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#1 2011-06-10 01:37:12

CassandraX
Gianas Sister
From: Thuringia, Germany
Registered: 2011-06-09
Posts: 28

SID 2 [i]position[/i] with tonal difference to SID 1

I recognized that there is a maybe "small" but for my purposes significant difference in sound characteristics of SID 1 and SID 2 on SID2SID with two 8580s ("only") with filters set (same instruments, of course). Even the change of both SIDs, the channels of the optical isolation amplifier (I commend for best protection) and of the mixer makes no difference for the SID 2 position: It has less bass and more high frequency like in the thread 'Difference between the SID 1 and the SID 2' here with the spectral pictures. So I conclude it's caused definitely only by the components on the SID2SID board. The whole pattern of filter frequencies seems to be "pitched" a little bit higher by that, what irreversibly "kills" the possible basses I need for my tunes (on both SIDs). sad I one time changed the filter cabs, with no difference.

So:

1. Is it possible that the 2N2222 preamp or its resistors and cab "pitches" the whole sound compared with my on board C945 transistor of SID 1? Anyone with experiences in changing transistors on SID2SID, i. e. an originale C945 on some C64C boards? Because, perhaps, it's only the weakness of the 2N2222 handling deep frequencies, while the C945 have little and negligible problems with the highs? (Compare the datasheets concerning the transition frequency, although far above relevant f.) So, SID 2 sound of basses, although weak and higher, has something more "distortion" or "overdrive", sadly in a bad sense.

Alternativly:

2. Are there some successes in experimenting with the filter cabs? Advices?

3. What happens if I take for instance some 33000pF instead (or 22nF + 33nF parallel)? Is there a problem with the higher current that would flow? Experiences with sounds and chips? I don't want to blow up my "babies". wink

Last edited by CassandraX (2011-06-10 13:11:53)

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#2 2011-06-10 11:26:05

firestARTer
Administrator
From: Germany
Registered: 2006-06-27
Posts: 579
Website

Re: SID 2 [i]position[/i] with tonal difference to SID 1

Welcome Cassandra. For part 3 i would point you to the Midibox SID Forum/Wiki.
http://www.ucapps.de/midibox_sid.html

They experimented alot with different caps and transistor alternatives.


firestARTer - Gameboy - C64 - Atari Music
Hardware developing for your favourite homecomputer musicsoftwares
http://www.sidsyn.com
http://www.myspace.com/firestartermusic

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#3 2011-06-11 06:29:40

deathstarchris
Nebulus
Registered: 2009-05-17
Posts: 64

Re: SID 2 [i]position[/i] with tonal difference to SID 1

Personally I went through a few 2n2222's before I found one that distorted the second sid MORE.  I also went through 5 8580s to find the most dissimilar sounding sids I could find.  For me I wanted both sids to sound completely different.

To make them sound exact, I would duplicate the same components off your main board by stealing them off an old board.

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#4 2011-06-11 11:10:58

CassandraX
Gianas Sister
From: Thuringia, Germany
Registered: 2011-06-09
Posts: 28

Re: SID 2 [i]position[/i] with tonal difference to SID 1

I found the problem myself! It's neither the cabs nor the transistor!

It's a failure of all SID2SID-boards and apparently also MIDIboxes with 8580s! It's resistor R8!

So all the searches for identical sounding 8580 chips I recognized in the web are senseless as long as R8 is soldered in the SID2SID board. The reason is that there is no R8 in all commodore 64s (6581 and 8580) at all! I didn't find it in my C64Cs and my C64G, neither in 91s "Rev. B", 2x 88s "Rev. 4" nor 2x 87s "Rev. 3". What you find is always a position labeled as "R8", but it's nothing soldered in. (It's electronically open. I checked the electric resistance with a analyzer device.) So I thought it's a failure of the schematics of the C64C. And really, there I found R8. But a footnote in the C64C schematics says: "R8 resistor should be remove[d] for 8580 SID". R8 never existed, only R6 with 1 kOhm in old C64s with 6581 only (also R4AR, I checked) as with the same function.

So, I soldered it out of the SID2SID board.

Results:

Both SIDs sound (subjective) identical now!
An enormous deviation to the state before. The whole sound pattern is better. No bad sounding distortion any longer.

Conclusions:

Most problems with sound differences can be leaded back not to the filter cabs or the transistor or the 8580 SID itself, but this seemingly unimportant R8.
It seems it doesn't matter which of the transistors is used. I think the reason for the "huge" difference in the spectre of frequencies ist the function of R9 and C74 as a lowpass filter (see i. e. wikipedia), that is corrupted by R8. I believe R6 for the C64s with 6581s has also the function to lower the basses, unless they are loud enough to overdrive the transistor, what makes the noises in some filter usages. (?) In C64C it's an malfunction.

Comments:

@8bit ventures: I suggest to mention the special issue R8 in the installation guide, like to mention the different filter cabs. Why did You never have mentioned or recognized it before?

@firestARTer: Thanks! Inspiring site.

@deathstarchris: I don't think that it is desirable to cut off the possibilities of every SID 8580 in its individual possibilities, even for you, isn't  it?

Last edited by CassandraX (2011-06-11 11:25:15)

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#5 2011-06-11 13:46:12

deathstarchris
Nebulus
Registered: 2009-05-17
Posts: 64

Re: SID 2 [i]position[/i] with tonal difference to SID 1

Yes you are correct in that R8 is not needed with 8550s.  It has been discussed in an earlier thread, and yes it makes a big difference.

But as to the 8550 possibilities, I would say that one of my favorite aspects of messing with these sid chips is their individuality.  I am currently playing with the 2A03 chips in the first gen Nintendo systems and they also have the same type characteristics.  Some chips are 'bright' bordering on 'tinty' while others are 'warm' almost to the point of being 'dull'.  I find if you can match a pair of sids, one being very 'bright' and the other being very 'warm', you get the best of both worlds.  Not evident on the monosynth as much, so keep your bright chip in sid 1 position, but the warmer chip in sid 2 position is a great addition in the sequencer.  You just have to remember to program your parts accordingly.  I.e. use higher clearer sounds with your bright chip and use base and drum parts on your warmer chip.  Best of both worlds:)

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