Thanks but I'm a bit lost.
Would one of you kind people be able to explain about checking / setting the bias in a bit more detail. Keep in mind I only have a standard digital multimeter!
Should I go ahead and get the capacitors to modify the inputs as the Arcam chap suggested?
Overall, what is my best way forward?
Thanks again.
I would say at this point that the current is not critical. If it is not running hot without a large signal, I would suggest that the quiescent current is, as we say, near enough. But to check it, there is a 0.22 Ohm resistor in each pair of output FETS. Carefully measure, with no signal, across the resistor and adjust the voltage to as near as you can get 3.0mVolts. That's it.
As for the capacitors, they should be fitted already. Replacing them may help but they probably won't be faulty. I would check their position, if they have been res=oldered as they may be in the wrong place. Ask your tame Arcam Man for a photo/drawing of the layout. That should help.
As for the capacitors, they should be fitted already. Replacing them may help but they probably won't be faulty. I would check their position, if they have been res=oldered as they may be in the wrong place. Ask your tame Arcam Man for a photo/drawing of the layout. That should help.
Sorry, perhaps I wasn't clear back in post no 15.
The capacitors he was suggesting are a mod which they have done to only a very few of these amps. What I described was his recollection of how it was done, he couldn't find any written notes!
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No, I am sure it isn't you. I find these links, confusing.
The only thing I would suggest, regarding the interference is to check the capacitors, C303 and C304 have not been re-soldered and therefore possibly put in the wrong position and fit ferrite cores to the cables that are giving you issues.
I hope that helps.
The only thing I would suggest, regarding the interference is to check the capacitors, C303 and C304 have not been re-soldered and therefore possibly put in the wrong position and fit ferrite cores to the cables that are giving you issues.
I hope that helps.
I understand Frugality all too well, however this is growing beyond silly.
Have the Factory repair it? Likely the thing has been ineptly Bodged.. and You bought it..
Factory repair/refits usually come with a warranty.
Buy Cheap... buy twice
I thought this forum was called DIY Audio?
Everybody else has done their best to be helpful!
As I mentioned in post 15, Arcam are far from keen to work on it and no longer stock any proprietary spares for these units (although presumably standard electronic components wouldn't be a problem). As I live less than five miles from their factory it would otherwise have been a serious possibility.
In any case two of the problems seem to be "issues" rather than faults if you see what I mean. Two Arcam staff have talked about making modifications to the standard design to deal with the RF problem which it seems they had to do on a "handful" of amplifiers 15 years ago. They say it is an obscure combination of circumstances that causes this issue which I believe as there is no trace of it if I connect it up in my workroom.
They also say the very, very slight hum on the right channel is a design flaw and you only have to look at the inside to see why. A small rotation of the transformer may well improve this but it is very firmly stuck down so not easy to do.
Whilst I'm no expert on amplifiers (hence asking questions here and from their service department) I've done more than enough small soldering work in the past to be able to tell if a circuit board has been worked on. The only trace of any work is the pins of the output fets. I'm certain nothing else on the board has been touched.
So, what I have here is a fifteen year old "mid" price amplifier which was bought cheaply as the case is not pristine. A new front panel is not available. Even if Arcam were willing to do a "factory re-conditioned" job on the insides I suspect at UK prices it would not be economic. It is highly likely they wouldn't experience the RF issue so would have to modify it blind according to their current staff's recollections of what they did a "handful" of times in the past.
So, those are the reasons I'm asking for help and advice on a DIY forum and I'm sorry you think that is "beyond silly"!
Those capacitors are present and show no signs of ever having been disturbed. They are very close to the input sockets. There are no unused holes in the PCB. I suppose they could be faulty but it seems unlikely?
The capacitors the Arcam chap has suggest fitting are, presumably, are to do much the same job but better? He wants me to fit the directly on the sockets which would be quite easy. They are also ten times the value of the factory fitted pair?
Can I just double check that we are looking at the same service manual?
The one I have says 2.3 to 2.8 mV for the 8r and 3.0 to 3.5 mV for the 7r.
My amplifier is an 8, not an 8r. I had assumed that the r simply stood for "remote" but apparently not according to the chap at Arcam. The 8r has a different badge on the front panel. He didn't say what, if any, differences there were in the power stage.
I can't find a service manual online for the 8, only one titled "Arcam Alpha One/ 7R/ 8R/ 8P Amplifier Service Manual
Issue 1 Serial Number 001 - (Paul Newton/ Haider Bahrani Sept ‘98)".
This won't be immediate as I need to find something capable of reading a few mVs accurately. The lowest range on my meter is 2 volts and I'm not confident of the calibration on my ancient scope. I have a few bare moving coil meters somewhere. Maybe one will be something like 10 mV FSD!
There is no sign of the amplifier getting hot so I doubt it is set significantly too high.
Update - RF Interference cured
Well, I've fitted the capacitors and braid as suggested by the chap at Arcam. In fact I fitted seven rather than eight as the last phono socket is the pre-amp output so I wasn't sure whether one should be fitted there or not.
That seems to have cured the RF interference completely.
I still have hum issues. With just the Arcam CD player and Tuner connected it is very slight although with the Arcam Alpha 5 amplifier in the same setup there was none at all.
However, if I plug my Sony BluRay player in the hum increases significantly regardless of which input is selected. Again, when connected to the 5 there was no problem at all.
Whilst I understand the chap's explanation about why there might be "slight" hum on the right I feel I have more than is reasonable.
There are other devices all around the setup and it is not easy to isolate. However, they didn't affect the Alpha 5.
The units are all plugged into wall sockets on a ring main, not trailing four ways.
Any other ideas would be most welcome.
Thanks
Well, I've fitted the capacitors and braid as suggested by the chap at Arcam. In fact I fitted seven rather than eight as the last phono socket is the pre-amp output so I wasn't sure whether one should be fitted there or not.
That seems to have cured the RF interference completely.
I still have hum issues. With just the Arcam CD player and Tuner connected it is very slight although with the Arcam Alpha 5 amplifier in the same setup there was none at all.
However, if I plug my Sony BluRay player in the hum increases significantly regardless of which input is selected. Again, when connected to the 5 there was no problem at all.
Whilst I understand the chap's explanation about why there might be "slight" hum on the right I feel I have more than is reasonable.
There are other devices all around the setup and it is not easy to isolate. However, they didn't affect the Alpha 5.
The units are all plugged into wall sockets on a ring main, not trailing four ways.
Any other ideas would be most welcome.
Thanks
Does the hum appear if you just touch the Sonys "ground" part of the output lead (the outer) on to the corresponding "outer" part on the Arcams input sockets ? That doesn't read very well does it.
I'm wondering... is the Alpha 5 grounded via its mains lead or is it a two core double insulated product and is the Alpha 8 a three core mains lead with ground connected ?
I'm wondering... is the Alpha 5 grounded via its mains lead or is it a two core double insulated product and is the Alpha 8 a three core mains lead with ground connected ?
Interesting, many thanks, I'll investigate that tomorrow.
The Alpha 8 has a three core lead with the case grounded. The "ground" on the input sockets are not connected to the case (well, they are now at RF via the capacitors)!
I'll look at the 5 to see how that compares.
It is a BDP-S185 and has a two core mains lead.
50 or 100 - Sorry to sound daft but I honestly don't know! It is 25 years plus since I used to play around with a little electronics so I'm not well tuned in. My guess is 50 Hz but I'll try to confirm.
Although interesting in terms of what on "earth" is going on here I don't actually need to connect the Blu-Ray player to the Arcam providing I can solve the next bit.....
More relevant is that I'm getting a similar problem connecting my TV via an optical to stereo phono adaptor . That has the inevitable plug in 5v power supply. Again, this was fine with the Arcam 5.
The whole installation is difficult to get to but I gong to haul the whole lot out today and rebuild bit by bit to try and be certain where the problem starts.
I will also double check the mains earthing etc.
Ok Harleyjon, Mooley and others.....
If you can stand it, here is my latest update.
I have removed TV, HD recorder Blu-Ray and everything else from the area and checked mains leads.
With the Arcam Alpha 8 amplifier only there is the faintest hum from the right speaker only just as the Arcam chap described as "normal". This is down at a level you would only notice with an ear close to the speaker. It maybe increases very, very slightly at full volume. The amp uses a three core mains lead.
Adding the Arcam 8 CD player with decent quality audio leads makes no detectable difference. The CD player does not have an earth pin in its kettle type socket.
The moment I connect anything else, including an Arcam 7 Tuner, I get a noticeable hum from BOTH speakers. This is audible in a quiet room at normal listening distance. The tuner also is two core mains. Using my highest quality phono leads maybe reduces this very slightly but it is still unacceptable.
My powered optical to phono converter is slightly better providing I use a short, high quality phono lead but my Sony BluRay player is the worst. Both have two core mains.
So, at the moment it is only good with the CD player, borderline with the converter and unusable with the tuner and BluRay.
If I substitute the Arcam 5 amplifier everything is perfect!
Help!!!!
Thanks
If you can stand it, here is my latest update.
I have removed TV, HD recorder Blu-Ray and everything else from the area and checked mains leads.
With the Arcam Alpha 8 amplifier only there is the faintest hum from the right speaker only just as the Arcam chap described as "normal". This is down at a level you would only notice with an ear close to the speaker. It maybe increases very, very slightly at full volume. The amp uses a three core mains lead.
Adding the Arcam 8 CD player with decent quality audio leads makes no detectable difference. The CD player does not have an earth pin in its kettle type socket.
The moment I connect anything else, including an Arcam 7 Tuner, I get a noticeable hum from BOTH speakers. This is audible in a quiet room at normal listening distance. The tuner also is two core mains. Using my highest quality phono leads maybe reduces this very slightly but it is still unacceptable.
My powered optical to phono converter is slightly better providing I use a short, high quality phono lead but my Sony BluRay player is the worst. Both have two core mains.
So, at the moment it is only good with the CD player, borderline with the converter and unusable with the tuner and BluRay.
If I substitute the Arcam 5 amplifier everything is perfect!
Help!!!!
Thanks
Many modern items (especially from Sony!) make a habit of injecting hum into their ground connection via the EMC suppression capacitors in the mains feed. I seem to recall the usual safety limit for this (to stop you dropping things on your foot when you get a sharp tingle) is 1mA. Sony equipment will happily inject several 100uA, which may be enough to generate audible hum. I first discovered this Sony 'feature' when my TV injected a serious tingle into the antenna wiring shared with my FM tuner.
Provided all audio signals are referred back via one path to one point this should not cause a problem. However, I guess your BluRay is also connected to the TV so that might introduce an alternative ground path. Does the hum go away when the HDMI/Scart is unplugged?
Provided all audio signals are referred back via one path to one point this should not cause a problem. However, I guess your BluRay is also connected to the TV so that might introduce an alternative ground path. Does the hum go away when the HDMI/Scart is unplugged?
Very interesting - thanks.
I thought I was imagining it with the tingle on the end of the leads!
Unfortunately I no longer have it connected as an easy solution was just to use the optical output from the TV (more chance of being in sync with the picture)! Now I've put everything back in the furniture it is not easy to get a connection to try it but I will do when I can.
Still doesn't explain why the Arcam Tuner should be nearly as bad though as that is the same generation as the amp and CD.
It all sounds like a classic case of a ground loop and unfortunately there's not always an easy fix.
Lifting or breaking mains safety grounds isn't recommended for obvious reasons but there are workarounds,
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Lifting or breaking mains safety grounds isn't recommended for obvious reasons but there are workarounds,
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Thanks for that link.
The optical to stereo phone adaptor I'm using has the inevitable plug in (presumably switch mode) power supply.
Is there an easy way of getting it a better source of 5volts that won't create a ground loop? Apart from a battery obviously!
You would need to be sure that this device really was the problem first but yes, there are easy ways to get 5 volts without a ground loop.
DIYing a small 5 volt PSU is easy.
If this SMPS is the problem (or a possible problem) you will be able to measure continuity from its mains plug earth pin to the ground on the 5 volt output. If there is no continuity then there's no ground loop via that route.
DIYing a small 5 volt PSU is easy.
If this SMPS is the problem (or a possible problem) you will be able to measure continuity from its mains plug earth pin to the ground on the 5 volt output. If there is no continuity then there's no ground loop via that route.
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