CVX-2 : covox adapter

[dreamblaster]

R2R ladder if you find suitable and affordable. We could make a solder kit.

[Scali]

R2R ladder if you find suitable and affordable. We could make a solder kit.

Would it be one of these? https://nl.mouser.com/ProductDetail/Bou ... X0%2fPY%3d

[Jepael]

R2R ladder if you find suitable and affordable. We could make a solder kit.

Would it be one of these? https://nl.mouser.com/ProductDetail/Bou ... X0%2fPY%3d

I think that would be good, except the minimum order is ten thousand because most suppliers don't have these in stock and they have to place order to a factory.

I think Jameco was able to sell some R2R-104 devices in multiples of five.

[Scali]

I think that would be good, except the minimum order is ten thousand because most suppliers don't have these in stock and they have to place order to a factory.

I think Jameco was able to sell some R2R-104 devices in multiples of five.

I couldn't find any on Jameco, but some googling found me this: https://www.onlinecomponents.com/bourns ... gipartFeed

[Scali]

Mouser does seem to have these, sold separately:
https://eu.mouser.com/ProductDetail/Bou ... ent=Bourns

[QBiN]

I would buy one if another batch is made.

Same here! I missed out on the first CVX4 run and am eagerly awaiting the next.

[Scali]

CVX4 got mentioned on Adafruit!
https://blog.adafruit.com/2017/12/01/cv ... ing-clone/

[dreamblaster]

CVX4 got mentioned on Adafruit!
https://blog.adafruit.com/2017/12/01/cv ... ing-clone/

Yeeha ! great

[dreamblaster]

I will inform for a new run of CVX4.

[matze79]

why not use Resistor Networks ? less pain to solder

[Scali]

why not use Resistor Networks ? less pain to solder

The goal of the CVX4 is to sound as good or better than the original Covox.
I suppose we'd need to have some prototypes first with resistor networks, before we can decide whether or not they are an accurate replacement for the discrete resistors used currently.

[Paralel]

As I mentioned earlier in this thread a Covox Speech Thing clone, the "SoundJr" uses:

"767163103 and 767163203, or 8A103 and 8A203 surface mount resistor array ICs"

and it has the following features:

"Level Control: 20 dB/ 8 Step software control
Frequency range: DC to 15KHz
Sample Rate: Set by software, typical 100s/s to 20Ks/s, 100Ks/s max.
Digital Code: 8 bit Linear PCM + 3 bit range"

It has roughly double the frequency range of the discreet R-2-R ladder Covox design, as well as volume control, and runs strictly off of LPT power.

I can say with certainty, the sound output is very nice as well as clean.

I would say, without a doubt, the SoundJr. resistor array IC design is the pinnacle of the Covox Speech Thing's potential. I don't think one can do better than a surface mount resistor array IC, as far as integration and simplification of components and design.

[Scali]

It has roughly double the frequency range of the discreet R-2-R ladder Covox design

What makes you say that?
Technically, the only limit for the frequency range of a Covox is the speed at which the CPU can bang out the samples through the printer port.

[gdjacobs]

Unless the circuit being driven has a low maximum slew rate.

[Paralel]

It has roughly double the frequency range of the discreet R-2-R ladder Covox design

What makes you say that?
Technically, the only limit for the frequency range of a Covox is the speed at which the CPU can bang out the samples through the printer port.

I don't honestly remember the calculation, but given the design of the R-2-R covox I remember someone calculated that the frequency range for it topped out somewhere around 7 or 8 KHz.

Also, aren't you talking about sample rate, not frequency range? The rate at which samples can be transmitted by the CPU to the Covox is the sample rate, no?

[Scali]

I don't honestly remember the calculation, but given the design of the R-2-R covox I remember someone calculated that the frequency range for it topped out somewhere around 7 or 8 KHz.

Are you sure you're not confusing the Covox with the DSS?
The example recordings at 44.1 kHz with the CVX4 should make it very obvious that it is not limited anywhere near 7-8 kHz.

Also, aren't you talking about sample rate, not frequency range? The rate at which samples can be transmitted by the CPU to the Covox is the sample rate, no?

Well, the maximum frequency is a function of the sample rate, namely the Nyquist frequency: https://en.wikipedia.org/wiki/Nyquist_frequency
So with our 44.1 kHz samples, the Covox should be able to produce 22.05 kHz max.

[Paralel]

Yeah, but has anyone tested to see what the actual cut off for the frequency range for the R-2-R covox is? Can it actually output a 22.05 KHz frequency?

I'd actually suggest maybe 15 KHz as a test. None of us here can probably hear into the 22 KHz range. If someone in their early to mid 20's can test the 15 KHz frequency that should be sufficient.

Generally speaking, anyone in their 30's can't hear beyond 15 KHz, and that's only if they have taken good care of their hearing. Hearing loss down to 8 KHz by the age of 40 is not uncommon in the west, which isn't a big deal, because nearly every natural source of sound we hear in everyday life is 8 KHz or below.

[Scali]

Yeah, but has anyone tested to see what the actual cut off for the frequency range for the R-2-R covox is? Can it actually output a 22.05 KHz frequency?

The Covox has no filter at all (and the CVX4 also has a no-filter setting). So theoretically there is no cutoff.

I think the easiest way to verify is just to create a test sample, play it back with CvxPlay and record it with a modern sound card that is high-end enough (like a 24-bit 192 kHz card, that should easily pick up 20+ kHz).

[gdjacobs]

The DAC circuit will have some reactive behaviors (i.e. parallel capacitance and serial inductance) that will naturally limit it's maximum rate of operation. This can, of course, be optimized and is unlikely to be a limiting factor for any period CPU.

[matze79]

My R2R DAC build from 0,1% Resistors playing MI Theme.
100nf Capacitor.

r2rdac.ogg

(1.65 MiB) Downloaded 15 times

Its pretty good for only Resistors.. its even hard to beat it with IC DAC.

i expect the CVX-4 also sounding similar but i don't have one

Also added Chip DAC for comparision, its has no filtering also and a TDA7050 Amp.
I will improve it in next few days.

chipdac.ogg

(1.89 MiB) Downloaded 10 times

The ChipDAC of course has more highs.
The noise is from the amp.
The build is not yet done.. i will improve it with Opamp on Output etc.

original track:
http://www.tentakelvilla.de/download/curse.zip

The Player used:
https://github.com/yeokm1/covox-music-player
http://yeokhengmeng.com/2017/01/a-scien ... g-to-2017/