What is the simplest way, to convert this GC to a subamp?

Franz G · 3rd November 2004, 01:24 PM

I am looking for the simplest idea, to convert this NIGC to a subamp:

- what is the easiest method to filter (lpf 100Hz), eg. use a buffer or not?
- what is the easiest method to mix both stereochannels?

Thanks for all ideas!
Franz

miguel2 · 3rd November 2004, 01:37 PM

In the Pass Labs diy site you find the articlle of el pipe-o with a filter to be connected to output of the main speakers amp.

Miguel

jackinnj · 3rd November 2004, 01:40 PM

try this:

Franz G · 3rd November 2004, 02:39 PM

Do I interpret this correctly?

This circuit is showing a crossover, mixing two channels and using two opamps (like OPA627).

So, I could bridge or paralleling the two output chips in this case.

Franz

carlosfm · 3rd November 2004, 04:38 PM

That's right.
You sum the two channerls, then filter after that.
That way, you use half the parts because you don't need to apply filtering per channel.
On an already-made amp it's more practical to parallel.

EDIT:
Oh.

The summing op-amp has to be inverted.

Franz G · 3rd November 2004, 05:32 PM

Quote:

Oh.
The summing op-amp has to be inverted.

Could you explain this? I dont understand.

Franz

jackinnj · 3rd November 2004, 05:41 PM

maybe we can dispense with the buffer, etc. in their entirety -- although I would hold my breath -- i haven't wired this up:

Franz G · 3rd November 2004, 06:07 PM

3.83M for the feedback resistor?

No, remember the t-net! Too high resitance for a good feedback, nearby 4M!

I think, it is better to use dedicated opamps for filtering, when I look at this circuit!

Many thanks, jackinnj! I will try the first circuit, you showed in this thread.

Franz

carlosfm · 3rd November 2004, 06:45 PM

Quote:

Originally posted by carlosfm
The summing op-amp has to be inverted.

Quote:

Originally posted by Franz G
Could you explain this? I dont understand.
Franz

Sorry, my confusion.
It can be inverting or non-inverting.
But with some requirements, if you don't want to have high DC-Offset.

Here is my sketch from when I made my sub.
I used an OPA2132 as input buffer and then an OPA4228.

Power amp is 2 // OPA549s.

Tube_Dude · 3rd November 2004, 06:57 PM

Quote:

Originally posted by carlosfm

Sorry, my confusion.
It can be inverting or non-inverting.

Hi Carlos

You were right!! A inverting stage is better for summing two channels, because the summing point is a "virtual ground" and don't permit signal leakage from one channel to the other...

À nossa!!

3rd November 2004, 01:24 PM	#1
Franz G diyAudio Member Join Date: Jun 2004 Location: Bern / Switzerland	What is the simplest way, to convert this GC to a subamp? I am looking for the simplest idea, to convert this NIGC to a subamp: - what is the easiest method to filter (lpf 100Hz), eg. use a buffer or not? - what is the easiest method to mix both stereochannels? Thanks for all ideas! Franz

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3rd November 2004, 01:37 PM	#2
miguel2 diyAudio Member Join Date: Jun 2002 Location: Portugal	In the Pass Labs diy site you find the articlle of el pipe-o with a filter to be connected to output of the main speakers amp. Miguel

3rd November 2004, 01:40 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	try this:

3rd November 2004, 02:39 PM	#4
Franz G diyAudio Member Join Date: Jun 2004 Location: Bern / Switzerland	Do I interpret this correctly? This circuit is showing a crossover, mixing two channels and using two opamps (like OPA627). So, I could bridge or paralleling the two output chips in this case. Franz

3rd November 2004, 04:38 PM	#5
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	That's right. You sum the two channerls, then filter after that. That way, you use half the parts because you don't need to apply filtering per channel. On an already-made amp it's more practical to parallel. EDIT: Oh. The summing op-amp has to be inverted.

3rd November 2004, 05:41 PM	#7
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	maybe we can dispense with the buffer, etc. in their entirety -- although I would hold my breath -- i haven't wired this up:

3rd November 2004, 06:07 PM	#8
Franz G diyAudio Member Join Date: Jun 2004 Location: Bern / Switzerland	3.83M for the feedback resistor? No, remember the t-net! Too high resitance for a good feedback, nearby 4M! I think, it is better to use dedicated opamps for filtering, when I look at this circuit! Many thanks, jackinnj! I will try the first circuit, you showed in this thread. Franz

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