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-   -   DCX2496 to TVA to 3 Charlize Amps (http://www.diyaudio.com/forums/class-d/104840-dcx2496-tva-3-charlize-amps.html)

ark 7th July 2007 06:19 PM

DCX2496 to TVA to 3 Charlize Amps
 
I recently purchased 3 DiyParadise Charlize Amps with the intention of using them for each of the outputs on a Behringer DCX2496 Digital Crossover.

The DCX2496 will be modified for a single ended direct output from the DAC. The DAC's direct output is something like 600 ohms
at 6v which is then wired into a 4.7uf capacitor and 1k resistor and rca jack - wired to a passive stepped attenuator (or tva).

So here's my question:
Given this situation, since there is already a capacitor in the output signal path from the DCX to the passive attenuator is the input cap on the Charlize really necessary at all?

And what if I used a transformer attenuator like the S&B tx102 wired DIRECTLY to the DAC no caps then out to the Charlize.. I shouldn't need an input cap in the path from the DCX's DAC to the Charlize at all. The Transformer decouples and provides the ness. isolation. Right?


In that case it would be..
DAC - TVA - Chalize (sans input caps.)

I don't want to burn anything up but don't want to be redundant by placing more than one cap in the signal path.

Please advise.
Thanks!

theAnonymous1 7th July 2007 06:34 PM

I believe you will need the caps on the charlize no matter what. Even if there is no DC in the signal they are still needed to block the 2.5v DC bias on the inputs.

ark 7th July 2007 07:25 PM

thanks! I'm glad i posted this question. I never thought about there being a dc input bias.

ark 7th July 2007 08:06 PM

what attenuator in this config
 
In the configuration above..
Source output 600ohms 6V - what type of passive attenuator would work best between the DCX and the Charlize?


I generally listen at lower volume levels and want attenuators that are optimal for this.

The two I was thinking about and would like feeback on regarding their advantage and disadvantages:

Intact Audio Autoformers? Very interested in these.. the price is right if they are a good fit - although someone once told me that Autoformer attenuators would not be good with the Charlize do to its input impeadance? is this true? If not would love to try this route.

Daven T-Attenuators: I have a few pairs on hand or available a 600/600 ohms pair a 4600/4600om pair and a 50k/50k pair


thanks

soundcheck 18th July 2007 12:37 PM

Hi.

I was running a DAC-TX102-Charlize config before.

With the TX102 in the loop you can't skip input caps on Charlize.
The secondary winding builds a DC bridge to the amp input and the primary to the DAC output.
Finally I connected my DAC directly to Charlize and got rid of one
out of two caps and the TX102.
I also decreased the value of the input cap for the mids and
highs down to 0,047uf. This heavily improved the transient response. At these low cap-values you can get real high quality caps at relatively low cost in the loop.

My volume is controlled via the PC (64bit floats).
This setup beats the prior setup in all aspects (sound quality, cost, handling)

Cheers

ark 18th July 2007 06:37 PM

Thanks Soundcheck. This is interesting.

When you said that you decreased the input caps down to .047uf are you referring to the input caps on the Charlize?

the stock input caps are 4.7 uf blackgates or something like that.

I had read that someone was happy with 10uf paper in oil caps on theirs..

I have 6 each of the following vitamin Q caps on hand..

.47uf
4uf
and 12 uf...

think any of these would work?

what is the effect of a lower or higher value input cap here.. I really am not understanding this part of the amp.

Thanks a lot!

soundcheck 19th July 2007 05:33 AM

Quote:

Originally posted by ark
Thanks Soundcheck. This is interesting.

When you said that you decreased the input caps down to .047uf are you referring to the input caps on the Charlize?

the stock input caps are 4.7 uf blackgates or something like that.

I had read that someone was happy with 10uf paper in oil caps on theirs..

I have 6 each of the following vitamin Q caps on hand..

.47uf
4uf
and 12 uf...

think any of these would work?

what is the effect of a lower or higher value input cap here.. I really am not understanding this part of the amp.

Thanks a lot!

Hi.

The input caps build a highpass with the 20k resistor. It'll depend
on your cutover frequency what exact value you can use.

The smaller the cap, the faster it gets, that's for sure.

I used to use 2 * 0.1 BG NX HiQ Type in super-E config.

Cheers

Pano 19th July 2007 09:49 AM

Quote:

Originally posted by soundcheck
The input caps build a highpass with the 20k resistor. It'll depend
on your cutover frequency what exact value you can use.

Correct-o-mundo! It's just a simple 1st order high pass. Usually the cap value is choosen to set the pole at 10Hz or lower. A 2.2uF cap will do fine for full range.

However, is you aren't using the full range - for example the amp is driving a midrange or tweeter, you can go with a smaller cap. Much smaller, in fact.

Loose rule of thumb. If a 2.2uF cap is good down to 20Hz or below, then a 0.2uF would be good for 200Hz and a 0.02uF for 2Khz. The idea here is - if you don't need those bass frequencies, why waste the power? The smaller cap will help keep you out of clipping, too. And that's a good thing.

A really big cap, like 5uF and up will give you a big turn on pop at power on. Unless you have a soft-start circuit.

You do need a cap to block the 2.5V input bias coming from the Tripath chip. You can only get away with no cap if you are very careful about your circuits and paths to ground on the inputs - there can not be ANY.

ark 19th July 2007 10:39 AM

thanks. since i am trying to make the three amps uniform to use the dcx for learning (and modeling conventional xover configs)...
perhaps i should use the 4uf vitamin q caps?

would these be better than the black gates that are in there?

i do have 6 of them.

also .47s vit-q's on hand

and some others.. some 2.2 paper in oils (russian)


do plan to use a soft start circuit basically one that takes the amps accross 6volts first then up to 12 (battery power)

AndrewT 19th July 2007 11:57 AM

Hi,
I recommend that the DC blocking cap be sized to allow a decade below your lowest usable frequency.
For 20Hz use 4u7F & 20k
for 3kHz use 27nF & 20k


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