View Full Version : HackerNap failed


Bemused
23-04-12, 09:53 AM
Really need your help now guys.

Vellerman speaker protection operated, 50V DC on HackerNap output.

Amp is currently discharging and I have to find my old build notes.

What do I check first?

Many thanks
Tony

Bemused
23-04-12, 10:39 AM
Just measured the output transistors (MJW21194G) base is short circuit to collector and emitter, collector to emitter short, in fact its now a three terminal piece of wire.

Oh, perhaps I should mention that I measured with the transistors still in circuit.

Just tried RS but they don't do MJW21194G, Farnell do but I have to order six of them for nearly 30, ouch
I think I need to get four to be safe, I already have TR7 (MJE15030) & TR8 (MJE15031) as spares

Any other UK supply?

Tony

Dik Dolan
23-04-12, 10:52 AM
How about this?

http://uk.farnell.com/on-semiconductor/mjw21194g/transistor-bipolar/dp/1703989

Bemused
23-04-12, 10:55 AM
How about this?

http://uk.farnell.com/on-semiconductor/mjw21194g/transistor-bipolar/dp/1703989

Thanks for taking the time to help, but I Farnell minimum order value is 20.00 so I up the order from 4 to six put on the VAT and its nearly 30


Going to have a large cigar and an even larger glass of whine and see if it lifts my mood :)

Tony

Dik Dolan
23-04-12, 10:59 AM
My fault, I didn't read your post properly.

Hopefully someone will come up with a bit of help, or can add your bits to a larger order.

Pete MB&D
23-04-12, 11:15 AM
Hi, Tony

I had a problem with my hackernap (self inflicted) and I have some MJE4281 in one now and I can't tell any difference.

I got them from Onsemi as samples you have the register amd make some stuff up about what you want them for but for about $20 they will senmd you some.

I have some used MJE3281s you could have for free.

Or if some one is ordering you could tag on to there order.


Pete

Jo Sharp
23-04-12, 11:17 AM
I would not just rush into replacing the output trannies without investigating why they failed. Did you short the outputs? If not then there could be a fault elsewhere that might repeat the expensive loss of those trannies!!

Sparts155
23-04-12, 11:17 AM
Sorry things have gone wrong Tony. Try "Future Electronics", they are usually well priced. Also measure the driver transistors cos they can go too. Good luck!

Bemused
23-04-12, 11:33 AM
Hi, Tony

I had a problem with my hackernap (self inflicted) and I have some MJE4281 in one now and I can't tell any difference.

I got them from Onsemi as samples you have the register amd make some stuff up about what you want them for but for about $20 they will senmd you some.

I have some used MJE3281s you could have for free.

Or if some one is ordering you could tag on to there order.


Pete

Thanks Pete, a kind offer but I need to keep to both amps the same, its a sort of obsessive problem I have.

What I need to do is workout what else I may need in the future and make up the Farnell order that way, unless someone else needs to pigyback or visa versa as you say.

I was eager to get the amp fixed in order to hear the B4 so initially thought to get the output transistors on the way.

Had a good slug of wine now though and are chilling back down ;)

Tony

toprepairman
23-04-12, 11:36 AM
Try CPC.
They are part of the Farnell group and have many of the same parts, but interestingly often at lower prices and in lower quantities.
Henry

Pete MB&D
23-04-12, 11:38 AM
Hi, Tony

I have 8 uesd MJE3281s you can have.

Add some solder http://uk.farnell.com/multicomp/507-1082/solder-wire-60-40-1-2mm-250g/dp/5071082
I wouldn't mind some my self if you need to add something to make up the minimum order cost.

Pete

Bemused
23-04-12, 11:41 AM
I would not just rush into replacing the output trannies without investigating why they failed. Did you short the outputs? If not then there could be a fault elsewhere that might repeat the expensive loss of those trannies!!

Thanks Jo
Yes I was rushing to get the transistors on there way but I would not fit them until the nice clever chaps helped me with some more detailed diagnosis.

I don't actually know when the amp failed, could have been any time over the last eight days since my last session.
I noticed the failure as a result of plugging in my newly built B4 http://www.pinkfishmedia.net/forum/showthread.php?t=118242

No shorts applied, just a power down (the amps are always powered up), swap interconnects then power back up.

Tony

Bemused
23-04-12, 11:43 AM
Sorry things have gone wrong Tony. Try "Future Electronics", they are usually well priced. Also measure the driver transistors cos they can go too. Good luck!

Thanks, just checked Future, it a stock item but current stock is zero.
Yes there must be a lot to check before powering back up.

Bemused
23-04-12, 11:59 AM
Hi, Tony

I have 8 uesd MJE3281s you can have.

Add some solder http://uk.farnell.com/multicomp/507-1082/solder-wire-60-40-1-2mm-250g/dp/5071082
I wouldn't mind some my self if you need to add something to make up the minimum order cost.

Pete

Well if you have enough for both amps it sounds better but then I would have to strip the other amp and they are a little tricky in my cases, again I need very long legs to reach the heat sink.

However the HackerNap is a great amp and its worth a lot more than 30, so I will order some new transistors, do the proper diagnosis and fix it proper.
Hey might even learn a little along the way.

Now to your solder, 1.2mm, not 0.75mm?
email me "tony at eclfirst dot co dot uk" I will pick up email in the morning.

Many thanks
Tony

Bemused
23-04-12, 01:12 PM
Update

Board now removed which was quite tricky in my amp.

Output transistors removed and verified short circuit.

Output transistor Tr9's emitter resistor R26 holed and open circuit.

Tr7 driver looks ok

Tr8 driver is open circuit,
Tr8 base resistor R19 is open circuit (fried)
Tr8 collector resistor shows signs of burning

Looking like I should rebuild the whole output stage, would the main rail capacitors C13 + C14 have been damaged?

Tony

Pete MB&D
24-04-12, 12:02 AM
Hi, Tony

Something went big time on that amp!

Check Tr6 and D3 near Tr8

I would replace the drivers Tr7+8, do you have a variac to power it up slowly?

Email sent


Pete

Bemused
24-04-12, 12:24 AM
Yes is went big time, although I heard nothing.
I originaly assumed it was the introduction of the B4 but not having listened for eight days it probably failed some time before.
The B4 looks fine, has hardly any dc on its output and there are output caps also.
The diode D3 measures ok but I am thinking to relace the whole stage to be safe.
I will look further into the amp over the next day or so.
Yes a variac is a good idea and I have one.

Thanks
Tony

Pete MB&D
24-04-12, 12:35 AM
Looks like the vellerman did its job then!

Pete

Bemused
24-04-12, 01:11 AM
Oh yes,
Sure glad that went in :D

graham-r
24-04-12, 02:22 AM
I noticed the failure as a result of plugging in my newly built B4 http://www.pinkfishmedia.net/forum/showthread.php?t=118242

No shorts applied, just a power down (the amps are always powered up), swap interconnects then power back up.

Tony

Tony

Just a quick question - how discharged was the amp before you connected the B4 ? It is possible that there was sufficient energy left for the amp to go into oscillation when the inputs were swapped. Some amps (Crimson Elektrik for example) are prone to this - I speak from experience, in my case the Velleman did not save the speaker driver !

337alant
24-04-12, 05:01 AM
Tony
Another point to be carefull of it to make sure that the 24 caps in your hacker caps are discharged before you start connecting to the board.
there are quite a lot of connections to the Hacker cap and one wrong touch with a charged up cap bank and its majic blue smoke time :o
I dont know if it makes any difference but I allways connect up all the grounds first
Alan

Bemused
24-04-12, 09:20 AM
Tony

Just a quick question - how discharged was the amp before you connected the B4 ? It is possible that there was sufficient energy left for the amp to go into oscillation when the inputs were swapped. Some amps (Crimson Elektrik for example) are prone to this - I speak from experience, in my case the Velleman did not save the speaker driver !

Not very, its a good point.

Bemused
24-04-12, 09:21 AM
Tony
Another point to be carefull of it to make sure that the 24 caps in your hacker caps are discharged before you start connecting to the board.
there are quite a lot of connections to the Hacker cap and one wrong touch with a charged up cap bank and its majic blue smoke time :o
I dont know if it makes any difference but I allways connect up all the grounds first
Alan

Thanks Alan, I have leds on the HackerCap to warn me not to fiddle.
Tony

Bemused
24-04-12, 09:27 AM
Well been through all my part bins and just getting the shopping list together for whats absent.
The only sourcing problem I have now is with R21, R22 & R23
Vishay Dale 100R 1 Watt 1%, marked CPF1 100R sort of matt pinkish brown.

Tony

lsinclair
24-04-12, 10:29 AM
CPF1100R00FKE14 if they are the same as the ones I have. I think that will mean a Mouser order if your obsessive problem is so serious that you can't abide the thought of a different colour resistor!

Bemused
24-04-12, 11:04 AM
Thanks, yes Mouser is a pain in the UK.
I can live with a different colour so I can now be sure of the spec and find an alternative.

RS have and equivalent but 5 each, Farnell have three equivalents but US stock so 15 delivery.

Thanks
Tony

Pete MB&D
24-04-12, 11:38 AM
Hi, Tony

Do they need replacing, or are you just playing safe?

If they don't look burnt and read o/k I would be happy to leave them in.

2x 200 ohm 0.6W in parallel will work or 2 50 ohm 0.6W in series

Pete

Bemused
24-04-12, 11:48 AM
Evening Pete
Two look fine and measure ok, one is a little burnt and is open circuit.
Was just going to change all three easy peasy until I found how hard they are to find at sensible money

Good idea about // series but
2x 50 ohm 1W in series.

Might just give RS a fiver for one of the buggers :p

Pete MB&D
24-04-12, 12:00 PM
Tony

Ebay is your frend

http://www.ebay.co.uk/itm/10-x-100R-100ohm-1W-1Watt-1-Metal-Film-Power-Resistors-/300623022275?pt=LH_DefaultDomain_3&hash=item45fe8748c3

Pete

Bemused
24-04-12, 12:24 PM
Pete, your a star

:D:D:D:D

337alant
24-04-12, 07:34 PM
And even freindlier:rolleyes: (1/4W?)

http://www.ebay.co.uk/itm/25X-DALE-RN55-95R-1-RESISTORS-100R-REPLACE-NON-INDUCTIVE-AUDIO-/170698156480?pt=LH_DefaultDomain_0&hash=item27be6729c0

Alan

mr_phil
24-04-12, 11:04 PM
On discharging the caps before connection - I always put an LED with resistor across the PSU outputs, it gives a visible health check and discharges the caps over a few minutes

Bemused
25-04-12, 12:45 AM
On discharging the caps before connection - I always put an LED with resistor across the PSU outputs, it gives a visible health check and discharges the caps over a few minutes

Good tip and I have just that but did not wait long enough perhaps, leds are on the inside...

Pete MB&D
25-04-12, 12:53 AM
I slapped some 4.7K discharge resistors on my PSU the other day.

I have taken out 2 lm317's by connecting up charged smoothers.

Pete

Bemused
25-04-12, 01:15 AM
And even freindlier:rolleyes: (1/4W?)

http://www.ebay.co.uk/itm/25X-DALE-RN55-95R-1-RESISTORS-100R-REPLACE-NON-INDUCTIVE-AUDIO-/170698156480?pt=LH_DefaultDomain_0&hash=item27be6729c0

Alan

0.125W
www.vishay.com/docs/31027/cmfmil.pdf

graham-r
25-04-12, 04:28 AM
Just as a kind of follow-up to my post about oscillating amps, it might be obvious but it is good to make clear that the Velleman speaker protection isn't designed to catch oscillations, unless there is also a DC component present.

The difference between my experience and what may have happened here is that for the O/P the relay was already tripped out after the amp was switched off.
In my case everything was still powered up (a gnd wire came adrift to cause the oscillation), and as a result bye bye (thankfully cheap) speaker driver - the amp survived possibly because it still had a load to absorb some of the power.

Anyone fancy designing a speaker protection device to catch an oscillating amp ?

sam_cat
25-04-12, 04:47 AM
Anyone fancy designing a speaker protection device to catch an oscillating amp ?


And DC... And all in one.

Sam

Bemused
25-04-12, 05:05 AM
Just as a kind of follow-up to my post about oscillating amps, it might be obvious but it is good to make clear that the Velleman speaker protection isn't designed to catch oscillations, unless there is also a DC component present.

The difference between my experience and what may have happened here is that for the O/P the relay was already tripped out after the amp was switched off.
In my case everything was still powered up (a gnd wire came adrift to cause the oscillation), and as a result bye bye (thankfully cheap) speaker driver - the amp survived possibly because it still had a load to absorb some of the power.

Anyone fancy designing a speaker protection device to catch an oscillating amp ?

Thanks for the information, perhaps my amp oscillated when swapping the interconect on the pre amps as the Nap caps were slowly discharging, this destroyed the output stage, raise lots of DC due to the shorted output transistors and then the Vellerman operated.

I will take more care in the future.

Regarding your improved protection circuit, I assume oscilation give rise to massive curents in the output stage, could we detect a volt drop over the output emitter resistors or capacitor bank resistors to fire a relay for disconnection?

Although there does not seem to be any other instances of guys craping out the HackerNAPs, and in my case it may well have been self inflicted through lack of thought.

Tony

PigletsDad
25-04-12, 08:11 AM
The problem with detecting oscillations is that you don't want loud music to trigger a shutdown - at the waveform level a loud burst of guitar feedback is just another oscillation!

So you need to build in some intelligence about what is an acceptable average output level, and what is likely to be damaging, as well as the DC detection.

Hmmm, I will think about - you could say something like if the 1second running average power is over half maximum, or the 5s second average over a quarter, you need to shut down. I fear that such a circuit would miss some damaging events, unless it was really sensitive, in which case it might shut down on innocent but loud music.

Pete MB&D
25-04-12, 08:16 AM
Hi,

The Naim protection circuit could be fitted, but that did have an effect on the music.

I am happy to run mine with out any protection and leave them on 24/7, my speakers have fuses and I have metal film emmiter resistors that blow very quickly.



Pete

Bemused
27-04-12, 01:22 PM
I replaced all the semiconductors and just the resistors that had gone open circuit or burnt, brought supply up slowly on a variac and got that satisfying magic click from the Velleman relay. Quite chuffed by now I went to set the bias, just about this time I buggered it up by catching the meter probe on 0v and the output emitter resistor.

So I replaced all the semiconductors again except the FETs and one damaged emitter resistor R27, this time I have been defeated by having some output volts.
Output -45V
Tr9 base -44.6V
Tr10 base -47.4V
Other than ordering a further set of parts I am at a loss and needing some diagnosis help.

Thanks
Tony

On the plus side I have now fitted emitter resistor test terminals

martin clark
27-04-12, 01:40 PM
The Naim protection circuit could be fitted, but that did have an effect on the music.Point of order, that circuit is only SOA protection - deals with secondary breakdown in transistors - and will not catch or manage the effect of driver or output stage failure. Many, many production amps at all scales feature the same, or variations on the theme BTW; it's just good housekeeping.

However if you really want DC/offset/failure protection - esp. on a DIY effort - something like the Velleman relay board is the way to do it.


PS detecting oscillation in a way you could protect against means you could probably fix it in the first place ;)

martin clark
27-04-12, 01:46 PM
Tony - I don't have the schematic to hand but since the output has gone hard to -ve rail that looks like the 'upper' or +ve rail half of the OP stage has gone (unreliable at least) - check this emitter resistor for connectivity too.

Bemused
27-04-12, 02:08 PM
Thanks Martin, emitter resistors have continuity, in fact I have continuity from the upper emitter to the lower collector.
I can increase bias up to say 4mV in the upper emitter resistor when its 3.4mV in the lower.
The upper transistor is warm, the lower is cold.

I seem to have -22 volt (negative 22 volt) on the output of the upper (+tve) front end FET, I cant actually get the probe to the FET pins but can get on the upper half of R7 so I measured at R7.
I think this should be around +46 volt.

Looking at the upper front end again I have 80 volts across the upper FET and 9 volts across the lower FET.
To my simple mind it seems as though the upper front end FET is not conducting.
Could I just jumper the positive front end across the FET to TO R7 to prove this?

Tony

Edit
Seemed obvious this morning to compare the upper front end on my other HackerNAP. Sometimes I cant see the wood for the trees.
So right now it looks like the FET has failed.

Bemused
28-04-12, 02:48 AM
Changed the FET and its all rock n roll now folks :)

Martin gave me the clue, until then I was chasing faults on the lower half, duhh I must get to dips the class B amps.

Tested a FET for the first time
N-Channel. I guess P channel is just the opposite procedure.
First connect dmm red lead to drain and black on the source.(meter should be on diode test mode)
in first case drain to source will be open.
Then connect meter red probe to gate and black to source and again connect the red probe to drain and black with source.
Now it will show the short circuit. After this short the gate and source with some wire now again drain to source will show open circuit.
If the above works the FET is ok.

Many thanks for your help
Tony

hacker
28-04-12, 08:25 AM
Glad to hear you're up and running again. Do you know what the root cause of the problem was?

Bemused
28-04-12, 08:41 AM
Hi Carl,
Yep root cause, = stupidity,
Not letting the capacitor banks to fully discharge before swapping pre amps seems to have led to some nasty oscillation which took out most the lower output stage.
Quite nasty, resistors with holes in them.

Second time it failed was just after the repair when setting the bias I shorted the upper emitter to the adjacent ground connector, I have since fitted some safer test pins to the emitter resisters. Would be a nice board revision?
As knew instantly what I had done I shut down and damage was limited to one output transistor, its driver and the FET. Just took a while to track down the faulty FET as I am limited in diagnosis skills.

Glad your here though as the bias has to be finally set, at the moment its 5mV over 0R22.
What is your recommended bias?
Also emitter voltage is different on the two emitter resistors giving 5mV on the upper and 4.1mV on the lower, I guess its just resistor tolerance. some hundredths of a ohm?
Should I worry.

Thanks
Tony

hacker
28-04-12, 09:48 AM
Ugh, sucks. Maybe think about fitting the resistor/LED bleeders to help discharge the cap banks.

The voltages sound fine, and for bias I'd aim for the value specified in the build manual - around 3.5mV.

Cheers,
Carl

Bemused
28-04-12, 10:04 AM
Thanks, its fitted with led bleeders but they are only set at 12mA so you have to wait a while, I wont get caught out again though, thinking of wiring them to the front panel as a visual also.

337alant
28-04-12, 11:02 AM
I must admit Tony its a good point with 24 Kendiels in there (like grey hound's fighting to get out of the trap) you realy do have to be carefull about connecting up the boards in particular.
I made a little resiter drain kit up for mine
I wouldn't have thought just connecting up a source would cause a failure if you have input caps but I know you can get quite a pop or crack if you have the gain up when connecting / dissconnecting to the pre amp, I allways just knock the pre amp switch to a position with no source when I am doing that.
Any way glad to hear its making music again;)
Alan

Chops54
28-04-12, 11:11 AM
Second time it failed was just after the repair when setting the bias I shorted the upper emitter to the adjacent ground connector, I have since fitted some safer test pins to the emitter resisters. Would be a nice board revision?
As knew instantly what I had done I shut down and damage was limited to one output transistor, its driver and the FET. Just took a while to track down the faulty FET as I am limited in diagnosis skills.



I've done that too on my clones and taken out the output devices as well. Now when I set the bias I use the Avondale method and put my test meter in the positive line and read the current draw. It's so much easier as you can simply leave it all connected up and monitor it over half an hour or so. Don't forget to make sure those caps are fully discharged before putting everything back together after though ;)

hacker
28-04-12, 11:46 AM
...Now when I set the bias I use the Avondale method and put my test meter in the positive line and read the current draw. It's so much easier as you can simply leave it all connected up and monitor it over half an hour or so....

I'm not sure that this method is applicable to the HackerNAPs because they use a separate front-end supply, which means the current drawn is actually quite different than you'd expect.

Unless you've done the necessary calculations I suggest measuring at the emitter resistors for the HackerNAPs or any other NAP derivative amp with a separate front-end supply.

Chops54
28-04-12, 12:07 PM
My NCC200s have seperate front end supplies. I remove the positive feed to the output section and insert my meter between the lead and the amp. As the HackerNap is more or less a copy of the NCC200 I can't see why this method won't work. Sure beats waving your test leads around in the middle of all those components ;)

hacker
28-04-12, 09:28 PM
My NCC200s have seperate front end supplies. I remove the positive feed to the output section and insert my meter between the lead and the amp. As the HackerNap is more or less a copy of the NCC200 I can't see why this method won't work. Sure beats waving your test leads around in the middle of all those components ;)

The front-end is a constant current circuit, which means that unless you know exactly how much it's drawing and you're subtracting that value from the ~38mA being measured in the +ve rail, you could be setting the bias inaccurately.

From memory I don't know what the front-end draws. It could be small enough to be negligable/irrelevant, but it's probably prudent to check. Edit: actually I think it's the -ve rail that has the CCS. Will need to go back and check.

john.luckins
29-04-12, 03:34 AM
The current draw of the front end is approx 11 mA per channel. With no signal both rails draw this constant current (any small differences between rails are due to gain imbalances in the output stage and LTP) The negative rail of the front end is truly constant current even when there's a driving signal. The front end positive rail has small signal related AC variations on top of this DC constant current.

If 11 mA goes to the front end that leaves 27mA for the output stage, all of which goes through the 0.22 ohm resistors, which gives us 5.9mV across each of these. To my mind this is a good way to set the bias up without poking around a live circuit. I believe it is what LesW recommends.

Bemused
29-04-12, 03:49 AM
Thanks John, some nice concise figures, seems a safer approach and negates ant emitter resistor tolerance error.

Tony

Bemused
30-04-12, 11:16 AM
I have had a look at Martin Clarks notes again on bias setting and also a few threads on here, it sure can give you a headache...

I have over the last day increased the bias from 3.5mv to 5.6mV.
Blimey what a game, lid on / lid off / heating on / heating off / speaker connected / speaker disconnected / breathing / holding breath, it all alters the voltage.

Source and pre connected, volume set to zero and source stopped, speakers connected.
There is 16mV on the output terminals which is pushing 0.16mA into the speaker.


I will try and table some voltages below

Upper_______________________Lower
5.6____Speaker connected_____3.2
4.8____Speaker disconnected___3.7

Does this make any sense?

I think I will try Johns current method next.
Should the speakers be connected during the test or not?

Tony

PigletsDad
30-04-12, 11:26 AM
Safest to not have speakers connected, and won't change the bias setting directly (does indirectly by making the amp run warmer at high volumes).

Chops54
30-04-12, 11:39 AM
Set the bias with the speakers disconnected. There will always be a small amount of dc on the output. 16mV is a pretty good result. If dc on the output bothers you then fit some loudspeaker protection boards.

337alant
30-04-12, 11:52 AM
Do not try the Avondale method with speakers connected:o phiz bang pop*

Alan

LesW
30-04-12, 01:06 PM
Do not try the Avondale method with speakers connected:o phiz bang pop*

Alan

Eh.!! Where did I recommend that?

The literature I publish clearly states that loudspeakers must NOT be connected during tests.

Kindly refer to your CD Alan.

martin clark
30-04-12, 01:12 PM
I have over the last day increased the bias from 3.5mv to 5.6mV.
Blimey what a game, lid on / lid off / heating on / heating off / speaker connected / speaker disconnected / breathing / holding breath, it all alters the voltage. Yes it does ;)

The real point of that old article was to point out that, providing your NAP-alike shows at least 4mV across an emitter resistor, you're into the 'diminishing -returns' ballpark, and about 6mV is 'enough'. NAP250s are set to 7.2mV IIRC, and even my humble graph shows why. But 5mV or so gets you close enough, and since the quasi-comp stage is not thermally-compensated by the Vbe 'base=spreader' it will drift/hold low when tested with the lid off. Expect it to rise 1 or 2mV when closed-up for 20mins+. So you're quite close enough. Mild or even drastic overbias does not improve distortion performance at all ( I really need to follow this up some more one day for the NAP)

Definitely set your amps up with speakers disconnected - only to save the speakers in case of a probe slip. It makes no difference to the amp of course, which will maintain dc offset and bias whether or not a load is connected (the very definition of a feedback-controlled amp)

16mV offset is in the 'trivial, don't care' bracket'; under 50mV is fine; and 100mV is about my own upper limit of acceptable. That said, as PD has pointed-out here before, even 100mV makes for a very trivial cone offset and thermal loading in the bass unit (<10mW for a nominal '8ohm' bass driver)

Hope this sets minds at rest.

337alant
30-04-12, 07:21 PM
I have had a look at Martin Clarks notes again on bias setting and also a few threads on here, it sure can give you a headache...

I have over the last day increased the bias from 3.5mv to 5.6mV.
Blimey what a game, lid on / lid off / heating on / heating off / speaker connected / speaker disconnected / breathing / holding breath, it all alters the voltage.

Source and pre connected, volume set to zero and source stopped, speakers connected.
There is 16mV on the output terminals which is pushing 0.16mA into the speaker.

I will try and table some voltages below
Upper_______________________Lower
5.6____Speaker connected_____3.2
4.8____Speaker disconnected___3.7

Does this make any sense?

I think I will try Johns current method next.
Should the speakers be connected during the test or not?[/Eh.!! Where did I recommend that?

The literature I publish clearly states that loudspeakers must NOT be connected during tests.

Kindly refer to your CD Alan.

Les 100% agree, You never recommended that you clearly state dont do it on your Diag, I was just warning Tony as he has been experimenting with his bias with and without speakers attached.
Alan

Bemused
01-05-12, 12:27 AM
Thanks to you all for you considered response.

I actually feel as though I know what I am doing now, last night I set the bias to 27mA using the series current method in the power rails.

Listening was curtailed by a power cut crapping the squeeze server data base and nas raid sync error, should all be ready for a listen tonight.

Tony

Jo Sharp
01-05-12, 01:14 AM
That is the bit we have all been waiting for...WHAT DOES IT SOUND LIKE??

Bemused
01-05-12, 09:35 AM
So some listening done after almost doubling the standing current to 27mA, got to be dramatic after all this fiddling around surely.

Well unfortunately not really, effect on low bass, mid bass, mid range - absolutely none, sounds just the same to me. Top end, well maybe an imagined improvement as its so slight, I think some instruments can be located a little more precisely in the room (imagined space) and then its only the delicate instruments within a well recorded piece.

Compared to fiddling with capacitors or getting the 0v feeds and internal cable its not worth a lot of time, Carl was right, so long as you have at least 3.5mV or 15mA don't worry and don't bother cracking it up to the upper levels unless your a little anal like myself.

Tony

chiily
01-05-12, 02:04 PM
If 11 mA goes to the front end that leaves 27mA for the output stage, all of which goes through the 0.22 ohm resistors, which gives us 5.9mV across each of these. To my mind this is a good way to set the bias up without poking around a live circuit. I believe it is what LesW recommends.

I'll have to check what I've set my Voyager clones at. I think I ignored the front end supply, but 11mA is nearly a third.

Thanks

martin clark
01-05-12, 02:15 PM
6mv across 0r22 is 27mA idle bias in the output stage; 7.2mV across 0r22 is 32mA; and the 'ballpark minimum' of 4mV is still 18mA.

Close enough is probably...close enough.