In addition to the fully implemented F5 circuit, I’ve tried 3 varieties of the minimal circuit (no current limiting and no thermal tracking).
1. Fairchild mosfets – no changes to other values.
2. Fairchild mosfets with reduced feedback (R1&2=20ohm, R5&6=100ohm, R11&12=0.91ohm).
3. Renesis/Hitachi paralleled pairs – not cascaded; no changes to other values.
As stated previously, the minimal circuit yielded a large improvement, although other changes such as going monoblock and better power caps muddy the waters in determining the relative value of deleting the current/thermal portions.
Type 1 presents highs that are at the same time pinpoint sharp, yet delicate and soft, like an exquisitely constructed snowflake drifting in motionless air. The bass is very tight and accurate, which may explain why some feel it sounds a bit lean. There is no sense of solid-state mechanics at work here. It is also far from tube-like. The best single adjective I can think of to describe Nelson Pass’ creation is “natural.”
Type 2 retains the same characteristics as Type 1, albeit to a less intense degree. Think of Type 1 as Usain Bolt in a 100-meter dash striving to the utmost versus a Kenyan marathoner cruising at 85% of maximum output. Its more relaxed characteristic is more forgiving of less-than-perfect source recordings. On a side note, it does have a little bit more gain and when I played one channel in conjunction with Type 1 there was a shift in the soundstage image.
Although I preferred listening to electronica with Type 2, on audiophile grade recordings I found myself missing the supernatural detail of Type 1.
If the Fairchilds can be described as neutral in the extreme, the same cannot be said of the Renesis, which come across as quite warm. Perhaps it is a result of unmatched devices, but it was relatively noisy compared to the very quiet Fairchilds, with some loss of detail in the ambient background. The bass has a rounder and heavier quality to it. When played at volume, it also feels less strained (A result of biasing them to 1A per device or 2A total?). I would say this sound best with Rock and Pop recordings as it lends a little bit of a punch to things.
Next up for me will be the Toshibas. EUVL seems to really like these.
1. Fairchild mosfets – no changes to other values.
2. Fairchild mosfets with reduced feedback (R1&2=20ohm, R5&6=100ohm, R11&12=0.91ohm).
3. Renesis/Hitachi paralleled pairs – not cascaded; no changes to other values.
As stated previously, the minimal circuit yielded a large improvement, although other changes such as going monoblock and better power caps muddy the waters in determining the relative value of deleting the current/thermal portions.
Type 1 presents highs that are at the same time pinpoint sharp, yet delicate and soft, like an exquisitely constructed snowflake drifting in motionless air. The bass is very tight and accurate, which may explain why some feel it sounds a bit lean. There is no sense of solid-state mechanics at work here. It is also far from tube-like. The best single adjective I can think of to describe Nelson Pass’ creation is “natural.”
Type 2 retains the same characteristics as Type 1, albeit to a less intense degree. Think of Type 1 as Usain Bolt in a 100-meter dash striving to the utmost versus a Kenyan marathoner cruising at 85% of maximum output. Its more relaxed characteristic is more forgiving of less-than-perfect source recordings. On a side note, it does have a little bit more gain and when I played one channel in conjunction with Type 1 there was a shift in the soundstage image.
Although I preferred listening to electronica with Type 2, on audiophile grade recordings I found myself missing the supernatural detail of Type 1.
If the Fairchilds can be described as neutral in the extreme, the same cannot be said of the Renesis, which come across as quite warm. Perhaps it is a result of unmatched devices, but it was relatively noisy compared to the very quiet Fairchilds, with some loss of detail in the ambient background. The bass has a rounder and heavier quality to it. When played at volume, it also feels less strained (A result of biasing them to 1A per device or 2A total?). I would say this sound best with Rock and Pop recordings as it lends a little bit of a punch to things.
Next up for me will be the Toshibas. EUVL seems to really like these.
The Toshiba's are on my list, and in one of my boxes of toys. I look forward to your findings. I've muddied my own waters a bit by putting some carbon film resistors in the signal path, and not Dales MF. I will probably swap between both once CVillers new boards arrive.
A big thank you for your observations🙂
The Ren/Hits were not the laterals I take it.
Hi Ichiban,
2sj162(p)&2sk1058👎
Ray
please keep us informed, I am interested in doing an identical system. super v's and f5's.(I am an audiphile and diy virgin....i will be hangining on your every word). What type of heat sinks/enclosures(very important here in San Antonio, TX) will you be using? Where are you getting your components? I definatley want to use high quality....if you don't mind me asking, how much do you estimate your amp build to cost?
thanks
thanks
Shane
I have long had my F5 without any protection circuitry, and your description for no. 1 above fits it exactly.
Fran
Fran
Thank you for a very clear and concise report , could you describe your ancillary equipment being used along with the F5 ?
Hello ,
Has a date been given on this as yet ? ......
Hi a.wayne,
My equipment:
samsung CD player modified by Reference Audio Mods (superclock, power supply and cap upgrades). This was before I got into doing things myself🙂
Lightspeed interconnect using 28g silver wire
F5
DC Gold 9.5R driver in a parts express 1cubic foot sub box. I wired 20g silver wire directly from the driver to the F5 amp.
Alazira, what is the RDS on for the Renesis/Hitachi (you have pairs per rail?) compared to the Fairchilds??
Thinking that maybe the bass difference is due to DF??
One could measure the output Z...
Thinking that maybe the bass difference is due to DF??
One could measure the output Z...
Hi Bear,
Sorry for the newb questions here, but what is RDS?
I don't know how to calculate or measure damping factor.
How do you measure output Z (and what is it?)
Can someone explain the difference between a lateral and vertical mosfet?
Happy New Year!
so, i was able to take part in a listening session earlier this week.
F5 v. F5
both were using the irf mosfets and 170/J74 jfets.
Amplifier 1 was built with an antec trafo, and a rather wimpy PS... 24.3V DC. The jfets were bl. pd's boards.
Amplfier 2 was built in monoblocs, with 33V DC CLC and more C filter. cviller boards, some audiophile parts, including caddocks on the input R. jfets were GR grade.
Amplifier 2 was much warmer, significant 2nd harmonic, but VERY pleasant sounding.
Amplifier 1 had the edge in clarity and speed especially in the treble, but definitely sounded cold in comparison.
source: decent dac/music server.
speakers: quad 63s
sub provided by dsp and dipole peerless woofers and icepower amplification.
we also listened to a 845 SET and a pair of 500W icepower amps. In certain circumstances, the 845 was just beautiful... and in other cases was a little mushy. I feel the F5s bettered both of the other amplifiers.
F5 v. F5
both were using the irf mosfets and 170/J74 jfets.
Amplifier 1 was built with an antec trafo, and a rather wimpy PS... 24.3V DC. The jfets were bl. pd's boards.
Amplfier 2 was built in monoblocs, with 33V DC CLC and more C filter. cviller boards, some audiophile parts, including caddocks on the input R. jfets were GR grade.
Amplifier 2 was much warmer, significant 2nd harmonic, but VERY pleasant sounding.
Amplifier 1 had the edge in clarity and speed especially in the treble, but definitely sounded cold in comparison.
source: decent dac/music server.
speakers: quad 63s
sub provided by dsp and dipole peerless woofers and icepower amplification.
we also listened to a 845 SET and a pair of 500W icepower amps. In certain circumstances, the 845 was just beautiful... and in other cases was a little mushy. I feel the F5s bettered both of the other amplifiers.
RDS stands for Resistance between Drain and Source and implies the minimum with the device "on".
Output Z is measured by the load resistance that results on the output being 1/2 the voltage of unloaded. Z is short for impedance, implying that the load need not be purely resistive.
Damping factor is the ratio of the load divided by the output Z.
A tube amp might have a 4 ohm output Z and its DF would be 2 if driving an 8 ohm resistor. if output Z were .1 ohm, DF would be 80 driving that same resistor.
As for the FET, different processes and geometries can be used to create specific characteristics. Personally its only important if you wanted to make more.
HTH
Doug
Interesting, so the amp with the better parts, and power supply sounded warmer than the amp without??
And how do you know there were significant 2nd harmonics present in Amp 2??
🙂
_-_-bear
The wimpy PS uses a 400VA antec trafo, 18V secondaries, and a 18mF 1R 24mF supply per rail.
The monoblock power supply uses toroid band 400VA and overkill CLC. The rails are 33V.
I can chime in on this as we were at my home. The mono block F5’s had a warmer signature similar to my 845 SET amp, but without the bloom you get in second harmonic distortion if you push the 845 above a few watts. The SET amps cant drive the Quad ESL 63’s very well if you push them. The F5 has no problem with the Quads.
My F5 build is like this. 400VA 22v transformer, Hex fred rectifiers, 18K uF, 2mH 16 g coil, 36K uF, cviller boards with Cadock MK132’s in R9, 10, 13 and 14. IRF outputs and biased at 1.6A. in an old chassis from other experiments
🙂
My F5 build is like this. 400VA 22v transformer, Hex fred rectifiers, 18K uF, 2mH 16 g coil, 36K uF, cviller boards with Cadock MK132’s in R9, 10, 13 and 14. IRF outputs and biased at 1.6A. in an old chassis from other experiments
🙂