Hi, I have a really nice Alpha 10 that has a problem with the left channel. The right sounds fine nice and clear, but i have to turn the left all the way up before i hear the slightest sound. I used the pre-amp outputs and plugged it into a separate amp, and sure enough the right sounded fine but the left was non-existent. So i think we are up too the pre-amp being the problem. I changed a couple of caps that were a little high but that did not solve it. Do you think perhaps i should change the LM1972? Do you think that would solve it? Also is this just a drop in part or does it need firmware? Thanks.
If you have no output from the preamp, there is more to look at than just the volume controller chip. First though, you might check that the chip's output levels are the same with the same input to each channel input.
Rather than guessing, use a signal tracer. Any small, preferably battery powered, sensitive amplifier and speaker or headphones will often do for the tracing part and any music or better, a tone source will do for the reference input. Your PC can supply masses of different tones (often free) from any number of music production and audio processing interest websites as required. Some are rather dense and difficult to get started with but I have no trouble with steering this one to simple tones and sweeps, which is all I want: Download | Audacity(R)
Terminate the tracer input and signal source output leads with small clips or tiny hooks, hand formed from solid wire, as I often do but ensure that they can't fall off and short anything else in use. Alternatively, insulated meter probes can be used with care, and these allow you to sweep quickly between points of interest.
For safety and DC isolation, fit a film capacitor inline with the tracer's input probe and the signal output probes - 0.1-1uF should be fine and permit reasonable sound. Battery operated devices would be preferable and we often have several of these around the home which could be adapted for use.
Here's a guide to audio signal tracing which you'll find helpful for general audio troubleshooting: http://sound.whsites.net/project164.htm
Check the referenced articles too.
Rather than guessing, use a signal tracer. Any small, preferably battery powered, sensitive amplifier and speaker or headphones will often do for the tracing part and any music or better, a tone source will do for the reference input. Your PC can supply masses of different tones (often free) from any number of music production and audio processing interest websites as required. Some are rather dense and difficult to get started with but I have no trouble with steering this one to simple tones and sweeps, which is all I want: Download | Audacity(R)
Terminate the tracer input and signal source output leads with small clips or tiny hooks, hand formed from solid wire, as I often do but ensure that they can't fall off and short anything else in use. Alternatively, insulated meter probes can be used with care, and these allow you to sweep quickly between points of interest.
For safety and DC isolation, fit a film capacitor inline with the tracer's input probe and the signal output probes - 0.1-1uF should be fine and permit reasonable sound. Battery operated devices would be preferable and we often have several of these around the home which could be adapted for use.
Here's a guide to audio signal tracing which you'll find helpful for general audio troubleshooting: http://sound.whsites.net/project164.htm
Check the referenced articles too.
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Thanks for that i do have output from the right. I will look into it, also with the sound turned right up and only the left speaker plugged in, the slight music I can hear, is coming from the amp itself, not the speaker? Is that strange?
This is likely just cross-talk. i.e. the leaking of one channel into the other throughout the signal chain due to the proximity of wiring, PCB traces, switches with contaminated insulator surfaces and via the common power supply. It's inevitable in any analog multi-channel system and you can read it from the amplifiers spec. (-80 dB @ 1kHz) but usually it's more at higher frequencies. Given the large dynamic range of audio, a little cross-talk becomes a significant and clearly audible quantity at the loudspeakers in the absence of the good channel's overriding power output.
You won't learn much following this line of investigation. You need to look for full strength signals by tracing them properly, following the schematic (see service manual).
Sign up here if not already, its free: Arcam Alpha 10 - Manual - Stereo Integrated Amplifier - HiFi Engine
You won't learn much following this line of investigation. You need to look for full strength signals by tracing them properly, following the schematic (see service manual).
Sign up here if not already, its free: Arcam Alpha 10 - Manual - Stereo Integrated Amplifier - HiFi Engine
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Firstly, decide if all inputs are at fault. If they are, select a L&R input, insert an equal signal to each side and trace the audio through the electronic switching and pre amp ICs. Continue until the fault is found.
I see I misread you and yes, you can sometimes hear sound from the power transformer windings, of all places and its often louder when the speakers are working hard too. You can even hear the output transistors singing with powerful PA amps.
I am wondering if i should get one of these you know, completely rubbish but it should suffice for what i want to do. Don't think much of the probes though, do you think this would take different probes like real oscilloscope ones?
DSO138 2.4" TFT Digital Oscilloscope DIY SMD Soldered Electronic Learn Set E8X8 | eBay
DSO138 2.4" TFT Digital Oscilloscope DIY SMD Soldered Electronic Learn Set E8X8 | eBay
The key is in the "electronic learn set" part of the title. You really need to know how they work and what to expect, how to read the display etc. to make it do what you want before you begin. Typically, there won't be any useful documentation or guide to use or for checking whether it's properly functional and suits your purpose etc. Chinese kits and bits like that one are fun but it's often a chore using them and difficult to get more than basic, uncalibrated indications on the tiny displays. You may just wind up with another toy to fill your storage box there.
Having said that, the fun you can have in learning to use mini-scopes alone can be worthwhile and you do learn something for the money, if you choose to assemble them as a kit. If you'd rather get on and fix your amplifier though, tracing where the signal stops is the name of the game and that doesn't require a visual aid. A little audio amplifier - even a cheap little radio where you can access the volume control and use that as an input point or a headphone amplifier etc. with a cheap little speaker and your ears is quite sufficient.
A pair of BNC/clip leads like those shown is usually fine for audio but will need a point contact (say, even a short piece of thick wire) for the lead you use as a probe (red) while the other (black) is used as is - clipped to ground. The fancy 'scope probes have the same BNC connector as shown and will be compatible though only really needed for RF and fast switching waveforms which are usually out of the range of learning 'scopes like this one. Still, properly adjusted, good quality probes are nice to use and will give more accurate waveforms with better noise immunity, if needed. Short, plain meter leads with probes or one you make up from a spare short BNC connector lead though, can do just as well for the few hundred Hz of audio frequency bandwidth needed.
Having said that, the fun you can have in learning to use mini-scopes alone can be worthwhile and you do learn something for the money, if you choose to assemble them as a kit. If you'd rather get on and fix your amplifier though, tracing where the signal stops is the name of the game and that doesn't require a visual aid. A little audio amplifier - even a cheap little radio where you can access the volume control and use that as an input point or a headphone amplifier etc. with a cheap little speaker and your ears is quite sufficient.
A pair of BNC/clip leads like those shown is usually fine for audio but will need a point contact (say, even a short piece of thick wire) for the lead you use as a probe (red) while the other (black) is used as is - clipped to ground. The fancy 'scope probes have the same BNC connector as shown and will be compatible though only really needed for RF and fast switching waveforms which are usually out of the range of learning 'scopes like this one. Still, properly adjusted, good quality probes are nice to use and will give more accurate waveforms with better noise immunity, if needed. Short, plain meter leads with probes or one you make up from a spare short BNC connector lead though, can do just as well for the few hundred Hz of audio frequency bandwidth needed.
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Thanks Ian, That was really helpful. I have used a scope before, but it was 26 years ago when i did a college electronics course. I did order the Chinese one because it was so cheap, and since i did not have all those other basic parts you recommended it probably would have added up close to the same. hoping it is only that LM1972 or the OPA2134UA. Not sure why the schematic shows it as OPA2134PA when that version seems to be through hole and the one in the amp is clearly sm?
For interest, just last year I paid only about the equivalent of ₤4 in total for a little AM radio and a tiny NE555 oscillator board to make up a tracer for a young experimenter friend. It took about 20 mins to work out where to disconnect the tuner, fit the power and signal wires then close up with a battery in place. It works a treat and I assume, for long enough to see in the next phase of audio tinkering.
Regarding the Alpha 10 schematic, I see there are a few early production board mods and when you see a change from thru-hole to SM, it probably means an availability issue. I can't think why else you'd change a board that was only a year in production unless there was a requirement for more features/space. I have to say, its a very busy design and build with more features than most people will even appreciate.
Regarding the Alpha 10 schematic, I see there are a few early production board mods and when you see a change from thru-hole to SM, it probably means an availability issue. I can't think why else you'd change a board that was only a year in production unless there was a requirement for more features/space. I have to say, its a very busy design and build with more features than most people will even appreciate.
I think it is because it was a modular design you could turn it into an AV amp with the addition of the DAVE module.
Most modern electronics are a bind to work on, just because the took away the screw on under flap.
Just on another thing while i am waiting for parts, I also have the power amp version of this i recently bought with the flashing red light problem. It looks like one of those units which was passed around with people thinking it was that TA7317P that was faulty. It looks like it has been changed several times. Anyway I found the fault and fixed it, it now powers on, but there seems to be a problem with DC offset. When you first power on and the speaker relays kick in, the offset reads about 14mv but then it starts to climb until it reaches about 390mv then it will pause and climb back down to close to 0mv and stay there all over the space of 1 minute and on both channels. I am not sure what to make of that. What do you think? Do you think it should be recapped. Thanks.
Maybe such an amp is it:
https://img.usaudiomart.com/uploads...d-amplifier-alpha-10p-power-amp-available.jpg
To start troubleshooting - at these connection points/nodes you must perform sound check with an independend low-output power amp/computer speaker as follow:
- output LM1972/input power amp
- input LM1972
- output source select (input selector)
- inputs source select (input selector)
Which nodes sounds identical to the working channel and which not - that is the question.
If there are C-MOS input selector IC parts, maybe one of them is faulty.
Check also the (very worse quality) speaker selector switches "SP1" and "SP2"
390mV DC could be a threat to your speakers for any length of time but not a problem to the amplifier. If the correction holds for the duration of use after the minute it takes to settle, it does seem that there is servo malfunction. However, there is a block diagram and full description of the cycle of events and LEDs which should light up at each stage of starting up and error detection in the Alpha 10/10P. Have you checked that to eliminate some possibilities?
Being a Mosfet amplifier, it has a DC servo (Z3) controlling offset. That is independent of the DC protection afforded by the TA7137 which trips quickly at a higher voltage, according to your measurement earlier. There are actually 2 DC servos to accommodate both DC and AC coupled operation - yes, it gets very complicated as you delve in there and personally, I would not play with this amplifier wthout a full understanding of how it is supposed to operate and monitor its own condition. This evidently, was too hard also for the previous owner and why it was sold on.
BTW, Tiefbass... has reiterated the advice to use a separate amplifier for troubleshooting (signal tracing) but suggested you use a powered PC speaker which is great idea for the repairer with nothing else. For that matter, you could use a 3.5mm stereo input lead with your PCs soundcard or whatever tablet/phone gadget you may have. If you don't even have spare leads you surely have something spare with one attached if you play with audio devices.
Hi Ian, The power amp initially at switch on, the led would be green then after 16secs it would switch off flashing red, I traced that to one of the four 6amp 400v diodes being short circuit and replaced. Now at switch on the led is amber then about three seconds later a relay click and green led. I believe this is correct for a no error functioning unit. So why it thinks this 390mv is okay is unclear?
I can not locate Z3, also Q59f seems to be missing not sure if that was deliberate in the power amp version of if has been removed. Also the heatsink for Z7 had gone walkies, so i had to source a replacement, and replaced the Z7 +8v regulator in case it was damadged because of this. Thanks.
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