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Old 3rd November 2009, 06:56 PM   #721
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Default Tone Control Questioned

Hi Geatan/and others,

Why was it not immediately apparent how inadequately a non-inverting gain-stage (op-amp) performs in a tone control application where symmetry in potentiometer setting (boost/cut) and linearity is the objective?

The graph of HAKSA tone control shown in your post is not at all representative of a tone control using a non-inverting gain-stage with the tone network in the feed-back loop.

I am sorry if I am being hard on you Geatan, but it is unfair to other readers of this thread (not having the skill to question) thinking that what they are going to build is a symmetrical bass & treble control (which is what your graph shows) while this is not the case at all.

Besides to achieve a "semi flat" response with the current design, the controls would have to be set closer to a 2 or even 3 o'clock position and not a 12-o'clock position that one would expect to achieve a flat response.

The objective of a group design is for skilled members to highlight problem areas and offer possible solutions.

The current tone control in my opinion is inadequate and the weak link in this simple HAKSA design. If nothing else I would encourage it to be a simple passive circuit and humping up the amp gain to counter for the losses.



Kind regards

Nico
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Old 3rd November 2009, 07:00 PM   #722
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Quote:
Originally Posted by AKSA View Post
Thanks Gaetan!

Very nice graph, you did that in Tina?

When you gun for more cut/boost with the circuit used in the HAKSA, when controls are flat there are serious discrepancies in the FR. With the values chosen, there is no such effect, but cut/boost are limited, also by the non-inverting issue, which is not usual for a conventional Baxandall and I wanted to avoid. Without the small 22pF cap on the fb loop of the opamp, there is serious gain peaking, but with it, all is well.

Merci,

Hugh
I am sorry Hugh, but I do not agree with you. See previous post.

Nico
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Old 3rd November 2009, 07:58 PM   #723
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Default Response Curves for inverting & non-inverting comparison

This is what I am trying to show, the difference between the response curves for the bass and treble control utilising either non-inverted and inverted feed-back configurations.
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Old 3rd November 2009, 08:11 PM   #724
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Default Response Curves for inverting & non-inverting comparison

What I am attempting to demonstarte is the difference between the response curves for the bass and treble control in the feed-back loop utilising either non-inverted and inverted configurations.

You can clearly see the non-linear operation of the tone controls in non-inverted mode.

On the other hand if this appeals to you then so be.
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Old 3rd November 2009, 09:40 PM   #725
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Some thoughts for the day

In my humble opinion, if one's objectives are that of wanting to listen to reality, then strict engineering sciences are applied with know quantities and a predictable outcome.

Audiophile hocus pocus has been for years trying to justify their existence using buzzwords such as focus, clarity, pin point, sound stage and all the other cr@p that they imagine but what audio engineers have been enjoying since the outset.

Imagine watching TV and fiddling with the chroma, contrast, etc to obtain a picture that you like and then walking into nature and seeing that it is totally different, then obviously nature must be wrong because the TVphile proving this to himself that he is right.

Take your audiophile hocus pokus equipment if you are not afraid, record the birds and animals and then play it back, see what you attract and scare away. The outcome is that your hi-fi equipment was designed by Audio Wizard so-and-so obviously the birds does not appreciate his subjective skills or generally birds are deaf.

The best fire-walk for your equipment is to grab your guts together, creep up on a lion male and record his call. This has been proven to be heard over 5 km away as food becomes very nervous even at that distance. Now replay what you have recorder and see if any food would be nervous at 5km away or are they just continuing as normal. The conclusion probably would be antelopes are deaf but they small the lions breath and get nervous.

My dog is totally afraid of fire crackers, try recording them and playing it back, how is the response of the dog who actually reacts on an audio signature not whether it is a warm cracker, a focused cracker, crisp cracker, an over dose of 2nd Harmonic and some feed forward compensation cracker, or a deep solid cracker.

When I do a cracker on my system the dog vanishes into thin air.

The same applies with tuning a car engine by ear or by sophisticated analysers thinking the hocus pocus guy is going to win the grandprix. No chance, the best engineering team is.

One should remove the jargon and Black Magic from amplifier design and rely on engineering science and first principles when developing a product leave guessing to those ill informed. Do something with conviction, do it properly and do it right (first time is nice)

These audiophiles have to first sell you the jargon and other hocus pocus, there after you are so tired that you buy the product untested becoming a disciple of the cult.

I told Hugh about my final amp I built. It was playing in the background when a Buddy/business associated walked in, stood still for about ten seconds and said I will give you $35000 for that. I was not even playing anything spectacular nor did I object and immediately proceeded to move the equipment to his house. I never had to tell him to listen to this or that, it was clearly the perfect product.

I say steer away from hocus pocks because if you do not, for the rest of your life you will have to prove to yourself that what you have is good while it is totally mediocre.

Nico
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Old 3rd November 2009, 11:40 PM   #726
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Quote:
Originally Posted by Nico Ras View Post
Hi Geatan/and others,

Why was it not immediately apparent how inadequately a non-inverting gain-stage (op-amp) performs in a tone control application where symmetry in potentiometer setting (boost/cut) and linearity is the objective?

The graph of HAKSA tone control shown in your post is not at all representative of a tone control using a non-inverting gain-stage with the tone network in the feed-back loop.

I am sorry if I am being hard on you Geatan, but it is unfair to other readers of this thread (not having the skill to question) thinking that what they are going to build is a symmetrical bass & treble control (which is what your graph shows) while this is not the case at all.

Kind regards

Nico
Hello Nico

The first simetrical graph was the Quad 34 preamp as I said, comming from Quad web site.

So I never said that Haksa tona amp graph was simetrical, but that it was less strong boost that the Baxandal type tone control.

And for the simulation I can't do other sim since my Tina-Ti simulator don't work properly.

Bye

Gaetan
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Old 4th November 2009, 12:12 AM   #727
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Excellent rant, Nico!




We are on the same page, I think.
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Old 4th November 2009, 12:24 AM   #728
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Nico,

Your virtual earth and crossfeed contributions have been both excellent and gratefully received. I believe we are all grateful for them.

I did not want a tone control for this circuit to begin with, but clearly it was a desired feature and so I agreed. You and I have discussed audio engineering at length and agreed that phase shift, filter or no filter, is undesirable. The non-inverting tone control, at the expense of a large control range, offers tiny phase shifts with gentle, albeit asymmetrical control, and that was, and remains, my choice. Set flat, there is almost no tone alteration and vanishinly low phase shift to the point where a defeat is not strictly needed. Correcting for mid-point flat setting should be easy with the output fixed resistors. Inverting the signal, right or wrong, is regarded by most in audio as a bad thing (although it can be remedied easily with a simple speaker lead swap) so I favoured that aspect too.

I think all here recognise your consummate abilities as an engineer. Low distortion is desirable, no question, but many high distortion circuits, notably single ended Class A, sound pretty good too, so there would appear to be more to it than very low THD20. Gaetan was using Tina for his simulations - flawed by his own admission - so I don't believe he should be upbraided for his post. No one is trying to be a 'guru' here, or a smartarse, so I'm at a loss to understand why you are invoking the high priesthood and highlighting the hocus pocus aspects so strongly. That is very alienating, and it is most unlike you.

Until I have a better option, I choose to continue with this tone tilt circuit for the reasons given, but I am grateful for, and will use, both your crossfeed and the virtual earth concepts. I'm hoping you will still be willing to lay out the pcb, too.

With thanks,

Hugh
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Old 4th November 2009, 12:59 AM   #729
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I agree with Nico's arguments, but I feel he set himself up to be misunderstood, and also went off-topic.

Nico seems to have observed how most of us seem to be either pulling teeth or picking out small things that aren't really important. I think it angers him that we aren't being very strict logically and are unorganized; we have made many guesses where it would have been simpler and faster to pull out a calculator. I've felt the same frustration, so I think I can relate to Nico.

I don't see an issue with the odd tone controls as long as the signal itself isn't distorted.

- keantoken
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Old 4th November 2009, 03:11 AM   #730
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KT,

This is always the price of design by committee. While it is true you can't keep everyone happy, when tempers fray wheels fall off the wagon, and there is absolutely no need for heated argument. Progress is slow, and people's expectations can be inordinately high in terms of quality and time to market, but it's just not possible to move quickly on these things, precisely because we do want it engineered right.

John, if you are not happy with proceedings you might like to suggest an improvement. I believe you realise we are happy to listen and will pay due attention.

This is a hobby project. It is not a money spinner, but it will be properly done. That will take a bit of time. Please keep the constructive comments coming.

Cheers,

Hugh
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