Singles - ($2.11/ea or $1.79/ea at qty. 10+)
McMaster-Carr
or
$9.88 for (50)
Amazon.com: Karcy Brass M3 Male x M3 Female Hex Head PCB Standoffs Spacers Hardware Nut 12mm Length 50 Pcs (M3x6+6): Home Improvement
McMaster-Carr
or
$9.88 for (50)
Amazon.com: Karcy Brass M3 Male x M3 Female Hex Head PCB Standoffs Spacers Hardware Nut 12mm Length 50 Pcs (M3x6+6): Home Improvement
I'm not sure what 6L6 uses but Room Equalization Wizard (REW) is quite popular in conjunction with a USB sound card. That is what I use with a Focusrite Scarlett.
Howto - Distortion Measurements with REW
220 Pcs M3 Nylon Hex Spacer Standoffs Screws Nuts Assortment Kit-Male Female Black: Amazon.com: Industrial & Scientific
I use these nylon ones....awesome and work great. And they will not melt in your class a builds.
I use these nylon ones....awesome and work great. And they will not melt in your class a builds.
Hymn, I do not get the correlation between how "strong" (A) inductor is and how loud the amp plays ... It is class A, so current is constant, regardless of input signal in (V) Or I am missing something ...Could you explain please?
You are right of course, I was thinking of a non class A case such as my other amp. There a speaker load of 4.37 ohms and a voltage rail of 21.87 Volts would hit 5 Amps at 107 watts, so keeping the volume down is a plus.
Has anyone calculated the current draw of the F4 with say 300mV bias?
M3-0.5X6 4.5mm Hex Male-Female - Standoffs - Aluminum | CDE FastenersWould you please share your link for the box of 500? PM me or just post it here
f4 in a 3U (it’s what I had). Also run a PP of the same power in a 3U. And these nylon standoffs are good even under these oven-like conditions.
Hi ggetzoff
This makes me curious... Everybody says a 4U chassis should be the least for a working F4. I was reluctant to follow even though I know they are really good...
Did you had to make any compromises? Mind to share a pic?
thank you
david
Very much...
Here are some measurements. The output signal was 3.5 Vpp into 16 ohm load.
Two first pictures are measurement for first and second channel. The last one is loop-back of my sound card.
I am a little worried with temperatures. Rectifier diodes works at 70 degree C, transformer mesures 50 C at its surface. Condensators are also at 50C ...
Attachments
That is a bit hot. Looking at the pictures in your post #1985, you probably don't have enough ventilation around your components. You have your power supply board with capacitors and rectifiers on top of your transformer. The power supply board is absorbing heat directly off the transformer and it is also impeding free air flow above the transformer. A fan or two under the amplifier case pushing air into the case would help cool the interior of the case.
By the way, 3.5 Vpp into 16 Ohm is 0.1W. Perhaps measure at 1W?
By the way, 3.5 Vpp into 16 Ohm is 0.1W. Perhaps measure at 1W?
This past weekend I finally got around to finishing the F4 headamp build that I’ve had on my bench for several weeks now.
The PSU consists of a 150VA 2x15VAC toroidy transformer with a CCRC filter. There are 3x33000uF filter caps per polarity, R being a 1R wire wound bolted to the bottom plate. Supply voltage at the last C is a symmetrical +/-18V.
The amp is using a single pair of FQA12P20 and FQA19N20C output FETs with Vishay CPF3 0R22 source resistors. The output FETs’ bias is set at 0.5A (110mV over the source resistors). The input JFETS have an Idss of about 8.5mA, with the p-channel having a 5R degeneration resistor to match the j74’s transconductance to that of the k170’s (see 5th image). I had to use 7k5 for R9 to get the bias up to 0.5A. Output offset is around 1mV when warmed up. I have 15mV of cold output offset in my notes, but I have to check that again, it just seems too low.
The numbers:
(THD measured with Boonton 1121 analyzer with 0.0009% THD baseline, F4 unloaded output)
Vsupply=+/-18.01V
Ibias=0.5A (110mV over R22)
gain -0.46dB (1V in, 0.948V out)
noise about 50uV unloaded (purple trace 6th image)
1V input (0.948V out) @ 1kHz:
95.46dB S/N
94.92dB SINAD
-94.9dB THD, 0.0019%
3V input (2.847V out) @ 1kHz:
105.56dB S/N
93.97dB SINAD
-93.98dB THD, 0.002%
THD spectrum 2nd>3rd>4th, with 2nd around 10dB over 3rd
visible clipping at 14V input (1.213% THD), above 7V input 3rd order dominant
output impedance: 0.33 Ohm
unloaded V1=521.2mVrms @50Hz
8R2 loaded V2=500.5mV
Z=R*(V1/V2-1)=0.33R
There are countless reviews on the F4, so I’ll keep it short. Source is a soekris 1021 R2R DAC with a DCB1 output buffer. Surprisingly, there’s enough voltage swing for the HD800, with a few dB to spare.
This amp is underrated. People have said it before, and they are right.
The soundstage is incredible. Solid, consecutive, almost holographic.
I’m looking forward to building different preamps already.
And lastly, damn, now I’ll have to build an F4 speaker amp, it’s just too good. I should have a kit stashed away somewhere…
The PSU consists of a 150VA 2x15VAC toroidy transformer with a CCRC filter. There are 3x33000uF filter caps per polarity, R being a 1R wire wound bolted to the bottom plate. Supply voltage at the last C is a symmetrical +/-18V.
The amp is using a single pair of FQA12P20 and FQA19N20C output FETs with Vishay CPF3 0R22 source resistors. The output FETs’ bias is set at 0.5A (110mV over the source resistors). The input JFETS have an Idss of about 8.5mA, with the p-channel having a 5R degeneration resistor to match the j74’s transconductance to that of the k170’s (see 5th image). I had to use 7k5 for R9 to get the bias up to 0.5A. Output offset is around 1mV when warmed up. I have 15mV of cold output offset in my notes, but I have to check that again, it just seems too low.
The numbers:
(THD measured with Boonton 1121 analyzer with 0.0009% THD baseline, F4 unloaded output)
Vsupply=+/-18.01V
Ibias=0.5A (110mV over R22)
gain -0.46dB (1V in, 0.948V out)
noise about 50uV unloaded (purple trace 6th image)
1V input (0.948V out) @ 1kHz:
95.46dB S/N
94.92dB SINAD
-94.9dB THD, 0.0019%
3V input (2.847V out) @ 1kHz:
105.56dB S/N
93.97dB SINAD
-93.98dB THD, 0.002%
THD spectrum 2nd>3rd>4th, with 2nd around 10dB over 3rd
visible clipping at 14V input (1.213% THD), above 7V input 3rd order dominant
output impedance: 0.33 Ohm
unloaded V1=521.2mVrms @50Hz
8R2 loaded V2=500.5mV
Z=R*(V1/V2-1)=0.33R
There are countless reviews on the F4, so I’ll keep it short. Source is a soekris 1021 R2R DAC with a DCB1 output buffer. Surprisingly, there’s enough voltage swing for the HD800, with a few dB to spare.
This amp is underrated. People have said it before, and they are right.
The soundstage is incredible. Solid, consecutive, almost holographic.
I’m looking forward to building different preamps already.
And lastly, damn, now I’ll have to build an F4 speaker amp, it’s just too good. I should have a kit stashed away somewhere…
