Well, a few days of building, and I have myself a fully functioning F5!
Done by-the-book - HiFi2000 case, Cviller boards etc. All biased up fine - actually running 400mV across R11/R12 for now to just drop the stress a bit during burn-in. Runs super cool at that - cant imagine any issues at the full 590mV.
One issue though - I do have some hum. Not much - through my 90dB bookshelves that I've been using to test, you can only hear it with your ear virtually touching the speaker cloth, but still annoying knowing its there - can this be improved?
It is dead silent with no input connected, but is not due to the input itself - even tried it direct to iPod, which obviously has no grounding. Also, I have tied chassis earth to audio ground, but disconnecting this link makes NO difference.
Done by-the-book - HiFi2000 case, Cviller boards etc. All biased up fine - actually running 400mV across R11/R12 for now to just drop the stress a bit during burn-in. Runs super cool at that - cant imagine any issues at the full 590mV.
One issue though - I do have some hum. Not much - through my 90dB bookshelves that I've been using to test, you can only hear it with your ear virtually touching the speaker cloth, but still annoying knowing its there - can this be improved?
It is dead silent with no input connected, but is not due to the input itself - even tried it direct to iPod, which obviously has no grounding. Also, I have tied chassis earth to audio ground, but disconnecting this link makes NO difference.
Do you have the rca's in contact or insulated from the chassis? Insulated is normally best.
Since it is only a small amount of hum, it could easily be related to some wires getting too close to each other. It is easy to e.g. have the input go through the supply loop, which could cause hum. How about if you only use one channel - are both then silent hum-wise?
Since it is only a small amount of hum, it could easily be related to some wires getting too close to each other. It is easy to e.g. have the input go through the supply loop, which could cause hum. How about if you only use one channel - are both then silent hum-wise?
Thanks for those thoughts.
I do have the RCAs isolated, but I'll try strapping them to ground, just to see if that helps. I dont have any AC power lines close to the I/P, but one speaker wire does go close to the traffo. I don't think this is the issue though, because the hum is on both channels. I haven't tried listening with only one channel connected - will try that tonight.
It isn't an issue at all for listening, but I'd still like to eradicate it.
Also, on the subject of hum, anyone use Airlink Transformers? My 500VA one has some mechanical hum - not too much, but certainly more than from the speakers! I think I might increase the rubber/foam isolation. Little bit disappointed with that, to be honest.
I do have the RCAs isolated, but I'll try strapping them to ground, just to see if that helps. I dont have any AC power lines close to the I/P, but one speaker wire does go close to the traffo. I don't think this is the issue though, because the hum is on both channels. I haven't tried listening with only one channel connected - will try that tonight.
It isn't an issue at all for listening, but I'd still like to eradicate it.
Also, on the subject of hum, anyone use Airlink Transformers? My 500VA one has some mechanical hum - not too much, but certainly more than from the speakers! I think I might increase the rubber/foam isolation. Little bit disappointed with that, to be honest.
Right, yes - I'll sort out some pictures of all the routing etc when I get back from work tonight.
If it is completely silent with no input connected (as you say) it seems that the amp is probably not to blame... 🙂 🙂 🙂
Is it also silent with the inputs shorted?
Looking forward to seeing photos!!
Is it also silent with the inputs shorted?
Looking forward to seeing photos!!
Right, as promised.
I have also tried changing a few things. I unmounted the transformer and moved it as far inwards in the chassis and away from the connectors as possible - not really any change - maybe 10-20% better. I bolted it down a bit further in as shown in the pictures. I also tied the input wires back, to keep them away from anything nasty - possibly another small improvement, but not much. However...! Exactly as suggested, disconnecting 1 channel - actually only the earth of one RCA - stops the hum completely. Can you please explain why this is? Is that a viable permanent solution (snip the ground off one of the RCAs)? To be honest, this does verge on OCD, as it is really hard to hear the hum, and I don't have any plans to buy 105dB horns any time soon.
It hasn't drifted on offset at all - +/- 5mV - and is playing some Gerry Rafferty really rather nicely as I write. Especially considering its plugged into some £120 Cambridge Audio Somethings. If it (or more accurately, my craftsmanship) hasn't blown those up by the end of the week, I'll get it hooked up to the S-HL5s. See how it compares to the A21SE...
I have also tried changing a few things. I unmounted the transformer and moved it as far inwards in the chassis and away from the connectors as possible - not really any change - maybe 10-20% better. I bolted it down a bit further in as shown in the pictures. I also tied the input wires back, to keep them away from anything nasty - possibly another small improvement, but not much. However...! Exactly as suggested, disconnecting 1 channel - actually only the earth of one RCA - stops the hum completely. Can you please explain why this is? Is that a viable permanent solution (snip the ground off one of the RCAs)? To be honest, this does verge on OCD, as it is really hard to hear the hum, and I don't have any plans to buy 105dB horns any time soon.
It hasn't drifted on offset at all - +/- 5mV - and is playing some Gerry Rafferty really rather nicely as I write. Especially considering its plugged into some £120 Cambridge Audio Somethings. If it (or more accurately, my craftsmanship) hasn't blown those up by the end of the week, I'll get it hooked up to the S-HL5s. See how it compares to the A21SE...
I had the same problem. Hum when source attached on F5 build. It drove me nuts until I found a bad solder joint at the rca ground input jack.
Just to update, managed to get some improvement here. Seems there is a potential between the main 0v points on both the LH and RH amp boards - my DVM says 0.2mV. 0.1mV was between the 2 points on the PSU board! Yes, 0.1mV difference between 2 joints ~8mm appart on a PCB! (well, that was a serious surprise to me, at least). Note that there was a reported 0mV difference from PSU board to amp board, measured from one end of the wire to the other, so the DVM seems accurate. The solder joints were definitely good - no doubt there. So I added the wire link in the photo, soldered right next to the wires coming off the board:
Now the DVM flicks between 0.1 and 0.2 mV across the 2 amp boards (so say 0.15mV) and hum is DRASTICALLY reduced. Not gone, but almost. I think if I rewire the +/0/- lines, using solid core from some twin and earth, tapping from the same points on the PCB and keeping both sides exactly equal length, I am confident that the issue would be nailed. As it is, it can live as it is until I get some 105dB horns! It sounds far too good to pull apart and stop listening to!!
An externally hosted image should be here but it was not working when we last tested it.
Now the DVM flicks between 0.1 and 0.2 mV across the 2 amp boards (so say 0.15mV) and hum is DRASTICALLY reduced. Not gone, but almost. I think if I rewire the +/0/- lines, using solid core from some twin and earth, tapping from the same points on the PCB and keeping both sides exactly equal length, I am confident that the issue would be nailed. As it is, it can live as it is until I get some 105dB horns! It sounds far too good to pull apart and stop listening to!!
Nothing stopping you from moving traffo right to the front of box
+ use comon point where to connect all grounds.
Mains in + ground from Capacitors + 2gound of 2 boards + 2 gounds of negative speaker therminals.
Snip snip of one of the RCA grounds work this way
Ground on Amp plug ground on Pre plug Also ground on RCA = loop
Ground on second RCA = another loop
when you move trafo to front twist Live and Neutral as well and run as close to botom of chassis
+ use comon point where to connect all grounds.
Mains in + ground from Capacitors + 2gound of 2 boards + 2 gounds of negative speaker therminals.
Snip snip of one of the RCA grounds work this way
Ground on Amp plug ground on Pre plug Also ground on RCA = loop
Ground on second RCA = another loop
when you move trafo to front twist Live and Neutral as well and run as close to botom of chassis
Hi jt1000,
Are you still suffering mechanical hum from the Airlink transformer?
I use a 500VA unit from them in the same HiFi2000 case for a F2J and get a little vibration. I think that it is most likely the bottom of the case being quite thin and not all that rigid.
I may try to put a foot or maybe some sorbothane underneath the case right where the transformer is to reduce this.
Nice build by the way!
Ian
Are you still suffering mechanical hum from the Airlink transformer?
I use a 500VA unit from them in the same HiFi2000 case for a F2J and get a little vibration. I think that it is most likely the bottom of the case being quite thin and not all that rigid.
I may try to put a foot or maybe some sorbothane underneath the case right where the transformer is to reduce this.
Nice build by the way!
Ian
Bksabath - that sort of scheme was pretty much what I was thinking if I needed to totally eradicate the problem. With the last mod (getting the two ground potentials MUCH closer with the additional wire link), there is no need for me to strip the thing down - I now need to take the speaker grilles off and get the dust cover practically down my ear to hear it hum!!!! If I were to do it all over again (quite fancying an F3 to compare now...) I would just go full dual mono (2 power inlets, 2 traffos, 2PSU PCBs...). No possibility of ground loops.
As with ianc13's post the mechanical noise from the traffo is an order of magnitude louder (well, 3-5x louder for sure). It could well be the resonance of the case. Has to be said that it is getting better (seemingly) as it runs in. It varies from time to time during the day, so maybe there is also some DC on the line at times. Extra rubber bushing of some sort is probably the way forward. In fact, just thinking out loud, there must be a front wishbone bush (for a car) that would fit nicely in the centre of the transformer = no direct coupling to the chassis at all!
As with ianc13's post the mechanical noise from the traffo is an order of magnitude louder (well, 3-5x louder for sure). It could well be the resonance of the case. Has to be said that it is getting better (seemingly) as it runs in. It varies from time to time during the day, so maybe there is also some DC on the line at times. Extra rubber bushing of some sort is probably the way forward. In fact, just thinking out loud, there must be a front wishbone bush (for a car) that would fit nicely in the centre of the transformer = no direct coupling to the chassis at all!
Sorry, but there is the very likely probability of ground loops when using a chassis shared between channels.
The problem is created by the requirement to connect all exposed conductive parts to the chassis.
This forces one to connect both channels of a two channel amplifier to the same chassis.
The two inputs each have their own Signal Ground and they are connected at the transmit end and they get connected at least once at the receive end. = ground loop on the input circuit. = amplified hum at the output/s.
Disconnect one Source to Power Amp interconnect and the hum is usually completely gone, not just attenuated so that is is inaudible. Connecting either of the interconnects alone avoids the loop. Connecting both creates the loop.
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Yes, in the final reckoning there will always be hum, if you have a sensitive enough way of measuring it, with 2 channels in a box; even with total and complete star earthing, every point of that earth (no matter how close) will have a different potential, thus there will be hum.
You could of course float the 0v of the 2 channels (no case connection) if you are happy with that risk. I connected to chassis through a CL60 as per the First Watt schematics - thus for large signals it can be considered tied to earth, for small signals it is "disconnected". Full mono in 1 box with CL60s from each 0V to common safety earth would be pretty much 0 hum I reckon (even through some crazy horns).
You could of course float the 0v of the 2 channels (no case connection) if you are happy with that risk. I connected to chassis through a CL60 as per the First Watt schematics - thus for large signals it can be considered tied to earth, for small signals it is "disconnected". Full mono in 1 box with CL60s from each 0V to common safety earth would be pretty much 0 hum I reckon (even through some crazy horns).
I had same problem with traffos at start (mechanical hum)
I sent one unit away and it was vacum resin dipped and came back totaly silent.
(tanks MaightyZen for advice)
As you mention that noise change during day DC in the mains may be possibility
I have made filter with bridge diodes and 8X 12mU 6.8 V capacitors.
Sorry can't post SCH at present as I am at work but gogle up for Mains DC filter and few shuld came up.
About slight hum on Horns (mean 10 times worst than on normal speakers) maybe a further RC stage on the PSU is what you need
I sent one unit away and it was vacum resin dipped and came back totaly silent.
(tanks MaightyZen for advice)
As you mention that noise change during day DC in the mains may be possibility
I have made filter with bridge diodes and 8X 12mU 6.8 V capacitors.
Sorry can't post SCH at present as I am at work but gogle up for Mains DC filter and few shuld came up.
About slight hum on Horns (mean 10 times worst than on normal speakers) maybe a further RC stage on the PSU is what you need
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