~ Since we are making PCBs and not importing one, the cost will come down, right ?
~ Can one make regular copper plated PCB along with gold plated one ?
The original Twisted Pear board was priced at $7 each + shipping, which made the landed price in India about $30 for a pair. My board is larger in area, at roughly 15 sq. inches and the cost at low volumes (25 units) will be about Rs.20/sq. inch + NRE of ~Rs.100 per board. So it's about Rs.400/board in costs, which is actually higher than the Twisted Pear board. I haven't got pricing for the immersion gold finish, which may increase the cost per board.
Say a maximum of Rs.500 per bare board in low to medium volumes. The price will be lower at high volumes, but volumes aren't guaranteed for a DIY project, so I'll have to stay with small batches initially.
~ What will be the rough estimate of PCB+quality components or PCB+regular components?
I'm committed to keeping the component BoM for the regular (value) build at Rs.1k per channel or less. This will include everything on the PCB except the big electrolytics (easily sourced anywhere) and the heatsink. Uriah's Diyaudio GB for the Ultimate BoM (~$68) also omitted the electrolytics and heatsink for similar reasons. Add Rs.500 for the PCB, and it comes to Rs.1.5k/channel.
The BoM for ultra-premium components can go through the sky - there's no upper limit. If you use Black Gate FKs for the main PSU electrolytics, it will be ~$980 for those two caps alone. There are numerous premium input caps that run to $100+ each, and boutique resistors (Riken, Kiwame, Shinkoh, Caddock, etc.) that cost $10+ each.
The aim is to use good enough components for most items, and concentrate the premium components where it will make the most audible improvement. My Value BoM has some components that are superior to the Ultimate BoM - for instance, I have two silver micas for C10 and C34 which have been confirmed independently by Dario to be an audible improvement as compared to the Ultimate BoM (he found this independently, even before I posted the Value BoM).
The cost of those silver micas is moderately high (say Rs.15-25 each) compared to janata-quality AEC disk ceramics (25 paise each), but it's worth the money. OTOH, I'm not going to use a $10 Rubycon Black Gate for C9 in the Ultimate BoM, even though I know that it might be superior - there's no way to source it in quantity in India, regardless of price.
~ I am OK with whatever mods you are doing for improving this amp. What is the difference you are making to Mauro's Reference C amp ? (Please use simple language.
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I'm retaining the exact same circuit schematic, but a few component types and values may change as outlined above. The PCB layout has been changed incrementally to fix some problems in the old layout. The main changes are:
1) Larger footprints (more space) for certain components, to allow better or more easily obtained components to be substituted, either now or in the future.
2) Improved star grounding and ground separation between the large signal and small-signal sections.
3) Better trace routing to reduce pickup and interference from the large-signal and small-signal sections.
4) Changes in component placement for similar reasons as above.
~ Can we combine power regulator circuit and amp circuit on one pcb ?
~ Can one connect Direct line out from CD Player ?
It doesn't need a power regulator - 24-0-24 from the main transformer is connected directly to each board. The board does have the bridge rectifier and PSU filter caps already on-board.
Yes, the input is high-impedance (~100k), line-level (< 1V), which should be fine for most CD players with a line-out or a headphone out. I'm testing it with a PC sound card line out, and it's fine at those levels.
~ When you are done with mods and satisfied with result You can start separate thread for Group Buy
Will do - right now I'm focusing on completing the PCB layout and getting the Gerbers out to the PCB fabrication house. Once that's out of the way, I can get back to component selection and sourcing. There are now only 2 components for which I don't have a reliable source locally:
1. A box-type Wima FKP or MKP series polypropylene cap, 0.1 uF, 100V or higher. This can be subtituted by a Wima MKS-3 or Evox MMK polyester, for both of which I have sources locally. I've tested the MKS-3, and it's adequate for now.
2: A 150 pF, 300V or higher Silver Mica or NP0/C0G ceramic capacitor (C32). A difficult one, mainly because of the value - 100pF and 220pF are readily available.
Also, Power ratings per channel?
