The extra voltage can make a substantial difference in sound quality(SQ) at all volume levels in many systems. It's very noticeable with horn tweeters. The soundstage grows and you hear much more detail.
What is the reason behind it?
I always question this in the back of my mind. I even asked here two or three times about what's the affect when rail is too low. But nobody ever answer me.
If there's a good reason, then it will be another thing to consider.
I don't own good enough test equipment to measure anything, but my theory is the extra voltage allows the whole amplifier perform more effortlessly. Resistances are overcome more easily. The surge of current can reach the speaker faster before it needs to reverse polarity. For years I've preferred higher voltage/power amplifiers because of the superior sound at low volume levels on my Klipschs. I've found one 50V CFA amplifier that is able to match the sound though. That kind of supports my theory of speed.
First all. I want to emphasis I mean no disrespect in this forum. I like to question deep into the theory, I got comment that I talk down to people. I absolutely do not mean that at all.
That said. Sounds like slew rate is what you think that makes the difference. That can be achieved by
1) Higher VAS bias current and or push pull VAS.....which I use 10mA bias and push pull.
2) High input impedance OPS....which I use 3EF diamond.
3) Able to swept out the base charge of the big transistors...which I use 50mA bias through the driver transistors.
4) High loop gain ( or feedback gain)....which I use active CCS for LTP in the IPS, using darlington push pull VAS.
In simulation, I easily got 500KHz BW with my design with 40V rail. So I should have feedback gain of about 25 at 20KHz to keep the distortion down and able to slew fast.
If slew rate is the concern, do you think this is good enough? I think the next step/next project is to use this OPS to pair with a CFA IPS to follow Ostripper. I just want to learn how to walk before running.
Thanks
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There's only one way to know for sure. Try it. The amp I was referring to was Vzaichenco's CFA-CFPx2. http://www.diyaudio.com/forums/solid-state/264259-cool-simple-clean-cfa-10.html#post4137207
The danger of current hogging at different bias levels can be calculated. It is dependent on Vce, Re, thermal resistance and degeneration voltage. For each resistor and bias voltage combination you can plot a curve showing what Vce is acceptable for a given heatsink for instance.
At low Vce such as perhaps a bridged amplifier, 0.1R resistors might be fine. I like to try to calculate the dangers so I'm not excluding legitimate options.
At low Vce such as perhaps a bridged amplifier, 0.1R resistors might be fine. I like to try to calculate the dangers so I'm not excluding legitimate options.
How do you test? driving a sine wave into the amp with resistor load? Let it heat up and then measure the voltage across all the Re to look for one that has the most voltage and calculate how much power through the transistor?
Digital music can have some pretty high transients. Finger snaps and
stick strikes I've measured almost 200W at slightly above normal listening
levels. FM radio - no such thing.
SQ is "sound quality" - HT is "home theater" - 200W+ transients here as well.
After them posts of what a 5 pair's Re measured , I finally get to listen (below).
I hit a few 200W peaks ... tested all 20 outputs after. All
were 12-13 mV except two (11.4 and 14mV).
Some of my builders go from design to a working prototype in 48 hours. I'm
a bit slower ... still - "take a leap of faith" , build and then perfect it.
Worst case , you will have to design a "R2" or "R3" (revision).
Nothing comes easy , man.
OS
Attachments
No , do what I'm doing above ... abuse the hell out of it - and
shake the house.
Then test...OS
Nice looking amp!! So you feed some high power signal to heat up the amp, then cut the signal and immediately measure the voltage across all the emitter resistors to see anyone has excess voltage across it?Digital music can have some pretty high transients. Finger snaps and
stick strikes I've measured almost 200W at slightly above normal listening
levels. FM radio - no such thing.
SQ is "sound quality" - HT is "home theater" - 200W+ transients here as well.
After them posts of what a 5 pair's Re measured , I finally get to listen (below).
I hit a few 200W peaks ... tested all 20 outputs after. All
were 12-13 mV except two (11.4 and 14mV).
Some of my builders go from design to a working prototype in 48 hours. I'm
a bit slower ... still - "take a leap of faith" , build and then perfect it.
Worst case , you will have to design a "R2" or "R3" (revision).
Nothing comes easy , man.
OS
Do you sell amps of your design?
You and Jwilhelm both advocate high rail voltage, what is your take on that. Why it sounds nicer with high rail?
No , we don't sell them ... we offer them dirt cheep through group buy's.
Members satisfaction is paramount.
To me a high rail is 90V. 72 is "normal".
Edit - yes , disturb the neighbors ... then test.
OS
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Hi Jan
Perhaps it is not wise to contradict my publisher
but I think Keantoken is correct on this.Surprised no one has mentioned that this is all covered quite well in Bob's book p299-301.
It is also relevant to Alan's concern's about low Re thermal stability.
The calculation there can determine if his proposals can be thermally stabilized.
My offhand approximations have it as achievable, maybe too close for peace of mind.
But best to have Alan do the numbers and satisfy himself.
Best wishes
David
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No , we don't sell them ... we offer them dirt cheep through group buy's.
Members satisfaction is paramount.
To me a high rail is 90V. 72 is "normal".
Edit - yes , disturb the neighbors ... then test.
OS
What do you mean group buy?
You use real speaker to do high power test? Luckily I don't live next to you!!!
Can I use dummy load to run it hot and read the Re?
Do you run high power until the heatsink heats up or you run it very short time before you read?
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What do you mean group buy?
You use real speaker to do high power test? Luckily I don't live next to you!!!
Can I use dummy load to run it hot and read the Re?
I run mine in on 4 ohm dummy loads.
Group Buy. http://www.diyaudio.com/forums/group-buys/257057-slewmaster-project-boards.html#post3945741 . We also share Gerber files.
Wow, when you said high rail, you're not kidding!! You run 100V!!! You can only have tiny bias current.
Did Ostripper said he only get about 12mV across the Re? that's not even as high current as Oliver's condition.
I remember you said you use lower than 26mV. I never quite get that. What is the reason you don't follow Oliver's condition of 26mV?
