Thank you for pointing that out. I forgot to order any resistors for RL, so hopefully the junk box has something that will work.
XR, I have some SMD resistors in the 1k to 1.5k range any reason these won't work?
Thanks
David
Thanks
David
Sure. Stack two 1k on top of ea other for 500R and that should be perfect. It bleeds off the initial DC charge up of the output cap output side quicker. The 500R will drain off a 1000uF cap by 0.3s.
Yes, all that aluminium should keep this little beast a bit cooler!
I just pulled the trigger on those Status Audio OB-1's for $55 - it's a steal.
No, I pay in $ and have it delivered to a courier (Aramex) in New York. So, no shipping costs to NY either. From there it is much cheaper to my door in South Africa. I have an Aramex Global Shopper account - it works best for shopping abroad. Got my speaker drivers from Parts Express like that too. But for now my diy budget is very low - have to report to SWMBO. 🙂
What does your shipper in NY use to ship to South Africa. Even when sending stuff by USPS 1st Class with tracking and insurance, it can take weeks to a month, sometimes more. I have an amp that I sent to someone there and it's been nearly 2 months. Priority Mail costs more but is not much faster, maybe 2-3 weeks. It's kind of ridiculous.
Yes, 1st Class or Priority mail is only faster in the US - the problem lies in Africa. I sent you a PM explaining this.
So I have been thinking of a desktop headphone amp project that would be a bit different and more value added (in addition to being SE Class A).
I am thinking along the lines of an all-discrete minimalist components single-ended input (usual RCA or 3.5mm jacks) to a SE Class A zero global feedback balanced drive output for balanced headphones. I think component count would increase by two transistors to perform the conversion from single ended to balanced and two x two transistor power stages per headphone channel. So that's 6 transistors per channel. The cool thing is that because both phases are fed from same power supply, there is a constantly perfectly divided load such that the PSU current is be definition, constant. Thus, large values of R can be used in the CRC filter for a very quiet power supply.
Balanced drive provides double the slew rate, +12dB mode dynamic range, more power delivered, an apparently higher sensitivity.
I am thinking along the lines of an all-discrete minimalist components single-ended input (usual RCA or 3.5mm jacks) to a SE Class A zero global feedback balanced drive output for balanced headphones. I think component count would increase by two transistors to perform the conversion from single ended to balanced and two x two transistor power stages per headphone channel. So that's 6 transistors per channel. The cool thing is that because both phases are fed from same power supply, there is a constantly perfectly divided load such that the PSU current is be definition, constant. Thus, large values of R can be used in the CRC filter for a very quiet power supply.
Balanced drive provides double the slew rate, +12dB mode dynamic range, more power delivered, an apparently higher sensitivity.
I have a noob question. So is it that an amp that is not balanced drive output then it's just single ended? Or there are something else that I am not aware of?
Yes, most amps are single-ended output. Not to be confused with Single Ended (SE) Class A which is different, as that is amp topology. Balanced lines are often used with pro audio for long cable runs. Balanced drive headphones generally have to be custom modified via a cable mod or swap. They typically don't sell balanced headphones.
I no longer saw the pcb on atsy website. They sold out? Besides if I was to run class-a pocket amp without batteries. How high voltage could you go and would there be an improvement, for example running at 20v+.
Send me a PM for PCBs if you are interested. There is an advantage with higher voltage as it increases bias current and max power. However above 18v heat is an issue with the resistors and MOSFETs existing PCB based heat sink. You can clamp the SMT side down with a silicone heatsink gasket and let a larger heatsink handle removal. Note that BF862 is limited to 20v max.
Making progress on an eventual balanced drive desktop amp. Under development here is a single ended to balanced drive phase splitter designed by Aksa that provides positive and negative phases to drive two power amp stages in opposition which then powers the headphone. The beauty of this circuit is its simplicity (two transistors) and it operates in SE Class A. It can drive 1.4v (0dBu) into 27ohm loads with only 0.0027% THD - and has headroom to drive 10v p-p if needed. Here is test with actual music you can see opposite phases on oscope.
Attachments
After a long journey had me a nice package today : )
Ab fabric xrk971 configured it 66mA bias current, Elna Silmic II on input plus output and 1000uF oscon on output, both in and out is bypassed with Wima films, and design is green tin / white LED.
Will need to solder some neutrik gold plugs for this nice amp and get back tomorrow about listening experience.
Into second picture think it looks got me a free via lead from another clipped component that sneaked itself into tin before it was closed 🙂
Ab fabric xrk971 configured it 66mA bias current, Elna Silmic II on input plus output and 1000uF oscon on output, both in and out is bypassed with Wima films, and design is green tin / white LED.
Will need to solder some neutrik gold plugs for this nice amp and get back tomorrow about listening experience.
Into second picture think it looks got me a free via lead from another clipped component that sneaked itself into tin before it was closed 🙂
Attachments
Nice to know package arrived safely. Funny how a stowaway snipped lead snuck in here. Must of have been stuck on foam stuffing I out inside to prevent rattling. Do you have 9v batteries?