Hi, this is kind of an offshoot of some of the questions I've been shooting to EchoWar about my SA-9100 in the DC-Offset thread, basically I'm wondering, what do you techs out there do when you get a system and want to bring it up to spec, and where the details count.
I see some consensus on going through and recapping everything, but I also see talk about replacing carbon resistors with metal film etc. And of course I see all the talk about Auricaps, or Blackgate Caps, etc.
Are these ostensibly fancier caps for anywhere you need caps, or just in certain stages? At a certain point I'm sure it turns into having more money than sense and may be on the level of gold-plated toilet seats, but I just don't know!
For me, I feel like if I'm going to pull out a board, and replace the caps, it seems like it's worth the time to also replace a couple resistors if it's going to make a difference in sound.
On the other hand there's the ever present likelihood that I might know just enough to be dangerous, and sometimes it's better to leave well enough alone.
So to all you techs that seem to be able to materialize incredible things out of your experience and will, if you had a old deck and you wanted to bring it back to it's glory what are the things you'd do?:scratch2:
Apologies in advance, as with so many great questions this may have already been answered many times?

KISS. Keep it simple.

On many units, I replace all signal-path capacitors with Blackgate non-polarized caps at the request of the owner, but if I need/want to save a buck, I use all Panasonic FM or FC (and/or Nichicon PW or HE if physical size is an issue and they fit better), and use Blackgate 'N' non-polars only where the original schematic shows a non-polar in the signal path. Non-polar caps not in the signal path are replaced with Panasonic SU caps.

The 9100 has a couple of axial electrolytics. Use BC Components AML 138 caps, or you can adapt a regular radial cap.

Fancy resistors are fine for a new design, but IMHO a waste of effort on a rebuild project unless you want to replace all of them, in which case your returns are pretty damn small considering the effort. On the few units I've done a 100% replacement with metal film caps, the noise floor dropped by less than 1db.

Not sure what else to tell you...I make many rebuild decisions 'on the fly'...IOW, once I have it open and get a feel for the design, then I decide what will work and what won't.

EW, I've plowed through threads here and at Diyaudio.com for almost two years but have never seen anybody adequately explain the differences between (for example) Panasonic FM and FC. There doesn't seem to be any decent information on any of the supplier's sites, either.

Can you explain some of it?

The FM caps are black with a gold writing, whereas the FC caps are dark blue with gold writing. At Digikey there is a wider selection of FC caps across the range of different capacitance values, when compared to FM caps. The advantage to the FM caps is that they are slightly cheaper than FCs (not sure why).

From the standpoint of the datasheets, FM caps appear to have slightly better specs on paper, with a higher ripple current. So I tend to get the FM caps when they are available in the value I am looking for. However, I would not worry about this. Either one will be far superior to what was there originally. It's not as though you would be able to hear the difference between FM and FC.

Cleaning, doing this basic recap, using only the Panasonic caps with no other alterations, and setting the bias, DC offset etc in accordance with the technical manual will bring about a noticeable improvement in sound and performance in quite a few units. In others, the change may be more subtle or not particularly significant.

The quality and actual value of the piece of equipment being worked on will play a role in making some decide to put more expensive parts into the process. Specific caps that are in the signal path could benefit from the use of non polar Black Gate caps. However the price of the parts will go up sigificantly. Is the amp/receiver you are working on worth the total cost in the price of parts? You will reach a point of diminishing returns, where you can spend a lot of $$ on a particular higher grade replacement part, without gaining anything very significant. In fact, if you try too hard to rethink and rework the original design, you can end up with something that sounds worse than it did before.
My advice is, if you really want to go all out and try all the fancy replacement parts that are generally reserved for Tube amps, consider putting the money towards better equipment instead.

Thanks for the information all. Do any of you guru's have the noob love to tell me which caps are actually the signal path caps in the SA-9100. I know the symbols on the schematic are, and can work a soldering iron, but as far as tracing a circuit I'm completely in the dark?

If you send me a copy of the schematic I will have a look and circle those caps.

So if a capacitor says, for instance "10,000uf 60v negative" that's a polarized cap?

A capacitor of that size used in an amplifier will be polarized.

You boys know anything about the old Gfa 1a's?

If someone is about to undertake his first rebuild project I'd suggest he start with the soldering iron and learn how to unsolder parts without damaging the board. Find some vintage junk at the thrift and perfect your skills on that.

D3, your advice is well taken! I feel pretty comfortable with a soldering iron, whatever I still have to learn I'd rather not learn on the job.

Rulerboyz - which circuits do you need? Just the schematics for the Amp boards, or the pre-amp also?

Thanks again everybody, it's great to see so much information out there, and it's a real treat to benefit from the combined years of experience.

Hi,

I've seen in previous posts that a pre-requisite for this job is being able to read a schematic. For those of us without the ability, a circled schematic seems to be a great idea and will be educational. The recommended type noted, the resistors, transistors and diodes that would be suspect also could be cirled. I have a working AU-11000 that I've cleaned up and painted. I found an olive drab color and showered it with a light coat of metallic black finished up with clear. Color closely resembles the original and looks great! Used Magic eraser on the face and knobs...But now for the insides!

If you send me a copy of the schematic I will have a look and circle those caps.

Ian, apologies in advance for hijacking your thread, but I have exactly the same question! I don't know whether the greater sin is hijacking a thread, or starting yet another parallel thread to dilute the info... :scratch2:

Rulerboyz, if I may beg your indulgence the schematic for my receiver is at http://manuals.harman.com/hk/Service%20Manual/HK930%20sm.pdf and I would much appreciate it if you could let me know which caps would be appropriate to replace.

I'm a mechanical engineer and not an electronics tech, but I have had training in leaded and lead-free soldering including SMT rework (I work for a biotech instrumentation company so I'm taking advantage of all the training I can get! :banana: )

Ian, you have asked all the right questions! Thank you for that from another "shade-tree mechanic"!

Best regards,

Randy

So I finally got moitivated tonight!

took the sa-9100 apart.
Replaced the axial electrolytics on the PS board.
Took a look at the protect circuit but didn't change the caps as they looked new. Didn't change the Protect transistor.

On the Left Channel I replaced the Q1 and Q2 with the new Zetek transistors.

Powered on and was really happy nothing went pop or sizzle!

However, now I have an ambient buzz going on. When I turn it up, it sounds like feedback and actually starts to make a warbling sound.

I'm going to replace the transistors on the other channel tomorrow so they match, but.....?

...I'm wondering what's going on? The protection light used to come on but at least the soundfloor was quiet!!

I'd love to know what all y'all know because I'm new to all this!

Thanks again to Echowar for helping get this far!!

@Ian C. - If you have replaced everything correctly and not rerouted any wires, then I would suspect a power supply capacitor (I gather that you are doing this incrementally).

@ all - I find that the selector switches are most problematic on old equipment. Is there any preferred treatment to remedy a switch that makes poor contact (preferred switch cleaner, perhaps)?

@Ian C. - If you have replaced everything correctly and not rerouted any wires, then I would suspect a power supply capacitor (I gather that you are doing this incrementally).

@ all - I find that the selector switches are most problematic on old equipment. Is there any preferred treatment to remedy a switch that makes poor contact (preferred switch cleaner, perhaps)?Best I've foumd is Caig Deoxit D5. It's available through Parts Express, one of AK's sponsors but I'd hate to see what they knock you for shipping to SA. You might be able to source it locally.

Not sure if that last post I tried went into cyberspace...

Shonver, when you talk about PS caps, are you talking about the caps on the PS board, or the large beer can filter caps (15,000uf)?

FYI that tonight I replaced the other channel, replaced a transistor and two caps on the protect circuit board, and still have the buzzing. Also listened via headphones and manipulated all of the harness wires to see if it was just an issue of me having put some wires out of place... still got the buzz...

Shonver, when you talk about PS caps, are you talking about the caps on the PS board, or the large beer can filter caps (15,000uf)?

I reckon it's more likely on a lower-current power supply, specifically if the power amp input stage or earlier stages have separate power supplies. My Optonica SX-9100 amp had this problem. The capacitor in question was the reservoir for a low-voltage supply. It sits right next to a heat source (the heat sink), and the electrolyte had eventually dried out. Replacing it eliminated the buzz.

But the big caps can also go. I don't know how likely this is, though.

Is there any way that me replacing the axial caps would cause/reveal this? or is this just poor workmanship on my part that caused the hum to appear when I "fixed" the old caps?

Sometimes, with the BC Components axial caps, it's hard to tell '+' from '-'. Two things to look at:

1) On polarized axial electrolytic caps, one end of the cap will have a 'crimp' for the rubber plug. This is always the '+' end of the cap.

2) Related to #1, look at both ends of the cap. One end has a rubber plug, the other end has a tin 'cap' to which the lead is directly attached. The tin cap side is '-', and the rubber plug is '+'.

Note that nonpolar electrolytic caps have a crimp and a rubber plug at both ends.

I once found a batch of new radial capacitors where some had had their polarities incorrectly indicated. This was possible because the plastic cover/label is simply a plastic tube that is heat-shrunk over the capacitor body. We did not continue using those. In this case, the more reliable indicator of polarity was the lead length. The longer lead is positive, while the shorter one is negative.

Reversing capacitor polarity can/does cause malfunction: electrolytics yield a significant reduction in capacitance, and can explode; tantalum capacitors become highly conductive- they can also explode.

Circuit Schematic Symbols
the link will help people that don't know circuit symbols

http://library.thinkquest.org/10784/circuit_symbols.html