More importantly, what's supplying the YAC512?

ISA pinout for reference: http://ferretronix.com/ixr/octagon/ISA_Bus_pins.png
The left side of the CT1600 is fed from the +5V B29 pin of the ISA port, that includes the Bus Interface (CT1336A), DSP (CT1341) and all CD-ROM IDE chips, and the YMF262.
But most analog components responsible for amplification are fed from the 78L05/79L05 TO92 regulators which is fed from the +12V/-12V rails , that includes the Mixer chip (CT1345), all the 3403 op-amps, and YAC512.
The big AN7809 regulator in the middle feeds 9V to the TEA2025B Power Amplifier chip and nothing more.

So the YMF262 and YAC512 are fed from different 5V sources.
All analog components regulated on board using a 78L05, but all digital components are fed straight from the 5V rail on the motherboard/ISA.

I cannot assume that the noise comes from the analog part of the board (+/- 5V from the regulators from the 12V rail) because the PCM audio and power amplifier are very quiet, that includes the YAC512 DAC.
It may very well be that the high frequency oscillation from the motherboard somehow affect the digital signal of the YMF262 chip before the YAC512.....?

Hmm, sounds like it might be more fruitful to look at the decoupling/suppression between the digital and analog sections and make sure there's no noise leakage. The signal itself should be fairly immune to bit flips.

The analog section is actually very well decoupled having caps on all ICs at the VCC close to the chip, same with the Digital part.
All regulators are decoupled and filtered well with electrolytic and ceramic right at the output of the regulator... everything is by-the-book and more.

The easiest test would be to cut the 5V from the YMF262 and hear if the thinking noises are gone with YAC512 still powered.
But that would devalue my CT1600 if I ever want to sell it.

Man, I wish I had a scope. 😒

Ebay, my friend. CROs go for quite low prices.

Nah CROs are ancient.
The chinese 100MHz Hantek looks decent, but College = no spare cash, so maybe later.
I already acquired tons of ISA audio cards for hundreds of dollars only to return to my first YMF719... the irony hurts my pockets more than the money spent.. 😵

DonutKing wrote:

Well short of replacing every cap and coil in the whole system, that doesn't really help me much.

Put a few dabs of super glue on every coil out side the psu. This will shut them up good.
And you could make a shield out of aluminum foil. Take a sheet of foil and ground it to the case and wegd it between to sheet of paper or cardboard to prevent shorting out anything.
Also changing caps on the sound card may help.

James-F wrote:

Nah CROs are ancient.
The chinese 100MHz Hantek looks decent, but College = no spare cash, so maybe later.
I already acquired tons of ISA audio cards for hundreds of dollars only to return to my first YMF719... the irony hurts my pockets more than the money spent.. 😵

Rigol is a better product than Hantek. However, since you're in University, why not get friendly with the Physics or Engineering departments. You can likely use or borrow some of their shared or surplus gear.

Actually, I study electronic engineering but I'm a freshman, Calculus and basic Physics are my food right now although electronics was my hobby for many years prior to university, so I'm in no position to ask for anything yet.

I traced the the rout of YMF262 -> YAC512 -> 3403 -> Mixer.
YAC512
3403

If you look in the datasheet of the YAC512 the configuration on the SBPro2 is EXACTLY as per the datasheet.
All four op-amps of the 3403 outlined in red are used for the YAC512, from there CH1 and CH2 go through electrolytic coupling caps directly into the mixer.
The most noise sensitive part of this configuration is the AOUT and CTB of the YAC512 right on the 3403 pin, if I touch them with my finger I can pick radio stations waving my other hand as antenna... 😁

I was just noticing this last night while playing Ultima Underworld 2 with ear buds. I never noticed it through the desktop speakers, but it was kind of neat. Different frequencies and pulses depending on where I stand, and how I'm oriented. Seems to go away (or just can't be heard over the digitized footsteps) while walking. PC is a 486/66 with an Aztech/Crystal SBPro2-compatible (Packard Bell sound/modem card).

James-F wrote:

Actually, I study electronic engineering but I'm a freshman, Calculus and basic Physics are my food right now although electroni […]
Show full quote

Actually, I study electronic engineering but I'm a freshman, Calculus and basic Physics are my food right now although electronics was my hobby for many years prior to university, so I'm in no position to ask for anything yet.

I traced the the rout of YMF262 -> YAC512 -> 3403 -> Mixer.
YAC512
3403

sbp2.jpg

If you look in the datasheet of the YAC512 the configuration on the SBPro2 is EXACTLY as per the datasheet.
All four op-amps of the 3403 outlined in red are used for the YAC512, from there CH1 and CH2 go through electrolytic coupling caps directly into the mixer.
The most noise sensitive part of this configuration is the AOUT and CTB of the YAC512 right on the 3403 pin, if I touch them with my finger I can pick radio stations waving my other hand as antenna... 😁

Well, don't touch it then 😁 Apparently AOUT is very high impedance line then.

Anyway, yes schematics-wise it may look perfect, but if you look at how the thing is wired on PCB, then you'll start to see things.
http://www.yjfy.com/images/oldhard/sound/ct1600_1991_1.jpg

As it is a cheap consumer product, I have to assume is made with only two layer PCB, so there are no ground layers between top and bottom layers. Can you verify this (my card is somewhere I can't reach it now)?

And every loop of wiring is a coil that picks up magnetically coupled noise, coming maybe from other loops (coils) on motherboard. Also look at the grounding if it is made in star configuration or just random, because if there are digital return currents on analog return path then the analog ground is noisy, so in this case it does not matter if the 5V is coming from a squeaky clean audiophile regulator (which of course the 78xx and 79xx aren't, but they should be good enough for analog audio...)

The thinking noise can be greatly affected by moving the sound card to different slot and moving other cards away from it (when possible).

Well, my monitor has a really subpar amplifier, so i end up turning the volume always nearly maximum- but not too much- because i hear a RF interference coming ouf my modern core i5 pc, and amplified by the sound system.Seems coming from the ide channel,i hear it when the hard drive is working.

I also have fun with SDR usb dongles, you can see RF spectrum from 50 to 1200 mhz.
If i turn on a nearby PC (fairly new) you can see all the rf noise spikes going up like crazy in a certain range of frequencies, often disrupting my fun in receiving faint signals from all around the world...

So i guess this still is a big problem, probably because RF shielding pc mobos or cards and especially PSUs it's too expensive and often misregarded by manufacturers.

Yep, only two layers front and back.
The digital and analog grounds are different and go to different pins on the ISA slot, the do not interconnect on the PCB.

There is a ground bus closer to the bottom in the digital part of the card and everything snakes down to it with thicker traces... close enough to star grounding.
The analog part has practically no ground in the signal path as it has +5V and -5V on all op-amps and practically no ground, this makes the card silent in the PCM part of it, most of the analog grounds are for Caps.
I believe the problem is in the YAC512 DAC part of the card because when FM is muted in the mixer the PCM part of it is very quiet as you can hear in the Doom gameplay demonstration I posted in my bump post.

I don't think the interference I hear is RF, I think it comes somewhere along the leads.
But why only on the YAC512 path? Why the PCM part is absolutely silent using the same regulators and grounds ??

mongaccio wrote:

So i guess this still is a big problem, probably because RF shielding pc mobos or cards and especially PSUs it's too expensive and often misregarded by manufacturers.

Shielding? What shielding?

It certainty can be regarded as modern art. 😁

voodoo5_6k wrote:

I have had comparable issues on even my newest PC (with a Sound Blaster ZxR), at least it sounds basically the same. […]
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I have had comparable issues on even my newest PC (with a Sound Blaster ZxR), at least it sounds basically the same.

I use two sets of speakers in combination with audio switches, Quadral Rondo Aktiv (for the main rig, WinXP & DOSBox machine and the PC I'm doing my office related tasks on) and Canton Plus Media 3 (for all my retro PCs).

The first time I noticed those sounds was when, years ago, I connected the former main rig and the former office PC to an audio switch. All of a sudden I could hear the mouse movements on the main rig and there was a constant whining or whatever you want to call that, changing pitch with e.g. cpu load.

When I started setting up more then one retro PC (using a KVM switch with audio) that too gave me those noises.

The solution that worked for me is this: http://www.palmer-germany.com/pro/en/PLI-03-L … annel-PLI03.htm

Expensive, yes, but now I don't have any noise at all. I use several of those boxes. Whenever I encounter a problem like that, I order another one, hook it up in between line out and audio switch and I'm fine.

Dumb question, but what does that do that a basic $10 ground loop isolator won't do? I bought half a dozen of those for like 25 cents each when my local RadioShack went out of business a few weeks ago.

James-F wrote:

But that would devalue my CT1600 if I ever want to sell it.

Pfft.

If that's your concern then why are you even /using/ any of this stuff?

Besides, the YMF262 is a surface-mount part, if you're careful you could lift the IC's leg without damaging anything, and restore it later without any sign that you were there.

There's a lot of induction pathways on that board. Just look at the routing from the bus chip on the back!

Ozzuneoj wrote:

Dumb question, but what does that do that a basic $10 ground loop isolator won't do? I bought half a dozen of those for like 25 cents each when my local RadioShack went out of business a few weeks ago.

Well, I didn't open it to investigate what's inside. But for me, personally, it was by far the best working solution for the given problem. I tested several other ones, but the really cheap ones didn't fully remove the noise and/or were heavily distorting/dampening/etc. the audio output. Then I used a not so cheap one from Monacor. That one got rid of the noise and had only a very subtle impact on audio quality (but still noticeable). Unfortunately, it didn't even last two full years. Then the device was defective, but until I discovered that, it was already out of warranty.

That's why I went with something more "pro-grade". The Palmer stuff has a five-year warranty (at least here in Germany and if I remember correctly). It got rid off all the noise that's in the two system sets (3 modern PC using the Quadral speaker set, and 4-5 retro PC using the Canton speaker set) and has virtually zero impact to audio quality (I don't hear any difference, it is only slightly quieter).

But I don't want to advertise it. It is only the path forward that I chose because I was tired of those cheap solutions that don't really fulfill all my requirements and have to constantly be replaced because of their way too short MTBF.

Of course, if one of the cheap ones I had would have worked to my satisfaction, I would not have had any reason to buy one of those expensive boxes. So, if the $10/25 cents one works for you, that's really great! I unfortunately had no luck at all with something like that.

Inside there are two isolation transformers with 1:1 turn ratio simply to galvanically isolate the interconnected equipment.
The AC sound transferred magnetically through the transformer... like magic no wires.
The source of the hum/noise these isolation transformers fix is usually ground loops noises and it is not the kind of noise this thread is all about.
The cheap ones from ebay cut the bass below 50Hz and alter the phase response, I have a few myself and do not recommend for any serious audio application where sound quality matters.
Further reading: http://www.epanorama.net/newepa/2010/08/12/au … n-transformers/

Hi James-F,

I know that you are now talking about something different. I only brought this up because feipoa specifically talked about "hearing" the mouse movement over the speakers when having everything connected to a KVM. And that issue (amongst other things) is exactly what those Palmer boxes fixed for me. Maybe it could help him too.

But for the purpose of the overarching topic, yes, please disregard those posts. Sorry.