No I mean that you amp is probably picking up EMI pollution of which the wiring in your house is a cause.
Have you ever prodded yourself with a scope. You will see a 50Hz (60Hz) signal. Thats what your body picks up from the mains through the air.
This is also being picked up by your amp, probably. Only a small amount of the hum is from the rails of the amp overcoming the PSRR of the amp.
However the toroid will be a cause of the general background mains EMI.
If you ground the inputs (all of them) of your amp the hum at full volume will probably (hopefully) mostly go away.
Have you ever prodded yourself with a scope. You will see a 50Hz (60Hz) signal. Thats what your body picks up from the mains through the air.
This is also being picked up by your amp, probably. Only a small amount of the hum is from the rails of the amp overcoming the PSRR of the amp.
However the toroid will be a cause of the general background mains EMI.
If you ground the inputs (all of them) of your amp the hum at full volume will probably (hopefully) mostly go away.
Thank you very much primalsea for the schematics.
Unfortunatley, I didn't win the broken A300 I was after on eBay (for reasons beyond my reasonable control).
However, I'm still in the market for either an A300 or A5 (quite possibly broken) and really appreciated your help.
Does anyone have any insight as to which amp is a better buy, since the specs are so similar on paper and there is no significant difference in price?
Unfortunatley, I didn't win the broken A300 I was after on eBay (for reasons beyond my reasonable control).
However, I'm still in the market for either an A300 or A5 (quite possibly broken) and really appreciated your help.
Does anyone have any insight as to which amp is a better buy, since the specs are so similar on paper and there is no significant difference in price?
Thanks for your reply, John.
Mike Creek also designed the Cambridge Audio A3i – it has his name printed on the PCBs inside!
I really, really like the A3i – it’s brilliant, is my favourite amplifier and is used daily with the CD4SE and ISOMagic, along with the computer (which is plugged into the ISOMagic). It sounds great with the CD4SE and ISOMagic. It is so heavy, too, although that does not matter because I do not tend to lift it regularly!
John, you don’t happen to know who designed other Cambridge Audio products after you left, do you – like the A500 RC amplifier, D500 (and D500SE) CD player, etc. The D500 and D500SE used the same DACs as the CD4SE, I believe, but with a Sony transport. I have a D300, which does sound very good indeed; however, the sound it produces affects me severely and so my sister uses that while I use the CD4SE.
My apologies for perhaps hijacking this thread.
Regards,
Carl
Mike Creek also designed the Cambridge Audio A3i – it has his name printed on the PCBs inside!
I really, really like the A3i – it’s brilliant, is my favourite amplifier and is used daily with the CD4SE and ISOMagic, along with the computer (which is plugged into the ISOMagic). It sounds great with the CD4SE and ISOMagic. It is so heavy, too, although that does not matter because I do not tend to lift it regularly! John, you don’t happen to know who designed other Cambridge Audio products after you left, do you – like the A500 RC amplifier, D500 (and D500SE) CD player, etc. The D500 and D500SE used the same DACs as the CD4SE, I believe, but with a Sony transport. I have a D300, which does sound very good indeed; however, the sound it produces affects me severely and so my sister uses that while I use the CD4SE.
My apologies for perhaps hijacking this thread.
Regards,
Carl
Hi,
Well I finally got hold of a working, second-hand A300 V2 ( about 4 years old and with a free Denon DCD-425 CD player) from eBay and connected it to some brand new Eltax Monitor IIIs - they aren't even burned in yet! First impressions have been pretty good (although this is my first foray into proper (albeit low-end) hifi).
However, a quick look inside revealed that the build quality isn't quite what I was expecting. Ceramic caps have odd length legs, with one example even being trapped between an electrolytic and the PCB. Also, a few of the electrolytics have lower (although just about adequate) voltage ratings than suggested by the schematic.
Sound wise it's very good. The only problem I can find is a quiet 50Hz hum in both channels. I guess this is down to the quality (or lack thereof!) of the power supply filter caps and it can only be heard up close to the speakers or in a very quiet room. A quick probe with my scope reveals that it's only in the region of a few mV - I think (my scope is pretty inaccurate – it has probably not been calibrated since 1973) and is mostly positive with respect to ground. Is a little noise normal for this amp and will it damage my speakers?. I think it's definitely produced by the power amp rather than the preamp, since the volume control doesn't affect this and it's a different noise than the 50Hz hum you get from a bad earth (it sounds like just the peaks of the wave, if that makes sense...)
Thanks to primalsea for the schematics, they've been very interesting. primalsea, can you elaborate a little on removing the VI limiting? I'd imagine it's achieved by removing R239 and R260 and R225 and R214 or something beginning along those lines. I'm curious and may attempt it in the future.
Can you tell I've already forgotten most of my Elecronic Engineering degree?
Sorry for the long post and thanks in advance,
Rob
Well I finally got hold of a working, second-hand A300 V2 ( about 4 years old and with a free Denon DCD-425 CD player) from eBay and connected it to some brand new Eltax Monitor IIIs - they aren't even burned in yet! First impressions have been pretty good (although this is my first foray into proper (albeit low-end) hifi)
.However, a quick look inside revealed that the build quality isn't quite what I was expecting. Ceramic caps have odd length legs, with one example even being trapped between an electrolytic and the PCB. Also, a few of the electrolytics have lower (although just about adequate) voltage ratings than suggested by the schematic.
Sound wise it's very good. The only problem I can find is a quiet 50Hz hum in both channels. I guess this is down to the quality (or lack thereof!) of the power supply filter caps and it can only be heard up close to the speakers or in a very quiet room. A quick probe with my scope reveals that it's only in the region of a few mV - I think (my scope is pretty inaccurate – it has probably not been calibrated since 1973
) and is mostly positive with respect to ground. Is a little noise normal for this amp and will it damage my speakers?. I think it's definitely produced by the power amp rather than the preamp, since the volume control doesn't affect this and it's a different noise than the 50Hz hum you get from a bad earth (it sounds like just the peaks of the wave, if that makes sense...)Thanks to primalsea for the schematics, they've been very interesting. primalsea, can you elaborate a little on removing the VI limiting? I'd imagine it's achieved by removing R239 and R260 and R225 and R214 or something beginning along those lines. I'm curious and may attempt it in the future.
Can you tell I've already forgotten most of my Elecronic Engineering degree?
Sorry for the long post and thanks in advance,
Rob
carl.stock said:Thanks for your reply, John.
Mike Creek also designed the Cambridge Audio A3i – it has his name printed on the PCBs inside!
Carl,
just to put the record straight
- there is Mike's name on the pcb's, however the actual design of A3i, including the pcb's layout was mine... Cheers
x-pro
Thanks again. I'll look into doing that.
Although I've yet to try shorting the inputs (I'm away from home 'til later today), the problem seems to be present regargless of source. I've tried both my CD player and my Creative Zen Touch (running from battery power only) with the same result.
I'm pretty sure it is to do with power supply decoupling / filtering, since for the few seconds when the amp is running off of capacitor power (after turning off the power switch) the buzz is not present.
BTW, did I see you bidding on an A500 on eBay yesterday? I was thinking about bidding on that one, until I saw a "primalsea" was the high bidder...
Although I've yet to try shorting the inputs (I'm away from home 'til later today), the problem seems to be present regargless of source. I've tried both my CD player and my Creative Zen Touch (running from battery power only) with the same result.
I'm pretty sure it is to do with power supply decoupling / filtering, since for the few seconds when the amp is running off of capacitor power (after turning off the power switch) the buzz is not present.
BTW, did I see you bidding on an A500 on eBay yesterday? I was thinking about bidding on that one, until I saw a "primalsea" was the high bidder
...Yep that was me but I was bidding on it for financial gain only. It went for about £27 in the end. With the delivery cost of about £13 it was'nt worth buying as I was hoping to repair it and put it back on Ebay for a profit.
I've stopped buying amps for the parts for a while as I just have too many at the moment.
With my old A300 I think I used the PSU caps for the preamp section and wired 4 10,000uF caps for the power section with their own rectifiers and fuses.
I've stopped buying amps for the parts for a while as I just have too many at the moment.
With my old A300 I think I used the PSU caps for the preamp section and wired 4 10,000uF caps for the power section with their own rectifiers and fuses.
Ah, I thought it was you. I can't say that the thought of fixing amps and putting them back on ebay for proffit hasn't crossed my mind before either .
I've been toying with the idea of upgrading the caps as you did, but then I'd probably also need to upgrade the transformer (as I'm aware you did), given the significantly higher inrush current. Perhaps my best bet is just to use two 10,000uF caps if I go down that route.
Unfortunately, at this moment in time, I'm unemployed and have a student loan to pay off so expensive parts are to be avoided if possible.
I'll try to get to the root of my problem later, but I wouldn't mind betting it is a cheap (and 4 year old) capacitor issue. A quick search for A300 hum on google's usenet portal reveals someone with apparently the same problem concerning a brand new amp, so I could be wrong.
Unfortunately I don't have any high vaule surpless 50-63V capacitors lying around, else I'd try paralleling them up with the existing ones. (Besides, all of mine are pretty old anyway).
.I've been toying with the idea of upgrading the caps as you did, but then I'd probably also need to upgrade the transformer (as I'm aware you did), given the significantly higher inrush current. Perhaps my best bet is just to use two 10,000uF caps if I go down that route.
Unfortunately, at this moment in time, I'm unemployed and have a student loan to pay off
so expensive parts are to be avoided if possible.I'll try to get to the root of my problem later, but I wouldn't mind betting it is a cheap (and 4 year old) capacitor issue. A quick search for A300 hum on google's usenet portal reveals someone with apparently the same problem concerning a brand new amp, so I could be wrong.
Unfortunately I don't have any high vaule surpless 50-63V capacitors lying around, else I'd try paralleling them up with the existing ones. (Besides, all of mine are pretty old anyway).
The 120VA transformer will probably be OK left in. The inrush from a capacitor not that bad. The transformers cause the biggest inrush current but even then they say you dont need soft starts until you have more than 500VA.
You could try removing all the PSU caps except 2 (one for each rail) and see what happens. If it humms still swap them out with 2 you have just removed. Chances are its only cap that causing the problem.
Have you resoldered all of your ground connections and cleaned and rebolted your chassis ground yet??
You could try removing all the PSU caps except 2 (one for each rail) and see what happens. If it humms still swap them out with 2 you have just removed. Chances are its only cap that causing the problem.
Have you resoldered all of your ground connections and cleaned and rebolted your chassis ground yet??
primalsea said:
Thanks for that advice. I had wondered about the transformer wattage - cheers.
Sounds like a good elemination technique there. I'll probably give it a try once I trust myself enough to take out PCBs carefully enough not to break the legs of the SAP10s. I suppose it's best to remove them from their heatsinks - in which case I'm going to need some new heatsink compound, since mine's ancient and has seperated
. Ah Nuts! - It's never easy.Another good suggestion. Not yet though, primarily for the reason above. I've always been good at destroying things I'm trying to fix
.I'll post on my progress when I've had a go at some of your suggestions.
Thanks,
Rob
Update:
Firstly - please excuse the double post.
The buzzing sound is only audible (in a quiet room) up to about 2.5m away from the speakers (depending on the speakers used, of course). It's quite noticeable with the speakers right up to my ears though. With music playing, it's easily drowned out.
I've been playing around with my scope and after finding it to be roughly calibrated (both voltage and frequency wise) have connected it to the amp again with the following observations:
With the volume control set to min. and inputs short circuited, or connected to a source which has been switched off, there is a 50Hz (Well that's what it sounds like – I can't get the 'scope trigger properly) sine wave on both channels, with an amplitude of 2mV or so. On the left channel there appears to be no DC offset. However, on the right channel, there is an offset of +2mV or so, with the wave being roughly the same shape (albeit with an occasional sharp peak which is a bit higher than that of the left channel, reaching about 6-8mV). Connecting a DMM across the right channel gives a DC reading of about 4mV, the left channel giving 0.3mV or so.
The above readings don't appear to be significantly different when the speakers are disconnected. By the way, is it ok to use this sort of amplifier topology with no load connected to the speaker outs?.
I've contacted my ex – housemate, who also has an A300 V2 of roughly the same vintage, and he seems to think that his speakers buzz a bit too. Perhaps I don't have a problem after all, and all I'm hearing is PSU ripple? It just seems weird that no web based review mentions such a problem.
Can anyone offer any clarification?
Thanks for all the help. I'm sorry if this is normal and I'm wasting your time.
Firstly - please excuse the double post.
The buzzing sound is only audible (in a quiet room) up to about 2.5m away from the speakers (depending on the speakers used, of course). It's quite noticeable with the speakers right up to my ears though
. With music playing, it's easily drowned out.I've been playing around with my scope and after finding it to be roughly calibrated (both voltage and frequency wise) have connected it to the amp again with the following observations:
With the volume control set to min. and inputs short circuited, or connected to a source which has been switched off, there is a 50Hz (Well that's what it sounds like – I can't get the 'scope trigger properly) sine wave on both channels, with an amplitude of 2mV or so. On the left channel there appears to be no DC offset. However, on the right channel, there is an offset of +2mV or so, with the wave being roughly the same shape (albeit with an occasional sharp peak which is a bit higher than that of the left channel, reaching about 6-8mV). Connecting a DMM across the right channel gives a DC reading of about 4mV, the left channel giving 0.3mV or so.
The above readings don't appear to be significantly different when the speakers are disconnected. By the way, is it ok to use this sort of amplifier topology with no load connected to the speaker outs?.
I've contacted my ex – housemate, who also has an A300 V2 of roughly the same vintage, and he seems to think that his speakers buzz a bit too. Perhaps I don't have a problem after all, and all I'm hearing is PSU ripple? It just seems weird that no web based review mentions such a problem.
Can anyone offer any clarification?
Thanks for all the help. I'm sorry if this is normal and I'm wasting your time.
Firstly, this is a very interesting thread, and I am following it closely.
Secondly – and probably more importantly! – thank you very much, x-pro, for taking the time in correcting me on the A3i.
I really do like my A3i, which is my favourite amplifier. It goes very well with my Cambridge Audio CD4SE and ISOMagic DAC (designer of both: John Westlake), and I found them all irreplaceable. Thank you!
Best wishes,
Carl
x-pro said:
Carl,
just to put the record straight
Cheers
x-pro
Secondly – and probably more importantly! – thank you very much, x-pro, for taking the time in correcting me on the A3i.
I really do like my A3i, which is my favourite amplifier. It goes very well with my Cambridge Audio CD4SE and ISOMagic DAC (designer of both: John Westlake), and I found them all irreplaceable. Thank you!
Best wishes,
Carl
carl.stock said:Secondly – and probably more importantly! – thank you very much, x-pro, for taking the time in correcting me on the A3i.
I really do like my A3i, which is my favourite amplifier.
Thank you, Carl.
lt cdr data said:
Unfortunately, I don't know.
I've updated my profile
.Cheers
x-pro
lt cdr data said:
Hi, lt cdr data.
I am led to believe that Douglas Self was involved in designing the Cambridge Audio 340A amplifier. I don’t know about the other models or indeed older models apart from the A1, A2 and A3i (all designed ‘under’ Creek, but the A3i was definitely designed by x-pro – Alex
).I know Douglas Self was certainly involved with the 840A amplifier – a much more expensive model than Audio Partnership has made before – because there is a link on the Cambridge Audio website providing a short interview with him. Go to Cambridge Audio’s website…
www.cambridgeaudio.com
… and click on the pages for the 840A. On there, there is a link to an interview with Douglas Self. I cannot provide a direct link because CA’s website does not appear to be working at the moment.
Regarding other units, John Westlake designed the following models for Cambridge Audio (all CD players or DACs):
CD4
CD4SE (amazing player!)
CD6
DiscMagic (a transport only – you can clock-link this with an ISOMagic)
DACMagic series
ISOMagic (very clever – you can clock-link it with a CA DiscMagic)
You can regularly find all of the above models by Alex (A3i) and John (the CD players and DACs) for very little on places like eBay, and they really are all worth a good listen.
I hope that helps.
Regards,
Carl
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