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Old 5th March 2011, 04:11 PM   #1
grakka is offline grakka  Sweden
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Default pros and cons for different builds/constructions

I've been reading so much about different types of.. anything and everything regarding chipamps lately and it's of course impossible to say that one thing is better then the other due that everyone have different ears and taste of sound. But one thing that you can compare would be the technical advantages and disadvantages of things used while building a gainclone. E.g different type of caps and resistors and how things technically affect the sound.

One thing that I've been thinking much about lately is the difference between a snubber psu and a non-snubber (could you say "normal"?) psu. This is my conclusion that I made by reading several threads around here, and I would like to hear what you more experienced people have to say about it.

Snubber psu:
+ Better dynamic characteristics due to quick and easy access to power.
+ Less distortion in mid & high due that power won't flinch at much dynamic.
- Mid & high may be colored due to higher resistance.

Non-snubber psu:
+ Transparent sound in mid & high due to less resistance and less components.
- Worse dynamic characteristics and no impact due to lack of fast/much power.
- Risk of distortion at the dynamics due to lack of power and the mid & high can't be well fed at the same time as low.


There are some other things that I would like to know the pros and cons of too.

1. Will the capacity be counted as the half of the total value if you are using a stereo amp instead of a dual mono? In my case, i have a dual mono kit from chipamp which of course includes two psu boards. There should therefore be a characteristics difference between the stereo and dual mono kit. I am thinking of building a new stereo amp instead of my current dual mono and I am afraid that I will lack dynamics due to the less power capacity. Anything technically better then the other?

2. Can less capacity be counterbalanced by more power from the trafo? E.g a dual mono amp with two 150v trafo compared to a singel 300v trafo in a stereo amp.

3. Pros, cons, thoughts of zobel network?

I feel unsure about the pros and cons of dual mono compared to stereo. Please share your experience and thoughts. I am aiming to build a high quality amp soon and my goal is to make a better amp then my current lm3886 dm clone, mainly by using a better selection of components, and I don't want the schematic/construction itself to be a weak link in the chain.
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Old 5th March 2011, 11:36 PM   #2
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I am just getting into diy audio myself but I have quite a bit of experience with opamps in non-audio aplications. From that I can say a zobel network is a great idea.

There are 2 types of power consumption resistive and inductive they are measured in Watts and Vars. By nature resistive loads (like resistors and transistors) generate heat as a side effect. Inductive loads (like relays and motors) generate magnetic fields.

A speaker has an inductive and resistive load. The resistive load is constant but the inductive load fluctuates with the music. The Zobel Network minimizes the fluctuations seen by the opamp.

Also by not allowing the reactive energy to return to ground it should theoretically keep your ground source cleaner.
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Old 6th March 2011, 12:31 AM   #3
CBS240 is offline CBS240  United States
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The Zobel network blocks RF noise that exists on the speaker wire, aka antanea, from entering the feedback loop and causing instabilites. This is quite important for global feedback amplifiers.
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Old 6th March 2011, 07:13 AM   #4
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Quote:
Originally Posted by grakka View Post
This is my conclusion that I made by reading several threads around here,
This is the conclusion the people who thought that snubber PSU up wanted to make you come to.
Snubber caps in the PSU belong right at the rectifier. Then come the big smoothing caps with several 10.000s of F. After that follow the recommendations in the datasheet with cascaded capacitors that end in small decoupling caps right at the ICs power supply pins.

Quote:
Originally Posted by grakka View Post
Will the capacity be counted as the half of the total value if you are using a stereo amp instead of a dual mono?
Yes.

Quote:
Originally Posted by grakka View Post
I am afraid that I will lack dynamics due to the less power capacity.
No need to be afraid. The gain in dynamics by doubling the capacitance is so small that you can hardly measure it. I.e. if the capacitance is reasonable to begin with, e.g. from 4.700 F upward.

Quote:
Originally Posted by grakka View Post
Anything technically better then the other?
No.

Quote:
Originally Posted by grakka View Post
Can less capacity be counterbalanced by more power from the trafo?
No. The transformer supplies power directly to the amp only for a very short amount of time. Its main purpose is to charge the capacitors and they supply power to the amp.

Quote:
Originally Posted by grakka View Post
Pros, cons, thoughts of zobel network?
Quote:
Originally Posted by Nelson Pass View Post
Fundamentally, you don't want to operate a chip amp without
an output RC network to ground. The open loop gain is just
too high and the phase margin too low to practically avoid it.

Even if you don't see oscillation in the output, you can often
hear the effects of circuits which are just barely stable - so
we use "Zobels" and throw away some open loop gain to
ensure what I think of as "relaxed" performance.
Quote:
Originally Posted by grakka View Post
I feel unsure about the pros and cons of dual mono compared to stereo.
Pros of dual mono
- better channel separation which may improve the spatial illusion of certain music.
- potential for less losses in speaker wires, because you can put the amp next to the speaker.
Cons
- price.
- space requirements.
- risk of ground loops.
- risk of noise induced in the long line cables you need, if you put the amp next to the speaker.
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Old 6th March 2011, 01:20 PM   #5
AndrewT is offline AndrewT  Scotland
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I cannot comment on switching supplies, since all my build experience is in linear supplies.
The transformer must supply all the power required by the amplifier.
It must not overheat due the demands that the load will put on it.
These demands are two fold.
A continuous demand and a short term demand.

The smoothing capacitors and the rectifier also have to meet these two demands. They too need to be sized to not overheat for the two different types of current demand.

The rectifier is turned on and off repeatedly when the capacitor asks to be recharged.
The snubber can smooth out the ON/OFF/ON/OFF of the rectifier. Thats' what Pacific was referring too.
The snubber can also smooth out a fast transient (step change) current demand. This smoothing results in less spiky DC supplied down the rails. This is what the "snubberised PSU" is about.

The range of transformers that can be used to power an amplifier is enormous.
Taking a 50W into 8ohm amplifier.
If the continuous current demand of the amplifier is low then a 25VA transformer can safely power the 50W amplifier, Provided the designer has used sensible precautions to prevent users overheating the transformer.

Similarly a 500VA transformer with all the bells and whistles added can be used to power your 50W amplifier. It will still work, but at great expense.
If you want good value for your transformer money, then I suggest that a 50W amplifier use a transformer rated from 50VA to 100VA. However, a small transformer has a much higher regulation. To avoid some of the sound quality issues brought about by transformer regulation, I normally suggest using 160VA or more for any power amplifier.

A slightly undersized transformer will not make a big difference to sound quality, just as a slightly oversized transformer will not make a big difference to sound quality, but there will be differences in amplifier performance (both measured and audible) using transformers from the lower and upper end of the transformer ratings.
I think that a slightly undersized transformer can be compensated by adding extra smoothing capacitance, for normal domestic listening. PA and Disco and Sound Reinforcement are in a different league.
I do not think that a bigger transformer can compensate for selecting too little smoothing capacitance.

Beginners must always start with a safe reliable design to build. You have cut your teeth on a chipamp. That should have taught you a lot. eg. Zobel must always be used when specified by the designer/manufacturer.
AC coupling must always be used to help protect speakers from damage.
INPUT filters must be adopted to minimise the risks of interference.
A sensible listener must be in control of the volume knob.

Once sufficient design experience (not the same as build experience) has been accumulated you can investigate alternatives and consider omitting some compulsory items in the search for better audio quality.

BTW,
I don't agree with Pacific that a con for monoblocks is increased risk of ground loops.
I stand by my advice that the easiest and best way to avoid Ground loops is to only build monoblocks. Then you don't have shared grounds between channels inside a chassis. I would move resistance to ground loops into the pro list for monoblocks.
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Last edited by AndrewT; 6th March 2011 at 01:26 PM.
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Old 6th March 2011, 02:16 PM   #6
grakka is offline grakka  Sweden
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Wow, that was all golden answers, thanks for that!

I have a questions that may be a little off topic. Anyway, I recently built my first chipamp. I'm using two 150v trafos and I wonder if that would count to the lower or upper end of the transformer ratings. The reason why I wonder about that is because I get some small brrrrr-sound from the amp, I think the trafos are causing the sound (are they working to hard?). I also feel a bit unsure about the grounding. I am able to hear a very low noise from the speakers when the amp is on but ain't playing. I have to put my ear about 1-2cm from the mid/tweeter to be able to hear it tho. I can totally live with the sound being there since it's so low, but is there anything danger/bad with it? (except that I can hear it).
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Old 6th March 2011, 04:46 PM   #7
AndrewT is offline AndrewT  Scotland
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A 150VA supplying a single chipamp is way above the minimum for the chipamp to operate safely. It is also above the doubled VA rating for a bigger transformer.
150VA is virtually the same as 160VA and thus overcomes much, if any, sound quality issues that may arise using a higher regulation transformer.
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Old 6th March 2011, 08:05 PM   #8
grakka is offline grakka  Sweden
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Whats the pros and cons of different layouts? Will the sound be affected due to longer cables and more connections? What I am mainly thinking about is the current layout I'm using (but probably a bigger case and more spacing between stuff) compared to the attached image. Even tho I like to build things for the look, the sound will have priority. I will probably go for the design with 5 cases unless there is anything bad with it.
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