Build This MoFo!

[xrk971]

Is the 1.5% THD typical of a resistive current sink SE Class A amp? For my headphone amps, I do same thing and distortion is typically in the 0.1% or less but then it's 70mA bias and 120ohm loads.

 

[needtubes]

The load impedance and the power you're putting into it (obviously) affect THD in a significant way. Plus, your headphone amp isn't a pure follower, is it?

 

[xrk971]

It's not a headphone amp - it's a preamp designed to drive higher impedance loads like power amp input stages. Schematic here:

As far as load I am giving it standard 8ohms and 2.83vrms - standard setup for testing amps at 1watt with 8ohm speakers.

 

[Ultima Thule]

Here my first one, again, thank you Mr. Rothacher.

JP

Beutiful PCB JP, but it has unusually many vias, I am a bit curious when you order these types of PCB with so many vias how does it affect the cost?

 

[Dennis Hui]

Starting to bag boards for the store. The first fifty pairs get a spiffy sticker.

Very nice Mike. Hope to see them in the store soon.

It's weird seeing an amp PCB with so few parts...almost like a chipamp.

Cheers,
Dennis

 

[JPS64]

@Ultima Thule

I thought so too but no extra cost!

JP

 

[Ultima Thule]

@JP

oh, I am surprised, especially to see the amount of vias in your example, thanks JP!

Regards

 

[hifibluedevil]

Starting to bag boards for the store. The first fifty pairs get a spiffy sticker.

First come first serve?

 

[xrk971]

I'm not sure if 4 resistors, 2 caps, a pot and a mosfet needs a PCB? P2P is really just the perfect thing here.

 

[Michael Rothacher]

I'm not sure if 4 resistors, 2 caps, a pot and a mosfet needs a PCB? P2P is really just the perfect thing here.

Perhaps, but there's large contingent of DIYers, who prefer to have a PCB. I'm trying lower the bar for beginners as much as possible. Also, many prefer the neatness of a board.

And it helps to support the forum we're using right now.

 

[Michael Rothacher]

Are those guys shilling for a board house? Which one?

 

[Soundhappy]

Starting to bag boards for the store. The first fifty pairs get a spiffy sticker.

Mr Rothacher You make my day with MoFo boards availability in Diy Audio Store.
Thanks for keeping a good work for DiyAudio hobby amateurs and support for community.
What beginner friendly and economic project because actual monoblock's no need for pricey metal chassis.
Neatly beautifully made, mature concept amplifier Photos courtesy of Audio Maker. Kindest regards

 

[xrk971]

So I hooked up my Fluke 101 to the output of the MoFo in mV scale. It read 0.0mV noise with no input (conformed by FFT). I thought to myself this is a really quiet amp, even when connected to basic 24v SMPS and a simple CRCRC. What would it sound like with headphones? I connected my OB-1's while the 8ohm dummy load was still connected, to hear what the dummy load "hears". Well 2.83vrms is way too loud so I backed it off to a loud but pleasant and clearly great sounding level. Very nice - like a great tube amp. Deep deep powerful bass, and smooth silky mids and delicate but articulate highs. No sibillance, No fatigue. Forgot to mention that I added a 10uF 35v Silmic II at the wiper of the pot to smooth the voltage reference out. I think that helps a lot. Anyhow, it sounds gorgeous, and made me wonder if the FFT now looks better, because my ears don't lie. It was a beautiful sound like the voice of angels.

Here is 2vpp into 8ohms, about as loud as I would listen with headphones to sound comfortable, THD is 0.23% and mostly H2:

And here is the FFT for 1.41vrms or 4vpp into 8ohms, now I see why it sounds great. Looks like a SET tube amp. Again, 1.9 amps bias current through 50w capable 4ohm current sink:

So, in short, this can be an excellent headphone amp as well.

This is the setup, now standing up to help cool the 45w of dissipation.

 

[Michael Rothacher]

First come first serve?

Yes, for the stickers anyway.

 

[Soundhappy]

MoFo music sessions & solid state preamp

But no one is writing down there thoughts on or compare too other amplifiers?

In your own words its sonic characteristics?

Thank you

Lawrence

Yes Please and thank you sir!

Hello Sir Lawrence
Update :
Recently changed triode preamp to solid state and try new configuration with MoFo.
Surprise only one tube stage of the CD player is sufficient.
The sound is focused and lively without much "warm colorations " of the triode vacuum tube preamp stage.
I do try huge 68 UF MKP at input and 10 of bipolar Nichicon " Muse " series.
Well, two sounds great and Muse are audio grade and cheap ~ 0.50 $ from my memory at Mouser, etc.
Conclusion: build MoFo with quality components and taste all goodness of class A amplification. The Dude is cool

 

[Zen Mod]

I don't care about your personal opinion about me........

your right and duty ..... even to be grumpy sometimes ;

though , I have soft spot for Wakoo Frenchies , since I had luck to meet and know my Yoda Manu

.....The Dude is cool

Dude abides , especially when some proper Iron is involved

 

[Sk8Ter]

Hello Sir Lawrence
Update :
Recently changed triode preamp to solid state and try new configuration with MoFo.
Surprise only one tube stage of the CD player is sufficient.
The sound is focused and lively without much "warm colorations " of the triode vacuum tube preamp stage.
I do try huge 68 UF MKP at input and 10 of bipolar Nichicon " Muse " series.
Well, two sounds great and Muse are audio grade and cheap ~ 0.50 $ from my memory at Mouser, etc.
Conclusion: build MoFo with quality components and taste all goodness of class A amplification. The Dude is cool

Thank you Sir!

so are you saying direct output of your tube stage cd player direct into the MOFO is working for you?

Lawrence

 

[Soundhappy]

Thank you, Sir!:
D so are you saying direct output of your tube stage CD player directly into the MOFO is working for you?
Lawrence

Sir Lawrence

Nope, please look again at the photos You have all stages.
Actual configuration is:

1 |CD player with class A triode stage
2| preamplifier is solid state (no more triode now)
3 |amplifier Big MoFo 22watts PSU 24V | 2.5 A bias
+
4 |12" wide range drivers speakers

I do experiment with CD player directly connected to passive pream AVC
autoformer volume control and MoFo, but musicaly was "short" feeling.
Adequate impedance and gain solid state preamplifier who match with MoFo bring instant fullness in bass, medium, highs.
Control nicely large 98 dB drivers with his 40 damping factor. Oh yeah
post scriptum : session vinyl turntable and phono can be fun !
SRPP Anzai and transistor phono next days..
Greetings

 

[Sk8Ter]

Sir Lawrence

Nope, please look again at the photos You have all stages.
Actual configuration is:

1 |CD player with class A triode stage
2| preamplifier is solid state (no more triode now)
3 |amplifier Big MoFo 22watts PSU 24V | 2.5 A bias
+
4 |12" wide range drivers speakers

I do experiment with CD player directly connected to passive pream AVC
autoformer volume control and MoFo, but musicaly was "short" feeling.
Adequate impedance and gain solid state preamplifier who match with MoFo bring instant fullness in bass, medium, highs.
Control nicely large 98 dB drivers with his 40 damping factor. Oh yeah
post scriptum : session vinyl turntable and phono can be fun !
SRPP Anzai and transistor phono next days..
Greetings

apologies sir, I read fast sometimes

sounds like a nice amplifier, I will have to put one together to see if i can be happy with lower EFF speaker but easy load 8 ohmish.


I wanted to mention for people like myself who are broke, its possible to use for the inductor part an old microwave transformer each one is 25mh and low low dcr of .4ohms....you could also series to make 50mh and still be under 1ohm just leave the hi voltage winding alone.

Lawrence

 

[xrk971]

I have a broken microwave oven. Hmm...