Amp problems

[hughandella]

I wonder if anyone can help ---- I sold a Clones AP1 pre to a member on here - it worked perfectly when it was sent but the new owner is experiencing issues -- 'popping and crackling' ...... he has a Croft 7 power amp that he has used happily with a Tisbury passive until now ...... ofcourse the pre could have been damaged in transit but I wondered if it may be an impedence mismatch issue ? ..... I want to make things right ofcourse and have assured I will take the Clones back but want ot explore possibilities too ....... I've asked if there is another power amp to try ---- any other ideas ? I just associate pops etc more with valves than transistors ..... I dont think there should be any issue in theory with standard Clones and standard Croft ---- all thoughts welcome
tks
chris

[walpurgis]

Could be a break in a lead making intermittent open circuit.

[Emmings]

This is a description of what is happening:

I've been carrying out some tests over the past couple of days - using a Croft Series 7 power amp and an Arcam Alpha 8 power amp.

I bought the Croft new about 4/5 years ago from a dealer and originally used it with a Croft pre-amp but couldn't get on with the dual volume pots so went with the Tissbury passive.

What happens is that every few minutes there is a burst of static about 5 seconds long followed by a loud pop/bang through the speakers.
I've timed (sad I know) the 'bursts' and they are every 5 to 6 minutes apart.
All the tests have been done with no other component attached to the system - simply the Clones/Croft/Speakers - all with the same effect

If I swap the Croft for the Arcam power amp then the problem does not appear - all is silent - no static/pops/bangs. I've tested the Clones/Arcam/speakers for 10-15 minutes with no problems.

I appreciate the help/advice and I'd love to get to the bottom of the problem 'cos I'd like to keep the Clones in the system.

I keep wondering if there is something on the mains which the Croft is picking up with the Clones in place - with a passive some 'spike' might not get passed down the chain. With an active it might get amplified/passed down. I have been trying switching off various items (fridge/TV etc.) but doesn't seem to make any difference. I don't use any network over the mains - it's all wifi or cabled.

The hifi system is supplied using a Custom Hifi cables powerblack distribution block with a super conditioner built in so in theory the power should be free of any high-frequency noise.

I've tried plugging the Clones/Croft/speakers into different sockets around the house (admittedly without the distribution block) and still the problem occurs.

[Arkless Electronics]

It sounds to me like a very rare incompatibility issue. I would try switching off all wi fi as a next test but it's fairly unlikely to be the issue. It's one of those things where if I was there to examine what was going on and had instruments with me I could no doubt diagnose it quickly but virtually impossible without being there. It's now't to do with impedances etc.

[rubber duck]

Are your interconnects shielded?

[Firebottle]

It sounds to me like there could be a dc bleed on the output of the Clones, the Croft will not tolerate this.

Without knowing the circuit of the Clones this is only a guess.

Try putting a blocking capacitor in line with one of the signal lines between Clones and Croft, this will tell you if that is the case if that channel is then without pops.

Any value between 0.1 microfarad and 1 microfarad will do to test.

[Arkless Electronics]

Yes that was the main nature of the incompatibility I was thinking of.... It would be unlikely to effect both channels equally and at precisely the same time though.

[Emmings]

With regard to the cables I have tried 3 different sets between the Clones pre-amp and the Croft power amp:

Van den hul The Name
Reference Fidelity Pluto Mk1
Reference Fidelity Venus

Interestingly when using the Reference Fidelity Venus the static pop/bang is happening on a more frequent basis (every 30 seconds or so) but with less 'volume'. Whereas the Van den hul exhibit the problem every 5/6 minutes with more volume.

As for putting a blocking capacitor in line - I'm afraid I that is well beyond my capabilities :)

[Arkless Electronics]

That tends to suggest more an RF issue. It's very unlikely you will find any cure for this I'm afraid. Probable instability in the Clones when driving certain capacitive loads... including the cable capacitance. The Arcam is probably "damping out" the issue.

[DSJR]

I'd have a rethink about the powerblock you're using. For a few quid, please try a cheapo basic trailing mains adaptor (perfectly ok when new imo) to see if the issue is still there and if you really can tell the difference?

I can't offer anything on the Clones preamp I'm afraid, other than asking that earthing be checked (granny - eggs - apologies). If both pre and power are earthed to the mains block, a hum loop may occur...

[Emmings]

I've tried the Clones pre-amp and the Croft amplifier using a 'normal' mains adapter - typical 'kettle' lead rather than using the power block. Each unit has been plugged into a seperate wall socket and the problem still occurs.

[hifi_dave]

Have you checked for DC offset from the pre ?

[Emmings]

I haven't no - but what does that mean/how would that be done :)

All I can find out from the web is that 'It is an active line stage with 9 dB of gain. 100k input impedance and 33k output impedance.'

[hughandella]

thanks to everyone for your thoughts and time ---- this is one of those immensely frustrating ones it seems ! ...... Dave as I've said I am happy to reimburse you if needed --- I used with a QUAD 99 power and no issues but I wouldnt wnat to 'blame' the Croft ( far from it ) ... a shame as I think the Clones is a bit of a star on the quiet .... but if it isnt working in your system for whatever reason then send it back to me ---- I think I can offer for sale again with a reasonably clear conscience (!) or as mentioned you are welcome to try it with the Quad which I can send to you

cheers again all

chris

[Emmings]

Just one more thing - I've checked on the interweb for DC offset and re-discovered my multimeter (things you didn't know eh) and I've taken this reading from the Clones pre outputs:

http://i1117.photobucket.com/albums/k592/emmings/dc-offset1.jpg (http://s1117.photobucket.com/user/emmings/media/dc-offset1.jpg.html)

[Arkless Electronics]

Check the meter by shorting together the probes and seeing it indicates 0V (+/- a couple). Do the same test as you have but watch it for a while and also short the output from the pre amp to make sure any output cap is fully discharged. Do both channels and report back.... Don't worry it's all safe:)

[Emmings]

Numpty alert - 'short the output from the pre-amp'. How can this be done?

Sorry but this is well beyond my knowledge :)

[danilo]

The Arcam is probably "damping out" the issue.

Fairly astute observation IMO Likely also half the dynamics and presence detail as well.

[Arkless Electronics]

Numpty alert - 'short the output from the pre-amp'. How can this be done?

Sorry but this is well beyond my knowledge :)

I presume you are measuring at the end of an interconnect between the body of the phono plug and the centre pin? Just short the two together with the metal probe of one meter lead for a few seconds and see if after removing the short it is down to 0V or somewhere close. The 22mV you had is low but more than I would like or expect to see... Monitor the output for a while to see if there is any cycling of the DC offset.

[Arkless Electronics]

Fairly astute observation IMO Likely also half the dynamics and presence detail as well.

What I meant was there could an issue with the pre (or power) going RF unstable and the clue being the different timing of the noise due to frequency of oscillation changing with the self capacitance of different interconnects... Asymmetric oscillation waveform could then cause a DC offset which changes with interconnect. Now't to do with sound quality;) It would be VERY unusual for this to happen... but the symptoms say to me it shouldn't be ruled out....

[Arkless Electronics]

If the OP has an in line attenuator or passive pre to hand try putting it/them between pre and power. If the RF instability issue is real this will almost certainly stop it and hence we have a diagnoses... It's unlikely as I say but the symptoms mean it needs ruling out....

[Emmings]

After actually doing the test correctly (thanks Jez) the following readings were taken:

Left hand channel - started at 00.0 and after taking readings for 2 minutes it rose to 00.5
Right hand channel - started at 00.0 and after taking readings for 2 minutes it rose to 00.4

I do have a passive pre - so can I simply connect this from the Clones to the Croft as follows:

Clones output -> passive pre input -> Croft input

[Arkless Electronics]

After actually doing the test correctly (thanks Jez) the following readings were taken:

Left hand channel - started at 00.0 and after taking readings for 2 minutes it rose to 00.5
Right hand channel - started at 00.0 and after taking readings for 2 minutes it rose to 00.4

I do have a passive pre - so can I simply connect this from the Clones to the Croft as follows:

Clones output -> passive pre input -> Croft input

I presume those readings were on the same 200m scale? If so that's fine and DC offset is ruled out.

Yes connect the passive as you say. put to about half volume and then control volume from the Clones.

[Emmings]

Yeh those readings were taken on the same 200m scale.

I've just connected the passive as discussed and it appears that the buzz/crackle/pops have gone away.

Just played 15 minutes of an album and there were no cracks or pops at all. Volume on passive set to half way and volume controlled from the Clones. Strange.

[walpurgis]

I've just connected the passive as discussed and it appears that the buzz/crackle/pops have gone away.

Just played 15 minutes of an album and there were no cracks or pops at all. Volume on passive set to half way and volume controlled from the Clones. Strange.

Nice result. We have some clever guys here! :)

[Arkless Electronics]

Yeh those readings were taken on the same 200m scale.

I've just connected the passive as discussed and it appears that the buzz/crackle/pops have gone away.

Just played 15 minutes of an album and there were no cracks or pops at all. Volume on passive set to half way and volume controlled from the Clones. Strange.

Looks like it was as I suspected.... It's a design fault then. probably just needs a couple of "stopper" resistors... 10 mins work for me if I was there but I'm not so I guess the outcome is they ain't gonna work together...

[hughandella]

its been an education for me ( not sure i understand it all still ) but if Dave wants to keep the Clones and Jez ( Arkless) is OK with it I'm happy to fund cost of postage and work ---- up to you Dave really


again tks to all ..... no where else surely can you get this level of expertise and commitment
tks all -- however it works out


Jez is the implication its 'a design fault' on the Clones ?
I'll send them a message if so ---- or feel free to prepare one that makes sense !!

tks

chris

[Arkless Electronics]

its been an education for me ( not sure i understand it all still ) but if Dave wants to keep the Clones and Jez ( Arkless) is OK with it I'm happy to fund cost of postage and work ---- up to you Dave really


again tks to all ..... no where else surely can you get this level of expertise and commitment
tks all -- however it works out


Jez is the implication its 'a design fault' on the Clones ?
I'll send them a message if so ---- or feel free to prepare one that makes sense !!

tks

chris

Yes it seems likely it's a design fault on the Clones. I can't say 100% without running tests though... I'd put a tenner on it though!
There's even a remote possibility it's the Croft and it only does it with one pre amp out of a hundred (same reasons) but it's very remote!
If the OP is confident to add 1 resistor to each channel I can take him through the process... But if he can't solder it's a problem.
Another issue is that to be certain of whats going on both units would be needed!

[Emmings]

Well I've certainly learnt something too - how to use a multi-meter for one :)

I REALLY wanted this to get sorted since I would have liked to include the Clones in the system - but I can't solder for toffee - never even tried.

And the help/advice from everyone has been an eye-opener for me - shows how helpful/willing to get a problem sorted people can be. Thank you to everyone.

But in this case I will , sadly, have to pass on the Clones - don't want to but I think this is the best way forward for me.

This doesn't mean the Clones is a bad pre-amp - far from it - if the Arcam Alpha was in the system then all would be good and it would be staying. But it's not and I don''t want to loose the Croft. And I'm sorry to have to go this way.

[hughandella]

no problem Dave ---send it back to me and i ll refund ---- as per original sales link I have another AP1 with a pair of 55 monos --- I'll try the pre again in the system ..... and offer it for sale again if it works ok ------ sorry to Dave for issues ( genuinely new to me ) and again tks for all input and expertise ......... anyone want a nice pre let me know !!!!

cheers

chris

[hughandella]

no problem Dave ---send it back to me and i ll refund ---- as per original sales link I have another AP1 with a pair of 55 monos --- I'll try the pre again in the system ..... and offer it for sale again if it works ok ------ sorry to Dave for issues ( genuinely new to me ) and again tks for all input and expertise ......... anyone want a nice pre let me know !!!!

cheers

chris

[StanleyB]

What happens is that every few minutes there is a burst of static about 5 seconds long followed by a loud pop/bang through the speakers.
I've timed (sad I know) the 'bursts' and they are every 5 to 6 minutes apart.
All the tests have been done with no other component attached to the system - simply the Clones/Croft/Speakers - all with the same effect
I only just saw this thread, and the description of the fault. But this kind of symptom has been observed by me before. Most of the time it is an earthing problem. And in most cases it tends to be a screw that is not making proper contact between its two points of contact, i.e. the case and the PCB earth for instance. In the old valve days we used a Megger( a kind of test equipment) to slowly build up a charge and try to find where the insulation or intermittent ground contact was.

[OD1]

This is a description of what is happening:

I've been carrying out some tests over the past couple of days - using a Croft Series 7 power amp and an Arcam Alpha 8 power amp.

I bought the Croft new about 4/5 years ago from a dealer and originally used it with a Croft pre-amp but couldn't get on with the dual volume pots so went with the Tissbury passive.

What happens is that every few minutes there is a burst of static about 5 seconds long followed by a loud pop/bang through the speakers.
I've timed (sad I know) the 'bursts' and they are every 5 to 6 minutes apart.
All the tests have been done with no other component attached to the system - simply the Clones/Croft/Speakers - all with the same effect

If I swap the Croft for the Arcam power amp then the problem does not appear - all is silent - no static/pops/bangs. I've tested the Clones/Arcam/speakers for 10-15 minutes with no problems.

I appreciate the help/advice and I'd love to get to the bottom of the problem 'cos I'd like to keep the Clones in the system.

I keep wondering if there is something on the mains which the Croft is picking up with the Clones in place - with a passive some 'spike' might not get passed down the chain. With an active it might get amplified/passed down. I have been trying switching off various items (fridge/TV etc.) but doesn't seem to make any difference. I don't use any network over the mains - it's all wifi or cabled.

The hifi system is supplied using a Custom Hifi cables powerblack distribution block with a super conditioner built in so in theory the power should be free of any high-frequency noise.

I've tried plugging the Clones/Croft/speakers into different sockets around the house (admittedly without the distribution block) and still the problem occurs.

Hi Dave,
If you do send the pre back, I believe you can now order a Croft pre with single volume pot from Adrian at Audioflair. Just a thought :)

[hifi_dave]

Hi Dave,
If you do send the pre back, I believe you can now order a Croft pre with single volume pot from Adrian at Audioflair. Just a thought :)

You could even order one from Radlett Audio..:)

[OD1]

You could even order one from Radlett Audio..:)

Sorry Dave, I thought this was an Audioflair special :oops:

[hifi_dave]

Nope. Glenn will fit a single pot, as his German market demands but his preferred option is the familiar double control arrangement. I reckon I sell 30 x 1 in favour of the double control.

[donmarrese]

Hi all ...
I'd like to give the Clones a test run on my system ....Croft series 5/Meridian 207B/KEF Series 103.3...let you know the deal asap..i'm based in Hornsey..can pay for Clones upfront, need dough back if unit is a wrongen...