Interesting use of the O2 headphone amp as a pre-amp. May I know what gain you use on the O2, and at what volume? Will it be very demanding on the O2? Since I'm also using the O2 as a pre-amp, I'm wondering is it better to go with F4 or F5 (at 1x O2 gain)?
I use the O2 with the gain switch on, and the volume knob most of the way or all the way up[/quote]
Any power amp will be very easy to drive compared to headphones
The O2 makes a wonderful preamp. I heartily recommend it. It sounds fantastic, is quiet, and is also a great headphone amp... 😀
The O2 can only swing a bit more than 7 volts on the output. That is more than enough to clip an F5, but only enough to get an F4 to about 1/2 it's output.
The F4 requires a different preamp (such as the Pumpkin, a Burning Amp front-end configured as a preamp, or ImPasse) to drive it to maximum output. In my current situation the O2 has plenty of gain, but it's a small room and I'm fairly close to the speakers.
So an O2 as preamp is not ideal for the F4, but it does get you playing music as you build another preamp.
As for amps, I strongly prefer the sound of the F4 to the F5.
Thanks! I think i'm leaning towards f5 + O2 then...much fewer transistors to deal with too. I never imagined when building the O2, it could double up as a wonderful pre-amp. Nice! Suppose I run the O2 pre-amp with 2.5x gain, plus the F5's gain, that's considered double amping right? Is it really that bad, from a signal purity point of view?
It's a fantastic preamp. One of these days I'm going to make some input/output selection, use a fancy stepped attenuator and make a desktop O2 (with Odac) Preamp.
It's not double amping, and there is no problem for signal purity. The O2 is very, very quiet and extremely neutral.
This one would be fine to drive F4 .
6SN7 SRPP Tube Valve Preamplifier Amplifier S3 DIY Kit Stereo | eBay
6SN7 SRPP Tube Valve Preamplifier Amplifier S3 DIY Kit Stereo | eBay
I recently built an EF86 based preamp that has gain of about 20, which is high in general for a line stage amplifier but it seems like it could work very well with the F4. I want to build an F4 soon to find out.
@6L6 "The F5, when compared to the F4 is, in my opinion, is a bit boring. The F4 is that good"
what if you compare F4 vs Aleph-J?
what if you compare F4 vs Aleph-J?
Its possible, but 2v swing aint much. I will be running an Altec system soon, and it doesnt get much more efficient than that without a full horn setup, adn i wouldnt try it. You also have to consider the performance of the DCB1 fully turned up. MOst preamps and driver stages are devevloped to have a certain sweet spot and a certain drive level. Look at BA3B and see the distortion graph vs power output. You can see there is a certain point where it is lowest and that related to what hapening in that VAs/amplification stage. There are also those who believe strongly in a preamp that lifts the signal "out of the dirt" a little bit. I believe Pano's article on Gain Structure may be a good reference.
dimkasta - a CD player, with a 2 volt swing, into an 8ohm speaker will give 1/2 watt.
2*2/8 = .5
So if you have some unnaturally efficient speakers, you will get some music. But in the real world, the most you will hear is a whisper.
Because power is voltage squared divided by the speaker impedance, the first handful of volts makes a big difference... I'm currently using my O2 headphone amp, which will swing 7 volts on the output -
7*7=49
/8 = 6.13W
Which although seems tiny, is actually quite loud.
If you want full output from a normal source, there are some dedicated circuits made for the F4, the Pumpkin and the ImPasse. A BA-2 or -3 front end has enough gain as well. John Broskie's Aikido preamp can be configured for enough gain.
2*2/8 = .5
So if you have some unnaturally efficient speakers, you will get some music. But in the real world, the most you will hear is a whisper.
Because power is voltage squared divided by the speaker impedance, the first handful of volts makes a big difference... I'm currently using my O2 headphone amp, which will swing 7 volts on the output -
7*7=49
/8 = 6.13W
Which although seems tiny, is actually quite loud.
If you want full output from a normal source, there are some dedicated circuits made for the F4, the Pumpkin and the ImPasse. A BA-2 or -3 front end has enough gain as well. John Broskie's Aikido preamp can be configured for enough gain.
So basically we need ~20db to get the full 25W specified
The question is how much we actually need... I need to do some math with my current setup...
The question is how much we actually need... I need to do some math with my current setup...