

  The new site looks great btw.

+1 I enjoy browsing through...

 

[miceblue]

I have a question, is there any advantage to listing the VRMS instead of the power output? Most people list the milliwatt power output, and is what I usually use for calculating how loud an amp can get with X headphone.

I remember stv014 posting his calculations for the power output of the C5 at various impedances, and had to account for the current limit in those calculations, which I don't know how to factor in.

Those calculations are not quite right. First, 14.0 Vp-p is actually 4.95 Vrms, because 1 Vrms = 2 * sqrt(2) = 2.8284 Vp-p. Second, the method of linearly extrapolating power is wrong, because power is inversely proportional to the impedance with constant voltage. With your formula, the power output into loads above ~900 Ω would be negative, and into a near-infinite impedance open circuit, an extreme negative value.

Now the difficult part is modeling how the maximum output voltage drops with decreasing load impedance. A simple model is shown below that assumes a linear open loop output impedance, and a hard peak current limit of 45 mA taken from the datasheet of the OPA2227. Using the following Python script to perform all the calculations:

#!/usr/bin/python

import math

vUnld = 14.0 * math.sqrt(0.125) # unloaded voltage
v150 = 3.337 # voltage into 150 ohms
v600 = 4.146 # voltage into 600 ohms
iSC = 0.045 * math.sqrt(0.5) # short circuit current of OPA2227 in Arms
rOut = ((vUnld / v150) - 1.0) * 150.0 # total open loop output impedance

rOut = (v600 - v150) / ((v150 / 150.0) - (v600 / 600.0))
vUnld = v600 * ((600.0 + rOut) / 600.0)

def calcPower(r):
 global vUnld, iSC, rOut
 v = vUnld * r / (r + rOut)
 i = v / r
 if i > iSC:
 i = iSC
 v = i * r
 p = v * v / r
 print "%3.0f ohms: V = %.3f Vrms, Ipeak = %.1f mA, P = %.1f mW" \
 % (r, v, i * math.sqrt(2.0) * 1000.0, p * 1000.0)

for r in [16.0, 32.0, 50.0, 62.0, 150.0, 300.0, 600.0]:
 calcPower(r)

I get these results:

 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 = 3.836 Vrms, Ipeak = 18.1 mA, P = 49.0 mW
600 ohms: V = 4.146 Vrms, Ipeak = 9.8 mA, P = 28.6 mW

Of course, due to the simplicity of the model, the numbers above are still not very reliable. Also, the maximum power into low impedances depends largely on the actual (rather than specified) short circuit current.

 

[jseaber]

I have a question, is there any advantage to listing the VRMS instead of the power output? Most people list the milliwatt power output, and is what I usually use for calculating how loud an amp can get with X headphone.

I remember stv014 posting his calculations for the power output of the C5 at various impedances, and had to account for the current limit in those calculations, which I don't know how to factor in.

 
Listing output power in VRMS is technically more accurate. Headphones are reactive loads (resistance + capacitance + inductance), while power measurements are typically taken with dummy resistive loads. Power output differs between a 32 ohm dummy load and a 32 ohm headphone, or even from one 32 ohm headphone to another brand/model.
 
Way too many calculations, above! Power in mW is a simple conversion if you wish. Plug in VRMS and R:
 
Power = (V^2)/R

 

[miceblue]

I have a question, is there any advantage to listing the VRMS instead of the power output? Most people list the milliwatt power output, and is what I usually use for calculating how loud an amp can get with X headphone.


I remember stv014 posting his calculations for the power output of the C5 at various impedances, and had to account for the current limit in those calculations, which I don't know how to factor in.

Listing output power in VRMS is technically more accurate. Headphones are reactive loads (resistance + capacitance + inductance), while power measurements are typically taken with dummy resistive loads. Power output differs between a 32 ohm dummy load and a 32 ohm headphone, or even from one 32 ohm headphone to another brand/model.

Way too many calculations, above! Power in mW is a simple conversion if you wish. Plug in VRMS and R:

Power = (V^2)/R

Ah okay. That's good to know.

It looks like the C5D offers a little more power at 32 and 150 Ω compared to the C5.

 

[jseaber]

Ah okay. That's good to know.

It looks like the C5D offers a little more power at 32 and 150 Ω compared to the C5.

 
It's the same circuit. Power is slightly higher due to lower output impedance; you shouldn't notice the difference.

 

[luisdent]

Excellent!  The custom bass boost lives!!!!  That's going to be amazing with iems like the er4s, etc.  Very nice.  The site looks awesome too.  I love the design, colors, etc.  Very very nice.  Awesome price point on the C5D.  Can't wait to hear one some day.  I love my C5 and use it exclusively with everything.

 

[chengsta]

I already have the C5, but I don't need a dac.  I may get it some day when I get my own house with no neighbors around so I can blast my speakers though.

 

[Mix0r]

Hey!

I've been lurking around many threads around here lately and finally decided to get C5 + ODAC, but then saw this wonder.

However, I am in the EU and would like to avoid import taxes - will your resellers get some C5D's anytime soon? If yes, where will they be available?

 

[BB 808]

Could you PM or email us more information (screenshot)?

We have a C5D release article ready to go. It will be published as soon as we're confident the site launch is running smoothly.

John, it's the IE8 we have at work and the restrictions the company put on our web browsing. The new website looks wonky at work (PC) but when I got home your website is so much better on my iMac. I was able to add it to the cart at home and am just building up the nerve to complete the transaction.

 

[howdy]

my JDS Labs C5 is up for sale

That's frekkin hilarious, you are going through amps faster than heck... All part of the hobby. I received my BH2 today and I really like this little guy!

 

[KamijoIsMyHero]

Would like to know as well when your distributors get this. Looks great

 

[Spadge]

I have no idea if this is useful or not, but I contacted an Australian reseller about the C5D and they said they would have stock in 'the next couple of weeks'

 

[howdy]

I have no idea if this is useful or not, but I contacted an Australian reseller about the C5D and they said they would have stock in 'the next couple of weeks'

You can buy it right from there website for 253.23 shipped, and under 270 to Australia.

 

[Spadge]

You can buy it right from there website for 253.23 shipped, and under 270 to Australia.

Thanks, I realise this, but several people were wondering when local (to them) retailers would have stock.