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Old 28th September 2011, 12:53 AM   #41
Reality first!
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Quote:
Originally Posted by madisonears View Post
Here's an idea: add one more pad to the right of C13, with a trace to the input path. Label it "DC signal" so that builders can make both AC and DC connections. The label about a jumper wire (and the jumper itself) is then not needed.
Hi Tom,

it's a nice idea but Mauro warned me about leaving off C13...

C13 is required for maintaining the correct beahviour of the amp (or better the specced performance), so I don't want that someone could think the coupling cap can be avoided.

I think in this way is more clear and if someone still wants to use it DC-coupled it is however possible (although not recommended).

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When will you be ready to have a prototype made?
If we are fine with the zener regulator we can order prototype PCBs tomorrow...

In fact I was thinking about doing an alpha run and test the candidate regulators on it...maybe.

Are you willing to partecipate?
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Old 28th September 2011, 03:49 AM   #42
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Dario,

You have recently emphasized the importance of C13 to the proper operation of the amp. I accept that, but then it calls into question the process of testing for the best candidate for C13 by comparing it to the sound of the amp without C13. If the amp doesn't perform properly without C13, then the sound of a cap closest to that is not the "proper" or best sound. Do you understand my concern? I have never tried an amp without a C13 in place. I judged my C13 candidates by what I think sounds most realistic.

If you want someone to build an amp from a prototype board, I would be willing to do that. My only problem is that my new speakers are still not satisfactory (active crossover phase difficulties between bass and mids/highs). I hope to have that resolved soon. In the meantime, however, I would be able to evaluate the mid and high frequencies of the amp (200Hz and above is superb), and I have access to other quality systems where it could be run full range.

Peace,
Tom E
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Old 28th September 2011, 10:03 AM   #43
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Originally Posted by madisonears View Post
You have recently emphasized the importance of C13 to the proper operation of the amp. I accept that, but then it calls into question the process of testing for the best candidate for C13 by comparing it to the sound of the amp without C13. If the amp doesn't perform properly without C13, then the sound of a cap closest to that is not the "proper" or best sound. Do you understand my concern? I have never tried an amp without a C13 in place. I judged my C13 candidates by what I think sounds most realistic.
According to Mauro C13 and R13 define the current presented to the inverting input of the LM318, which is very sensible to that current.

What changes, if I've understood correctly, is the dynamic impedance (in fact with DC coupling the bass response is the most affected).

So comparing a cap with DC coupling makes sense for quite all but timbre and, maybe, dynamic. (particularly bass response), IMHO.

Thus I consider my results with C13 still valid.

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Originally Posted by madisonears View Post
If you want someone to build an amp from a prototype board, I would be willing to do that.
...
and I have access to other quality systems where it could be run full range.
Wonderful!

Stay tuned...
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Last edited by ClaveFremen; 28th September 2011 at 10:07 AM.
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Old 28th September 2011, 11:17 AM   #44
AndrewT is offline AndrewT  Scotland
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Originally Posted by ClaveFremen View Post
...........it's a nice idea but Mauro warned me about leaving off C13...

C13 is required for maintaining the correct beahviour of the amp
complete balderdash.
No one is suggesting converting the AC coupled My RefC to mixed AC & DC coupling. Which I never recommend.

The C13 bypass allows the user to choose which DC blocking capacitor to use when the source equipment already has an output DC blocking capacitor.
It's your responsibility to spell out the advantages and the dangers in the build manual. This then allows builders to make their own informed decisions.

Following someone else's AC coupling recommendation without passing on the facts is not a "service" to the DIY community.
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Old 28th September 2011, 11:32 AM   #45
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The C13 bypass allows the user to choose which DC blocking capacitor to use when the source equipment already has an output DC blocking capacitor.
It's possible also with the actual layout.

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Originally Posted by AndrewT View Post
It's your responsibility to spell out the advantages and the dangers in the build manual. This then allows builders to make their own informed decisions.
It will be explained in the build manual, no problem about it.

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Originally Posted by AndrewT View Post
Following someone else's AC coupling recommendation without passing on the facts is not a "service" to the DIY community.
Mauro is not 'someone else', he is the designer of the original circuit... and he warned that without the 1uF input cap it doesn't work as intended.

If someone prefer to not follow his recommendation about it he's free to do it, the PCB layout still allows it but I don't want to make it 'easier' as it could be read as a suggestion to do it....
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Old 28th September 2011, 11:56 AM   #46
AndrewT is offline AndrewT  Scotland
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I think you have completely missed the technical aspect of Mauro's statement. The point you are failing to recognise is that the DC blocking capacitor does not need to be located on the amplifier PCB.
The DC blocking capacitor can be on the PCB, or off the PCB but inside the amplifier case or in the cable connecting Source to Amplifier or inside the Source equipment. Any of these locations will effectively block the DC route and all of them work technically identically.

The on board C13 can have an optional bypass and then the source equipment takes over the DC blocking duty. Used this way the MyRefC works exactly as Mauro is telling you it should.
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Old 28th September 2011, 12:24 PM   #47
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Simple question for Andrew - What if anything results when two or more components in a system are trying to assume the DC blocking duties? Does one or the other take priority or are they maybe additive?
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Old 28th September 2011, 12:29 PM   #48
AndrewT is offline AndrewT  Scotland
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It's addition of series connected capacitors.

Apply the formula and use the result to see the effect on the Passive Input Filter.

If one of these capacitors were of reputedly very high Audio coupling quality and the other were devoid of this attribute, then it is very likely the low quality parameters would dominate the resulting sound at the output.

It is for those reasons I advocate dual outputs and dual inputs for amplifiers and sources respectively. The dual facility incorporating the DC blocker bypass, allows one to listen to the three alternative DC blocking situations:
a.) Source DC blocker acting alone.
b.) Amplifier DC blocker acting alone.
c.) Series combination of both DC blockers acting on the sound output.

Note that nowhere am I advocating removal of the DC blocker at the input. That DC blocker is and should be part of the amplifier design and the Designer should have taken account of it at the design stage to achieve his desired performance characteristics. That meets with Mauro's intent in his statement.
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Last edited by AndrewT; 28th September 2011 at 12:59 PM.
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Old 28th September 2011, 12:53 PM   #49
bcmbob is offline bcmbob  United States
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Thanks Andrew - a bit further concerning "acting on the sound output". I'm assuming you are referring to sound quality in that phrase. Is this the same "DC' that has the potential to destroy the voice coil in a speaker or is that "blocking" handled by a separate section of the MyRef and/or what you understand of Dario's new design?
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Last edited by bcmbob; 28th September 2011 at 01:00 PM.
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Old 28th September 2011, 01:01 PM   #50
AndrewT is offline AndrewT  Scotland
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Speaker damaging output offsets are a different issue. I believe that comes within the more general topic of Protection

And yes, sound quality.
Quote:
the low quality parameters would dominate the resulting sound at the output.
Sorry if I was ambiguous.
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