audio-talk

Start of another long slog, this time venturing into the dessert.

After my initial foray with my Cheap as Chips amp using bargain Chinese LM3886 and 6J1 pre-amp boards/kits, I am once again inspired following positive comments on the Pass F5 and also seeing some of Nick's behemoths.

So this is my first project as I consider my planned retirement. No rush, and potentially plenty of time to try and get it right (read no excuses).

But this imminent change of lifestyle is not going to have me shrug off my nurtured frugal attributes. I find myself somewhere between the two amp extremes, probably lacking the confidence to jump straight in and build an F5 that would probably be circa £400 for a vanilla 25W jobbie.

So with the LM3886 chips sometimes being referred to as Overture, the thread name suggests a blend of the two, perhaps a gradual morphing to my aspired F5.

One book lent to me by Nick (still to be returned) talks about the character of an amp being determined by the driver stage, so perhaps this could be an opportunity to find my oasis. So if it all goes well the amp will probably be stripped down into a power amp and I can then think about a SET pre-amp.

Time to start planning my route and get some good heat sinks for this hot journey.

If it helps at all, I use heatsinks from

http://www.fischerelektronik.de/en/home-en/

UK supplier is

http://www.dau-components.co.uk/

Added to favourites...

I'm still a big supporter of conrads

http://www.conradheatsinks.com/welcome.htm

ed wrote: ↑Wed Feb 28, 2018 5:07 pm I'm still a big supporter of conrads

http://www.conradheatsinks.com/welcome.htm

I would have been if they ever reply to my emails.

So the quest for parts has just begun. With picking-up 4 off 300VA 2* 0-18V toroidals including 4x10,000uF caps and 4 bridges, I can pretty much think about whatever power supply configuration I want. So thought is to go all out from the start (space permitting), perhaps even dual mono to cover something ultimately like the F5 Turbo with having 1.2kW of transformers and 120,000uF of capacitance (that could be increased).

How far is it worth going with the power supply if I have the parts available? I was thinking of using at least 600VA for my first stereo 20 or 30W attempt, (I think 400VA was recommended for the F5).

Apart from halving the DCR, are there any other benefits of increased power capacity in terms of sound quality when running amps of 20, 30 or perhaps 50W per channel max?

So I have 2 separate secondary windings. What benefit is there of using the 2 bridge circuit rather than the more usual 1-bridge (other than halving the load through each bridge)? I see the original supply for the F5 used 2 bridges, and the F5T literature only has one. There is also here on TNT that used two bridges: http://www.tnt-audio.com/clinica/ssps3_e.html

How close can I mount the toroidal transformers? In an ultimate build I could have all 4. Could they be mounted in a stack - read that if so, should all be in the same orientation and put a metal disk between each (I assume each taken to the chassis). Or at least vertically with a space between each (and if so what should be the minimum gap)?

Need to get some thicker wire!

My f5 wot nick built is a dual mono one, you're welcome to come and have a listen at some point mike

So I now have a donor chassis, (or at least from Sunday). Don't think the tx nor heatsink will be much use but I like the simple retro look. Main thing was a reasonably sized enclosure and conventional buttons and knobs. Wish it was in this condition:

Transformers arrived yesterday. I plan on using two of these with a couple of filter pcbs I have in a CRC config as attached to roughly copy the F5/F5T suggestions.

2 questions for the experts:

With the series resistor being so small, the benefit in terms of a RC filter is limited. Why is this so small at say 0.1R other than to preserve voltage and limit the series resistance of the supply legs whilst giving some degree of filtration? In terms of filtration, can see the benefit of adding a couple of chokes but at circa £50 not a cheap option when the rest of the amp is looking like costing around £100.

Some filter designs have a damping RC leg, whereas others not. The components of say a 1R 3W resistor and series film/ceramic cap are not expensive so why aren't they used universally? I note neither of the pass F5 and F5T filters have damping components.

Well, 0R1 and 22000uf has a -3db point at 80Hz, so will be reducing ripple, but more importantly will be reducing the harmonics of the charging pulses, so I think will be doing more than you may expect. As to the RC I don’t know for certain which ones you mean. I see you have caps across the rectifiers, I would not do that, and instead have a CRC network in the secondary, but to do that you need to measure the transformer.

In terms of the damping network, this is a series RC from V+ to GND and GND to V- to supposedly overcome parasitic inductance in the main filter cap bank. It is mentioned here but I found some theory and formulae that would suggest his values are not optimized. http://www.tnt-audio.com/clinica/ssps1_e.html

The theory suggested that Cdamp is greater than 16 times Cbypass, so if Cbypass was 0.01uF, Cdamp would be 0.22uF minimum.

Rdamp > 2 Sqr(L/Cdamp) where L is the capacitor bank inductance. It invariably comes out at one ohm or slightly greater which is a common value seen, but often 3 or 5W, not the 17W suggested in the article which I don't believe!

Perhaps seems logical if I am not using very good spec filter caps with higher L and also a limited V/sec time.

Perhaps a load of c**p when some people don't even use bypass caps, (couldn't see any on your F5 build).

Who knows, try it and see. I like using a CRC to damp the transformer to stop the rectifiers switching from making it ring.

http://www.diyaudio.com/forums/power-su ... t-jig.html

I found this thread suggesting cap only values on the secondary of the tx: http://www.diyaudio.com/forums/chip-amp ... one-2.html

If I extrapolate, I require 20nF across the two AC terminals to the rectifier boards using the downloadable spreadsheet.

So the donor Sony ta-212 arrives.

1st thought is I should have bought an amp with a bigger chassis!

Now just awaiting all of the bits from around the globe.

Just starting to think of the wiring.

Why on some amps is the neutral switched as well as the live?

For a solid state amp, is single or double pole switching recommended, as I am leaning towards the idea of having the neutral unswitched?

Thanks,