T-network: the better feedback solution?

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#141
Does the same apply to using resistors in amplifiers?
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Well, using that analogy, I think that we should say that each GC should consist of at least three different types of component! 😉

Back to the resitors, and if we accept that a type of resistor has a signature, then if we use 3 of them, that signature should be more prominent. On that basis, it may make sense to mix resistor types to avoid any one signature becoming predominant.

Carlos will no doubt add to this when he is back from the wine bar where he is sampling three different wines! 😀
 
#142
Nuuk said:


Well, using that analogy, I think that we should say that each GC should consist of at least three different types of component! 😉

Back to the resitors, and if we accept that a type of resistor has a signature, then if we use 3 of them, that signature.... 😀
Click to expand...

I have an idea for a replacement to tone controls, switchable series resistors between, for example, preamps and power amps?

Ahem, I wonder why, in the very system I am listening to now, I have absolutely no desire to change resistors. Am I missing something. I'm not saying they don't make a difference, that's not the point I'm making. It's just that I have been working on mechanisms that has made a lot more impact than just twiddling with resistors. That's more of a fine tuning process, there are other priorities that cannot be ignored.

Lately I have been tweaking a discrete buffer circuit used in first generation Sony SACD Players (like the veritable SCD-1), and gotten improvements that no change of resistor could ever achieve. In fact it sounds so good and its strengths are apparent even when using cheap Taiwanese MF resistors. It's just that it puts things in the right perspective for me. Now use better components and sure enough, there is the expected incremental improvements. Like getting better pots as they ARE more coloured than resistors. I prefer genuine tin foil caps rather than metalised etc.

OK, tell me to duck... I see the missiles coming.

Joe R.
 
#143
Nuuk said:
A word of warning may not go amiss here. The T-feedback experiment will usually involve soldering to the pins of the chip and then removing the resistor again later. We know how fragile the pins can be so extra care must be taken when doing this work.

That's the main reason that I have decided to do my T-network experiment with a new GC! :att'n:
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Now you seem to be getting where I knew P2P advocates for DIY projects would be one day!

Do use a pcb for your next GC, with large pads where gain resistors should be. That is one reason why I also prefer pcb designs where copper areas are very large, and not just the ground area.


Carlos
 
#145
Nuuk said:
A word of warning may not go amiss here. The T-feedback experiment will usually involve soldering to the pins of the chip and then removing the resistor again later. We know how fragile the pins can be so extra care must be taken when doing this work.

That's the main reason that I have decided to do my T-network experiment with a new GC! :att'n:
Click to expand...

hmm, you can mount resistors vertiacally on the board. i fit 2 of these hi3gc's onto a 1.2" x 2.2" pcb with fairly good results. 70mV DC offset was the only issue. chip was lm4780.

edit -- ok, i misunderstood the original meaning.
you could wire the 3 resistors over the board though, not needing to solder to IC pins (unless you normally needed to.)
 
#146
Nuuk said:
Carlos will no doubt add to this when he is back from the wine bar where he is sampling three different wines! 😀
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I was finishing my pre.:bawling:
😀
Got up early this morning and did 30 km by bike.
After listening to the pre.😀

Joe Rasmussen said:
OK, tell me to duck... I see the missiles coming.
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Not at all, I agree completely with your post.
Sometimes changing the value of a resistor makes more improvement than changing the brand of the resistor.
The place where to put a particular resistor is important too.
Instead of spending big money on some passive components, one should be more careful with the design an layout.
IMHO.

Oh, thanks for the tip on the Alpha pots, joe.
Cheap and very good indeed.
Not easy tweaking for something "better", definitely.😀
 
#147
Sometimes changing the value of a resistor makes more improvement than changing the brand of the resistor.
The place where to put a particular resistor is important too.
Instead of spending big money on some passive components, one should be more careful with the design an layout.
Click to expand...

Carlos

I could subscribe this statement.

I use NOX 1% resistors, cheap and ok. You could use carbon resistors as well, as it is not a phono or other pre with very high gain.

It is an advantage, to use a t-network with low resitance values, composed of cheap and common resistors, instead of one very high quality resistor with high value!

Franz
 
#149
I'm not saying they don't make a difference, that's not the point I'm making. It's just that I have been working on mechanisms that has made a lot more impact than just twiddling with resistors.
Click to expand...

Joe, I agree. It is much better to get the important things correct and then fine tune later. I was just suggesting (in answer to the question put) a sensible way of choosing the resistors for those that are worried about that sort of thing. 😉
 
#151
Nuuk said:


More Portuguese humour Carlos? 😀 (Yes I realise that you are the 'other one' 😉 )

Seriously, who has a PCB to acommmodate the extra two resistors? As soon as anybody designs a PCB for the GC, the circuit changes again!
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Of course that is always a problem. But it's much easier to deal with pads, especially if they are large, than with pins.

To those having designed a pcb for an IGC, like I did, it will only be a matter of doing a "three resistors tree" and soldering the extremes accordingly. It might be a lot trickier to those what P2Ped.

I always knew this DIY forum on chip amps would take us further on, and having good copper space to allow for that would be necessary.

And this is particularly better if you have a single side pcb. 😉


Carlos
 
#154
#155
#159
I changed my mind.
I was going to try T-network and tube buffer with LM1875s.
But to be a more direct comparison with what I have on my main system, I decided to do this with the LM3886.
It also allows me to easily use the muting feature of this chip, at power-on, while the tube gets warm.😎
I should start this in a week or two, after finishing some things.
 
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