Input transformer for Pascal S PRO2

[Kjeldsen]

I haven't done measurements in like 20 years, when i studied electronics. But, I hope it's common knowledge that electronic components have to settle in (stable temperatur etc). I finally decided another road, and am now in finance

I have never been able to tell a difference over several day. With a completely cold amplifier, not used in several days, I can hear a difference after one or two hours.

 

[JohnnyInBris]

I would like to introduce a filter stage between the Jensen JT-10-KB-D and
the Pascal S-Pro 2 module to limit bandwidth reaching the S-Pro 2.

How do I calculate this, I have a input resistance of 2k2 on the module, a DCR from the transformer secondary of 91 Ohm in parallel with the 2k2.

Can I just put a cap parallel to this or would this create a problem because
of the inductance of the secondary of the transformer?

Would a Zobel be a better solution?

Someone from JRDG mentioned that to get the best out of a class D amplifier
it would be good to limit the incoming bandwidth to the module.

Please advice,
Thanks

A 1K series resistor on the input side of the transformer and 2.2nF cap in parallel with the secondary (assuming 4:1 transformer ratio) will give a 3dB cutoff at 38KHz.

A Zobel can be useful to dampen resonances caused by transformer leakage inductance but either a complete spice model of the transformer or trial and error with an oscilloscope is needed.

 

[Veeren]

Thank you very much JohnnyInBris!
Thank you Arthur for the Lundahl pics!

 

[Cal Weldon]

Commercial posts in non-commercial areas are not permitted.

Post removed.

 

[jencelo]

@Eva: I have ZERO experience making and/or understanding about amps or any electronic equipment. However, I know something; the specs do not mean much as long as the sound is good to your ears.

1965 Mercedes does not have good specs as the 2018 Mercedes but which one is more fun to drive is up to the driver.

 

[biagio79]

Hi,
does someone have a pinout of the mentioned pascal s-pro2 connector? Which are the input pins?

 

[Kjeldsen]

you can find the pin outs in this document

https://www.madisoundspeakerstore.com/pdf/Accuton_DSP192-4-111_manual.pdf

 

[biagio79]

Thank you!

 

[Guerilla]

There is a little group in Denmark, also trying to designing the ultimate class D right now. It's always fun follow such projects[/QUOTE]


Kjeldsen could you tell on which forum and thread this group is roaming?

 

[Kjeldsen]

hifi2you but the one participating is no longer on that forum (kurt von kubik is one of his forum names). I think he can be found on Nerds as well. The group also made a DAC, and had a facebook site covering this project. They also made som modifications the a TC Electronic class d module and sold some of the modifiedes modules

 

[Manro]

Hi Veeren,
you wrote:"I bypassed all the electronics of the STA 1000D input module, not difficult to do just remove 4 resistors and 2 coupling caps." Can you or someone please explain what happens with this and about the location of the resistors and Caps on the input?

 

[Subtonal]

Hello,

i also would get some more informations please.
I own the IMG STA-1000D and so far it performs good.
When i interpret the J7 connector right the Pascal S-Pro2 does
has an unbalanced input right?
Would like to replace that IMG input module but also like to do
bridged mode eventually.
Anyone here uses/modded STA-1000D/2000D ?
greetings Subtonal

 

[Veeren]

Hi all,

Now that I have more information on the S-Pro2 it seems that the input impedance is not
2.2k Ohm but 47k Ohm with 2.2k Ohm in series, see schematic attached.
The schem. also reminds me to check weather the IMG Stage Line STA1000D has its channel 2 input and output reversed...


Yes Subtonal the input of the module is unbalanced.

 

[Veeren]

Somehow the schematic is not loading, here it is again.

 

[Kjeldsen]

Don't be to disheartened about this module, I am driving it now from a ALIENTEK D8 headphone output with good results so far.
I bypassed all the electronics of the STA 1000D input module, not difficult to do just remove 4 resistors and 2 coupling caps.
Careful though,by doing this no DC should be present from your source unless you leave the input board`s output coupling cap in place.
Be very patient, this module requires 500 to 1000 hours to burn in
Please read about it on this forum thread:
Class D = Trash? | Audiogon Discussion Forum
You will loose warranty by doing this unless it is done reversible and invisible
when the need for repair arises...
I am not taking any responsibility for what you do to your amp!

Headphone output is normally pretty low output Z, so this should work well with low input impedance

 

[Veeren]

Yes it works well like that but heed to EVA´s warning that it needs a input buffer otherwise you might blow something up connecting and disconnecting the module to a source.
That is why I used an input transformer.

 

[Kjeldsen]

I never connect or disconnect sources with active electronics. For all the years I have worked with hifi, this have been a no-go.

 

[Veeren]

Yes same here usually but sometimes a power cut that happens here occasionally could send something nasty into the module.

 

[Manro]

Hi, at the Moment i use s-pro2 without a Input transformer.
How set the module to bridge Mode (BTL4 Ohm Pin to Ground is this all?)and what to do (in simple way) to Invert CH2 input?
Thanks

 

[Veeren]

Hi Manro, the original input board uses a extra op amp to phase reverse one channel.
Without an op amp or transformer I would not think that is possible unless you have a balanced source where you can invert the phase.