- surface mount (guitar amp hisses) question - 4 Updates
- watt meters - 14 Updates
| Mike S <mscir@yahoo.com>: Jan 14 08:41PM -0800 I've got a Stagg 10 GA 10W RMS Guitar Amp, it has a serious hiss that comes and goes even with nothing plugged into it. So far I can't find a schematic for it, asked Stagg for one but no reply yet. I don't see any swollen caps, cleaned the pots with contact cleaner, the only things I can find so far (with no o-scoe) - are one component, I believe it's a zener diode, gets hot to the touch, and two surface mount components may have fallen off, I don't see them anywhere but they may have fallen out and been eaten by the carpet during disassembly. This is the amp. https://imgur.com/jIXc5Be These are the two locations on the ct. bd. where there is a little glob of red stuff, which might mean that a component lived there at one time. https://imgur.com/CzGJ1LS https://imgur.com/jIXc5Be What I think are Zeners, one of which gets pretty hot. https://imgur.com/NQu2dDS A terrible shot of the whole ct. board from the top, there's one output transistor, there are two preamp chips (I believe) on the bottom of the board. https://imgur.com/zBnbbjR Do those red globs mean anything? |
| "ohg...@gmail.com" <ohger1s@gmail.com>: Jan 15 06:38AM -0800 On Friday, January 14, 2022 at 11:41:59 PM UTC-5, Mike S wrote: > board. > https://imgur.com/zBnbbjR > Do those red globs mean anything? The fact that the adhesive exists in those locations doesn't mean those locations were ever populated. I've worked on thousands of smd boards and most have locations that were never populated from the factory, but every location had the adhesive applied anyway. This could be because it was decided those components weren't needed, there was a running change of other values of components loaded, or there may be circuit "refinements" that are only used on some more featured boards. Because they are designed with "ZD" and you can see "12V", those diodes are zeners. What is the voltage across the zeners? The fact that there are two of them tell me they're not just crowbars, but are active devices that are meant to provide a more or less regulated 12V all the time. If the voltage across them is 12V, they're still good most likely. If the voltage is low, one or both are probably leaky. If they read 12V across them, you want to verify the voltage fed to them on other side of the current limit resistor. For instance, if they were being fed by a 15V regulated source that has failed and is now feeding 20 volts to them, they will get hot and may not short for some time. |
| "ohg...@gmail.com" <ohger1s@gmail.com>: Jan 15 06:40AM -0800 On Friday, January 14, 2022 at 11:41:59 PM UTC-5, Mike S wrote: > What I think are Zeners, one of which gets pretty hot. > https://imgur.com/NQu2dDS Oops, those two zeners aren't paralleled. Still, the advice to check the voltage across the hot one and the feed voltage across the feed resistor is the same. |
| "Peter W." <peterwieck33@gmail.com>: Jan 15 08:10AM -0800 My observations are as follows, with the caveat that I know nothing at all about this amp specifically. a) I see a lot of what looks like corrosion at the solder points. Check to see if any of those are cracked or otherwise corroded beyond reliability. b) Intermittent hissing is more often than not thermal in nature, and typically a semi-conductor (diode, transistor or similar) goes short with heat. Your first answer is directly on-point for testing the zeners. c) I would not hit a glass 1/2-watt diode with freeze spray - but do check upstream of those diodes and try to determine if they are being fed too high a voltage, or downstream for a short such that they are passing too much current. Good luck with it! Peter Wieck Melrose Park, PA |
| "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com>: Jan 14 04:06PM -0500 I want a watt meter, but the prices are all over the place. Some are too cheap to be good. The one that Big Clive uses is nice but maybe more expensive than necessary to get basic accuracy and reliability. I don't see any that look like it anyway. At what price point do they transition from good to worthless? -- Defund the Thought Police |
| Phil Allison <pallison49@gmail.com>: Jan 14 03:36PM -0800 Tom Del Rosso wrote: ==================== > I want a watt meter, ** Watt for? > but the prices are all over the place. ** Bullshit. > Some are too cheap to be good. ** More bullshit. > expensive than necessary to get basic accuracy and reliability. I don't > see any that look like it anyway. At what price point do they transition > from good to worthless? ** Sure - lots of folk here have bought many, many such meters in order to compare performance and value. JUST IN CASE some fucking nut job like you asked this very question. .... Phil |
| Trevor Wilson <trevor@rageaudio.com.au>: Jan 15 10:55AM +1100 On 15/01/2022 8:06 am, Tom Del Rosso wrote: > expensive than necessary to get basic accuracy and reliability. I don't > see any that look like it anyway. At what price point do they transition > from good to worthless? **I use a couple of these on my bench: https://au.banggood.com/PZEM-028-AC-40-400V-100A-Digital-Multimeter-Voltage-Current-Power-Meter-Electrical-Instrument-Power-Factor-Meter-p-1790201.html?imageAb=1&rmmds=myorder&cur_warehouse=CN&DCC=AU¤cy=AUD&akmClientCountry=NL They're cheap and work fine. |
| Michael Trew <michael.trew@att.net>: Jan 14 09:05PM -0500 On 1/14/2022 16:06, Tom Del Rosso wrote: > expensive than necessary to get basic accuracy and reliability. I don't > see any that look like it anyway. At what price point do they transition > from good to worthless? I use this Kill-A-Watt meter for testing appliances. It displays the current Wattage/Amperage draw and kWh. It is reasonably priced to boot. It is available from many retailers, but here's an example: https://www.harborfreight.com/kill-a-watt-electric-monitor-93519.html |
| "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com>: Jan 14 11:03PM -0500 Trevor Wilson wrote: > **I use a couple of these on my bench: > https://au.banggood.com/PZEM-028-AC-40-400V-100A-Digital-Multimeter-Voltage-Current-Power-Meter-Electrical-Instrument-Power-Factor-Meter-p-1790201.html?imageAb=1&rmmds=myorder&cur_warehouse=CN&DCC=AU¤cy=AUD&akmClientCountry=NL > They're cheap and work fine. Thanks but I forgot to mention it should have an outlet rather than a terminal block. -- Defund the Thought Police |
| "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com>: Jan 14 11:07PM -0500 Michael Trew wrote: > boot. > It is available from many retailers, but here's an example: > https://www.harborfreight.com/kill-a-watt-electric-monitor-93519.html Thanks. I wanted confirmation that one of the inexpensive ones has been tested and approved. The $17 models might still be crap but if this is above that price point then that's what I needed to know. -- Defund the Thought Police |
| Trevor Wilson <trevor@rageaudio.com.au>: Jan 15 03:20PM +1100 On 15/01/2022 3:03 pm, Tom Del Rosso wrote: >> They're cheap and work fine. > Thanks but I forgot to mention it should have an outlet rather than a > terminal block. **Ah. Since this is a technical group, I assumed.... |
| "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com>: Jan 14 11:29PM -0500 Trevor Wilson wrote: >> Thanks but I forgot to mention it should have an outlet rather than a >> terminal block. > **Ah. Since this is a technical group, I assumed.... Thanks anyway, but if a device has a plug I'm not going to chop it off just to be technical. :) -- Defund the Thought Police |
| Trevor Wilson <trevor@rageaudio.com.au>: Jan 15 03:58PM +1100 On 15/01/2022 3:29 pm, Tom Del Rosso wrote: >> **Ah. Since this is a technical group, I assumed.... > Thanks anyway, but if a device has a plug I'm not going to chop it off > just to be technical. :) **Nor do I. I have one permanently wired into my variable auto-transformer (aka: Variac™), so I can monitor power consumption, as I slowly wind up the juice. |
| danny burstein <dannyb@panix.com>: Jan 15 05:50AM [snip] >Thanks. I wanted confirmation that one of the inexpensive ones has been >tested and approved. The $17 models might still be crap but if this is >above that price point then that's what I needed to know. There are a bunch of Kill-a-watt brand name meters. The basic one typicaly sells for about $25 and is available at lots of places, including (sometimes) Harbor Freight. I've been using them for two decades and have been quite satisfied with them. (Back when Usenet was still a thing people in the various household, energy, and similar groups would constantly reference them). So yeah, that's the way to go. One issue is that most of their models reset to "zero" if you unplug it, so you have to place it inline with your load in a location where you can see the display. SOme of them do (or at least did...) have the ability to "lock" those readings and hold them if you moved it off the outlet and then plugged it in elsewhere. (I last used one of those a decade ago..) -- _____________________________________________________ Knowledge may be power, but communications is the key dannyb@panix.com [to foil spammers, my address has been double rot-13 encoded] |
| Phil Allison <pallison49@gmail.com>: Jan 14 11:51PM -0800 Trevor Wilson wrote: ================= > **I use a couple of these on my bench: > https://au.banggood.com/PZEM-028-AC-40-400V-100A-Digital-Multimeter-Voltage-Current-Power-Meter-Electrical-Instrument-Power-Factor-Meter-p-1790201.html?imageAb=1&rmmds=myorder&cur_warehouse=CN&DCC=AU¤cy=AUD&akmClientCountry=NL > They're cheap and work fine. ** I note the ferrite ring used for current sensing. With just one pass through, the unit is not very sensitive. With 10 turns of 1sq.mm enameled copper instead or as well - it acquires a new purpose at mW levels. ..... Phil |
| Trevor Wilson <trevor@rageaudio.com.au>: Jan 15 07:43PM +1100 On 15/01/2022 6:51 pm, Phil Allison wrote: > ** I note the ferrite ring used for current sensing. > With just one pass through, the unit is not very sensitive. > With 10 turns of 1sq.mm enameled copper instead or as well - it acquires a new purpose at mW levels. **Good thinking. I'm pleased I bought two. Best of all, none of those horrible LCDs. Proper LED display. Fast and readable. |
| Phil Allison <pallison49@gmail.com>: Jan 15 02:27AM -0800 Trevor Wilson wrote: ================= > > With just one pass through, the unit is not very sensitive. > > With 10 turns of 1sq.mm enameled copper instead or as well - it acquires a new purpose at mW levels. > **Good thinking. I'm pleased I bought two. ** That is how my two range " RMS Current Monitor" operates. See EA magazine, May 1997. > Best of all, none of those > horrible LCDs. Proper LED display. ** You on drugs ? the display is very clearly LCD - with an orange backlight. .... Phil |
| "Peter W." <peterwieck33@gmail.com>: Jan 15 04:59AM -0800 You have not stated the purpose. If it is for monitoring basic consumption of an appliance of some sort, about any cheap plug-in device will work reasonably well. Say... US$20 or so from Amazon. If you are looking to see what your entertainment system is using and wish to add surge protection, then one of these: https://m.media-amazon.com/images/I/71MnT9n5upL._AC_SL1500_.jpg also from Amazon is useful. I keep one for the main system and it does work nicely. If you are looking for a bench tool and also for isolation, then look at something like this: https://www.byan-roper.org/steve/steve-at-play/antique-electronics-and-2/heathkit-ip-5220-variable.html I keep two. One permanently on the bench, one in the travel kit. Please ignore the Drongo from Down-Under. It is off its meds and aging out, a wretched and pitiful combination. Peter Wieck Melrose Park, PA |
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