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adamgillingham 13th December 2012 07:49 PM

Nackamichi IA-3 Upgrde paths
Hi all, I'm a bit of a noob at this and would appreciate some input on upgrade paths for my amplifier.

I don't have a schematic I'm afraid, and I have spent many hours looking online but with no luck.

I have however opened her up and been able to follow the signal path for as far as I can understand it, as well as recognise the major components that are common upgrade paths.

I'm really after suggestions based upon the currently installed major components for the best upgrade path in general terms. I know that many other factors affect these components so that each substitution may not have the same effect as in any other amplifier, but do enjoy the process of modding and have already 'upgraded' my speaker crossovers and DAC with great success and I'm now keen to have a play with my amp.

So I'll take a deep breath now and thank all those who make it through to the end of this post in advance.

Firstly main power supply is via a hefty transformer with a central tap on the output, Via a rvb602 bridge rectifier into two Nichicon 68000uF 50V caps marked as 'Great Supply'. Now I'm assuming something like +/-35V on each main rail, but this is as far as delved and am not to keen to power it up and find out with a multimeter as its all quite tight in there.
I am thinking of doubling up the smoothing caps with similar modern Nichicions via some lead out wires? The rectifier is rated at 6A cont and 200A peak so i'm thinking that this would handle the extra inrush surge, but that's a guess and would really need someone to tell me if this would be OK?

Next, the main coupling caps as far as I can tell are Elna Cerafine two per channel as far a I can see 2.2uF, 50V (first) and 100uF, 16V (after first stage) both with small (poss ceramic) bypass caps fitted alongside. I'm thinking of upgrading all eight (four per channel) but not sure about values and specs, are all audio polyprops better than audio electrolitics as a general rule and do I really need 100uF after the first stage or can I get away with less?

Resistors in the signal path I have only followed to the first stage (then I get confused), but in order they are 100R, ALPS 305C 50KA (dual gang vol pot) and 1K. Now I have no idea of their quality, but am assuming after seeing the higher quality caps that they wont be terrible? Should I look into upgrading these, they are some of the easiest parts to get at and the two set values look low wattage (they are both before the first stage)?

Screwed to the heatsink are the larger output transistors Sanken C4468 and A1696 along with a single Toshiba C3421 (per channel), I am not so great with semiconductor specs what to look for and such. I'm not sure if any of these are possibilities for an upgrade (without too much hassle, I'm not sure I would be up for changing any of the biasing without schematics)?

Bare 13th December 2012 11:22 PM

Suggest adding some Bypass Caps on the Main Caps. Basic Diy dicking around mod and it can't hurt although it's likely there are some already fitted :-)
Then call it a day... for a while at least.
Resistors rarely give tangible improvement.. unless the originals were wayy out of spec or damaged.

adamgillingham 14th December 2012 03:34 PM

Bypass caps on the main supply caps had occoured to me, I don't think there are any there atm. Would definatley be the quickest and easiest option.
Any suggestions on size and type?

Bare 14th December 2012 04:33 PM

Hmm there was/is a rule of thumb for bypass cap size,, of which I have forgotten :-) But I've had success with anything from 1% to 5% of the cap being bypassed. Low ESR film caps are Ideal. Personally I like Solens as they are available., inexpensive and of good quality, without getting into religious belief varieties at foolish pricings

adamgillingham 15th December 2012 05:33 AM

Ordered some Solens, 80uF for the main caps and a few others to have a play with elsewhere! Should keep me busy this Christmas, thanks for the advice.

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