Advice and interest check for a Nano Stereo Amplifier built for beginners.
- Thread starter sureshkuranjalayil
- Start date
novice-akki
New Member
^^ all the best !
Please keep us updated.
Please keep us updated.
Sounds interesting! Could you kindly share more details like it's tech specs like power rating etc and also, approximate cost.
Hi Captain - the output specs are nearly identical to 2x MyRef Rev C: about 40W/channel into 8 ohms with a 24-0-24 trafo. Voltage gain is also the same at (1 + 12k/390) ~= 32.
The price of a bare board in small prototype quantities is Rs.450 (which can be brought down once it is produced in volume). An average professional-quality BoM will run to about Rs.2.5k-3k for 2-channels. Even if you go with premium parts for everything in the signal path, it should still be < Rs.5k for everything on the board. In addition, you'll need the trafo, cables, connectors, switches, volume pot, heatsinks, chassis components and hardware, etc. that are in any case required for any DIY amplifier.
Advice for all newcomers there is nothing less labour in building a gain clone of basic type just because the circuit looks small.also no big savings than myref.Myref is pretty proven .so thjnk that .because diy means cabinet fitting knobs sockets ..roaming for cabinet tobe done.etc.so no matter
If u solder 20component or 40 u will have same effort.because soldering is just 20% of the total effort....ya if u wanna experiment have some little sensitive speakers..well known class a types are good start.
If u solder 20component or 40 u will have same effort.because soldering is just 20% of the total effort....ya if u wanna experiment have some little sensitive speakers..well known class a types are good start.
sureshkuranjalayil
Active Member
Here's a prototype build of a MiniRef variant using LM1875 pentawatt chipamps (it could probably use the TDA2030, 2040, 2050, etc. with minor changes to some components as well as lower power supply rails):
The prototype shown works prefectly stably and with excellent sonics, comparable to a MyRef Rev C. This is rated at about 2x 25W rms into 8 ohms with ~ +/- 26V rails. Adequate power, and very compact, allowing it to be installed in small cabinets, and a variety of other applications like bookshelf/mini-Hifi setups, bi-amping, HT satellites, old amplifier case-retrofits, boom-boxes, HTiB, etc.
This is a link to the original diyAudio thread about the MiniRef topology:
MiniRef Schematic and PCB layout - diyAudio
saheb11123
Active Member
Cost of kit?
saheb11123
Active Member
Where did you buy this from? Costing?
I have bare PCBs and the BoM is pretty much the same as what is shown on the schematic that I posted at diyAudio last year. PM me if you want the bare PCBs or a full kit (may not be exactly the same as that of the prototype build above, but all component values will be fairly close).
Virtually all the parts have locally-available professional-grade equivalents - I'm guessing that everything required for a stereo board can be self-sourced locally for sub-Rs.2.5k. The only expensive parts are the input coupling caps, the PSU filter caps, the protection relay and the LM1875T chipamps themselves.
saheb11123
Active Member
Thanks for the reply. Going to be doing a full 6 channel system. Decided on Lm3886 for fronts , will for with something less powerfull for rear's then another set of bridged LM3886 for sub.
Your kit looks good. It will take me some time for arranging funding and time as exams are nearing and vacations coming.
Your kit looks good. It will take me some time for arranging funding and time as exams are nearing and vacations coming.
anujmishra
Active Member
The 4 power transistors are placed one behind other, wouldn't it will be issue with heat sink placement?
The ones you are referring to do not require a heat sink I guess.
There are just two TO220-5 chipamps that will be mounted on the heatsink at the edge of the board, and they get barely warm to the touch at normal listening volumes. The other two devices near the chipamps are 5W metal-plate resistors in ceramic casing, and they don't require heatsinks (passive convection cooling is fine).
The remaining four TO220 devices are fast-soft MUR power rectifiers which are also convection-cooled - they dissipate around a watt each even at full-power operation, and much less at normal listening volumes.
Pic of the MiniRef 1875 installed in a compact aluminium 1105 enclosure (available from EBay vendors in China). It fits snugly with 2x 19.5V/2A netbook AC adapters re-purposed as the PSU to supply +/- 19.5V/2A (~78W total). This is still work in progress - sockets, wiring, etc., are still to be installed, but no problems foreseen. The tricky stuff relating to the AC adapters is completed.
The main advantage of this approach is an extremely compact cabinet - way smaller than an Amp Camp Amp., but with comparable or higher power and sonics.
The main advantage of this approach is an extremely compact cabinet - way smaller than an Amp Camp Amp., but with comparable or higher power and sonics.
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Pic of the completed and fully-wired MiniRef 1875 in the type-1105 cabinet with 2x 19.5V/2A netbook AC adapters as the PSU:
The landed cost of the cabinet, netbook AC adapters, gold-plated RCAs, banana sockets, gold-plated banana-plug adapters, heatsink, knob and potentiometer (basically all chassis components alone) works out to around Rs.4k, which is more than all the remaining amplifier electronics put together. However, it's still a good deal compared to trying to CNC machine an aluminium cabinet - it's hard to get the same finish, and costs more (from my experience with the aluminium and wood cabinet which I built earlier).
Some costs can be shaved by omitting all the gold-plated connectors and doing a group import (say 10x) of the cabinets and netbook AC adapters from Shenzhen, as suggested earlier by Capt. Rajesh - say Rs.3k in volume, which is in the same ballpark as the remaining electronics (Rs.2k to 3k). So you're looking at a costing of Rs.5k to 6k, all inclusive. If you go for premium parts and connectors, you're looking at Rs.10k.
What you get is an extremely compact 2x 20W Class-AB nested gainclone with sonics approaching some high-end Class-A amps. It's basically limited only by the quality of the opamp that you install in the outer loop - it works well with generic DIP8 monolithics, but can also accommodate discrete opamps depending on the available height.
The landed cost of the cabinet, netbook AC adapters, gold-plated RCAs, banana sockets, gold-plated banana-plug adapters, heatsink, knob and potentiometer (basically all chassis components alone) works out to around Rs.4k, which is more than all the remaining amplifier electronics put together. However, it's still a good deal compared to trying to CNC machine an aluminium cabinet - it's hard to get the same finish, and costs more (from my experience with the aluminium and wood cabinet which I built earlier).
Some costs can be shaved by omitting all the gold-plated connectors and doing a group import (say 10x) of the cabinets and netbook AC adapters from Shenzhen, as suggested earlier by Capt. Rajesh - say Rs.3k in volume, which is in the same ballpark as the remaining electronics (Rs.2k to 3k). So you're looking at a costing of Rs.5k to 6k, all inclusive. If you go for premium parts and connectors, you're looking at Rs.10k.
What you get is an extremely compact 2x 20W Class-AB nested gainclone with sonics approaching some high-end Class-A amps. It's basically limited only by the quality of the opamp that you install in the outer loop - it works well with generic DIP8 monolithics, but can also accommodate discrete opamps depending on the available height.
Has anyone Built This miniref 1875 Designed by linuxguru? It has got op amp rolling facility and Mr.Siva has developed many hybrid and discrete op amp modules which infuse a class A like sound.Anybody who had assembled this kit can share their views.
Vijay, you're probably the first to have completed assembly of a standard kit in India (though there are a few DIYers in S.Korea and Indonesia who've built prototypes).
Vaguely unrelated stuff: The sound of your Fenda (F&D) A-520 subwoofer amp with my mods (which I'll list out later after I complete auditioning it), driving a pair of Jamo Compact-60 2-way bookshelves, is pretty good.
The main change is that I've shifted the lower frequency -3 dB cutoff point from around 400Hz to about 130 Hz, thus allowing a fair amount of lower mids/mid-bass into the satellites, rather than just the sub. It works well with the Jamos, and should probably also work fine with the Hi-Q full-ranges or the Sony 6".
There's just a slight amount of brightness left in the upper mids, which can probably be tamed if it persists after run-in. The A-520 is amazing value straight out-of-the-box, but just a few mods make it much better. The main difficulty is that most of the capacitors that can benefit from upgrades are SMD ceramics, and it's a pain to desolder them and solder the upgrades. Same with resistors - mini- or micro-MELFs in the signal path can improve the sound even further, but require too much effort to install.
Maybe I'll do a 2.1 sub-woofer amp with a MiniRef-derivative driving the satellites at some point in the future, with premium passives across the board in the signal path.
For excellent sound that won't break the bank, the 5 Star Award Winning Wharfedale Diamond 12.1 Bookshelf Speakers is the one to consider!
