F6 Amplifier

[Antoinel]

I've played with a very similar idea about 7 years ago and exchanged some emails about it with Ben Dunkan. Here is the basic circuit. At the time I couldn't find a similar feedback circuit - at least not in LF applications, however I also thought that something like this has been done a long time ago.

Cheers

Alex

Alex: This is an interesting circuit. How low a Zo at a voltage gain = 1 [Transfollower] did it achieve?

 

[Zen Mod]

"there will not be breathing , when fed with CCS"

So you have experienced a similar low frequency oscillation. How much modulation of the bias voltage (or current) have you seen? Do you fully understand the feedback mechanism?

nope , in fact

I didn't make one sole solder joint in direction of making F6

I'm speaking (all the time) from previous experience , both with small bias circuits intended for SJEP's and fun with xformers (various purposes)

 

[Antoinel]

Preliminary results make me think less feedback, not more. I currently have .47Rs, bias of 1.3A per fet, 8dB of gain. I have some 330R mills, so Iam gong to try that. BTW, Bypass cap is necessary. I have 1K Nichicon Muse and they add their electro sound to the amp. Don't stone me please. I have some 470uF Silmic II's to try. I will be byassing with fancy Film more than likely. Although i cant grasp why you would want to do so considering the balanced nature of the circuit, I have considered putting two resistors in series to form the Rs Total. Put pot across top one and pull modulation point from their. Wouldnt lose all you DF and would allow for Zen adj.

buzzforb. Are the results from auditioning?

 

[Zen Mod]

...... 8dB of gain. .....

8db ......... or 8x (18db) ?

 

[buzzforb]

Yes, but just single channel. Maybe get the other up tonight. Voives come across as very natural, clear and airy, but there seems to be a veil with more complex music. I don't think much of it for now. I need to hear two channels. I added 4uF Film caps. Helped some. I will try other things tonight. It has enormous potential. I am sure we will be very surprised at Nelon's version. All others are just play things. I will try the trafos from BudP tonight. THey should have a little greater extension, but I am in no way saying that it is the transformer. Just havent listened enough.

18dB. My bad.

Ikebana

 

[Zen Mod]

don't be surprised if surprised , when you include BudP's xformers

 

[buzzforb]

I tend to agree. More info for folks interested. I am driving it with a DCB1 with shunt cranked up slightly. It makes me want to hook up my Alpair12's with their 92dB efficiency or plug in my 6V6 pre with about 15dB of gain. THis is an amp for efficient speaks. I have a feeling it has a wonderful amount of detail in that FW region. My current setup does not allow for this. It will be rectified😀

 

[lhquam]

It will be rectified

Half-wave or full wave? 😛

I tend to agree. More info for folks interested. I am driving it with a DCB1 with shunt cranked up slightly. It makes me want to hook up my Alpair12's with their 92dB efficiency or plug in my 6V6 pre with about 15dB of gain. THis is an amp for efficient speaks. I have a feeling it has a wonderful amount of detail in that FW region. My current setup does not allow for this. It will be rectified😀

 

[Zen Mod]

considering lowish gain , it will benefit from using livelier pre , whatever SPL needed

 

[buzzforb]

THis means its time to redo 6v6.

 

[Zen Mod]

aha

cascoded , CCS loaded

or even better - choke loaded

but ,for choke you must ask BudP , not Dummy ZM

 

[buzzforb]

Somehow I think Choky has some ideas, but BudP probably knows a few things as well. Only tried simple resistor load. Never done choke loaded. WAit a second, focus,focus😀

 

[Tea-Bag]

Nice burn marks from Fets Buzz. Means your doin something while the rest of us wait.

 

[buzzforb]

Burn baby burn.

 

[Zen Mod]

MC5 - Motor City Is Burning - YouTube

 

[x-pro]

Alex: This is an interesting circuit. How low a Zo at a voltage gain = 1 [Transfollower] did it achieve?

Ideally the output impedance is similar to what you would expect from a traditional PP complementary follower - 1/S.

Cheers

Alex

 

[lhquam]

1/S or 0.5/S due to transconductance doubling?

Ideally the output impedance is similar to what you would expect from a traditional PP complementary follower - 1/S.

Cheers

Alex

 

[x-pro]

1/S or 2/S due to transconductance doubling?

If the FETs are biased into Class A ~1/2S. In Class B/AB ~1/S.

Alex

 

[Antoinel]

If the FETs are biased into Class A ~1/2S. In Class B/AB ~1/S.

Alex

Thank you Alex and lhquam. What is the value of S and thus Zo for Teaser-6 operating in Class A?

 

[buzzforb]

question. How do we calculate the size of the cap. What parameters are we considering and what is its official name? Boostrap cap?