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6581 Alternative Output   [2013]

6581 Alternative Output Released by :

Release Date :
12 November 2013

Type :
C64 Hardware

User rating:awaiting 5 votes (4 left)   See votestatistics

Credits :
No credits found

Download :
http://csdb.dk/getinternalfile.php/122790/MOS6581_Alternative_output_V2_0.pdf (downloads: 522)
http://csdb.dk/getinternalfile.php/122813/6581_alternative_output_V2.0_non-destructive_installation.pdf (downloads: 277)

Look for downloads on external sites:

User Comment
Submitted by Fungus on 14 November 2013
I agree with onebitman, calling such basic circuits "audiophile" is an insult really. If you want to listen to SID on a 3 inch speaker and run through an RF modulator that's your choice. But listening to sid on a decent pair of headphones or through your stereo is hardly audiophile, I did that 20 years ago.

Commodore was so cheap, that the audio output circuit uses a SWITCHING transistor that cost probably 1 cent for a hundred of them.

Audiophiles are retards that think discreet A/D converters and solid silver power cables add to the "transparency" of music, and are presumptuous enough to think they know how an artist intended their music to be heard. QUITE THE DIFFERENCE.

This is like the difference between watching demos on your shitty TV or using a nice commodore 1701/1702 monitor ;)
User Comment
Submitted by onebitman on 14 November 2013
@bitbreaker: well i told my story why i made this circuit. i always heard c64 sounds from my monitor speaker, later from my stereo when i hooked it up, and i loaded games just to hear the music, over and over. if it sounds too good, just turn back the treble on your amplifier. if you don't have a treble knob, this mod is not for you anyways. also the circuit provides a little more output protection. i care about the noise, and for me it was distracting. death metal? you mean like chuck schuldiner's band death? you need very good audio to listen to this kind of music, there is not less detail in that music than in c64 music. what is lofi squealing sid sound for you is fine detailed synthesizer music for me, i listen on headphones, i want sound as good as possible. there is no other synthesizer in the world with such good features that can be programmed in such a fine detail (multispeed tunes) easily like the sid. look at modular systems, look at synth keyboards, nothing beats the sid feature wise. and that is why it deserves to sound good. if the sid is not more for you than some shit x86 beeper then re-evaluate it. there is a reason bob went on and founded ensoniq, and look at the impact this company had! the 6581 is the brilliancy of yannes in a nutshell. the word is WAVEOPHILE. period
User Comment
Submitted by Bitbreaker on 14 November 2013
Seriously, it is like playing death metal and taking care that there's less background noise on the line. It is lowfi squealing sid sound in mono (in the past even feed through the modulator and playd back by a tv), who cares about additional noise? It just destroys that feeling and gives even more unnecessary diversity when it comes about doing sid. Painful enough that one has to decide between old and new sid. Thus, for audiophiles i'd say :-)
User Comment
Submitted by onebitman on 14 November 2013
thanks for your feedback fungus. so maybe i will leave the original 1k in as i don't want to change sound even more. actually i have quite a few TL-072's around so thats why i have chosen it, maybe also easier for future stereo upgrades. thanks for the hint with the capacitor, i had one in before and couldn't notice differences, but i will add it again. also i noticed a layout mistake with the 220pF, so i updated it. !!!BUILDERS - only use V2.0 version with 2x 10uF!!!
User Comment
Submitted by Fungus on 14 November 2013
My circuit of course is the same as the original idea, it is an emitter follower circuit any first year student learns. I also chose components based on my own experience (20 years or so) designing audio circuits. I only wanted to increase the impedance load on the sid (because mos stuff is high impedance) which lowers the noise floor, and also to increase bandwidth, but also without altering the sound TOO much. I still wanted it to sound like a c64 (including distortions). lemming agreed with me on transistor choice and came to the same conclusions with his own ears, and a general purpose audio transistor was chosen. I had built the circuit before with both a j-fet and a mosfet and it just sounded too different for my tastes. TL-072 is also a mosfet general purpose dual opamp used in many audio equipment over the years. You could of course use a TL071 to avoid wasting half the chip too. You should also have a bypass capacitor from your floating ground to ground to remove any rf noise and to stabilize the voltage division. 10uf is a good value to use.
User Comment
Submitted by onebitman on 13 November 2013
@bitbreaker: absolutely not. this is not for audiophiles and its not a minor improvement, this is something anybody with decent ears can hear in a blindtest. also you can see it in a frequency waterfall display or notice it when you inspect 2-3 duty cycles of one waveform in comparison (original circuit vs. alternative output).
User Comment
Submitted by Bitbreaker on 13 November 2013
do i need handwoven goldwire to be able to enjoy this circuit?
User Comment
Submitted by onebitman on 13 November 2013
@Lemming: i checked the circuit in VN#60, respect to fiddling out the values and trying different transistors, but tbh i expected more, in the end it is a modding of the original circuit. it is even unsure if the 10k to GND is good for the sid chip, as datasheet points out 1k in typical application.

@Style: only PAL machine sorry. samples are very loud on this chip though.

@Mixer: yes that is soundcloud streaming, it is more noticeable on sharp edges (chiptunes), thats why i recommend leeching the tunes.

@bepp: it is a voltage follower circuit, done with an operational amplifier, the TL072 - a classic device many audio nerds swear on, like joe meek for example used it in all of his designs.

@Style: it reduces the "drifting" (dc offset) of audio a little. the sound is more crisp, better amplification of the original waveform (better shape than original transistor), also the overall sound has more clear highs. compare SOASC 6581 R2 with my recordings, his chip has nearly the same filter; also my recordings sound more crisp than Trurl6581R3_4885 ~Follin in sidplay, which also has a similar filter. i need to build another circuit in my c128dcr, as far as i see it, the circuit will work with the 8580 without a problem when you remove the 1k resistor to ground right after pin27.
User Comment
Submitted by Style on 13 November 2013
what does this do, and how would it differ on 8580?
User Comment
Submitted by bepp on 13 November 2013
I don't understand a thing of this - but it seems interesting. Would someone care to do a brief summary "for dummies"? :) Thanks!
User Comment
Submitted by Mixer on 13 November 2013
Sounds good. The slow release compression on the SoundCloud streams sounds awful though. Is that really forced on all streams?
User Comment
Submitted by Style on 13 November 2013
skate or die is recorded @ 60Hz??? :)
User Comment
Submitted by apprentix on 13 November 2013
I listened to ProjectHubbard_-_Lightforce_[audiophile].wav and it sounds awesome! Great sound quality!
User Comment
Submitted by lemming on 13 November 2013
I'm sure it's a good circuit :) however y'all might want to check the hardware corner in Vandalism News #60
User Comment
Submitted by onebitman on 12 November 2013
as i was recording hubbard songs and looked at the waveforms i was dissatisfied with the dc offset and the shape of the waves, so i found some sidplayer design using a OPA as output stage, upon that i created this circuit using the popular TL072. using dual supply (with max1044, using 5vdc) did not produce good results, so "negative supply" is done with a virtual ground. values have been selected by ear, not by math, so if you are smarter than me i would not be offended if you tell me how dumb my design is - as long as you point out how to do it better (using the tl072!). this is proof to be working and sounds better than the original transistor circuit, i built it once on breadboard and twice on veroboard, now it is working inside my c64. these recordings are all done with this new circuit: https://soundcloud.com/zerozillion/sets/project-hubbard
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