internals 47 labs 4717 integrated

[carlosfm]

I started with the LM3875.
But happens that I have difficult speakers (Epos 11) and the LM3886 works much better for me.
Soundwise, it's the same, believe it or not.
High-end.😉

 

[ThorstenL]

Konnichiwa,

Fedde's pcb is IMO standard quality FR4 material (post 112). "Original" pcb (post 113) looks like "hygroscopic" pertinax.

I am familiar with both materials and their behaviour. Unless you spring for the PTFE board you will find pertinax the superior material in practice. Try it, make a circuit once on FR4, once on Pertinax and once hardwired, then listen.

Sayonara

 

[KT]

Hi,

Is pertinax a generic name for that brownish board material, or is it made to a certain spec by a certain company?

Thanks,
KT

 

[ThorstenL]

Konnichiwa,

Is pertinax a generic name for that brownish board material, or is it made to a certain spec by a certain company?

I suspect that it used to be a specific brand but tends to be used generically these days (like the term "velcro" - I once had a request to replace the term "velcro" by "generic hook & loop fastener" on web-pages as velcro is trademark and I was infringing!!!!).

Not all of the pressed wood and resin PCB materials are equally good BTW.

Sayonara

 

[Jamh]

Looks to me like they already are using a small circuit board. What am I overlooking?



Why? They apparently already have a circuit board with the traces and holes right where they want them.



Why? I don't see any problem unless you planned to use it in a marine environment or something.

se

steve,

We are fortunate in Sacramento with very low humidity. Bit closer to the coast this could become a problem. As for circuit board, I meant something like Brian's so that you can speed up the manufacture. But like I said earlier, I dig their sense of esthetics.

 

[Steve Eddy]

We are fortunate in Sacramento with very low humidity. Bit closer to the coast this could become a problem. As for circuit board, I meant something like Brian's so that you can speed up the manufacture. But like I said earlier, I dig their sense of esthetics.

Yeah, we're not as bad as places like the deep south, but by the same token not as dry as places like the southwest. The humidity here can get sufficiently high though that our evaporative cooler is little more effective than a fan, at which point I don't feel too fortunate. 🙂

Not sure a more formal circuit board would speed up production. Since the innards of the 47 Labs stuff just screams "cheap" I'd guess they decided it would be less epxensive to just cobble the boards themselves rather than pay to have more formal boards made.

se

 

[Frank Berry]

"Since the innards of the 47 Labs stuff just screams "cheap"

Amen!
There is "fair profit" and there is "gouging".
47 Labs is gouging.

 

[powerflux]

Took one apart.

The inputcapacitor is a bipolar, probably around 2.2uF
the feedback-decoupling capacitor is polar, 22uF - 47uF ( i suspect the latter)
The powersupply caps are no more then 3300uF, i suspect 2200uF @ around 35v judging by their size.

gain is set by 22K+680R (pretty high, i always read that you'd want a gain as low as stable with the 1875 to unleash it's magic)

outputfilter is a red 0.01uF WIMA (i suspect a clone) in series with 10 ohms

 

[Art M]

April Fools joke machine.

Looks like a poorly executed Hieronymus Machine. Just get some card board and a Sharpie to draw the Components. Why waste time with parts ?

 

[powerflux]

Looks like a poorly executed Hieronymus Machine. Just get some card board and a Sharpie to draw the Components. Why waste time with parts ?

well, it's almost exactly the same as the typical application note in the datasheet. it does work.

 

[TB]

Hello powerflux,
What is power supply output voltage?

 

[powerflux]

Included old post to put all the information in one.

Took one apart.

The inputcapacitor is a bipolar, probably around 2.2uF
the feedback-decoupling capacitor is polar, 22uF - 47uF ( i suspect the latter)
The powersupply caps are no more then 3300uF, i suspect 2200uF @ around 35v judging by their size.

gain is set by 22K+680R (pretty high, i always read that you'd want a gain as low as stable with the 1875 to unleash it's magic)

outputfilter is a red 0.01uF WIMA (i suspect a clone) in series with 10 ohms

Hello powerflux,
What is power supply output voltage?

17-0-17 2x3A E-core transformer

wiring as follows (very bad, lots of noisy current through long wires..)

and you see correctly: HALF BRIDGE rectifier even if the LM1875 datasheet promises 80dB of PSRR, this is still BAD PRACTICE!


also, the amplifier is always on, the 'power switch' just disconnects the loudspeaker ground from the amplifier ground.

--------------
i've made a very tiny clone (well, it's better so it's not a clone anymore.) with good capacitors (wima bipolar for the input, panasonic FC for the supply, decent PSU decoupling etc) + higher voltage, decent ground-plan, sufficient buffering and it sounds a lot sweeter with better dynamics..

 

[powerflux]

EDIT: i made a mistake.

also, the amplifier is always on, the 'power switch' just disconnects the loudspeaker from the amplifier output.

 

[lohk]

half bridge?? can you explain that with four wires as secondary from the transformer?

 

[powerflux]

half bridge?? can you explain that with four wires as secondary from the transformer?

sorry. full bridge indeed. it was early for me 😀
no further mistakes tough. i doublechecked.

 

[lohk]

To switch off the loudspeaker alone is not necessary a bad idea: the amp stays on with proper settings. The only disadvantage could be the quality of the switch. But if you consider the thousands of amps which have relais for that porpose (relais often mean hard working contacts without cleaning possibilities). A self cleaning switch can be a much better choice next to no switch at all.

 

[lohk]

Powerflux, how can you be so sure about the capacitors (bipolar/polar) and about the values when the original ones are stripped of their plastic caps?

 

[lohk]

I fell a little bit like a defender of the 4717 here: Can the long wires not also act as a definite tiny resistance before loading the powers supply capacitors?
I must admit that I tried this technique once with one of my older clones but was never happy with the result (for unknown reasons) - since then I always use the rectifier near the caps. But a small resistance before the caps could help to stabilize the power supply with a more definite loading current for the deliberately small capacitors.

 

[lohk]

It is still funny: Before I tried my first "clone" I would never have made a power supply with such low valued capacitors. But the first tests very easy established the the snaller ones gave a much better sounding amp. Since then I am very careful judging a design by "well established categories".
Of course others have tried and made that before: The famous Nytech amps had just one (!) 3.300yF for both channels, the Spendor 50W amp one 3.300yF per channel, the Naim NAP140 and the INCATECH Claymore 2x4700yF per channel, all without further regulation.

 

[powerflux]

Powerflux, how can you be so sure about the capacitors (bipolar/polar) and about the values when the original ones are stripped of their plastic caps?

size & application with basic calculation for the crossover-frequencies + the datasheet. in other words: statistics.
i'll try to get a LC-meter to confirm my suspicion. but it all fits together.

and the bipolar/polar thing: there are blue markings in the correct orientation (when polar) to denote the negative of the capacitor, but no markings on the 2u2 input capacitor. so the guys that removed the sleeves still needed some markings further down the production line 😛