VOGONS


First post, by Eep386

User metadata
Rank Member
Rank
Member

I've decided to start a running log, that catalogs which Creative Labs-built ISA sound cards suffer floating op-amps, and where to look on the cards in particular. Do note that the locations of the parts in question tend to vary between different revisions of the same CTxxxx model number, so don't be surprised to find that your card doesn't match the description of a log posted here. I'll occasionally add more to this post (and make further posts as needed), as I discover Creative-made ISA cards with this problem.

Sound Blaster Pro 2

CT1600
Pins 8-10 and 12-14 of the quad amp at U11 are floating. No other floating amps detected on this particular board.

IMG_1506.JPG
Filename
IMG_1506.JPG
File size
537.76 KiB
Views
868 views
File license
Public domain

Sound Blaster 16

CT2940
U5 and U7 have floating, unterminated amps at pins 12-14 each. This fault is common to both CQM and YMF289-fitted versions.

CT2940-Float.jpg
Filename
CT2940-Float.jpg
File size
254.99 KiB
Views
865 views
File license
Public domain

Sound Blaster AWE32

CT2760 (first revision, TDA1543T DAC)
The entire left half of U22, the right half of U27 and the bottom half of U30 are floating.

CT2760-Float1.jpg
Filename
CT2760-Float1.jpg
File size
272.22 KiB
Views
865 views
File license
Public domain
CT2760-Float2.jpg
Filename
CT2760-Float2.jpg
File size
356.73 KiB
Views
865 views
File license
Public domain
CT2760-Float3.jpg
Filename
CT2760-Float3.jpg
File size
455.43 KiB
Views
865 views
File license
Public domain

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 1 of 21, by zoinknoise

User metadata
Rank Newbie
Rank
Newbie

nice. i've got a CT2760 here that i'll mod according to your diagrams.

protip for anyone doing the same: recap the card too. you will be amazed how much recapping an old sound card helps quiet it down. the older the card, the better. my CT1350B went from being pretty much unusable, to being an acceptable-sounding card. night and day.

it would be nice if there were some high-end quad opamps out there, like on the level of the LM4562 or even the NE5532. would make upgrading a heck of a lot easier.

Reply 3 of 21, by Tiido

User metadata
Rank Oldbie
Rank
Oldbie

CT3620 has floating opamps in at least one spot :

IMG_9973.jpg
Filename
IMG_9973.jpg
File size
32.77 KiB
Views
724 views
File license
Public domain

I no longer have the card as it got sent to new owner today...

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 5 of 21, by Tiido

User metadata
Rank Oldbie
Rank
Oldbie

In those quad opamps you can do it by shorting the two outer pins (output and negative input) and then the remaining pin (positive input) with middle one (power rail). This creates a buffer connected to one of the voltage rails, and this would stop it from oscillating or doing some other strange things.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 6 of 21, by Eep386

User metadata
Rank Member
Rank
Member

On the floating amps of Sound Blaster 16s, I suggest connecting the positive / non-inverting input to ground, as the amps are *usually* running on a dual supply design (+5V and -5V). You want the signal going into the op-amp to remain 1/2 way between the positive and negative rails in any case. In dual-supply setups like the ones on the cards mentioned, ground is a pretty good midpoint. On a single-supply though you'll want to make a voltage divider (two matching value resistors between positive and ground) and feed the output of that divider (that is, the point where the two resistors connect) into the positive / non-inverting input.

Make sure the inverting (negative) input and output pins are shorted together though.

@Tiido Thanks for finding the floating amp!

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 7 of 21, by Tiido

User metadata
Rank Oldbie
Rank
Oldbie

It isn't strictly necessary to connect things to a ground or some other midscale point, the point is to stop the opamp from misbehaving and connecting an input to some rail will put it into steady state where it will be stabilized and incapable of starting any problems. There may be slightly higher power due to one stage of the output push-pull stage being always on, but the chip is still essentially unloaded so it shouldn't make much difference anyway...

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 9 of 21, by Eep386

User metadata
Rank Member
Rank
Member
Tiido wrote on 2021-02-16, 12:15:

It isn't strictly necessary to connect things to a ground or some other midscale point, the point is to stop the opamp from misbehaving and connecting an input to some rail will put it into steady state where it will be stabilized and incapable of starting any problems. There may be slightly higher power due to one stage of the output push-pull stage being always on, but the chip is still essentially unloaded so it shouldn't make much difference anyway...

I dunno about that... it's my belief that not all op-amps particularly like having their inputs and outputs railed. You probably won't damage the amp per se, but it'll burn more current as you mentioned, and who knows what else might happen if the circuitry behind the output stage doesn't like being driven all the way to the positive rail. The input common mode swing parameter of any given amp is unfortunately a force to reckon with, when dealing with modding audio gear.

The best approach of course would have been for Creative to use dual amps, instead of using quads and then leaving half of their devices floating, or at least integrate their quad amps a bit better, so that no amps are floating. Of course, Creative wasn't really in the business of delivering sound cards that were well-designed...

Cloudschatze wrote on 2021-02-16, 17:04:

For the mentioned instances, what are the measured noise level differences between the uncommitted and the terminated op amps?

I'll have to take some measurements, but I cannot guarantee that my data will be overly useful given my consumer-grade recording gear and relatively limited software (Audacity). Might be enough to show any 'night and day' differences though. It'll involve me undoing the fixes to my sound cards, so that will have to wait til my next solder-rama session at least.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 10 of 21, by Tiido

User metadata
Rank Oldbie
Rank
Oldbie

A low grade opamp will exhibit phase reversal on its output when the input goes out of range but it isn't gonna cause damage or anything. It is a major annoyance with things that actually do something in the signal parth, since the effect is similar to digital overflow and produces loud cracking like sounds.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 11 of 21, by Doornkaat

User metadata
Rank Oldbie
Rank
Oldbie
zoinknoise wrote on 2021-02-14, 01:29:

protip for anyone doing the same: recap the card too. you will be amazed how much recapping an old sound card helps quiet it down. the older the card, the better. my CT1350B went from being pretty much unusable, to being an acceptable-sounding card. night and day.

Sorry for hijacking the thread but since the subject has been brought up: can somebody tell me what to look for in capacitors as replacements in audio applications?
Do I just use general purpose electrolytics? So much audio stuff is marketed with "gold caps" so I'm wondering if this is pure marketing or if there's more to that.
I have multiple sound cards and two 80s amplifiers that started sounding somewhat off and scratchy so I assume the capacitors are on their way out and I'd like to replace them.

Thank you for your feedback!👍

Reply 12 of 21, by Eep386

User metadata
Rank Member
Rank
Member

'Gold' and 'audiophile' caps are just gimmicks, really. I've fitted sound cards with them, and it made no appreciable difference to my ear. Only really measurable difference was the caps look prettier, and my wallet was lighter for it.
Just use a decent brand of aluminum electrolytic caps of the appropriate values.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 13 of 21, by Doornkaat

User metadata
Rank Oldbie
Rank
Oldbie
Eep386 wrote on 2021-02-19, 17:25:

Just use a decent brand of aluminum electrolytic caps of the appropriate values.

Thank you for the response.👍
But how do I know what those appropriate values are when the capacitors have no markings apart from polarity, capacitance and voltage or the series is discontinued and there are no datasheets to be found? Is there any rule of thumb or a go-to-series of capacitors for such applications? This is mainly the question, sorry if my post somewhat blurred that.

Reply 14 of 21, by Eep386

User metadata
Rank Member
Rank
Member

On Sound Blaster 16s, general purpose 85c caps are typically used. A handful might use 105c rated caps in some places, likely due to the factories having those on hand for one reason or another, but high temperature rating is not important for these cards.
Any general purpose electrolytic caps should suffice.

Typically for Sound Blaster 16 cards, I like to use Matsushita / Panasonic M series caps, and Kemet ESK caps as they are relatively cheap and more than adequate parametrically.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 15 of 21, by Cloudschatze

User metadata
Rank Oldbie
Rank
Oldbie
Eep386 wrote on 2021-02-19, 06:30:
Cloudschatze wrote on 2021-02-16, 17:04:

For the mentioned instances, what are the measured noise level differences between the uncommitted and the terminated op amps?

I'll have to take some measurements, but I cannot guarantee that my data will be overly useful given my consumer-grade recording gear and relatively limited software (Audacity).

The RightMark Audio Analyzer might be more helpful than Audacity in this regard. Here's a summary comparison that I'd worked on a few years back, just as an example:

TestComp.PNG

Reply 16 of 21, by Doornkaat

User metadata
Rank Oldbie
Rank
Oldbie
Eep386 wrote on 2021-02-19, 22:03:

On Sound Blaster 16s, general purpose 85c caps are typically used. A handful might use 105c rated caps in some places, likely due to the factories having those on hand for one reason or another, but high temperature rating is not important for these cards.
Any general purpose electrolytic caps should suffice.

Typically for Sound Blaster 16 cards, I like to use Matsushita / Panasonic M series caps, and Kemet ESK caps as they are relatively cheap and more than adequate parametrically.

Great! Thanks again!😃

Reply 17 of 21, by zoinknoise

User metadata
Rank Newbie
Rank
Newbie
Doornkaat wrote on 2021-02-19, 17:42:

how do I know what those appropriate values are when the capacitors have no markings apart from polarity, capacitance and voltage

that is all the information you need when replacing capacitors. they certainly DO NOT need to be the same part, or from the same series, or from the same manufacturer. after all, when i am replacing capacitors with interesting brand names like "Fuhjyuu" and "Chhsi," i want the new ones to be made by a company that's actually reputable. 😀

i generally stick to brands like Rubycon, Nichicon, Chemicon, Kemet and Illinois. Panasonic is my favorite, but sometimes gets expensive. Elna is another good brand but they are always overpriced and i personally never buy them.

don't buy 85 degree caps. buy 105 degree caps. they are built better and they only cost pennies more. also buy "low ESR" capacitors whenever possible. on a sound card, low ESR is not necessary, but if you are like me and you replace a lot of caps on a lot of computer parts, sometimes low ESR is critical, so it becomes economical to only buy low ESR caps in quantity.

and of course, when replacing caps on a sound card, it's important that they physically fit. space is tight. if in doubt, measure the old caps and replace with the same size or smaller. electrolytic caps have gotten a bit smaller since the 80's/90's, so sometimes when you are replacing with the same capacitance/voltage, the new part is physically smaller. don't be alarmed by this.

lastly, if you are VERY serious about replacing the caps on something and you want them to last forever, use tantalums for low values and modern polymer caps for higher values. polymer caps are state-of-the-art low ESR, high temp parts that will practically last forever, but they cost about 10x as much as regular aluminum electrolytics in quantity. so i only use them for REALLY special stuff, like my CT3900. 😀

Reply 18 of 21, by Eep386

User metadata
Rank Member
Rank
Member
zoinknoise wrote on 2021-03-21, 21:08:

don't buy 85 degree caps. buy 105 degree caps. they are built better and they only cost pennies more. also buy "low ESR" capacitors whenever possible. on a sound card, low ESR is not necessary, but if you are like me and you replace a lot of caps on a lot of computer parts, sometimes low ESR is critical, so it becomes economical to only buy low ESR caps in quantity.

...

lastly, if you are VERY serious about replacing the caps on something and you want them to last forever, use tantalums for low values and modern polymer caps for higher values. polymer caps are state-of-the-art low ESR, high temp parts that will practically last forever, but they cost about 10x as much as regular aluminum electrolytics in quantity. so i only use them for REALLY special stuff, like my CT3900. 😀

It's not strictly required to use 105c caps for a Sound Blaster 16; 85c caps work just fine here. Despite the usually low hour ratings (1000 or 2000 at 85c) in the datasheets compared to what decent low-ESR, 105c caps offer, bear in mind those are rated at the quoted temperatures; in your typical vintage PC which seldom exceeds 45c ambient (and typically hangs around ~35c), if they're of reputable manufacture they will last well over a decade just as most of the originals did. I mentioned the Panasonic M specifically as they are usually the cheapest Japanese-branded capacitor money can buy going by Digi-Key prices, and they work well on Creative cards.
Expensive 'long life' caps won't really last that much longer at ambient room temperature either, as beyond a certain point something non-electrolyte related will likely give (such as the rubber bung) long before the electrolyte does.

But if you feel better using expensive caps, then by all means use them. Just don't feel too guilty if you're forced to use 85c aluminum electrolytics on your Sound Blaster 16.
The ultra elite-grade stuff is best saved for things that actually need it, such as the motherboard (when its design calls for ultra-low ESR or long life at rated temperature) or professional audio gear that DOESN'T suffer from amateur design mistakes such as floating op-amps.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 19 of 21, by Doornkaat

User metadata
Rank Oldbie
Rank
Oldbie
zoinknoise wrote on 2021-03-21, 21:08:
that is all the information you need when replacing capacitors. they certainly DO NOT need to be the same part, or from the same […]
Show full quote
Doornkaat wrote on 2021-02-19, 17:42:

how do I know what those appropriate values are when the capacitors have no markings apart from polarity, capacitance and voltage

that is all the information you need when replacing capacitors. they certainly DO NOT need to be the same part, or from the same series, or from the same manufacturer. after all, when i am replacing capacitors with interesting brand names like "Fuhjyuu" and "Chhsi," i want the new ones to be made by a company that's actually reputable. 😀

i generally stick to brands like Rubycon, Nichicon, Chemicon, Kemet and Illinois. Panasonic is my favorite, but sometimes gets expensive. Elna is another good brand but they are always overpriced and i personally never buy them.

don't buy 85 degree caps. buy 105 degree caps. they are built better and they only cost pennies more. also buy "low ESR" capacitors whenever possible. on a sound card, low ESR is not necessary, but if you are like me and you replace a lot of caps on a lot of computer parts, sometimes low ESR is critical, so it becomes economical to only buy low ESR caps in quantity.

and of course, when replacing caps on a sound card, it's important that they physically fit. space is tight. if in doubt, measure the old caps and replace with the same size or smaller. electrolytic caps have gotten a bit smaller since the 80's/90's, so sometimes when you are replacing with the same capacitance/voltage, the new part is physically smaller. don't be alarmed by this.

lastly, if you are VERY serious about replacing the caps on something and you want them to last forever, use tantalums for low values and modern polymer caps for higher values. polymer caps are state-of-the-art low ESR, high temp parts that will practically last forever, but they cost about 10x as much as regular aluminum electrolytics in quantity. so i only use them for REALLY special stuff, like my CT3900. 😀

Thank you for your detailed reply. 😀
I have recapped a couple of PCBs and when I encountered Choyo, G-Luxon, Teapo etc. I stopped looking for a datasheet because even when I found one at all it never seemed very insightful. Instead I opted for the same advice you gave "get something reputable with low ESR" - expecting the circuit to be tolerant.
Since the human ear isn't as forgiving as many VRM designs and because I am completely unable to estimate the influence of the capacitors' properties on the sound the card produces I was reluctant to just use some general purpose caps but I'm more confident after the replies I got.
I hope I do not offend you by asking but what's your expertise in this field?
I have been personally told by electrical engineers that the general online sentinent of

that is all the information you need when replacing capacitors. they certainly DO NOT need to be the same part, or from the same series, or from the same manufacturer.

may apply to many voltage regulation circuits but can be dangerously wrong in more complex circuits and especially in analog applications.
You discern between polymer and tantalum while from my (very limited) knowledge there are polymer tantalum capacitors as well as polymer aluminium capacitors. I always believed the difference between polymer and "traditional" capacitors to be in regard to the electrolyte/cathode material used, not the anode material (i.e. tantalum vs. aluminium).
I have also regularly read (and can not assess the validity of those claims) that due to their different frequency characteristics in most cases tantalum capacitors as well as polymer aluminium capacitors are not a good replacement for "wet" aluminium electrolytics in most audio applications outside of power delivery (although they can be strategically used in new designs).
Since some of your statements contradict what I have heard/read from what I believe to be reputable sources please forgive me for asking. I don't mean no disrespect, it's just hard to know whose word to rely on in the anonymity of the web and I'm often overthinking things.