I'd be most grateful for some help........
About a year ago I had two longish threads running on here regarding problems with my Arcam Alpha 8 amplifier. With help from a number of kind posters I made some progress but never really solved the problems. Other life issues have got in the way and it is only now that I have time to revisit the issues.
Rather than re-open the old threads I thought it best to start again with a (hopefully) clear summary of the problem. I've put links to the old threads at the bottom in case anybody wants to read them.
Problem 1 - RF Interference (maybe solved)
The amplifier suffered from bad RF interference to the point that you could hear what was being said on a radio station! This was on all inputs and was not affected by the volume control. Arcam themselves suggested a "mod" of fitting a row of 10 nF capacitors between the phono socket grounds and a length of copper braid attached to the screw for the turntable earth on the back panel. Although this worked it always bothered me that it should be necessary and that I was perhaps masking the real problem. An Arcam Alpha 5 amplifier, used in substitution for the 8, showed no problems at all.
Problem 2 - Hum from Rt Channel
Even with nothing connected to any input (or with the input shorted) there is a noticeable hum from the right hand speaker only. Arcam say this is a known issue and that I may be able to improve this by rotating the mains transformer. I've not tried this as it is very firmly stuck down so hard to do. There are bigger problems (see Nos. 3 & 4 below). If I can solve these first then I will make the effort to get the transformer unglued and try rotation. Despite Arcam's comments I would have thought there was more hum than could be regarded as acceptable. Again my Alpha 5 does not show this problem and is of a similar design.
Problem 3 - Hiss
Again with nothing connected or with the input shorted there is a slight but noticeable hiss from both channels. Not huge but more that I would regard as normal or acceptable. Again the Alpha 5 does not have this problem.
Problem 4 - Susceptibility to ground loop / hum issues
This is by far the biggest problem. This amplifier seems to have "issues" with just about any item of equipment I connect to it! The only exception seems to be my Arcam Alpha 8 CD player. I can plug this in and it works fine with no hum other than that described in Problem 2 above. Anything else, including my Arcam Alpha 7 tuner produces significant hum from both speakers and some other items are even worse. Last year we worked through various things and reduced the hum slightly but never got down to an acceptable level.
Basically I cleaned and improved the PCB to case earth connection, re-soldered all of the socket 0V connections, cleaned all the sockets and checked the integrity of the 100 ohm resistor that separates 0V from mains / case earth. Whilst this certainly made an improvement I would only describe it as about a third better, nowhere near a complete fix.
A ground loop isolator phono lead does not solve the problem either!
So there we are, hopefully I'm missing the blindingly obvious and somebody will spot it!
Many thanks.
Here are links to the old threads......
http://www.diyaudio.com/forums/solid-state/228030-arcam-alpha-8-rf-interference.html
http://www.diyaudio.com/forums/solid-state/228750-power-supply-question-arcam-alpha-8-a.html
About a year ago I had two longish threads running on here regarding problems with my Arcam Alpha 8 amplifier. With help from a number of kind posters I made some progress but never really solved the problems. Other life issues have got in the way and it is only now that I have time to revisit the issues.
Rather than re-open the old threads I thought it best to start again with a (hopefully) clear summary of the problem. I've put links to the old threads at the bottom in case anybody wants to read them.
Problem 1 - RF Interference (maybe solved)
The amplifier suffered from bad RF interference to the point that you could hear what was being said on a radio station! This was on all inputs and was not affected by the volume control. Arcam themselves suggested a "mod" of fitting a row of 10 nF capacitors between the phono socket grounds and a length of copper braid attached to the screw for the turntable earth on the back panel. Although this worked it always bothered me that it should be necessary and that I was perhaps masking the real problem. An Arcam Alpha 5 amplifier, used in substitution for the 8, showed no problems at all.
Problem 2 - Hum from Rt Channel
Even with nothing connected to any input (or with the input shorted) there is a noticeable hum from the right hand speaker only. Arcam say this is a known issue and that I may be able to improve this by rotating the mains transformer. I've not tried this as it is very firmly stuck down so hard to do. There are bigger problems (see Nos. 3 & 4 below). If I can solve these first then I will make the effort to get the transformer unglued and try rotation. Despite Arcam's comments I would have thought there was more hum than could be regarded as acceptable. Again my Alpha 5 does not show this problem and is of a similar design.
Problem 3 - Hiss
Again with nothing connected or with the input shorted there is a slight but noticeable hiss from both channels. Not huge but more that I would regard as normal or acceptable. Again the Alpha 5 does not have this problem.
Problem 4 - Susceptibility to ground loop / hum issues
This is by far the biggest problem. This amplifier seems to have "issues" with just about any item of equipment I connect to it! The only exception seems to be my Arcam Alpha 8 CD player. I can plug this in and it works fine with no hum other than that described in Problem 2 above. Anything else, including my Arcam Alpha 7 tuner produces significant hum from both speakers and some other items are even worse. Last year we worked through various things and reduced the hum slightly but never got down to an acceptable level.
Basically I cleaned and improved the PCB to case earth connection, re-soldered all of the socket 0V connections, cleaned all the sockets and checked the integrity of the 100 ohm resistor that separates 0V from mains / case earth. Whilst this certainly made an improvement I would only describe it as about a third better, nowhere near a complete fix.
A ground loop isolator phono lead does not solve the problem either!
So there we are, hopefully I'm missing the blindingly obvious and somebody will spot it!
Many thanks.
Here are links to the old threads......
http://www.diyaudio.com/forums/solid-state/228030-arcam-alpha-8-rf-interference.html
http://www.diyaudio.com/forums/solid-state/228750-power-supply-question-arcam-alpha-8-a.html
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Start with the basics.
Hum can only come from 5 places.
1. Airborne.
2. Ground Loop.
3. Supply.
4. External Input.
5. Poor Design.
5. Is unlikely, I've had one of these and had no such issues with it.
If the transformer is a possibility, remove it and place it ouside of the case just to test it.
Hum can only come from 5 places.
1. Airborne.
2. Ground Loop.
3. Supply.
4. External Input.
5. Poor Design.
5. Is unlikely, I've had one of these and had no such issues with it.
If the transformer is a possibility, remove it and place it ouside of the case just to test it.
Really?
Given that 17 years on a guy at Arcam can recall a mod to fix the "rare" RF issues and admits that they are prone to the right hand hum problem (due to the PCB layout where that power amplifier virtually wraps round the transformer) I would hardly say it was a good design?
Whilst I accept that rotating, moving or maybe screening the transformer may well fix the right hand only hum what I don't understand is how that could affect the other issues. Given that I feel I have more right hand hum than they could possibly regard as acceptable I can't help feeling there is another problem that is making the circuit more susceptible to hum?
A slight hiss isn't really a problem, it is likely just resistor noise.
Unless you want to replace them with low noise resistors you are stuck with it.
Valve amplifiers are always critical with hum due to inherent high impedance circuitry.
I have designed a couple of high gain valve amps and had lots of feedback and hum noise.
This was mainly due to poor heater wire routing, bad pcb layout and lack of decoupling.
You could try earthing the input signal ground to get rid of hum.
I find with mp3 players I get hum which goes if I attach my oscilloscope which is grounded.
Unless you want to replace them with low noise resistors you are stuck with it.
Valve amplifiers are always critical with hum due to inherent high impedance circuitry.
I have designed a couple of high gain valve amps and had lots of feedback and hum noise.
This was mainly due to poor heater wire routing, bad pcb layout and lack of decoupling.
You could try earthing the input signal ground to get rid of hum.
I find with mp3 players I get hum which goes if I attach my oscilloscope which is grounded.
Erm. Shouldn't that be ~10R? Otherwise, the obvious question regarding hum is what's so different about the CD player input that prevents hum, as opposed to other inputs, hmm?
If the CD player is swapped to other inputs and least hum level transfers with it, that suggests an unsuitable earthing arrangement for the other sources (like mains grounding) rather than an amplifier fault. If the least hum level stays at the CD input sockets only, it suggests a remaining input wiring fault, since the sockets and switches are effectively the only other difference.
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Ahh..interesting. The Alpha 5 has mains earth (wait for it) actually connected to the chassis as Protective Earth, like most us would like to see. The 100R resistor interposed in the Alpha 8 is the significant design difference. Why that scheme that floats the whole system at 100R above ground, I don't know but wiser heads, electrical safety standards etc. etc.
Download the Arcam Alpha 5 service manual for free - Hifi Manuals
Download the Arcam Alpha 8-R service manual for free - Hifi Manuals
The reference to 8R instead of 8 seems to mean the manual covers several models as there is no 8R.
Download the Arcam Alpha 5 service manual for free - Hifi Manuals
Download the Arcam Alpha 8-R service manual for free - Hifi Manuals
The reference to 8R instead of 8 seems to mean the manual covers several models as there is no 8R.
Apologies, I was assuming the OP's comment in an earlier thread had vetoed R for RC. Perhaps he misunderstood the Arcam rep. but his Alpha 8 came with remote - perhaps an aftermarket addition?
Anyway, I'll suggest the hum issue is down to this dicey earthing arrangement. Any problem with shorting the 100R ohm resistor, lighting the blue touch paper and standing back at a safe distance to see, or rather hear?
Anyway, I'll suggest the hum issue is down to this dicey earthing arrangement. Any problem with shorting the 100R ohm resistor, lighting the blue touch paper and standing back at a safe distance to see, or rather hear?
Thanks.
Yes, I've wondered about this too. Arcam's first reaction was to ask me to check that resistor. They told me how to check it in circuit (can't remember details now) rather than just measuring across the component. It was fine.
I will try this at some point, along with simply rotating the transformer. However both involve getting it unstuck from the board without doing damage which I'm told is not easy.
No, as I understand it both versions have the circuit and motorised pot built in but only the 8r is supplied with a remote control. Otherwise, like me, you use the extra buttons on the CD player's remote control to adjust the amplifier volume.
What this does mean, unlike the Alpha 5, is that there are an additional pair of twisted wires (6 volts AC) going from the transformer all the was across to the remote circuit on the extreme left. I have tried moving these as far as possible but it doesn't seem to affect the hum.
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The CD player (and come to that the tuner and pretty much everything else I've tried) do not have mains earth connections. Arcam seemed to use the same "kettle" type plug on everything but with the earth pin missing except for the amplifier.
So there is nothing obviously different about the CD player that works OK compared with the tuner that gives problems. I've tried just using an indoor aerial in case the proper one was causing an earth loop but no better.
I follow the intention but according the OP's advice, there ain't no earth connection anywhere else to form such a loop, since all other devices, including TV are 2-pin only (hopefully double insulated). The grounding of any phono player in the conventional way presents a bit of a problem there too. The only mains earth is at least 100R away for the whole Hi-fi system.
The amplifier, when earthed as with the Alpha 5 amplifier, no longer has the hum problem. I think that's the clue to where the basic problem lies.
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That is very much my thought too.
I've not tried it with a turntable. The only one I own is a Dual 505 and that too has only a two core mains lead. It is used with the Alpha 5 elsewhere and works fine.
To be honest I'm so fed up the Alpha 8 issues I'm trying to fix it with a view to selling with a clear conscience . What I don't want to do (although it would be interesting) is modify it to get round the problem for my particular setup.
If anybody wants to make me an offer for Alpha 8 amplifier (issues described in detail on this forum) an Alpha 8 CD (perfect) and an Alpha 7 tuner (one segment failed on right hand display digit, otherwise perfect) then I love to hear from you!!!
Update
OK, so I've managed to unstick the transformer and tried rotating it by varying amounts. Unfortunately the length of the leads only allows me to go about 15 degrees anti-clockwise but I can go easily 90 degrees or more in a clockwise direction. I've tried moving in 5 to 10 degree increments all the way round this arc but can detect no difference. A slight hum remains on the right speaker, completely unaffected by the volume setting. There is no increase in hum even on the phone input at full volume although there is a lot more hiss! This seems roughly equal in both channels so presumably must be a power supply issue?
As part of the strip down I again cleaned the case earth connection (pcb board to right hand side) and also where the back panel bolts to the side. This may have made a slight improvement but it is hard to tell.
The right hand power amplifier virtually wraps round the transformer so I suspect this is largely a design problem and / or a poorly would toroid!
I've not tried extending the leads and moving the transformer outside. Whilst I suspect this may well work it wouldn't really get me anywhere.
Hey ho!
OK, so I've managed to unstick the transformer and tried rotating it by varying amounts. Unfortunately the length of the leads only allows me to go about 15 degrees anti-clockwise but I can go easily 90 degrees or more in a clockwise direction. I've tried moving in 5 to 10 degree increments all the way round this arc but can detect no difference. A slight hum remains on the right speaker, completely unaffected by the volume setting. There is no increase in hum even on the phone input at full volume although there is a lot more hiss! This seems roughly equal in both channels so presumably must be a power supply issue?
As part of the strip down I again cleaned the case earth connection (pcb board to right hand side) and also where the back panel bolts to the side. This may have made a slight improvement but it is hard to tell.
The right hand power amplifier virtually wraps round the transformer so I suspect this is largely a design problem and / or a poorly would toroid!
I've not tried extending the leads and moving the transformer outside. Whilst I suspect this may well work it wouldn't really get me anywhere.
Hey ho!
Some amplifiers are noisier than others but increasing hiss with volume is characteristic of all preamplifiers and integrated amplifiers as DIYs and audio veterans know well. It has nothing to do with power supplies since it's the tiny random noise of the currents flowing in the components of low level (sensitive) circuits.
If hum doesn't change with volume, it only means the point of injection is after the volume control. In this integrated amp, that means just the tone control circuits and power amps. You could go on, disconnecting the inputs to the power amplifiers and prove that the hum is from the power supply and must be an earthing issue but you are then back at the beginning.
As on a lot of double insulated equipment, there is a foil shield between transformer primary and secondary windings, presumably to squish mains noise getting in via inter-winding capacitance. This is joined (green lead) to mains earth via a connector. Test the continuity to mains earth at the mains socket on the rear panel there (unplugged!) and remake the transformer lead connection. A bad one could make a difference.
If hum doesn't change with volume, it only means the point of injection is after the volume control. In this integrated amp, that means just the tone control circuits and power amps. You could go on, disconnecting the inputs to the power amplifiers and prove that the hum is from the power supply and must be an earthing issue but you are then back at the beginning.
As on a lot of double insulated equipment, there is a foil shield between transformer primary and secondary windings, presumably to squish mains noise getting in via inter-winding capacitance. This is joined (green lead) to mains earth via a connector. Test the continuity to mains earth at the mains socket on the rear panel there (unplugged!) and remake the transformer lead connection. A bad one could make a difference.
That is an electrostatic screen and is used for helping with EMC conducted emissions and/or keeping mains-borne noise out of the secondary. By definition double insulated equipment has no mains earth connection, but that's getting into semantics and away from the topic! It will not have any impact on the hum or noise issue here.
I'm wondering if there is a 0V connection/track on the humming channel that is broken on the PCB. Try getting a piece of wire and put one end on the outer of the phono socket of the humming channel and the other end on the screw on the rear panel that the mains earth is connected to. Also try touching it to the other channel's phono socket outer.
I'm wondering if there is a 0V connection/track on the humming channel that is broken on the PCB. Try getting a piece of wire and put one end on the outer of the phono socket of the humming channel and the other end on the screw on the rear panel that the mains earth is connected to. Also try touching it to the other channel's phono socket outer.
Thanks.
Just to clarify, the amplifier is not double insulated (although both the CD player and tuner are).
The amp has a toroidal transformer which has a green / yellow earth wire. Continuity from this to the case and to the earth pin of the mains plug is good. I suppose it is possible there is a break in this wire either close to, or just inside, the transformer but it seems unlikely.
I'm almost certain I re-soldered the green / yellow to the PCB some months ago when also I re-soldered all of the socket 0V connections. I will do it again next time the amplifier is apart but I'm not hopeful.
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