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Old 28th May 2016, 10:58 PM   #1
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Default Regarding a Toshiba SY335 preamp

After following the advice from Irrebeo and Ian Finch on a Toshiba SC335 power amp, it has been working nicely over the past 10 days or so.

As fate would have it, I came into possession of a companion SY335 preamp. Earlier in the week I encountered someone selling it for the cost of 2 fast food meals. Since it was so cheap I bought it but before parting company with the seller, I was given another SC335 power amp at no charge. For the latter I shall repeat the previous process but it's questions about the preamp that I'm posting about.

I intend to replace all the electrolytic capacitors but while looking for some online opinions of this unit I found several forum threads concerning the 4558 op amp. Changing it for a more modern one was recommended - an NE5532 or (I believe) an OPA2134.

Both are available locally for $1.80 & $4.00 respectively. I can buy both because they are quite cheap but since I would prefer to only remove and replace once, is there a preference of one over the other?

I also read about changing resistors in the phono preamp to 1% metal film of different values. Is that, or changing non-electrolytic capacitors, something worth doing?
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Old 29th May 2016, 03:15 AM   #2
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It's good that you are happy with the amplifier and your work on it. The preamp is not a particularly well specced unit though and may well benefit from some minor improvements, if only to the components.

OPA2134 is a JFET input opamp whilst NE5532 is a Bipolar, like the 4558. Any advantage of the JFET type is not likely to realized in the preamp, so it may not make much difference what you use but certainly, 5532 would be good move and at $1.80 is not expensive. If I had a choice, I would avoid the Texas versions though. Digi-key have an On-Semi version that's even cheaper at US 94 cents but that saving may be offset by other costs in your location. Still, that's my pick of standard thru-hole types.

With passive components, it is a good idea to replace carbon film resistor types with metal film, particularly in low signal areas of preamps, where noise is a significant part of the signal. Phono preamps certainly fit that description and you could replace like for like values, expecting at least a small audible improvement in background noise level.

RIAA equalization is a part of phono preamp design and this requires close tolerance R and C components anyway. If your advice is to use different resistor values, I would check that the advice is relevant first. It may mean a change to an old (1976) amendment by IEC to the RIAA standard equalization. That was withdrawn in 2009 due to bass replay problems, so you can't be certain what benefit if any is possible in upgrades without knowing the reason and dates.

Changing capacitor types in circuits involving many caps, can reduce overall distortion by very small amounts but generally, there is little improvement by changing film caps when size is limited by the PCB layout and increased noise proneness. Polypropylene film (MKP) types are popular as a replacement for MKT or greencaps now but size and cost is significantly greater. As a general replacement strategy, its probably not a good idea in a complex preamp. A strategic replacement of a few caps in critical locations might be smarter. However, without a schematic or the prior experience, I would not like to suggest how to proceed with that. You may also get more specific replies and advice in the Analog Line Level forum, when it comes to preamps.
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Old 30th May 2016, 12:37 AM   #3
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What you say makes sense and coincides with the (AK) thread about revamping one of these. That poster made some extensive changes but proposed that the most significant were changing the op amp and installing same voltage power supply capacitors with 3X the value. At this point my intention is to do likewise plus I think I shall put 1% metal film resistors in the phono section. I believe that coincides with your comment. I won't be changing anything else save for new electrolytics all around with those of the same capacitance but one voltage level higher.

Too bad this preamp is a recent acquisition because I have no knowledge of how it sounds in it's present form. Before I start doing any component swapping, I will hook it up for a day or so just to see if I can notice a difference afterwards. Plus I should find out if it actually does work.

With the cover off, there's a lot of vacant space. The sparseness reminds me a lot of a NAD 1020.
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Old 30th May 2016, 12:49 AM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by 62vauxhall View Post
Too bad this preamp is a recent acquisition because I have no knowledge of how it sounds in it's present form.
Before I start doing any component swapping, I will hook it up for a day or so just to see if I can notice
a difference afterwards. Plus I should find out if it actually does work.
If the preamp works, run it for a few days before doing any serious listening.
The sound will improve with the break-in.
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Old 30th May 2016, 05:50 AM   #5
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As it sits, in it's unmolested state, it works and sounds OK just needs control and switch cleaning. It will probably be few days before I get the new parts so I'll leave it on in the meantime and listen through it as time allows. Unfortunately my 6 day 80+ hour work weeks will not allow a lot of that.
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Old 30th May 2016, 07:02 AM   #6
darg is offline darg  United States
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As I got my SY335 I had it running for a couple of days unchanged. Voltages internally were ok so no immediate need to rescue the PS or anything else.
Short of words, I would say it sounded ok over Aux and tape inputs. The phono stage compared to my little bear t10 was a little bit thin sounding and the highs not very well developed. As that I would have not been happy with it but since I was planning on going through the mentioned (AK) mods I used the time to get a feeling for it.
I started out with the PS upgrade which did not do anything to it that would have been obvious to my ears. Changing the opamp in the line stage made the Aux and tape loops a little bit better but the cap changes did the major trick. I upgraded all electro lytics and substituted the output caps with film.
In the phono stage changing the opamp to NE5532 was helping but not that much to consider it done. Following through with the resistor and cap upgrade inclusive omitting the resistors and caps mentioned on (AK) changed it completely and opened not only the bass region but also the HF up.
I went in both stages with NE5532 since I had these on hand, the Opa were not available locally here and it seems to be ok for me.
After the upgrades done it sounds much better than stock so upgrading is worth it and transforms this little unit from average to pretty good..
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Old 30th May 2016, 07:06 PM   #7
Welcome is offline Welcome  France
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Do you even need the pre-amp? It can only make the sound worse. Pre-amps are a thing of the past, and these days (well, since the late 70s), all you need is a volume knob and maybe source selector. A pre-amp has no real use.
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Old 31st May 2016, 12:39 PM   #8
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So I guess we can conclude that ditching the 3.5-decades-old electrolytics (especially smaller ones of presumed average quality) makes a major difference, with small extra improvements yielded by opamp upgrades (though I'd proceed with caution as the board layout in a late-'70s devices is likely to conform to various definitions of "sucks", and e.g. extra local bypassing may be helpful). Can't say I'm overly surprised there.
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Old 14th June 2016, 07:27 PM   #9
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Over this past weekend I was able to install the new metal foil resistors, electrolytic capacitors and op amp in the phono section. I posted in the Parts forum a question on two caps indicated as low leakage so I used current standard ones rather than overpay for modern "low noise" ones. I left two of what I believe are carbon film resistors in place (tan colour) because the local shop had no metal film with the right value.

Thinking it would be an interesting option, I installed a socket for the op amp and bought both NE5532 and OPA2134 in case I wanted to compare them. The 5532 went in and there is less noise than there was so I'll leave it alone.

As luck or something would have it, I wound up with yet another one of these pre's along with the power amp for again, next to no money but they're the Aurex branded versions. Since I believe them to be the same internally and I have enough parts left over, I'll replace the same devices - except the op amp. In this case I'll use the OPA2134 and compare both entire preamps.
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