CVX-2 : covox adapter

Discussion about old sound cards, MIDI devices and sound related accessories.

Re: CVX-2 : covox adapter

Postby dr.zeissler » 2017-3-03 @ 17:33

I will go for a PCI Soundcard instead. Thx!
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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-3-03 @ 20:59

Hi all, the CVX4 pcb's arrived.

I soldered 2 prototypes this evening, one with both 1% 100k resistors, and one with 0.1% 100k resistors, did some blind testing.
As jepeal predicted, 0.1% sounds the best, in fact it sounds amazing through amplified speakers.
I decide to go for the best, 0.1% resistors !!

The dip switches allow to set :
dip 1-5: the low pass filter (my favorite setting is dip 2),
dip 6-7 : volume divider : allows to influence the volume (but not strong enough to connect headphones directly, you do need an amplifier).
dip 8 : DC bypass : in practice, no audible effect on my speakers.

This is the quickly hand soldered 0.1% prototype :
CVX4_PROTO.jpg


Will have a batch assembled professionally, if there is interest.
Last edited by dreamblaster on 2017-3-03 @ 21:17, edited 1 time in total.
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Re: CVX-2 : covox adapter

Postby keropi » 2017-3-03 @ 21:03

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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-3-03 @ 21:23

Bottom side :-)
CVX4_PROTO_BOTTOM.jpg
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Re: CVX-2 : covox adapter

Postby Stiletto » 2017-3-04 @ 01:37

Want to win brownie points in my book? dreamblaster's and reenigne's got the right idea: shoutouts to VOGONS inscribed on the hobby PCB, shoutouts in the credits of demoscene demos. :D
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do the Fandango!" - Queen

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Re: CVX-2 : covox adapter

Postby Jepael » 2017-3-04 @ 01:57

Looks very nice - my only question is why put a tantalum capacitor on audio path instead of general purpose aluminium electrolytic?

You also might want to check which one is cheaper - bunch of 0.1% resistors or one R2R ladder component for DAC applications with guaranteed 0.5 LSB error.

I also built my CVX-3 a while ago, with accompanying 100k 0.1% resistors.
I used 29 of the resistors when building and measured all of them after soldering with a Keithley 2000 multimeter that has not been calibrated for over 10 years.
The average of resistances were 99.965 kohms so either the resistors were just biased towards low end or it could just be the multimeter.
All resistors were within 0.071% of the ideal 100 kohms, or within 0.055% of the measured average.
Four of the resistors were paralleled to make the 25kohm output resistance to ground like in original Covox.
I did not use any filter caps, and bypassed the AC coupling cap (just because I had no suitable electrolytics lying around).

To test I used a game with Covox support (it uses ModPlay unit by Mark J. Cox to play music at max 22kHz).
At first I used very long cable to Cambridge Soundworks 2.1 amplified speakers, and it sounded great at first, but I think it is lacking high frequency content.
Next I tried to record the output with another PC, just by connecting with short cable to line input on motherboard-integrated sound hardware, and this time I think there is too much high frequency content, and I think the PC line input may have some issues with the DC coupled signal.

So clearly the sound quality depends on the cable and receiving equipment due to the large output impedance of the Covox.

On a side note, I know the PC currently driving the Covox is almost too modern - it has 3.3V CMOS output drivers on the parallel port so it can drive huge loads symmetrically.
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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-3-04 @ 08:36

Jepael wrote:Looks very nice - my only question is why put a tantalum capacitor on audio path instead of general purpose aluminium electrolytic?


Well this is a solid (manganese dioxide) tantalum cap : Small, easy to assemble, looks and sounds good, and long lifetime : no need to recap after 30 years :-).
In my setup i did not hear any difference between using and bypassing this cap (you can do so using dip switch 8), but indeed it may depend on your cabling and receiving end.
Anyway could still change if you have any suggestions.
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Re: CVX-2 : covox adapter

Postby konc » 2017-3-04 @ 16:20

dreamblaster wrote:Will have a batch assembled professionally, if there is interest.


I believe interest is obvious!
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Re: CVX-2 : covox adapter

Postby keenmaster486 » 2017-3-04 @ 19:53

konc wrote:
dreamblaster wrote:Will have a batch assembled professionally, if there is interest.


I believe interest is obvious!

Interest?

Are you kidding?

You've got us all like NEW COVOX MUST HAVE NOW
I flermmed the plootash just like you asked.

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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-4-04 @ 18:14

Okay will go for it :-)
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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-4-07 @ 21:26

recorded the crystal dream demo played through CVX4 on PC Punaise (my new retro pc, thanks to PJ, celeron A 533Mhz), sounds good.
--> see youtube video https://youtu.be/V3vJunu6YLo
Visit http://www.serdashop.com for retro sound cards, video converters, ...
OPL2LPT, OPL3LPT, X2, S2, S2P, MCE2VGA, ... many projects !
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Re: CVX-2 : covox adapter

Postby dr.zeissler » 2017-4-08 @ 08:12

interesting that it works with a c533a
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Re: CVX-2 : covox adapter

Postby dr.zeissler » 2017-4-08 @ 17:49

Some LPT-Dac stuff.
Attachments
LPTDAC.ZIP
(904.59 KiB) Downloaded 36 times
CPU: PII 133-333 MOBO: SNI-D981 RAM: 512- FDD: Dualfloppy 3,5"HD/5,25"HD - 3,5"HD - 5,25"DD ISA-Catweasel HDD: 2x40GB - DVD
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Re: CVX-2 : covox adapter

Postby dreamblaster » 2017-4-08 @ 20:31

thanks, I made some recordings using CVX4 on PC Punaise (the 533Mhz Celeron, I disabled secondary cache now) :
- electroman game 1993 : https://youtu.be/QWtn8E2VKhU
- 'dig-ice' demo 1992: https://youtu.be/Pi3KLw_to8Y
- 'physical' demo 1993: https://youtu.be/vvGPcPhEM4I
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Re: CVX-2 : covox adapter

Postby PhilsComputerLab » 2017-4-08 @ 21:44

^^ Nice, very nice!
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Re: CVX-2 : covox adapter

Postby Scali » 2017-4-08 @ 21:47

I guess we can definitely recommend the CVX4 as the highest-quality Covox clone available for the avid retro-gamer.
The biggest problem I see is the price. You can get cheap, crappy clones for about 6 euros. That's a big gap there.
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Re: CVX-2 : covox adapter

Postby keropi » 2017-4-08 @ 22:48

Yeah but the 6eur clones sound nothing like the cvx4 plus they are not machine-assembled. Actually I think that for this limited run the price is good since it's not hand-soldered.
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Re: CVX-2 : covox adapter

Postby Scali » 2017-4-09 @ 08:20

keropi wrote:Yeah but the 6eur clones sound nothing like the cvx4 plus they are not machine-assembled. Actually I think that for this limited run the price is good since it's not hand-soldered.


Yea, but I was thinking, this one is the 'uber' model that lets you fine-tune the sound and everything... Great if you're into that sort of thing, but it will only appeal to a small niche.
If you could make a 'cost reduced' version that just has the 'default' setting that is closest to the real Covox, and no DIP switches or anything (basically what the CVX2 was, just with the right values for all components based on the research and testing we've done since)... if you could get that around 10-12 euros max, it might be an actual competitor for the cheap junk that's available.

I could do a blog on it, show the unit with some pictures, add some sound clips, explain how we analyzed the real Covox, release the tools to stream audio on them, etc.
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Re: CVX-2 : covox adapter

Postby dr.zeissler » 2017-4-09 @ 08:31

https://www.youtube.com/watch?v=D8B1BapyJQc

If someone has this mod-file let me know :) It is one of my all time favorites and would be a really fine test for the CVX4.
btw. I changed some music in the LPT-DAC archive because I did not like some original-music but the gfx, animation. sorry.
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