viral projects, sort of

[WBS]

WBS, feel free to post pictures, this thread is just for fun while covid is still raging

I build many other amps, and rebuilt some older ones...

here is picture of two 2.1 amps based on LM1875 chips, cheap partsexpress board, with one chip for each channel and bridged out for sub, works fine

You make some cool stuff! I can't believe how long it's been since my last post. Watching my grandson 3 days a week has slowed me down quite a bit. 🙂

I have all the foam pieces cut and some assembled into panels. Photos soon, I promise!!!! 😀

 

[nigelwright7557]

Working on a stereo hybrid amplifier 25w + 25w with valve front end and TDA7376B.

Also awaiting a usb scope pcb from China.
Its extremely simple and cheap.
+/- 3v3 in with x1 scope probe or +/-33v in with x10 probe.
Up to about 5 millions samples/ second.

 

[adason]

i have been working on a20 preamp
started work on MTM with peerless mids and hiquphon tweeter
both still work in progress

i have finished f1j amp, and will make another, this time just f1
since I like the sound of transconductance amps, i was experimenting with various chip amps, since they are cheap and available

here is my first prototype conversion of XY LM3886 chip amp
i will describe step by step procedure if anyone is interested in doing so
the sound is much more musical after the conversion

 

[adason]

for the conversion, only two resistors are required, I use 220 ohm and 0.22 ohm, feel free to experiment

in first step i remove 22uF feedback capacitor

 

[adason]

in next step i disconnect the output wires (live one could stay, it will go back) and attach those two resistors per side, 220 ohm between the live and ground speaker terminal, 0.22 ohm from ground terminal sticking out

 

[adason]

i reattach live speaker wire, but the ground speaker wire goes to the 0.22 ohm resistor leg in the air

 

[adason]

now to reassemble the feedback, I lift one leg of the 22k feedback resistor as shown, the leg pointing away form the chip
resistor stays in, ok?

 

[adason]

now in final step, I place feedback wire from the lifted leg of the resistor to the ground speaker terminal, just between the resistors
this will read the signal on 0.22 oh resistor and provide current feedback
make sure you do not switch feedback between the channels

 

[adason]

I made this change on 3 amplifiers, no DC adjustment was needed on any of them
when you measure dc on the output without the speaker, it may be few tens or few hundreds of millivolts, but once you plug the speaker in, it will be just few millivolts

good luck!

 

[Boden]

@Adason: your mod into currnet drive worked fine I presume, coz I see no burnt parts?

Is this along the lines of the diagram you uploaded some time ago in of the Current Drive threads?

 

[adason]

pretty much, but slightly different mod

previously it was in Joe Rasmussen's threat using LM3875 chip, and his circuit

this time I made mods into three of my XY LM3886 chips, much simpler mod, no adjustments

I have now finished all three and are using them with 3way active crossover. I should post picture.

 

[adason]

Here are some pictures, all three amps stacked, as well as all three separate power supplies. Active crossover still needs some better box.
These are the speakers I am currently using it with, Aurum Cantus mid, Beston planar tweeter, and pseudo Pioneer woofer, dynamic drivers are open baffle in the back. The crossover is set to 300/3000 Hz, and I do not like it, I would prefer, say 200/5000, yes, the Aurum can go as high as 5000, I used it with ribbon before.
One thing I noticed, even though there is absolutely no passive crossover between the amps and speakers, it needs tweeter to be in switched polarity. Measurements showed that.
Happy New Year!

 

[Boden]

Could you show us a raw nearfield measurement of the woofer as driven by the modified amp?

 

[adason]

your wish is my command!

 

[adason]

and all together

 

[adason]

mid, btw, is admirably performing

 

[adason]

I am not happy with crossover points
while 3kHz between the mid and tweeter may be ok, I want to push it higher, maybe to 5kHz, so it can be used with ribbons
on the other hand, mid can easily handle 200Hz, so I want to modify the crossover point lower
but this is low priority project, I am building F1, Aleph J and Whammy all at the same time

 

[Boden]

Thanx, that + 5dB peak @ 35 Hz is exactly what I was looking for.

 

[adason]

we aim to please

 

[Boden]

And we are being served beyond any call of duty