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Old 23rd March 2009, 09:50 AM   #1
richloh is offline richloh  Singapore
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Default Help To Identify Capacitor Functionality

Hi All,

Newbie here and hope for some help on my vintage car amplifier before I work on some recapping effort. I am not an EE and do have some trouble understanding the various electronic terminologies.

Can some someone explain what are the various capacitors w.r.t. the common terminology on of input/output capacitors, coupling/decoupling capacitors, feedback capacitors etc. see in various recapping threads as show in the below? Thanks

http://img297.imageshack.us/my.php?i...apacitorsf.jpg http://img297.imageshack.us/my.php?i...apacitorsf.jpg


BTW, this car amplifier is 4 channels topology, zero feedback and bridgeable to 2 channels.

Thanks.

Richard
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Old 23rd March 2009, 11:26 AM   #2
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Actually Richard its very easy..Capacitors are merely defined as an insulator between two conductors. That said, yes two bare wires seperated by an air gap would indeed be a capacitor.
There are polarized and unpolarized (Or Bipolar) capacitors....since the absolute definition is wide ranging, manufacturers use a wide range of insulating materials. The most common you might be familiar with is the small can shaped(20mm high) capacitor is of the Electrolytic type. Capacitors are rated as Microfarads......as the Farad is an unwieldy value...it is broken down to millionths of A Farad.
The common notation is uf or sometimes Mf (Not to be confused with Mega as it is uppercase). Other notations exist for the really small "paint drop" looking ones but the notations...I'd have to look it up.
They are noted also with the voltage notation with working voltages as in 160uF200WVDC OR Working Volts DC.
Yes, caps are used to isolate between stages(Coupling)(Pass AC block DC) or shunt AC voltages to ground(Decouple).
Perhaps someone has the listing of different types....can't remember where I left my book.
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Old 23rd March 2009, 03:53 PM   #3
richloh is offline richloh  Singapore
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Hi Rick,

Thanks for the quick introduction which is certainly helpful.

However, I am seeing at least 2 types of capacitors near the input power (22uf/25V, 680uF/25V), 2 types of capacitors (470uf/35V, 47uf/50V) after the DC-DC convertor if I under the link correctly, 2 types of capacitors (47uf/50V, 10uF/16V) at the output signal connecting wires and 2 types of capacitor at input signal (10uf/16V NP, 100uf/10V) with I thought can give some clues for at least guessing as to what functionality of these are.

For example the 10uF/16V NP should be decoupling caps for input signal and the 22uF/25V must be decoupling caps for the input power right??

Thanks.

Richard
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Old 25th March 2009, 09:09 PM   #4
richloh is offline richloh  Singapore
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Hi, Anyone else can help to advise??? Thanks. Richard
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Old 26th March 2009, 12:20 AM   #5
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Quote:
Originally posted by richloh
Hi Rick,

Thanks for the quick introduction which is certainly helpful.

However, I am seeing at least 2 types of capacitors near the input power (22uf/25V, 680uF/25V), 2 types of capacitors (470uf/35V, 47uf/50V) after the DC-DC convertor if I under the link correctly, 2 types of capacitors (47uf/50V, 10uF/16V) at the output signal connecting wires and 2 types of capacitor at input signal (10uf/16V NP, 100uf/10V) with I thought can give some clues for at least guessing as to what functionality of these are.

For example the 10uF/16V NP should be decoupling caps for input signal and the 22uF/25V must be decoupling caps for the input power right??

Thanks.

Richard
The image link isn't working for me, what kind of vintage amp is it?

Power supply 12V input is typically has an LC filter, and diode protection for reverse voltage.

Signal inputs are often decoupled (series capacitor), and if there are low and high impedance inputs, there are probably caps on both inputs. There may be additional signal filtering, especially if the amp is zero feedback.

Whatever is being used as a vibrator, pwm controller, etc to switch the power supply transistors is likely to have decoupling filters at the power connections, and in whatever circuit sets the switching frequency, etc.

Transformer output voltage will of course be filtered after the rectifiers, and it wouldn't be out of line to find multiple values or more elaborate filters here.

Car amplifier circuits vary nearly as much as home gear, and you're liable to find more filter caps near the transistors at rail voltage, in the bias circuit, in Zobel filters at the output, AC-coupling output caps, etc

It sounds like you'd enjoy our own Perry Babin's very comprehensive and informative site. Be prepared to spend some time there if you visit.
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Old 26th March 2009, 05:21 AM   #6
richloh is offline richloh  Singapore
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Hi tsmith1315,

Thanks !!!

I will need to take some time to digest these good information but do kindly take a look at the refreshed link on the PCB layout and list of capacitors used.

This is a 15-year old car amplifier from Japan that was reputed to be one of the best at its time and I still find it to be better than many of the current big $ products. I also looks it unique orange colored appearance and solid aluminium body as heatsink ... more detail in the below link:

http://www.sgsoundsystem.com/forum/s...ghlight=phonon

Hope to see your further advice after the review of the PCB layout.

With appreciation.

Regards,

Richard


URL=http://img255.imageshack.us/img255/1363/capacitorsfunctionalityn.jpg]http://img255.imageshack.us/img255/1363/capacitorsfunctionalityn.jpg[/URL]
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Old 29th March 2009, 04:30 AM   #7
richloh is offline richloh  Singapore
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Hi Again,

Can someone help to look at the link to the PCB layout of my car amplifier and advise specificiallyl what are each type of capacitors could be for.

Thanks.

Richard
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Old 2nd April 2009, 08:06 AM   #8
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To advise you on what each capacitor's specific function is would really require a schematic, or at least more detail, and someone more capacitor-concerned than me


Disclaimer: These are my interpretations and assumptions based on what I see and what has been posted. Inaccuracies, while not guaranteed, are expected and free of charge.

Looking at the far left of your picture, there are two vertical cards between the power terminals and the switching transistors. Those cards appear to contain the PWM control circuitry. I expect the 22uF caps located there to be supply filtering and/or part of the circuit that actually determines the switching frequency (I would expect to see smaller values there, but am not the expert on that).
Capacitor quality may be non-critical, but values for frequency-related caps shouldn't be fooled with. I'm not a follower of expensive cap upgrades, anyway.

Next over are the 680uF, which I see as filter caps for the incoming +12V.

The transformers #K002 look to be for voltage step-up, and the 470uF's that follow are the main caps for smoothing out the rail voltage.

The other E-cores #K001 are confusing. I'll punt a guess that they are chokes for +12V input filtering and not directly related any rail voltage for two reasons:
1) I don't see any otherwise, and
2) It would make no sense to have mono power supplies and then have them inter-relate through a magnetically coupled device.

Given that line of reasoning, the 47uF caps next to the little blue chokes would be filter-related as well.

The next group of 47uF caps on the amp board are located at the power supply connections, and therefore are likely to be for supply decoupling.

The proximity of the 10uF caps to the output and the fact that they are film leads me to assume they are in the signal path. I would say they were part of a zobel, but there don't appear to be any resistors nearby of suitable power dissapation? And no emitter resistors?

What (heatsinked) transistors are used in the output stage on this amp? How about those on the input stage near the RCA's?

The 10uF caps on the input side are located next to 2 plugs. Maybe to AC couple speaker-level inputs?
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Old 2nd April 2009, 10:02 AM   #9
richloh is offline richloh  Singapore
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Hi Tsmith1315,

I had been checking this thread several times a day for >1 week and thanks so much for helping out here. I believe I am understanding more on the functionality of the capacitors now from your description and thoughts although far from fully appreciated.

Please find below my comments:

The proximity of the 10uF caps to the output and the fact that they are film leads me to assume they are in the signal path. I would say they were part of a zobel, but there don't appear to be any resistors nearby of suitable power dissapation? And no emitter resistors?
My mistake to misled you to the film caps ... the 10uF are actually the green E caps in the dotted box that the arrow head somehow did not point very accurately to them.

What (heatsinked) transistors are used in the output stage on this amp? How about those on the input stage near the RCA's?
I will check when I am back home and advise accordingly.

Please also advise the possible functionality of the 100uF 10V green e capacitors.

Thank again and hope you will not be too frustrated with someone who will be needing to read about mentioned Zobel ckt after this enlightening advice.

THanks again.

Richard
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