It can swing 80Vp-p in the current configuration, which is 28 Vrms. That would need 2.8Vrms on the input because the gain is 10X or 20db.
The peak swing may be affected by other things. I haven’t tested it yet.
Edit: just confirmed that it is swinging 24Vrms with 2.3V input. Couldn’t push the input any higher for now.
The peak swing may be affected by other things. I haven’t tested it yet.
Edit: just confirmed that it is swinging 24Vrms with 2.3V input. Couldn’t push the input any higher for now.
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Yes, look at post 88 of this thread. Mike R. Posted an easy source follower at Burning Amp last year. Would be a great pairing. I currently use this preamp with a choke-loaded VFET follower. It sounds lovely. The VFET amp easily shows differences between preamps and also between different caps at C102.
The second one you listed looks fairly good. Low input capacitance that stabilizes quickly and decent SOA for TO-92. Worth a try. But I have not yet established what separates good from astonishingly good. So far, I’ve heard good sounds from ST’s supermesh and powermesh series.
I am happy to send you a couple of STQ1NK80ZR-AP for free.
200 mm x 220 mm.
PCBs and FETs shipping out tomorrow.
PCBs and FETs shipping out tomorrow.
Some folks asked for sonic impressions about the three FETs that went with the PCB:
STQ1NK80ZR-AP: all-rounder. Does everything very well. One of my favorites.
STP30N10F7: Another great all-rounder, but also has thundering bass. Has come right to the top of the heap.
SIHP10N40D: There is something about this one that just makes the walls melt away. It conveys so much of the recording space and really takes you there. It does not have quite the liquid highs as the two above, but worth playing around with.
So much of the preference for the gain FET will depend upon the rest of the system, mainly the power amp and the speakers. Like ZM says, it depends on how much sugar you like in the sound. My impressions are mostly with a choke-loaded source-follower (no gain) Sony VFET amp. The SCG has to provide the full voltage swing and drive the 2000+ pF gate of the VFET, which is a difficult place to be in.
My dad is visiting and last night we cycled through the 10Y and 300B tubes on the tube preamp (Rod Coleman heaters, LCL B+ supply, and the same CCS load as the SCG). The 300B has the most amount of "sugar" and it really rounds things off. The 10Y is very neutral and my favorite. And the SCG has them both beat (in combination with the VFET). My dad, who is a tube guy (his regular amp is a 2A3 with high-efficiency horn-loaded full range drivers), also begrudgingly admits that the SCG+VFET combo sounds the best.
To me, the SCG shows just a bit more than the 10Y. I get the sensation that the singers are singing into the mic, to the point where you can almost imagine their facial expressions. That may sound ludicrous but it takes you to that point. A lot of this is the VFET too. You can hear (yes, hear!) the body movements of the musicians--spooky. This is because you can play it louder without straining your ears and you can hear further down into the recording. The 10Y--to a much less degree--and the 300B take away every so slightly from this level of performance. Once you hear the SCG+VFET, you can tell when something is missing. Nelson calls the VFET a prima donna, which is to say that it likes to dominate the sound. I really believe that. The tubes like to add their own flavor and the VFET says, no thanks.
After all that waffling, I feel like I should post some measurements. Will try to get those today.
STQ1NK80ZR-AP: all-rounder. Does everything very well. One of my favorites.
STP30N10F7: Another great all-rounder, but also has thundering bass. Has come right to the top of the heap.
SIHP10N40D: There is something about this one that just makes the walls melt away. It conveys so much of the recording space and really takes you there. It does not have quite the liquid highs as the two above, but worth playing around with.
So much of the preference for the gain FET will depend upon the rest of the system, mainly the power amp and the speakers. Like ZM says, it depends on how much sugar you like in the sound. My impressions are mostly with a choke-loaded source-follower (no gain) Sony VFET amp. The SCG has to provide the full voltage swing and drive the 2000+ pF gate of the VFET, which is a difficult place to be in.
My dad is visiting and last night we cycled through the 10Y and 300B tubes on the tube preamp (Rod Coleman heaters, LCL B+ supply, and the same CCS load as the SCG). The 300B has the most amount of "sugar" and it really rounds things off. The 10Y is very neutral and my favorite. And the SCG has them both beat (in combination with the VFET). My dad, who is a tube guy (his regular amp is a 2A3 with high-efficiency horn-loaded full range drivers), also begrudgingly admits that the SCG+VFET combo sounds the best.
To me, the SCG shows just a bit more than the 10Y. I get the sensation that the singers are singing into the mic, to the point where you can almost imagine their facial expressions. That may sound ludicrous but it takes you to that point. A lot of this is the VFET too. You can hear (yes, hear!) the body movements of the musicians--spooky. This is because you can play it louder without straining your ears and you can hear further down into the recording. The 10Y--to a much less degree--and the 300B take away every so slightly from this level of performance. Once you hear the SCG+VFET, you can tell when something is missing. Nelson calls the VFET a prima donna, which is to say that it likes to dominate the sound. I really believe that. The tubes like to add their own flavor and the VFET says, no thanks.
After all that waffling, I feel like I should post some measurements. Will try to get those today.
Thank you for your thoughts and subjective listening impressions Ra. This will be a fun preamp to play around with!
Few measurements of the STP30N10F7 and comparison with 300B as a preamp operated at 170V, -30V grid bias, 30mA CCS.
All measurements at approximately 2.8Vrms out. That's 1W into 8 ohm for a source follower power amp (such as the VFET follower I am using).
STP30N10F7:
FFT for 1 kHz.
THD v Freq.
300B
FFT. Does this look more triodey or does the one above?
THD v FR. This is spectacular.
All measurements at approximately 2.8Vrms out. That's 1W into 8 ohm for a source follower power amp (such as the VFET follower I am using).
STP30N10F7:
FFT for 1 kHz.
THD v Freq.
300B
FFT. Does this look more triodey or does the one above?
THD v FR. This is spectacular.
Nice!
Curious though that your impression of the 300B having the most amount of "sugar" but the distortion profiles are very similar.
Curious though that your impression of the 300B having the most amount of "sugar" but the distortion profiles are very similar.
Frequency below 100Hz starts dropping, could that be attributed to input/output capacitors creating a high pass filter?
Were the measuments taken using the SCG onboard power supply?
Were the measuments taken using the SCG onboard power supply?
Yes, only a 10 uF cap was in the C102 position, which creates a high-pass. Coupling caps are also 1 uF. That is the reason for the roll-off. It is also working into a 10k ohm input of the ADC. With higher loads, it will be better.
Yes, it was measured with the onboard supply.
edited: incorrectly wrote “low-pass” when it should say “high-pass”
Yes, it was measured with the onboard supply.
edited: incorrectly wrote “low-pass” when it should say “high-pass”
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Great question! I was expecting to measure higher 2nd order from the 300B also, but it measures about the same. I don't know where that perception comes from, but it certainly has too much sugar in combination with the VFET. Things are too rounded and overly liquid for my taste. The SCG in comparison sounds sweet but not overly sweet. And the window into the lower reaches of the recording is simply astounding. You can easily hear how many mics were used and where they were placed. You can hear the floor and the ceiling of the recording space and so on.Nice!
Curious though that your impression of the 300B having the most amount of "sugar" but the distortion profiles are very similar.
Another thing that is scarcely believable is the importance of polarity. It definitely has a preference for polarity and on some songs it is much better one way than the other way, and on some others not so much. I have left it with reverse phase at the output of the VFET and I switch the input polarity from JRiver. When I play from iTunes into JRiver, it is almost always better with reverse polarity in JRiver. When I play from an HDD via JRiver, it goes with no polarity switch.
Here's a 10 kHz square wave. Yellow is input (1V/div) and blue is output (2V/div). That's a 10V 10 kHz square wave. Can't ask for more.
I have been pondering the relationship of harmonic distortion and enjoyment of reproduced music with respect to your 300B and SCG preamps. Like you I have SIT/VFET single ended follower amplifiers and enjoy a bit a second harmonic distortion. Even though my horn speakers are very sensitive (102dB), my SE amplifiers vary from 5W to 50W output. With my sensitive speakers I can take advantage of the first Watt as most of the time, and perhaps all of the time, I am listening to the first Watt and the lower distortion level that comes with the first Watt.
So that got me thinking about your 300B preamp, and whether its distortion at higher output voltage is higher than that of your SCG preamp. It would be interesting to compare the distortion levels at higher output voltages. Of course the sensitivity of your speakers and the actual output voltages at your listening levels would be factors.
So that got me thinking about your 300B preamp, and whether its distortion at higher output voltage is higher than that of your SCG preamp. It would be interesting to compare the distortion levels at higher output voltages. Of course the sensitivity of your speakers and the actual output voltages at your listening levels would be factors.