Onkyo A7 question

[cliffforrest]

I am familiar with this and other Olson papers.

Perhaps you can explain what this has to do with increasing a 3.3uF cap to 10uF on 25,000uF reservoir circuit "changing the bass more than I know"?

But you can't, so let's just leave it there.

BTW I DO have a A7 amp on the bench next to me, with the top off. I've had it for years, but what do I know? I'm only an EE.

 

[Fast Eddie D]

I am familiar with this and other Olson papers.

Perhaps you can explain what this has to do with increasing a 3.3uF cap to 10uF on 25,000uF reservoir circuit "changing the bass more than I know"?

But you can't, so let's just leave it there.

You're building a strawman. That is not my position. In fact I explicitly stated that I would not support that statement.

The bass is supported by the big caps, no question.

 

[cliffforrest]

You're building a strawman. That is not my position. In fact I explicitly stated that I would not support that statement.

The bass is supported by the big caps, no question.

Then why are you stating

"Cliff notes - if your 4.7 uf Caps have a high enough resonance, it will be equal or superior to the original caps for this application.

As djk noted, these caps work harder than you think. A 10 uF capacitor with equal or higher resonance would be an upgrade. Higher temp and extra long life (2000+ hours) is just a bonus."

In a thread about the purpose of local small decoupling caps? It does not help the OP who had a genuine (and I suspect beginners) inquiry.

Piling in about multicap bypassing and resonances without considering the OP and the level of the inquiry is very unhelpful and smacks or arrogance.

enough said.

 

[Fast Eddie D]

Anyway, here is a pdf link that is relevant to a local bypass discussion.

http://blog.audioworkshop.org/amplifiers-oscillation-stability-bjt-circuits/#.VHJBnFItBiA

 

[Fast Eddie D]

Then why are you stating

"Cliff notes - if your 4.7 uf Caps have a high enough resonance, it will be equal or superior to the original caps for this application.

That is correct. It is the resonance that is relevant for a local bypass cap. It is a fact that different types of electrolytic capacitors have different resonances, and it is a fact that one kind of capacitor in a value of 4.7 uF can have a higher resonance than another kind in a value of 3.3 uF.

That's all I was saying. I mentioned what series of Nichicon capacitors he was planning on using, because this is relevant to the topic.

As djk noted, these caps work harder than you think. A 10 uF capacitor with equal or higher resonance would be an upgrade. Higher temp and extra long life (2000+ hours) is just a bonus."

In a thread about the purpose of local small decoupling caps? It does not help the OP who had a genuine (and I suspect beginners) inquiry

Well I am trying to help. It is a topic of interest and it helps to understand that different series of electrolytic capacitors are different, wouldn't you say?

If you think I'm confusing the OP, you could address him directly.

Piling in about multicap bypassing and resonances without considering the OP and the level of the inquiry is very unhelpful and smacks or arrogance.

enough said.

You're certainly entitled to your opinion. I think resonance is very relevant to a bypass capacitor discussion.

 

[pwdiya12]

thanks

HI

thanks for what has been a very stimulating and informing discussion ( well for me at least).

I believe the choice of 3.3uf with the bypass ceramics by the original designer, suggests from what I have no read (inc the links herein, plus Hood, Self and some other theory books), was to smooth/damp the frequency response in some manner. I have used 4.7uf Nichicon FG capacitors, mainly for convenience.

What I had hoped to understand was "why", what is the purpose of this arrangement, which I feel a little more on top off, and recognize that to really understand requires quite a deal of math and calculations- perhaps more than I am prepared to invest time in understanding.

As to the amp and refurbishing, I have replaced all the electrolytics, and consequently found three that were leaky or out spec. I have used Nichicon KL to replace the low leakage units originally installed. I figure if the designer chose these low leakage types, they did so for a reason. All the other electrolytics I have replaced with Nichicon "Muse" Audio types (KZ where possible, else KA, FG).
The original 25000uf units are at about 18000uf but with zero ESR- I use the peak ESR70- but I have not replaced these.

The results when running tones through the unit and monitoring on a scope are good, the audio is clean and clear.

As to me, well I have made a number of records in the 80's (yes those vinyl things), have worked in the worlds great recording studios and been involved in building 5 studios....oh and could be accurately described as an audio geek...

so the topic of decoupling caps is something I will research further, as they occur in many circuits and if there is a principal I can understand, that would be useful, however if it is a complex calculation that is required for each implementation (which is now my suspicion), then as I do this for fun, I will simply try and do a direct replacement or very close substitution.

thanks again

 

[cliffforrest]

+1

 

[Fast Eddie D]

so the topic of decoupling caps is something I will research further, as they occur in many circuits and if there is a principal I can understand, that would be useful, however if it is a complex calculation that is required for each implementation (which is now my suspicion), then as I do this for fun, I will simply try and do a direct replacement or very close substitution.

thanks again

Decoupling caps basically short the stray inductance of power supply leads (wire and circuit traces) to ground, as close as possible to the active device. The inductance can interact with the collector-emitter capacitance to form a resonant circuit. The decoupling cap shorts the resonant circuit to ground at high frequencies.

I rarely make complex calculations. You can make ball park estimations by considering what you want the cap to do, and what kind of impedance the device is driving. Taking this into consideration for this particular application, we know that a 3.3 uF capacitor (or 4.7 uF or 10 uF capacitor) is not going to support bass response locally. No calculations are necessary to appreciate this. And what we accomplish with careful decoupling is stability courtesy of isolation from stray inductances.

The pdf goes into great detail on this stuff, and shows some of the math too. The models are very helpful for understanding what's going on.

I hope this helps.

http://blog.audioworkshop.org/amplifiers-oscillation-stability-bjt-circuits/#.VHKphVItBiB