BUF634T Power Amp: Do it?

[Antoinel]

Prophetmaster: Absolutely impressive pictures and amplifier product.

 

[qusp]

Yeah, 40pcs per channel might be a little overkill, even for driving 4-Ohm loads bridged. It will give a little more Class-A working room without additional bias though and each device will be dissipating less heat.

theoretically yes, but not 40 IMO. if you look at the extensive measurements of the LPUHP in the first post of the thread, hes bouncing off or below the capability of a top shelf agilent analyzer in every one except the SNR, which is sitting -125.335 down or something ridiculous; its hard to think of what could really be improved on noticeably with more class A. IMD maybe, but. …

the heat is unlikely to be huge anyway

 

[Prophetmaster]

I see he used 41pcs per channel and only SE on +/15V rails. From what I can read I guess he used that many for the higher Class-A power output.

Hi!
41pcs per channel, PP on +\- 15 V, 10 W/8 Ohm full class A. 4 Ohm - class A up to 11.5 W

I don't understand a few things in his schematic though; like why the 330R on the input to each buffer and a 56K to ground. Is an output zobel really needed? He also uses 10R output resistors when the application note for parallel BUF634 says they are not needed....
[URL="http://www.ti.com/lit/an/sboa065/sboa065.pdf"]http://www.ti.com/lit/an/sboa065/sboa065.pdf[/URL]

1. 330 Ohm - for decrease in influence of total input capacity of 41 buffers (328 pF)
2. 56 k Input to each 10 buffer - equivalent of one resistor of 10 kiloohms to ground
3. Zobel not needed, it was removed long time ago. On the old scheme remained
4. 10 Ohm needed, when there are a lot of BUF634 - it is necessary to level output currents of buffers

More about this amplifier (but my english is not good):

http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-141.html#post2161415

http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-161.html#post2398074

Testing in high-class audiosystem (Moscow)
http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-162.html#post2398539

 

[Prophetmaster]

theoretically yes, but not 40 IMO. if you look at the extensive measurements of the LPUHP in the first post of the thread, hes bouncing off or below the capability of a top shelf agilent analyzer in every one except the SNR, which is sitting -125.335 down or something ridiculous; its hard to think of what could really be improved on noticeably with more class A. IMD maybe, but. …

the heat is unlikely to be huge anyway

In main Amplifier, each BUF634T working (Speakers 4 Ohm) for load: 4Ohm * 41 + 10Ohm = 174 Ohm
Speakers 8 Ohm: 41 * 8 + 10 Ohm = 338 Ohm
BUF634T may work without problems for load 100 Ohm.

heat is no more, then 55C

Prophetmaster: Absolutely impressive pictures and amplifier product.

Many thanks for kind words!

 

[theAnonymous1]

Thank you very much for the replies Prophetmaster.

I understand the need for current sharing resistance for parallel devices. As I pointed out in my previous post, the TI document sboa065 explains that the BUF634 has 10-Ohm output resisters built internal to the IC. So is an additional 10-Ohm per device really necessary?

 

[Prophetmaster]

Thank you very much for the replies Prophetmaster.

I understand the need for current sharing resistance for parallel devices. As I pointed out in my previous post, the TI document sboa065 explains that the BUF634 has 10-Ohm output resisters built internal to the IC. So is an additional 10-Ohm per device really necessary?

Your are absolutely right!
I remembered - additional resistors are necessary, because my amplifier has the speakers protection relay, but its contacts not in a signal line - relay close amplifier output to the ground in case of DC voltage (made for receiving a good sound). At this time each bufer output is loaded on resistor 10 Ohm/0.6 W. Otherwise, at operation of the relay of protection there will be a short circuit.
Dempingfactor remains high - more than 900 (resistors 10 Ohm are inside the feedback)
I hope, what my explanation in English to your is clear? I studied English very mach, but 25 years ago

 

[theAnonymous1]

Thanks for clearing that up.

I studied Russian never, so your english is easier for me to understand then your Russian.

 

[Prophetmaster]

Thanks for clearing that up.

I studied Russian never, so your english is easier for me to understand then your Russian.

Then I will try to explain the main idea of my amplifier

1. The amplifier has negative feedback, but speed inside a loop very very high (about 250 V/us). Sound of the amplifier with very high speed inside loop of negative feedback is same "live" as at the amplifier without negative feedback (it is my opinion), and also has some advantages: high dampingfactor (low output impedance), very low level of distortions.
2. Amplifier has't input and output filters - frequency range: 1.25 Hz - 5 000 000 Hz, has't capacitors in a feedback loop and has only one high-quality input capacitor (MKP) in sound chanel.
But adjustment of my amplifier was very difficult. I have good laboratory with measuring devices at home
3. Amplifier has completely stabilized and powerful power unit (300 Watt) with 200000 uF of capacitors + MKP shunt capacitors. The majority of capacitors are installed after stabilizers and was made softstart
4. Contacts of the relay of protection aren't in the sound channel - the relay of protection is connecting output of the amplifier to the ground. Only In operating time of protection, other (temporaly) loop of negative feedback is working - which is connecting to voltage amplifier output (output of AD811) On the electronic scheme isn't present.
It is made against high-frequency generation during protection operating time, when output relay is in short circuit.