Selecting replacement capacitors for ones that are long obsolete (audio) - Page 1
Forum section: electronics / beginners

author: Pyral
author_rank: Contributor
timestamp: September 18, 2025, 07:45:21 pm
content: I’m trying to recap a Sanyo RD5370 tape deck, it was high end in 1978. The original capacitors are letting too much noise in. As expected, many capacitors aren’t available in their original capacitance and voltage combinations. Any capacitor below 1 uF was not available as an electrolytic capacitor anymore.I was sourcing higher voltage capacitors, like a 6.3V might be replaced with a 25V or 50V one. I did this for availability, convenience, and packaging (the modern ones will not match the lead spacing since they’ve shrunk in 50 years) reasons.As I was looking for the <1uF capacitors, I read that using a higher voltage will cause a higher ripple current thanks to lower resistance. Will this matter because these capacitors will be used in the audio path?Also what capacitor type best replaces the <1uF capacitors I can no longer buy as aluminum electrolytic capacitors? These 3 values (.1, .33, .47 uF) are used in amp pcb assembly, “IOI” (maybe 101) pcb assembly, and Dolby circuit (noise cancellation). So whatever type of capacitor selected, should match the original characteristics as best as possible.Finally the service manual specifies some capacitors as “Alsicon”, I don’t know if that is a brand name or product line Sanyo was making, but I’ve never heard of them. Can I substitute normal aluminum electrolytic capacitors?

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2025, 08:03:47 pm
content: Define "noise"; frequency, amplitude, etc.Different types of capacitors are used for different purposes, and hence have different strengths and weaknesses. Knowing type and purpose is necessary before selecting a replacement. Examples: bulk decoupling for linear/SMPS PSUs, signal filtering, EMI/EMC, coupling signals between amplifier stages.

author: Pyral
author_rank: Contributor
timestamp: September 18, 2025, 08:47:15 pm
content: I mean it literally, I can hear a 60hz buzz in the audio output because the capacitors are dried out and old.What that lools like on a scope I cant say.Im replacing all the capacitors, amp, power supply, dolby circuits, control circuits.

author: TimFox
author_rank: Super Contributor
timestamp: September 18, 2025, 08:58:20 pm
content: An essential clue:Is the “buzz” 60 or 120 Hz?Without knowing that, you are operating in the dark.In the usual case of 120 Hz, the problem is in the power supply filter capacitors.There is no reasonable way for 60 or 120 Hz to enter a previously working unit through bad capacitors in the other locations you enumerated.Bad capacitors in the non-power supply sections can cause distortion (when you have a signal) or “hiss” (random, not periodic noise).

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2025, 09:06:59 pm
content: Quote from: Pyral on September 18, 2025, 08:47:15 pmIf 60Hz, it is probably EMI entering the signal chain. Ground loops are a classic cause.If 120Hz it probably comes from failed bulk electrolytics smoothing the bridge rectifier output. They can be replaced by electrolytics with a higher voltage and appropriate ripple current, but the capacitance isn't critical. I wouldn't bother with changing tantalum electrolytics unless they are know to be faulty. Don't replace any X and Y capacitors unless they are RIFAs - in which case definitely replace them.Other non-electrolytic capacitors are unlikely to be faulty.A cheap component tester measuring C and ESR is useful to confirm whether electrolytics need replacing.

author: Pyral
author_rank: Contributor
timestamp: September 19, 2025, 01:25:57 am
content: https://imgur.com/a/yDOjLw4Here is a mp4 of the humming in question, to hear it you'll probably have to turn the volume all the way up (I did, and I have good hearing) even with earbuds because I didn't set the record levels from their default level in audacity. In person it is very noticeable, this is through the RCA output, which has the least noticeable hum.I don't know if this is a ground loop or not, but I've taken a few different models apart, none of them had a hum like this disassembled or not. It sounds like the 120hz hum youtube videos.What should I use in place of the low capacitance electrolytic capacitors? I can't get replacements of that type anymore.Also will using significantly higher voltage capacitors affect sound quality because of the lower resistance?

author: jwet
author_rank: Frequent Contributor
timestamp: September 19, 2025, 03:22:32 am
content: Ceramics are now available up to 10 uF+ at reasonable prices. Tantalums are available again after a long hiatus and come in radial packages. Unfortunately, ceramics which are really nice aren't in radial packages. There are two newer classes of electrolytics do come in radials that didn't exist 20 years ago- HF electrolytics and OS-Con type electrolytics. Panasonic invented the HF type and Sanyo invented OS-Cons. Both were designed for switching power supply application and I don't know what they "sound" like. You also could just go way up in voltage with modern caps of the same value but likely 10x the V ratings. This is one place where NOS- (new old stock) won't bail you out really. Caps have a shelf life unlike most other components.Elliot Sound labs and Maxim wrote some app notes about distortion contributions from caps, especially coupling caps. Good luck.

author: tggzzz
author_rank: Super Contributor
timestamp: September 19, 2025, 09:37:03 am
content: Quote from: Pyral on September 19, 2025, 01:25:57 amUse audacity's analyse>>plot spectrum. What is the frequency of the peak? 120Hz or 60Hz or something else?

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 19, 2025, 02:33:32 pm
content: Quote from: Pyral on September 18, 2025, 07:45:21 pmIt depends of cause on original type of cap you want to replace, but if you are talking about 6.3V, 10V etc voltage ratings then it means you are talking about replacing electrolyte type caps.It depends a bit on different things (like size on PCB), but in general every cap <=1...2 uF can be replaced with small film caps (63-100VDC rated), and larger values possibly can be replaced with general use electrolyte types (with 16-63 VDC voltage rating). Yes, you can replace 6.3 V rated cap with 16-63 VDC rated.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 19, 2025, 02:39:00 pm
content: Quote from: Pyral on September 18, 2025, 08:47:15 pmIf you hear "a 60 buzz" loudly means you hear 60 Hz and harmonics (120 Hz, 180 Hz, etc). This means power supply caps are possibly weak.But having this age I guess every electrolytic cap possibly can be in bad or very bad state (I mean in signal path too).When signal path caps are totally dead you likely wan't hear anything from that channel.

author: Pyral
author_rank: Contributor
timestamp: October 01, 2025, 02:49:03 am
content: I some more pictures and footage of the humming that it is suffering from. Linked below is a video of the output on an oscilloscope, as you can see it is choppy. I did the same test on another deck that has acceptable noise to get a baseline, the ripple was under a quarter the amplitude you see in the video despite it too having it's original capacitors that are only 5 years newer.I also did a frequency analysis on another recording of the audio output you can see for yourself. The video has the audio from the line out, it's been boosted by 200% so you don't have to crank the volume.Could this be a ground loop or is it defective capacitors?https://imgur.com/a/oQgnxyW

author: floobydust
author_rank: Super Contributor
timestamp: October 01, 2025, 04:42:10 am
content: A very common problem with cassette decks is the REC/PLAY switch getting oxidized and making poor connections.So during PLAY an open head connection can be heard as hum and noise. It resembles a dried out filter capacitor.The proper fix is applying a contact cleaner with PPE like DeOxit - but without getting the spray on any rubber parts, like belts, idler wheels etc. A paper towel liner, the deck oriented so the liquid only runs down the length of the long switch, and then move the switch a few times. I've done this repair many many times.You can gently, manually cycle the switch 100 times - using a screwdriver to move the slider back and forth, instead of using contact cleaner. It's a hassle.Another way to prove all this is put the deck in REC mode (you can tape or finger push the erase lockout tab to override it) and see what signal if any is there.With no incoming audio on LINE IN, the record level knobs should not have too much dirt when you turn them up - unless it's power supply hum and noise.If it's dead, won't record then it's the REC/PLAY switch.For the low value electrolytic caps say under 2.2uF, just use film caps. Like Kemet R82 series, Wima MKS0B04, Epcos B32529 etc.

author: Zoli
author_rank: Frequent Contributor
timestamp: October 01, 2025, 05:25:05 am
content: Quote from: Pyral on September 18, 2025, 07:45:21 pmSMD film capacitors; solder wire on the ends, heatshrink over the assembly. All three values (.1, .33, .47 µF) are available in 1206 size, for around 16-25V ratings.

author: tggzzz
author_rank: Super Contributor
timestamp: October 01, 2025, 10:10:37 am
content: Quote from: Pyral on October 01, 2025, 02:49:03 amPlease put the picture on this forum and not on some random server, since historically they disappear for a range of reasons.

author: Pyral
author_rank: Contributor
timestamp: October 04, 2025, 06:44:37 pm
content: I can't put the video on the forum because it's too large even as a zip. Here's a screen cap from the video and the frequency analysis of the audio. This is the base line audio, if you weren't playing anything you'd be listening to this buzz.I had to buy more .33 uF capacitors, the mom and pop store only had NTE mylar capacitors marked .33 MFD. Never heard of NTE capacitors. But they also have USA made LEDs made by them, so it's probably not new stock.

author: wraper
author_rank: Unknown
timestamp: October 04, 2025, 06:55:12 pm
content: Quote from: Pyral on September 18, 2025, 07:45:21 pmThat's some bullshit. Ripple current is how much current is pushed through the capacitor and in any normal circuit capacitor's own ESR does not play any significant role in that unless circuit was designed terribly wrong. Also in most cases very low value electrolytic capacitors can be replaced with 1uF with no negative side effects.

author: tggzzz
author_rank: Super Contributor
timestamp: October 04, 2025, 07:02:56 pm
content: No peak at 60Hz, so not mains hum getting into the input and being amplified by the signal chain.Peaks at 120/240/360/480Hz, so that probably means the PSU smoothing capacitors need replacing. They are probably electrolytics immediately after a bridge rectifier.First check: measure the DC voltage across the capacitors and compare with manual.Second check: measure the AC ripple voltage ideally with a scope, but if not then a voltmeter will do.Third check: measure the AC ripple voltage on the power rails supplying the signal chain. It should be a few mV at most.Don't bother with the signal chain until the power supply is working correctly.PSU smoothing capacitors are not going to be critical: choose anything with vaguely similar capacitance, equal or higher voltage rating, and a suitable ripple current at 120Hz (not 10kHz).

author: Pyral
author_rank: Contributor
timestamp: October 05, 2025, 02:29:21 am
content: I am in the process of replacing all the roughly 108 electrolytic capacitors.I tested the deck after only replacing the 3 large power supply capacitors, it still hummed. The light blue capacitors this thing is filled with, corresponds to the capacitors specified as Alsicons. The light blue capacitors are also know to develop crazy high ESR values as they age.

author: wraper
author_rank: Unknown
timestamp: October 05, 2025, 03:13:41 am
content: Hum usually appears when a relatively small value capacitor (like 10-100uF) fails in some sensitive circuit's power. Usually it's a capacitor after series resistor (tens to hundreds ohms) from a normal power rail. Also may have a Zener diode in parallel if it's stabilized. An example below:

author: wraper
author_rank: Unknown
timestamp: October 05, 2025, 03:26:41 am
content: I'd start from checking these.

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 05, 2025, 09:59:55 am
content: And some old audio devices make slight hum just by design.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 05, 2025, 10:59:32 am
content: Quote from: Pyral on October 05, 2025, 02:29:21 amIn this case, most probably it will still humm even after you replace them all. The ESR is critical in new devices with switching power supplies and very harsh current spikes (like in digital equipament/computers/etc.).For old analog audio, where usually there is no SMPS and no big switching currents, ESR is not an issue. If the capacitors after the bridge are not dried out (their capacitance is dtill in range), then the ESR is irrelevant. There were no low ESR capacitors back then, at least not in analog audio.Check the ripple after the bridge (with an oscilloscope, or with a DMM set to measure AC only), and if there is any significant ripple in standby, then check for any dried out filtering caps on the Vcc, right after the bridge, or like the ones highlighted before in the schematic.If those are OK, check if any metal shields (and the enclosure) are all properly grounded, check the shielded cables, too, particularly the ones in the preamplif/small signal areas.ESR is a problem in more recent equipment, mostly in SMPS power supplies, and not much anywhere else. Blindly changing all the capacitors in vintage analog audio is generally a bad idea. New ones will last less.Another thing, -40dB humm might be normal for a device where the S/N ratio is about 40dB or so, like in a casual tape recording. Check if the hum is not from the magnetic field of the transformer (so, noisy by design). Try to power the deck from another DC source (or remove the mains transformer from the enclosure, and keep it at a distance, with some half a meter wires to connect it to the rest of the deck). This will tell if the hum noise is induced magnetically, by the fields escaped outside of the magnetic core of the mains transformer. If that's the cause, that would be a design problem. Magnetic shields are hard to make, though there are special metals (e.g. Permalloy) shields for transformers. Or use a toroidal mains transformer instead of an E+I one. Toroidal ones confine their magnetic field way better than E+I cores.The most practical dirty fix (for magnetic induced hum) is to remove the transformer from the proximity of the sensitive audio stages, for example by removing it from the deck enclosure and put it in another box, at half a meter or so away. Not elegant, but trying to shield magnetic (not electric) fields is very hard.

author: floobydust
author_rank: Super Contributor
timestamp: October 05, 2025, 07:34:12 pm
content: In many cassette decks, the power transformer could be rotated for minimum hum, they have a circle of mounting holes for them. It was kind of decided late in production how to orient them. But the transformer should have a metal shield case.Where/how is the enclosure grounded to audio ground? Some have isolated RCA's. Would be nice to see more pictures of the internals.

author: Pyral
author_rank: Contributor
timestamp: October 05, 2025, 10:17:49 pm
content: The tape mechanism is opposite corner of the transformer, and anything handling audio is directly behind the tape mechanism. The EQ/Dolby are daughter boards off the amplification circuit, and all that is under a large metal shield. The amplification board is grounded by the same screws that hold the metal shield down over the pcb. The transformer has a metal shield over it too.The left ground point (for amp pcb) terminates on a metal frame rail which is connected to the metal tape mechanism and metal face plate. The other ground point screws into a metal plate in the back of the cabinet. Neither of these ground points looked tarnished or corroded when I removed them. The metal shielding over the transformer does have a bit of surface rust, which I might address.Here are some photos I took before I took it apart. The best I can do of the orientation of parts is a diagram from the service manual which I'll link below. I don't see why replacing the capacitors would be a bad idea, I using s-tier brands (Elna/TDK/Nichicon/Vishay).Service manual:https://elektrotanya.com/sanyo_rd5370_sm.pdf/download.htmlIn hindsight, the wire nuts going to the transformer do seem a little close to the ground point for the amplification circuit.

author: Pyral
author_rank: Contributor
timestamp: October 08, 2025, 06:53:51 am
content: Update: I finished the capacitor replacement. It is whisper quiet, the noise is gone 100%, and I didn't even reattach the shielding and most of the ground points yet.I'll get a photo from the scope of the new noise floor if my Tek 488 can capture the difference. It is exactly how I hoped. I need to make some speed adjustments, route cables better, and screw in panels, normal stuff. I went with my gut based on previous experience, it was the right choice.