Jan,
ahhh, gotcha. Yes, the cap after the reg. So avoid the low ESR caps.
I have one of the cheap USB scopes. Next year, I'm going to throw some $ at a good used refurbished scope on ebay. I had a chip head amp that sounded like it had superb detail. Little did I know until I hooked up the scope that the negative reg was oscillating. I wasn't sure what was happening and sent an image capture to SY for his 1 second analysis (at no charge!).
I learned a good lesson from that. I would hate to give an inaccurate opinion on this head amp project due to poor implementation of my psu circuit.
ahhh, gotcha. Yes, the cap after the reg. So avoid the low ESR caps.
I have one of the cheap USB scopes. Next year, I'm going to throw some $ at a good used refurbished scope on ebay. I had a chip head amp that sounded like it had superb detail. Little did I know until I hooked up the scope that the negative reg was oscillating. I wasn't sure what was happening and sent an image capture to SY for his 1 second analysis (at no charge!).
I learned a good lesson from that. I would hate to give an inaccurate opinion on this head amp project due to poor implementation of my psu circuit.
Regarding PSU, I have planned to use a transformer-full wave rectifier-cap filter plus cap-multiplier (to improve the filter action) and shunt regulator (this near to the HeadAmp). From what I have seen on the LTspice it seems that the HeadAmp may need a very good PSU as the PSRR is moderate. Maybe i am wrong but is what I saw.
Javier
Javier
The better the PS, the less need for PSR in the amp. Low Zo Regulated supplies are easy to come by. Your supply will do quit well for this amp.
It will help if you place a cap across your C Multipliers outputs. This will cancel and stablize the relative variations on + and - supplies. It cancels Differential-mode noise and variations.
If you want to look at CMR, you can trim input Z to match the feedback port Z. Might do this with the input 330 ohms plus Zo of your source.
Thx,
Richard Marsh
It will help if you place a cap across your C Multipliers outputs. This will cancel and stablize the relative variations on + and - supplies. It cancels Differential-mode noise and variations.
If you want to look at CMR, you can trim input Z to match the feedback port Z. Might do this with the input 330 ohms plus Zo of your source.
Thx,
Richard Marsh
Thanks for very valuable comments. As for the cap in the output of Cap-Multiplier, any advice on value and characteristics? I can choose from normal cap (type NHG from Panasonic) or low Z (type FC or, even lower, type FM both from Panasonic).
Javier
Warp speed? Nope...
I ordered those 10 cent jfets and they are all dogs. Jan Didden shipped the MJE's asap but they haven't arrived. Taking all the patience I can muster!
I am going over the layout of the board to be sure I haven't missed anything. It's coming together. I have about 90% of the parts now.
I ordered those 10 cent jfets and they are all dogs. Jan Didden shipped the MJE's asap but they haven't arrived. Taking all the patience I can muster!
I am going over the layout of the board to be sure I haven't missed anything. It's coming together. I have about 90% of the parts now.
Javier, if this is the cap after the reg, you normally don't want it to be super-low ESR. The ESR part is required for loop damping to enhance stability.
Very high quality film caps are a no-no here.
I have a prototype 400VDC reg where I actually had to insert a 1 ohm R in series with the output cap to quiet it down - my electrolytic was simply too good
jan
Yup. One can do a back-of-the-envelope estimate of required ESR by looking at the regulator spec, inferring ESL from the output impedance curves, and setting R = ESL / C. The humble 7815 / 7915 parts come off fairly well by that measure, amusingly enough.
Hi, mine is going on step by step. Right now I'm concentrated on the PSU and later on I'll started the HeadAmp. I'll report on the evolution. As for the HA PCB, I'll be using Jack's design (after all he started this very wonderful and informative thread
).By the way, I think you mentioned earlier on the thread that this design is optimized for low-Z headphones. Just in case we would need it adapted to higher Z ones (like the old AKG K340 or Sennheiser HD800, both of them around 300 Ohms), could you please give us some directions to adapt the design? Thanks in advance.
Javier.
Hi, mine is going on step by step. Right now I'm concentrated on the PSU and later on I'll started the HeadAmp. I'll report on the evolution. As for the HA PCB, I'll be using Jack's design (after all he started this very wonderful and informative thread
By the way, I think you mentioned earlier on the thread that this design is optimized for low-Z headphones. Just in case we would need it adapted to higher Z ones (like the old AKG K340 or Sennheiser HD800, both of them around 300 Ohms), could you please give us some directions to adapt the design? Thanks in advance.
Javier.
Yes, I have Senn 300 ohm phones as well. I asked him before about adjusting resistor values but he warned me that I couldn't increase it that much more. It's in one of my previous posts somewhere. I believe it was R8.
Thanks Javier for your answer. Well it might not be the best option for this type of headphone, but anyway it may be helpful to know the limits for this little wonder:
- Maximum Vout for a typical +/-12v or +/-15v supply (considering the use of well matched pairs)
- Maximum Iout while working in class-A and absolute limit (considering the use of adequate heatsinks to avoid dangerous temperatures on the final TRT)
Javier
It all depends on the efficiency of the headphone driver; its max input before damage or gross distortion sets in. Give it a try first with 300 Ohm headphone as-is. then tell me.
The 30 Ohms just means it can drive lowZ without distortion. many amps cant do this and IC amps cant do it at all.... even with IC buffers. It's just takes too much current.
I didnt mean that it wouldnt do as well with higher Z. In fact, the thd is even lower into higher than 30 Ohms. I am having a hard time measuring the level.
All -- keep us posted on what you hear when it gets done or if there are problems or different power supplies.
The max power is about 10-12 W... heat sink dependant.
Thx, RNM
The 30 Ohms just means it can drive lowZ without distortion. many amps cant do this and IC amps cant do it at all.... even with IC buffers. It's just takes too much current.
I didnt mean that it wouldnt do as well with higher Z. In fact, the thd is even lower into higher than 30 Ohms. I am having a hard time measuring the level.
All -- keep us posted on what you hear when it gets done or if there are problems or different power supplies.
The max power is about 10-12 W... heat sink dependant.
Thx, RNM
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