Yes, that's pushing it, but if you recall that low Gate current is often
a crucial spec for JFETs, you will appreciate that the voltage rating
is pretty conservative. I have tested groups of these parts and found
them actually breaking down between 40 and 45 volts.
Also, the Drain resistor of the JFET typically has about 5 volts across
it, subtracted from the power supply voltage.
a crucial spec for JFETs, you will appreciate that the voltage rating
is pretty conservative. I have tested groups of these parts and found
them actually breaking down between 40 and 45 volts.
Also, the Drain resistor of the JFET typically has about 5 volts across
it, subtracted from the power supply voltage.
Thanks again - I figure it's borderline but it'll survive... Around 10 good watts is good enough actually, even with 86dB speakers like I have.
Babowana: I already have 50V parts for the PSU filter caps, I was more worried about the active devices. I'm leery of PSU caps that are close to the rail voltages, I'm used to seeing 35V caps exploding at 25V rails, so I generally allow a lot of margin when using parts available here.
I will check the heat at 500mA, 1A and 1.3A and finalise the operating point from the heatsink temperatures. Our country is a hot one this time of the year, so I doubt I would have been at full bias even with the right voltages.
Now I just have to wait for the parts from Jack
Babowana: I already have 50V parts for the PSU filter caps, I was more worried about the active devices. I'm leery of PSU caps that are close to the rail voltages, I'm used to seeing 35V caps exploding at 25V rails, so I generally allow a lot of margin when using parts available here.
I will check the heat at 500mA, 1A and 1.3A and finalise the operating point from the heatsink temperatures. Our country is a hot one this time of the year, so I doubt I would have been at full bias even with the right voltages.
Now I just have to wait for the parts from Jack
Nelson Pass said:Yes, that's pushing it, but if you recall that low Gate current is often
a crucial spec for JFETs, you will appreciate that the voltage rating
is pretty conservative. I have tested groups of these parts and found
them actually breaking down between 40 and 45 volts.
Also, the Drain resistor of the JFET typically has about 5 volts across
it, subtracted from the power supply voltage.
That means that if we get, say, +/-27V from a Xfrm > bridge > CRC arrangement we don't care too much and we are're not forced to increase the value of the dropping R to respect the 24-25V of the original deisgn?
feedback resistor to 100 ohm
Maybe the question has been asked and answered, a pity you can't search within the thread alone (reading 188 pages you say ..). I've just build the F5 and it is playing here in test-modus.
Because I found the gain of 15dB on the low side, I decided to try one 100 Ohm (per feedback rail) resistor instead of the 2 resistors (making it 50 Ohm as in the original circuit). I guess the gain becomes around 20 dB (more like the average amp, but still on the low side). Of course there will be some drawbacks coming with the higher gain? Has anybody tried different levels of feedback and assessed the differences, subjective and measure-wise?
Second point is that the offset is very critical or sensitive. Changing one pot affects the other half of the circuit too. Changing it too much at a time is not a good idea, I discoverd quickly. But after some fiddling you get the feel.
About the gain: the French profet amplifier uses other feedback resistors and (I think) has a gain of around 25 dB. So one would think this is a feasible option for the F5 too? Or is this blasphemy and an insult to the designer of the F5 (aka mr Pass)?
Maybe the question has been asked and answered, a pity you can't search within the thread alone (reading 188 pages you say ..). I've just build the F5 and it is playing here in test-modus.
Because I found the gain of 15dB on the low side, I decided to try one 100 Ohm (per feedback rail) resistor instead of the 2 resistors (making it 50 Ohm as in the original circuit). I guess the gain becomes around 20 dB (more like the average amp, but still on the low side). Of course there will be some drawbacks coming with the higher gain? Has anybody tried different levels of feedback and assessed the differences, subjective and measure-wise?
Second point is that the offset is very critical or sensitive. Changing one pot affects the other half of the circuit too. Changing it too much at a time is not a good idea, I discoverd quickly. But after some fiddling you get the feel.
About the gain: the French profet amplifier uses other feedback resistors and (I think) has a gain of around 25 dB. So one would think this is a feasible option for the F5 too? Or is this blasphemy and an insult to the designer of the F5 (aka mr Pass)?
Thanks for the reply.
I figured there would be a reduction in the bandwidth (and other nice things) if I got the entire additional gain by tweaking the feedback in the amp. Of course that is the easiest way of doing it. Apologies for making you mention it twice
I was planning on a preamp also because I've never used one before, I generally go straight out of the Buffalo into an amplifier, using the PC to control volume. This is said to be suboptimal, but maybe it's because of poor impedance matching so I am keen to try a good preamp.
Again, the additional gain is not always required, I generally run my system at around -20dB or -18dB, but some of my music has very low levels and I need the system to go all the way up to -4dB (this is read off the mixer controls in my soundcard control panel). That amp has 26dB gain, so I need about 21-22 dB total.
I was looking at the BOSOZ project on the Pass DIY site and it seems simple enough to cook up (and has the required gain), so it's a likely candidate for sure.
Now if I could figure somewhere I can go learn about tube basics...
I figured there would be a reduction in the bandwidth (and other nice things) if I got the entire additional gain by tweaking the feedback in the amp. Of course that is the easiest way of doing it. Apologies for making you mention it twice
I was planning on a preamp also because I've never used one before, I generally go straight out of the Buffalo into an amplifier, using the PC to control volume. This is said to be suboptimal, but maybe it's because of poor impedance matching so I am keen to try a good preamp.
Again, the additional gain is not always required, I generally run my system at around -20dB or -18dB, but some of my music has very low levels and I need the system to go all the way up to -4dB (this is read off the mixer controls in my soundcard control panel). That amp has 26dB gain, so I need about 21-22 dB total.
I was looking at the BOSOZ project on the Pass DIY site and it seems simple enough to cook up (and has the required gain), so it's a likely candidate for sure.
Now if I could figure somewhere I can go learn about tube basics...
works fine indeed
Thanks Nelson. It's working now for around 24 hours with the 100 Ohm feedback resistors (all other thing being equal). Sound is fine and offset is shifting around a bit (when everything is at right temperature, it's within plus and minus 50 mV of so, no problem with me). I've not done serious listening yet, but first impressions are of a more modern, more snappy, more open sound than I remember from the aleph 30 and mini-A I used years ago (which was slightly more warm, but for my taste too laid-back and lazy, kind of diffuse (in contrast to 'pinpoint') highs sometimes). Yes, strange audio-mumbo-jumbo, not too easy to describe what you think you hear.
Thanks Nelson. It's working now for around 24 hours with the 100 Ohm feedback resistors (all other thing being equal). Sound is fine and offset is shifting around a bit (when everything is at right temperature, it's within plus and minus 50 mV of so, no problem with me). I've not done serious listening yet, but first impressions are of a more modern, more snappy, more open sound than I remember from the aleph 30 and mini-A I used years ago (which was slightly more warm, but for my taste too laid-back and lazy, kind of diffuse (in contrast to 'pinpoint') highs sometimes). Yes, strange audio-mumbo-jumbo, not too easy to describe what you think you hear.
High Impedance speakers and the F5
If this has been covered please accept my apologies fro laziness.
I want to use the F5s in a bi-amplified installation.
I am using TAD 4001's which are nominally 15 ohms.
Usually this is either benign or advantageous for an amplifier. Is that case, also, with the F5.
Thanks for any opinion offered.
If this has been covered please accept my apologies fro laziness.
I want to use the F5s in a bi-amplified installation.
I am using TAD 4001's which are nominally 15 ohms.
Usually this is either benign or advantageous for an amplifier. Is that case, also, with the F5.
Thanks for any opinion offered.