Hello, finally I succeded getting sound in both channels, thanks to NUUK which guided me through the grounding connections a month ago. In the meantime I've been able to build another, and they are both sounding very impressive, very natural sound which I enjoy listening to. They are very stable, preliminary with no capacitors at the input. The first one has a bit too high DC offset, 85mv right channel and 120mv left channel connected to a CD-unit. I have decided to unsolder the chips on this one and see if a completely new wiring will normalize the offset values. The last one has 32mv at the left and 7.5mv at the right channel, connected to my CD-unit. Thats pretty normal, isn't it?
I'm using a minimal configuration, having transformed the schema for 3875 presented by Peter Daniel in this forum to the lm3886-schema. The cooling is at the moment confined to a single 10mm aluminium bar measuring 50 X 170 mm. The chips are bolted to this bar with a suitable alubar from underneath. The bar is getting pretty hot when the amp has been playing a while, but the chips heatprotection has not yet been activated. I've planned bolt an alu topcover to the alubar which will increase the cooling area.
Components used: Standard resistors, values of 22k for Rf, Rin, Rm, and 680 ohm RIn-, and 220 ohm In+. Elna LPH 2200/63 uf/V Caps near the chips, 20.4 V secondaries, of unknown origin gives 28.6 v on the rails. 4 Mur860 diodes at each rail.
The work has been progressing thanks to NUUK's excellent supporting website and in my darkest periodes the constructions from Peter D's hands was cheering me up!
In addition I was inspired by MAD's construction using the TI's opa541 chips presented here in an earlier thread in des. last year.
Thanks to you all!
Finn-M
I'm using a minimal configuration, having transformed the schema for 3875 presented by Peter Daniel in this forum to the lm3886-schema. The cooling is at the moment confined to a single 10mm aluminium bar measuring 50 X 170 mm. The chips are bolted to this bar with a suitable alubar from underneath. The bar is getting pretty hot when the amp has been playing a while, but the chips heatprotection has not yet been activated. I've planned bolt an alu topcover to the alubar which will increase the cooling area.
Components used: Standard resistors, values of 22k for Rf, Rin, Rm, and 680 ohm RIn-, and 220 ohm In+. Elna LPH 2200/63 uf/V Caps near the chips, 20.4 V secondaries, of unknown origin gives 28.6 v on the rails. 4 Mur860 diodes at each rail.
The work has been progressing thanks to NUUK's excellent supporting website and in my darkest periodes the constructions from Peter D's hands was cheering me up!
In addition I was inspired by MAD's construction using the TI's opa541 chips presented here in an earlier thread in des. last year.
Thanks to you all!
Finn-M
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