Metalman makes a MDF case. For shame. 
Very nice. One question. What's the advantage of the Aleph CS? I think it a excelent compromise in a 100W amp, but an unneeded evil in a HP amp. I'm not picking, I'm a hack and seek to understand the use of a heat saving device when we're only talking a few watts in the first place. I'll likely make a Zen HP amp before I make a case for my CCS Aleph and use the one that pleases me the most.
Happy listening
Very nice. One question. What's the advantage of the Aleph CS? I think it a excelent compromise in a 100W amp, but an unneeded evil in a HP amp. I'm not picking, I'm a hack and seek to understand the use of a heat saving device when we're only talking a few watts in the first place. I'll likely make a Zen HP amp before I make a case for my CCS Aleph and use the one that pleases me the most.
Happy listening
Brian,
Yes, the MDF is quite shamefull, but I was in too much of a rush to wait for my next chance to get into a metalshop to build a proper chassis. Which actually brings me to the reason for the Aleph CS. Since I don't have a metal chassis to act as a heatsink for the Fets, I am using the individual sinks you can see in the pictures, which have quite a limited heat dissipation capacity
. As it is, you can touch the heatsinks for a second or so but not much longer than that without crying ouch! To get a higher maximum current output I thought I needed for my Grado's, I went with the Aleph CS which roughly doubles it. Now that I have it up and running, I can say with some confidence that I didn't need the extra output current , and a plain CS would probably have worked fine. But hey, you can never have too much bias!
I've been following your progress on your headamp and I look forward to seeing how it comes out. Trust me its worth the effort.
Yes, the MDF is quite shamefull, but I was in too much of a rush to wait for my next chance to get into a metalshop to build a proper chassis. Which actually brings me to the reason for the Aleph CS. Since I don't have a metal chassis to act as a heatsink for the Fets, I am using the individual sinks you can see in the pictures, which have quite a limited heat dissipation capacity
. As it is, you can touch the heatsinks for a second or so but not much longer than that without crying ouch! To get a higher maximum current output I thought I needed for my Grado's, I went with the Aleph CS which roughly doubles it. Now that I have it up and running, I can say with some confidence that I didn't need the extra output current , and a plain CS would probably have worked fine. But hey, you can never have too much bias!I've been following your progress on your headamp and I look forward to seeing how it comes out. Trust me its worth the effort.
Re: It Lives!
Well, those Grado's are like 32-ohms? With 30V into those 32-ohms, you're way way overkill. 98db spl at 1mV, so you're talking like upwards of 140 dB with those rails, enough to seriously harm your hearing
There isn't a chance that you've got a center tapped transformer and just floating the CT? Otherwise I'd say half your rails and if you want, double your bias. Same power dissipation, less distortion. Still capable of liquifying your ears.
Anyway, looking at your pics, I'd suggest that you consider using some shielded cables instead for the audio and for the power. As far as your signal grounding goes, one pretty common way to isolate the GNDs is to connect your power GND (gnds from your circuit and the IEC and the transformer) to one star point and your signal GND (input gnd and output gnd) to another star point and then connect between the two with a single wire or a 10-ohm resistor. I think this is mentioned
on the passdiy pages somewhere.
Nice work though. Now I'm thinking about putting one together
--
Danny
metalman said:
Well, those Grado's are like 32-ohms? With 30V into those 32-ohms, you're way way overkill. 98db spl at 1mV, so you're talking like upwards of 140 dB with those rails, enough to seriously harm your hearing
There isn't a chance that you've got a center tapped transformer and just floating the CT? Otherwise I'd say half your rails and if you want, double your bias. Same power dissipation, less distortion. Still capable of liquifying your ears.
Anyway, looking at your pics, I'd suggest that you consider using some shielded cables instead for the audio and for the power. As far as your signal grounding goes, one pretty common way to isolate the GNDs is to connect your power GND (gnds from your circuit and the IEC and the transformer) to one star point and your signal GND (input gnd and output gnd) to another star point and then connect between the two with a single wire or a 10-ohm resistor. I think this is mentioned
on the passdiy pages somewhere.
Nice work though. Now I'm thinking about putting one together
--
Danny
Re: Re: It Lives!
Yep, I've got 300 ohm Sennheisers and I get by just fine with +/-9V rails.
JF
azira said:
Well, those Grado's are like 32-ohms? With 30V into those 32-ohms, you're way way overkill. 98db spl at 1mV, so you're talking like upwards of 140 dB with those rails, enough to seriously harm your hearing
Yep, I've got 300 ohm Sennheisers and I get by just fine with +/-9V rails.
JF
If my calcs & measurements are correct, I am getting ~1.44W(RMS) into my 32ohm headphones, due to the output current limit. That works out to just a hair over 138dB max volume (headphone output is rated at 98dB at 1mV).
I designed for max power output roughly at 32 ohms to coincide with my headphone impedance, and max power is ~1.6W(RMS) into 38ohms. If my thinking is right, this is a graph of output power vs. headphone impedance.
I designed for max power output roughly at 32 ohms to coincide with my headphone impedance, and max power is ~1.6W(RMS) into 38ohms. If my thinking is right, this is a graph of output power vs. headphone impedance.
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metalman said:
My hat's off to you. I just ran some hand calcs to verify what you were saying. That is a very interesting way to approach a class-A amplifier design. Actually it's a lot like how a friend (more like a mentor) of mine went about designing his headphone amp as well. In this way, you are maximizing your power efficiency into your headphones, minimizing the bad effects of a class-A. Your numbers sound dead on.
--
Danny
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