Technics SH-9010 Equalizer Recap—a few questions

DrTebi

Active Member
Recently I acquired a Technics SH-9010 parametric equalizer to help compensate for the low frequency loss in my open baffle speakers.

This 1978 EQ is in quite good shape. It was advertised as "serviced", which seems to have been done well, but was limited to cleaning and de-oxidizing switches and trim pots (while the sliders were left alone). None of the electronics appear to have been touched.

However, when I put it into the tape loop of my pre-amp, and switch back and forth between tape and source, with the EQ set to the "off" position, I notice that it sounds different. "Muffled" is probably exaggerated, but it sure sounds just a bit less alive when the EQ is in the chain.

I am sure there can be numerous reasons for that, but my first thinking is, why not start to re-cap this guy a bit... after all, it is now 40 years old, and chances are the caps are not quite up to spec anymore.

There is a total of about 50 caps in there :) I figured I start with the power supply, and probably the "logic circuit" and input circuit. I started to make a list of caps that I would need for the power supply... and now finally to the questions:

1) As far as I know, a higher voltage rating of a capacitor can do no harm, and may even be preferred. Correct?

2) Since the replacement capacitors won't cost much, does it make sense to order multiples, and check their values in order to get the best matching capacitors?

3) Should I stick to one brand? I wanted to use all Nichicon FG caps, but it turns out that some values are not available in the correct µF/V, or too small/too large to fit. I would mix in some from the KW series (for the large 470µF caps).

4) When a capacitor is specified as "audio grade", would that make a difference to the audio if the cap is in the power supply section?

Here a list of the values that I need for the power supply section:

Code:
Part No.  Voltage µF  Quantity
C701-C704      35 470        4
C705-C706      25 47         2
C707-C708      25 10         2
C709-C710      25 100        2
C711           25 33         1

Any suggestions are greatly appreciated.
 

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Not familiar with the item so only general comments

Basic technique for cap selection is to work out the function/key attribute
of the cap and select accordingly. Some people like to exclusively use low
noise/leakage types like Wima MKS2, but I find this unnecessary in some cases.
You can make some gains by replacing audio path caps with quality replacements
like Nichicon KZ, FG, KW,,,

1) Going up 1-2 voltage ratings is ok but you do pay when you hit the big numbers
like 100V +. I try and stay away from 6.3V, 10V and even 16V as the specs (tan delta)
show them to be ordinary
2) What do you measure capacitance with and how accurate is it. The 20% tolerance
on caps is not great but the OEM may have been -10 +50%. I wouldn't bother but maybe
try on some critical caps.
3) Nichicon carry a wide range.
for audio path the pecking order is KZ then FG then KW
For smaller amps (50W?) KW is fine for main filters however increase the uf by
1/4->1/3 since the ripple rating is a little low. OK to use KW for power supplu output
and on the voltage rails. Nichicom UPW for the power supply itself.
4) My opinion only. Most of the watts we hear comes from the main filter caps supplying
the output transistors and pushing amps out to the speakers. The preamp signal is a
few volts only. UKW for mains, UPW for PSU, UKZ for psu output and rails.

Will try and track down sm to comment on the caps.
 
Power consumption is 8W.

C701,2,3,4 470/35V, Main filters.
Go with best cap that fits in available space
eg, KZ or FG 470/50V, tempted to try KW 1000uf/50V

C705, 6, 7, 8 can be FG or KZ or KW. I would normally
use PW but ripple won't be an issue

C709, 710 100/25V KZ or FG
 
Thanks a lot! Great suggestions.

I had one value wrong though, the C711 cap is actually 3.3, not 33µF. Couldn't make it out on the service manual, but the original cap definitely has a dot between the 3s... That value I cannot find in the KZ KW or FG range, at least not with the same lead spacing. So I guess I'll use a PW for that.

My Amprobe Multimeter 37XR-A has the ability to measure capacitance by the way, no idea how accurate that is.
 
C711 and C713 are for the muting/protection circuit, no audio path, so no KZ or FG. PW recommended
 
My Amprobe Multimeter 37XR-A has the ability to measure capacitance by the way, no idea how accurate that is.
ESR and leakage are probably more important than capacitance reading. When caps age the capacitance can go up, but ESR also goes up.
 
C711 and C713 are for the muting/protection circuit, no audio path, so no KZ or FG. PW recommended
Thanks. I did suspect that these were not part of the power supply.

A question comes to mind, if the muting circuit doesn't work right anymore (e.g. a "pop" noise when turning on/off the unit), will a capacitor replacement fix that, or is that more likely due to the relay?
 
C701,2,3,4 470/35V, Main filters.
Go with best cap that fits in available space
eg, KZ or FG 470/50V, tempted to try KW 1000uf/50V
I am limited to 25mm height... so the best thing I can do is a KW 470µF/100V for those. I reckon that should work just fine...?
 
so the best thing I can do is a KW 470µF/100V for those.
A 100V cap is overkill, the voltage on that rail is about 23V, so 35V is ok and 50V is plenty. KW would be fine

A question comes to mind, if the muting circuit doesn't work right anymore (e.g. a "pop" noise when turning on/off the unit), will a capacitor replacement fix that, or is that more likely due to the relay?
Could be either. The mute time is set by an RC timer, if the cap drifts lower then it charges up quicker gives shorter mute time, maybe
transients haven't settled. Otherwise the relay could be seized, contacts can be welded etc... but this is unlikely, hardly a monster
power amp. Replace the mute caps as a first step.
 
After double and triple checking, I have now a complete "BOM" for all 55 capacitors (see attached image). All µF values are the same as the original, voltages are in most cases double the original (often this was the only option anyway).

There are a few curiosities that I have encountered.

1) Quite a few 3.3µF / 25V polar caps are used throughout the board, all of the same variety, except for two orange ones. These have the same values, are also polar, but appear to be a different cap? These are the originals (in the brochure one can also see that these two are orange). They were used in the "Input Buffer Circuit". I wonder why these are of a different kind?

2) There are a few bi-polar caps on the board. The replacements I chose for those are the Nichicon pi-polar caps from the UES "MUSE" series. I suppose that was a good choice?

3) There are two empty spots... in other words, two film-caps are entirely missing (see C617 in the attached image). They are missing in the image of the brochure as well. I assume this was an intentional, last minute, design change?

4) The RCA input and output jacks are quite a bit worn. I am tempted to replace those. These are mounted to non-conductive plates, which in turn are mounted to the chassis. Yet, I measure continuity between the RCA ground and the chassis... If I replace these, should I also use an insulated plate, or could they be mounted to an aluminum sheet without insulation pads? There are also two resistors soldered between the output L/R lines, what's the purpose of those?

Any ideas greatly appreciated :)

P.S.: Here is a link to a better image of the parts list in case the attached one is not quite readable:
http://drtebi.com/dump/audiokarma/technics-sh-9010-recap-parts-list.png
 

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If you haven't already, download the SM from hifiengine. The schematic portion of it shows quite a few caps directly in the audio path. There's nice arrows to help you see how the audio signal progresses. Though it doesn't appear that Technics specified the use of Low Leak caps in the audio path (which those two orange ones most likely are), Pioneer, Kenwood, Sansui, Onkyo and others did specify LL caps if in the audio path.

My suggestion to you would be to use Nichicon UKL for any value above 1uF, and a film cap for 1uF and below. Others try to go as high as 10uF for film caps, but lead spacing and size constraints usually will limit film caps to 4.7uF and below. Here's a link to a different EQ, but I had a similar experience with "lifeless" sound before the recap. It also used those lavendar Matsushita caps, several of which were open.

http://www.audiokarma.org/forums/index.php?threads/harman-kardon-eq8-recap.669546/

If, as it appears, you already ordered the caps on your list, don't fret about them not being LL. However, use this info for future projects. Also, as to the RCAs, just swab them with deOxit and then hit them with the "gold" if you have it.
 
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Thanks for your suggestion.

I actually haven't ordered yet.
Your suggestion to use UKL caps was only for the two orange ones, correct?

The lowest µF of all caps is 3.3µF. I chose Nichicon FG for those, what would be the advantage to replace those with film caps?

The RCA caps were already cleaned by the previous owner. They are a bit scratched up though, hence my idea to replace them. Maybe I will just leave them in and clean them a bit more. Do you know why there are resistors soldered to the RCA outputs?
 
Not just the orange ones...all of the ones that are IN the audio path. These usually will be 10uF or less in value.

I wouldn't go out and buy more caps if you've already purchased the ones you listed. The advantage to using film caps are many, LONG life since there's no electrolyte to dry up or leak, better sonics, low to no leakage...

The best capacitor is no capacitor when it's in the audio path. So, if you have to have them, you want ones that will give the lowest noise profile (which equates to leakage current). I'm sure you'll like the results using FGs though.
 
Not just the orange ones...all of the ones that are IN the audio path. These usually will be 10uF or less in value.

I wouldn't go out and buy more caps if you've already purchased the ones you listed. The advantage to using film caps are many, LONG life since there's no electrolyte to dry up or leak, better sonics, low to no leakage...

The best capacitor is no capacitor when it's in the audio path. So, if you have to have them, you want ones that will give the lowest noise profile (which equates to leakage current). I'm sure you'll like the results using FGs though.
I have not yet ordered.

I am happy to follow your suggestions, since I am quite unexperienced in this regard. So, to recap (pun intended), I would replace the 3.3µF and 10µF caps that are in the audio path with UKL caps on my shopping list? Then again, I am not exactly sure which ones are in the audio path, wouldn't that be anything that is not in the voltage regulator or muting relay? There are quite a few caps beyond that, 3.3, 10, and of higher values (including those bi-polar caps).
 
The schematic portion of it shows quite a few caps directly in the audio path. There's nice arrows to help you see how the audio signal progresses.
See the sm.

Agree with @jheu2 on cap selection. For bipolar caps use Nichicon ES.
 
See the sm.

Agree with @jheu2 on cap selection. For bipolar caps use Nichicon ES.
When I look at the schematic, it seems to me that pretty much everything is in the audio path except what's labeled "Regulator" or "Muting", but maybe I don't understand it correctly...

I have already the Nichicon ES bi-polar caps in my list... so I am fine with those I suppose.

So should I now use Nichicon UKL caps instead of the FG ones for whatever is not bi-polar, or in the regulator/muting circuit?

Still a little confused... also checked on some film caps, they seem to be quite large even at 3.3µF.
 
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I've been a long time user of Nichicon KL for replacing low noise/low leakage (orange, pale green...) caps especially in the phono
and preamp stages. I have been using them elsewhere in the audio path, even power amp, but I'm finding that the sound can be
somewhat "dry", transparent is probably a better word. In any case, I've recently started using Nichi KZ's which probably colour
the sound, but I think it sounds better. If you have a noise issue or if your spkrs have a moderately high SPL, ie, 95+ then certainly
use the UKL or consider WIMA MKS2 or ... I don't see any harm in using the FG's in other cases.

For 3.3uf it will need to be Wima MKS2, which some people (+1) say can sound harsh.

Caps that connect to power rails eg C756 (220uf/16V) can be KZ, FG, KW. Not KL.
 
Well, I have to admit I am a bit overwhelmed by the choice of capacitors... I have read a bit more about it in posts at AK and diyaudio, and it seems that everyone has a different opinion... when it comes to sound, at least. I do get the low leakage advantage though. I think I will stick to the choices on my sheet, but just change the orange caps to UKL caps.

So basically it boils down to this:
KW in voltage regulator
FG in muting relay, logic circuit, and input circuit
ES for the bi-polars in the bandpass filters
FG for remaining caps in the bandpass filters

In the end of the day... my main goal is to replace some 40 year old capacitors due to their (soon to be) end of life :)

I think I am ready to push that checkout button now...
 
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Caps are very much subjective, I'm as guilty as the next guy. You need to work out what works for you.
You've selected quality parts from a reliable source so you can't go wrong. People will have different
opinions, hopefully along the way we learn something...
 
Caps are very much subjective, I'm as guilty as the next guy. You need to work out what works for you.
You've selected quality parts from a reliable source so you can't go wrong. People will have different
opinions, hopefully along the way we learn something...
I learn something every time I post a question :)

Thanks again for all responses.
I will report back when I have made some progress.
 
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