Does anyone have first sound on their postage stamp buffer boards yet?
# different subject but related #
I got the Desktop Diamond Buffer headphone amp verification build in and testing it now. Sounds great. It does need a clean +/-15v PSU though. I am using a cheap DCDC switcher (no linear regulators post switching) and heat some residual noise. Bit for purposes of testing it out if circuit works, it’s good enough.
The outputs are supposed to be TTA004/TTC004 but all I had in hand are my prized NOS 2SC4795/2SA1837 which have flipped pin out so they are mounted from the bottom:
Pesky 6.3 MHz oscillation so I will have to reduce the resistor in the Zobel. Currently at 15ohms. Will go to 6.8R next. The diamond buffer has some very high speed performance so transients and highs sound great but this can have some issues with oscillations which we tame with an output Zobel filter. These typically need to be hand tuned as simulations don’t always predict them as models are not perfect.
I’ll swap out the resistors and report back.
# different subject but related #
I got the Desktop Diamond Buffer headphone amp verification build in and testing it now. Sounds great. It does need a clean +/-15v PSU though. I am using a cheap DCDC switcher (no linear regulators post switching) and heat some residual noise. Bit for purposes of testing it out if circuit works, it’s good enough.
The outputs are supposed to be TTA004/TTC004 but all I had in hand are my prized NOS 2SC4795/2SA1837 which have flipped pin out so they are mounted from the bottom:
Pesky 6.3 MHz oscillation so I will have to reduce the resistor in the Zobel. Currently at 15ohms. Will go to 6.8R next. The diamond buffer has some very high speed performance so transients and highs sound great but this can have some issues with oscillations which we tame with an output Zobel filter. These typically need to be hand tuned as simulations don’t always predict them as models are not perfect.
I’ll swap out the resistors and report back.
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I received the Diamond Buffer boards and have forwarded them on to the other UK-based members - I passed my own pair of boards onto @jimk04 as he will make use of them a lot sooner than I will as I have a long backlist of projects to complete - I'll purchase another pair from the XRK Etsy site when the time arrives.
For those who missed out on the giveaway, I have just ordered more fully assembled buffers with the proper Kingbright emerald green LED’s to get the proper bias current on the front end. Now I am making the buffer with an upgrade to FZT953/853 output devices (5A capable SOT223’s same as ones used in the powerful Pocket Diamond Buffer headphone amp) - not that you will need to drive that much current - but for those wishing to try mods later. Be sure to clamp / glue a heatsink on top if you do. 
They should be here in my shop in say, 2 weeks.
They should be here in my shop in say, 2 weeks.
Mine showed up, but it will be a bit before I can get them in a case. I tried my hand at replacing the red LED with a green one. First board I used my solder iron and that went sideways quickly, ended up pulling the pad off the board. I managed a repair with piece of a resistor leg and too my amazement the board lights up when power was applied not sure about a signal. This convinced me to buy a 40 dollar hot air station off amazon, the second board was much easier and went flawlessly. The board on the left is the one I butchered
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Just collected mine today from shipper. Excitedly changed out the red led to the green ones. Powered up and all went well. Connected the inputs to ground and DC offsets were measured to be 4.5mV and 6.8mV. Just a simple power up test today. Putting them into operation will be a couple weeks later after the long holidays.
Nice boards, 🙏 thanks @xrk971
Nice boards, 🙏 thanks @xrk971
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Hi Folks,
The new boards have arrived and the have the correct green LED. These also have the upgraded high current capable FZT853/953 output BJT’s. I just tested them with a +/-18v power supply and I am getting 14mA of bias current through the outputs. The DC offset is only 1mV and 3mV on these two samples. I also did a quick sound check with headphones and they play music. Although I must warn against using them as headphone amps unless you really boost the bias current up to at least 70 to 80mA for playing into 32ohm headphones. I’m going to put them up in my shop for immediate delivery. Holiday pricing until Jan. 14, 2024 will be $39/pair.
Happy holidays!
Order here:
https://xrkaudio.etsy.com/listing/1619024473
The new boards have arrived and the have the correct green LED. These also have the upgraded high current capable FZT853/953 output BJT’s. I just tested them with a +/-18v power supply and I am getting 14mA of bias current through the outputs. The DC offset is only 1mV and 3mV on these two samples. I also did a quick sound check with headphones and they play music. Although I must warn against using them as headphone amps unless you really boost the bias current up to at least 70 to 80mA for playing into 32ohm headphones. I’m going to put them up in my shop for immediate delivery. Holiday pricing until Jan. 14, 2024 will be $39/pair.
Happy holidays!
Order here:
https://xrkaudio.etsy.com/listing/1619024473
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I have had a lot of requests as to how to convert these to powerful headphone amps.
More info here:
https://www.diyaudio.com/community/threads/jhoflands-diamond-buffer.401231/post-7563106
You need to switch these resistors in order to have amp operating with low distortion with as low as 32ohm cans.
The resistors in red need to be swapped with values shown above. Leave the blues ones.
Note well, the board or the BJTs need heatsinking if you do this. They will burn about 1.5W per board with +/-15v rails.
More info here:
https://www.diyaudio.com/community/threads/jhoflands-diamond-buffer.401231/post-7563106
You need to switch these resistors in order to have amp operating with low distortion with as low as 32ohm cans.
The resistors in red need to be swapped with values shown above. Leave the blues ones.
Note well, the board or the BJTs need heatsinking if you do this. They will burn about 1.5W per board with +/-15v rails.
As a line level buffer, no more than 30mA per rail is needed. So budget for 35mA and you should be good.
The 12v to +/-15v DCDC converters from Murata with 70mA seems like a good way to do this. Those are same ones I used on BTSB. Add an external LC filter and they are good to go.
As a headphone amp it’s a whole different animal. To drive 32ohm cans to 1.5W is about 700mA from what I recall. But it all depends on how much power you need and what impedance is.
The 12v to +/-15v DCDC converters from Murata with 70mA seems like a good way to do this. Those are same ones I used on BTSB. Add an external LC filter and they are good to go.
As a headphone amp it’s a whole different animal. To drive 32ohm cans to 1.5W is about 700mA from what I recall. But it all depends on how much power you need and what impedance is.
I have eventually managed to put it into a test. First impression is pretty good. Tone is balanced and natural with good details. The only issue is that the sound stage is a bit flat. Otherwise it can be a superb buffer amp for my system immediately.
I will remove the adapter board and give it a better power supply. At the moment it has only a very basic 7812/7912 +/-12V PS.
Great work XRK!
I will remove the adapter board and give it a better power supply. At the moment it has only a very basic 7812/7912 +/-12V PS.
Great work XRK!
