Having been used to find help in this forum, I decided to open this thread about the Kinshaw Perception range.
I have one power amp in perfect working order but the preamp produces a terrible noise (motorboating).
I measured the preamp psu and it is outputing +-15v.
As I can not find schematics anywhere, I hope someone can help me debuging this one.
Here is the link to the manufacturer site:
Kinshaw - sound without compromise
Best regards
Ricardo
I have one power amp in perfect working order but the preamp produces a terrible noise (motorboating).
I measured the preamp psu and it is outputing +-15v.
As I can not find schematics anywhere, I hope someone can help me debuging this one.
Here is the link to the manufacturer site:
Kinshaw - sound without compromise
Best regards
Ricardo
Are you sure it's motorboating as that is quite a specific low frequency instability.
I have only ever come across one instance of that in solid state gear and it was on a Toshiba TV with TDA3000 (it does exist) outputs. PSU fault was the cause here... common fault at the time.
First thought has to be dried out caps...
A check with a 'scope should pinpoint a fault like that in minutes.
Are both channels affected, if so that points to PSU issue... caps ?
I have only ever come across one instance of that in solid state gear and it was on a Toshiba TV with TDA3000 (it does exist) outputs. PSU fault was the cause here... common fault at the time.
First thought has to be dried out caps...
A check with a 'scope should pinpoint a fault like that in minutes.
Are both channels affected, if so that points to PSU issue... caps ?
Both channels are affected.
I do not have a scope.... can I use some kind of resistor ladder to connect the psu directly to a speaker (so I can hear the psu alone )?
I do not have a scope.... can I use some kind of resistor ladder to connect the psu directly to a speaker (so I can hear the psu alone )?
I'm not familiar with the amp at all... but instability and motorboating have definite causes.
Both channels affected points to a PSU problem.
That's inventive using a speaker. You must AC couple the speaker with a largeish cap >220uf and use (at first) a series resistor of say 220 ohms to initially charge the cap and see if you hear anything. Observe correct polarity of cap 🙂 Once the cap is charged short the resistor out, and a stable PSU should be silent.
Discharge the cap via the resistor each time you move to a new voltage/rail etc.
Try it on the unregulated as well as regulated side. Common 7815 7915 regs can do weird things sometimes, might not show on a DVM... hence the scope recommend.
Both channels affected points to a PSU problem.
That's inventive using a speaker. You must AC couple the speaker with a largeish cap >220uf and use (at first) a series resistor of say 220 ohms to initially charge the cap and see if you hear anything. Observe correct polarity of cap 🙂 Once the cap is charged short the resistor out, and a stable PSU should be silent.
Discharge the cap via the resistor each time you move to a new voltage/rail etc.
Try it on the unregulated as well as regulated side. Common 7815 7915 regs can do weird things sometimes, might not show on a DVM... hence the scope recommend.
It seems quite a complex procedure... I guess I will replace the caps and verify.
Thank you so much !
Ricardo
Thank you so much !
Ricardo
Lol... what's complex about that... no sense of adventure 🙂
You need to try and pin the fault down, otherwise you could waste time and money.
How old is this thing anyway... is it a classic sort of design... pure analogue audio or is it microprocessor controlled with loads of facilities etc.
You need to try and pin the fault down, otherwise you could waste time and money.
How old is this thing anyway... is it a classic sort of design... pure analogue audio or is it microprocessor controlled with loads of facilities etc.
It is an opamp based pre with an opamp based riaa.
Has balanced outputs.
I do not have any spare caps anyway so I guess I will give it a try with the speaker test... Why must I use such a large cap ?
Can I use a 10u film cap instead ?
Has balanced outputs.
I do not have any spare caps anyway so I guess I will give it a try with the speaker test... Why must I use such a large cap ?
Can I use a 10u film cap instead ?
A good chance it is just a cap or regulator fault then. Sounds a fairly straightfoward design.
You need a largeish cap to ensure that low frequencies are passed to the speaker. Try your film cap... it won't do any harm, but any LF noise on the PSU will sound faint with only 10uf coupling to the speaker.
You can place caps across any suspect ones to prove if faulty. Even a cheapo 470 or 1000 uf cap of suitable voltage is OK to bridge those 22000 ? uf Philips ones. Don't discount a regulator as being faulty... it happens.
You need a largeish cap to ensure that low frequencies are passed to the speaker. Try your film cap... it won't do any harm, but any LF noise on the PSU will sound faint with only 10uf coupling to the speaker.
You can place caps across any suspect ones to prove if faulty. Even a cheapo 470 or 1000 uf cap of suitable voltage is OK to bridge those 22000 ? uf Philips ones. Don't discount a regulator as being faulty... it happens.
Hi Mooly
The problem is not on the PSU.
I replaced the caps and the situation did not change. Also tested the old caps with an analog MM and they charge and decay nicely.
I experimented with the pre unpowered (PSU removed) and the loud hum persists... even without power and/or signal.
I then connected the earth terminal on the pre to the amp GND and the hum was greatly reduced..... It seems the problem is inside the pre and related with GND loop.
This pre is equiped with small TX to produce balanced outputs... can these be faulty ?
Here you have some pics.
Best
Ricardo
The problem is not on the PSU.
I replaced the caps and the situation did not change. Also tested the old caps with an analog MM and they charge and decay nicely.
I experimented with the pre unpowered (PSU removed) and the loud hum persists... even without power and/or signal.
I then connected the earth terminal on the pre to the amp GND and the hum was greatly reduced..... It seems the problem is inside the pre and related with GND loop.
This pre is equiped with small TX to produce balanced outputs... can these be faulty ?
Here you have some pics.
Best
Ricardo
Attachments
Not really. A ground connection, cold solder joint, broken wire seem more likely than anything more complicated.
your preamp has a earth connection, and it s possible that
there s a ground loop with the amp that has probably an earth connection
as well...
find a 230 v power outlet adaptor so only phase and neutral of your
preamp is plugged to the main AC , leaving the earth unconnected..
anyway, the preamp will be connected to earth via the shielded
cable that bring the signal to the amp, so there will be no security issues..
i
there s a ground loop with the amp that has probably an earth connection
as well...
find a 230 v power outlet adaptor so only phase and neutral of your
preamp is plugged to the main AC , leaving the earth unconnected..
anyway, the preamp will be connected to earth via the shielded
cable that bring the signal to the amp, so there will be no security issues..
i
From what you now say I have to agree with analog_sa and think you must look at all the grounding arrangements.
You are going to have to measure all these for continuity... I can't really make it all out from the pictures.
All this sounds a bit vague but without actually having it front of me all I can suggest is you begin by seeing if the ground of the RCA input sockets read to the ground of the RCA output sockets ?
Does the chassis earth tag read to the output sockets ? if not it may be by design so trace it and confirm.
Does the RCA ground read to the O volt line of the PSU and the OV line of the main PCB.
Where the boards join at 90 degrees, are all those connections OK... the grounds ? not cracked print or anything ?
And what's this in the picture... it looks a wire unsoldered or broken of the green terminal 🙂 probably not though.
You are going to have to measure all these for continuity... I can't really make it all out from the pictures.
All this sounds a bit vague but without actually having it front of me all I can suggest is you begin by seeing if the ground of the RCA input sockets read to the ground of the RCA output sockets ?
Does the chassis earth tag read to the output sockets ? if not it may be by design so trace it and confirm.
Does the RCA ground read to the O volt line of the PSU and the OV line of the main PCB.
Where the boards join at 90 degrees, are all those connections OK... the grounds ? not cracked print or anything ?
And what's this in the picture... it looks a wire unsoldered or broken of the green terminal 🙂 probably not though.
Attachments
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I can not see any loose wires or dry solder joints.
The one you point is correctly soldered to the output gnd socket.
I will make all sugested tests and report latter.
Thank you again for the support.
The one you point is correctly soldered to the output gnd socket.
I will make all sugested tests and report latter.
Thank you again for the support.
From the home of Kinshaw
HI Rcruz,
The site for Kinshaw is not the one posted. Please look out for Hawkshead Designs Ltd. The fault is likely not to be with the blue caps. If it is a PSU fault it is more likely to be transformer or rectifier.
You have one of a very small number of the Perception Pre with transformer coupled output. This is an upgrade/modification not a standard production item.
Is there any chance of getitng the unit back to the UK?
I'll keep any eye out for new postings.
HI Rcruz,
The site for Kinshaw is not the one posted. Please look out for Hawkshead Designs Ltd. The fault is likely not to be with the blue caps. If it is a PSU fault it is more likely to be transformer or rectifier.
You have one of a very small number of the Perception Pre with transformer coupled output. This is an upgrade/modification not a standard production item.
Is there any chance of getitng the unit back to the UK?
I'll keep any eye out for new postings.
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