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CFH7 Amp
CFH7 Amp
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Old 29th July 2016, 03:37 PM   #1
xrk971 is offline xrk971  United States
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CFH7 Amp
Default CFH7 Amp

Following the naming convention for amps used in this thread and also first posted here, I am starting a new thread as this is not anything like an Apex design offshoot anymore:

100W Ultimate Fidelity Amplifier

However, I think I will keep the standard naming convention that Apex Audio likes to use. So CFH7 stands for Current feedback HexFET with 7 active components. The amp arose out of the surprisingly successful FH9 and FH11/12 amp designs from the same thread, but with a current feedback topology that I believe was first used by Gaborbela as described here:

http://www.diyaudio.com/forums/solid...-years-go.html

Click the image to open in full size.

This same topology is also used in the very popular VSSA series of amps (VSSA, PeeCeeBee, FET-hex explendit, etc). My biggest inspiration for using the Gaborbela topology came after I built the amp described here:

http://www.diyaudio.com/forums/solid...ml#post4781474

Now, I have applied the Gaborbela topology with the great sounding, popular and cost-effective IRFP240/9240 hexFETs, while reducing the number of active component parts count from the FH9, which has 9, to 7 transistors by elimination of two transistor CCS's. The simulations of this amp in TINA indicate a surprisingly good level of performance. The usual BD139 is still used for temperature compensation as a Vbe multiplier. Very large 4700uF rail caps are needed if you want the squarest square waves, but smaller 1000uF caps would probably sound just fine.

Here is the schematic:

Click the image to open in full size.

And here are the simulated results:

1kHz sine wave at 50v p-p with 80mA quiescent bias current:
Click the image to open in full size.

50kHz square wave:
Click the image to open in full size.

200kHz square wave:
Click the image to open in full size.

FFT spectrum at 1kHz:
Click the image to open in full size.

HD components at 1kHz sine wave excitation:
Click the image to open in full size.

HD components at 20kHz sine wave excitation:
Click the image to open in full size.

Gain and Phase as a function of frequency:
Click the image to open in full size.

As you can see, the predicted HD of 0.00084% at 1kHz and the clean, sharp-edged square waves are very good indeed for a 7 active element amp that uses nothing exotic or special. Vishay hexFETs are available for under $1/ea, so this amp is literally under $5 to build. The bang for the buck on this amp is pretty much up there.

So, it's still in simulated schematic stage at this point and un-tested. I would welcome someone taking a crack at the layout for a Sprint/Gerber file and we can then test and listen.

Edit Aug 3, 2016: several members have pointed out that this topology probably originated from Japan in the 1970's:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Version 1.1 schematic that Idefix will design layout for:
Click the image to open in full size.

Update Aug. 7, 2016: Idefixes generated the new layout (with associated schematic for parts numbering):

Click the image to open in full size.

We are going to press with this layout - a masterpiece - great work Idefixes!
Click the image to open in full size.

BOM for above amp:

http://www.diyaudio.com/forums/attac...p-cfh7-bom.txt

Edit: Aug 15, 2016 - Sonal Kunal has just developed a single sided layout - still not final but very cool looking.

Click the image to open in full size.

Edit: Aug. 16, 2106 - Latest layout from Sonal with no onboard inductor but 100mm max size
Click the image to open in full size.

Edit: Aug. 17, 2016 - Idefixes has a beautiful new 2-layer layout that re-routes the ground bus to reduce RF spray onto the input stage:
Click the image to open in full size.

So many layouts to try!

Still4given or Andrewlebon will probably be the first to reach first sound.

Andrewlebon in progress...
Click the image to open in full size.

Still4given in progress...
Click the image to open in full size.

I can't wait to see someone with a small waisted F1 car style board as Sonal has prescribed.

Edit Aug 19, 2016: Still4given had built and verified that Sonal's layout works but requires fixing wiring of Vbe multiplier as that has an error and also 4.7R gate stoppers are not enough to prevent oscillation. 100R seems to work there.

CFH7 Amp

Click the image to open in full size.

Here is a dual output pair version called CFH9:
Click the image to open in full size.

CFH9 works well - nice square wave:
Click the image to open in full size.

CFH9 in stereo with Juma's Easy Peasy cap multiplier:
Click the image to open in full size.

This is one of my top 3 amps.


Dec 16, 2016: Thanks to Thimios for finding grounding issue in design. Here is final mod to achieve very good PSRR and low THD. See post here

CFH7 Amp

Click the image to open in full size.

Last edited by xrk971; 18th December 2016 at 12:18 PM.
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Old 29th July 2016, 04:15 PM   #2
anatech is offline anatech  Canada
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CFH7 Amp
Hi xrk971,
Quote:
Very large 4700uF rail caps are needed if you want the squarest square waves, but smaller 1000uF caps would probably sound just fine.
With those supply voltages, this amp has a lot of power available. However, your capacitance values for the power supply seem to be a factor of ten off, just wondering how to reconcile the capacitance values vs the apparent power output. If your rails are really bipolar 53 volts, what is your expected output power, and shouldn't you use another output pair for that level of power?

-Chris
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Old 29th July 2016, 04:21 PM   #3
Mosquito is offline Mosquito  Argentina
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sure a typo, fliped (+ -) 53 mean (+ -) 35 ...
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Old 29th July 2016, 04:21 PM   #4
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by anatech View Post
Hi xrk971,

With those supply voltages, this amp has a lot of power available. However, your capacitance values for the power supply seem to be a factor of ten off, just wondering how to reconcile the capacitance values vs the apparent power output. If your rails are really bipolar 53 volts, what is your expected output power, and shouldn't you use another output pair for that level of power?

-Chris
I was also warned of this with the FH9 but I tested it with 52v rails at 125w for 15min with no issues. The big 4700uF caps were chosen based on simulations of square waves having extra flat topped square waves at 50v P-P.

100W Ultimate Fidelity Amplifier

With FH9HV 34.5vac (48.7v p-p) into 10R load was no problem:
Click the image to open in full size.
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Old 29th July 2016, 04:37 PM   #5
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Mosquito View Post
sure a typo, fliped (+ -) 53 mean (+ -) 35 ...
No, it's really 53. I tested FH9HV at 35 but it works fine at 53v. I assume same rails can be used for this amp.
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Old 29th July 2016, 04:59 PM   #6
Mosquito is offline Mosquito  Argentina
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Ok, I ll follow with interest, sure I can learn something valuable to apply to my similar but unsuccessful Darlington tryout
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Old 29th July 2016, 05:29 PM   #7
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Mosquito View Post
Ok, I ll follow with interest, sure I can learn something valuable to apply to my similar but unsuccessful Darlington tryout
What happened with your circuit? Link?
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Old 29th July 2016, 05:45 PM   #8
xrk971 is offline xrk971  United States
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Can someone show me how to simulate or calculate PSRR in TINA? Put an AC voltage source on supply rail and measure AC at output of amp?
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Old 29th July 2016, 05:53 PM   #9
ilimzn is offline ilimzn  Croatia
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There is a link missing between the two zener diodes and output.
Not sure the MOSFETs will survive a half-nasty real speaker at those rail voltages. 4 ohms is an accident waiting (not very long) to happen.
Also, the Vbe will be overcompensating. A LED in series with the emitter and a recalculation of the resistor values might solve this simply.
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Old 29th July 2016, 06:05 PM   #10
Mosquito is offline Mosquito  Argentina
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Oh well, where to start... TIP 142-147 continue blowing well before reaching the + - 35VDC rail target, THD 1 watt 20Khz a mediocre 0.08%, FFT at 1W 20Khz shows a spray of harmonics, the odd ones clearly dominant throughout...
Darlington VSSA

Your s instead, shows excellent result from the start on.
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