I was having some trouble with the term "Diamond Buffer". I found a short write up and figure 22 that helped a bit.

http://web.engr.oregonstate.edu/~bat...tes/AB-183.pdf

Others here are probably familiar with the diamond structure.



JF

You can also see on the Burr-Brown BUF634 datasheet:

http://focus.ti.com/lit/ds/symlink/buf634.pdf

Several Headphone-amp use this 250mA high-speed buffer.

I just changed it to discrete components.

Quote:




The text in the BUF634 mentions nothing about diamond structure and the simplified diagram does not resemble your schematic. Are you sure you mean BUF634? Maybe OPA633?


JF

As you mention on the Burr-Brown Application Bulletin of OPA660
page 2 schematic, between pin5 and pin6 it is called Diamond
Buffer (DB), it construced by the same base NPN & PNP and two
push-pull emitter follower, other 2 BJTs function like current source
which I use 2 CRD instead.

So if you check the BUF634 structure page 7, it will be the same,
only BUF634 built-in input output protect circuits.

My DB-01 built one BJT bias at 0.6V ~ it will give the output R 10£[
to have 0.3V each, it means 30mA static current, quite a lot for
headphone amp.

Great work!!
Impressive layout. Although I know little about the circuit, the transformer and the enclosure always looked amazing to me..

This is the DB-01 full circuit diagram, it should be made as a tiny
module as several SMD produucts do. But it is quite small now.



Sorry, I have no tool about circuit drawing, I just can use paintbrush only.

The two resistors R* are suggested by ppl, DIYers can add them on the original PCB,
don't have to cut any copper side.


Quote:

Looks good, although the driver transistors need Base resistors and since you have them pluged in to the main board with probaly some lenght of wire you should use a resistor at the base or the alternate method sugested by jefferyj by sliping a ferrite bead over the base lead. BTW put these parts as close to the atual base lead of the Driver transistors as possible.

Quote:



Thank you, you are very kind.



The DB-01 is all on this tiny PCB, the Diamond Buffer BJTs are on the top of the photo,
when use as a pre & Head-amp ,it is no need to be pluged in to the main board.

The main board is called DT-02, there are some holes for power MOS like 2SK1529/2SJ200 or
power transistors like Sanken 2SC2922/2SA1216.



150W MOSFET module using Toshiba 2SK1529/2SJ200
DT-01 is a little different from the DB-01, the drive voltage is +/-68V,
and it does not have diamond buffer but IRF610/IRF9610 or
Hitachi 2SK214/2SJ77 instead.





Ultima-1 DT-01+DT-02 and power transformer.

Ultima-1 also included a special stand-by circuit, that can stop
Q16 constant current, and cease the two voltage sources at the
same time, and shut-down the output stage, so it need relay
board. The two LEDs are designed for showing power-down or not,
DB-01 doesn't have this function, so the LEDs can be shorted to
get more higher output voltages.

good trick on the shutdown circuit. Also note that mosfets tend to be more unstable than BJT's so quite large resistors should be in series with the Gate of these and right on the Gate leed 220-1K should work ok. slipping a ferrite beed over the gate leed in addition to the resistor is also helpful. you might give some thought to playing around with the value of C9 typicay 0.1UF is used hear by default however some circuits sound better with higher value capacitors and Some high End Amps use a Non polar electrolytic and bypass that with a film cap. a polar Electrolytic is not a good idea at this point although i have seen them used at this location.

You also might give a try to driving the Base of Q25 right off the colector of Q5 and Q6 and not making the signal go through the LED. do the same with Q26 and Q18 & Q19.

As above I said,
Quote:



C9 I use 2.2uF/100V WIMA MKS4, yes I think it is important to use
film cap. here, it is at the top on the PCB two big red ones.

C9 can also mentain some current when shutdown stared, I have to
make sure that the relay is off first.

ppl said,
Quote:



I have double checked again that the C7 22pF across the feedback can be removed no problem now, I have fixed the problem of the start-up 1.5 MHz oscillation caused by the shunt regulator.

Thanks, ppl.

This is one pre-amp made by my friend cjr84, he used shunt regulator and hand-made stepped attenuator by himself.

Very low noise! And pure DC amp without DC servo or output capacitor.

Nice. I like that work. Nice metal enclosure. JFETs and low noise--kind of like the project I'm finishing soon.

I wonder what gain you are using. As low as 10uV rms noise is it seems higher than I would expect (maybe more like 2uV). It's difficult though to measure such low level signals. You may be using high gain too--like 20+???.


JF

The gain is 20dB, i don't have professional test equipment to
measure how low noise it will be, next time I should try to borrow
an AP2 again.

I've spent 4 days to build up this Full Balanced pre & headphone
amp, I used 4 DB-01 amp-module and a large hand-made stepped attenuator by
my friend cjr84, with shunt regulator and speaker (headphone) protector.
I also used a copper shielding tolimit noise from the transformer.