Creek 4040 help please!

[mole42uk]

Hi, I have a Creek 4040 which had shorted the output pair on one channel. I checked the driver BD139 which tested okay and replaced the output pair. I connected a pair of 8Ω speakers, switched the power on with a meter in place of the supply fuse and noted a current of 0.5A. Seemed okay and the same current as the other channel which works.

Replacing the meter with a 2A fuse I checked the audio by touching the input terminals and heard a buzz, equal in intensity on both channels.

I left the amp on while looking for a suitable audio source to check the sound output, upon connecting I noticed that one channel was producing no sound. Further investigation revealed that the power fuse had blown, and checking the output transistors revealed that the new devices had gone short circuit.

I have now got more replacement devices, I have tested all the semiconductors around the output and can't find anything except the power transistors that are damaged. I am not anxious to switch it on again until I find out why the last pair failed. Creek sent me a selection of circuit diagrams but the 4040 amplifier seems to have morphed though several iterations and, of the six drawings I have, only one is close to the circuit on the PCB.

I have attached the circuit and wonder if anyone could shed any light on the problem?

['LIVEWIRE?']

Because this is a d.c. coupled amplifier, it is good practice to check, and possibly replace, all associated semiconductors, since failure in one device can trigger, as you have found out, failure(s) in other devices. In the case of the Creek 4040, also check the speaker coupling capacitor. If it is electrically leaky there will be D.C. present on the speaker, and increased current through the o/p transistors.

[snowman_al]

Are you sure that is the diagram for your amplifier.
There are a few different output types for the same 'name' of amp. Some with single rail and output cap, some with dual rail no cap. Some with darlingtons, some individual transistors.
A picture (or list of actual transistors) might help?

I would be concerned with 0.5A current with no signal! I would expect idle to be 30 or 40mA.
Did you check DC offset and reset the bias? Did the heatsinks get hot soon after switch on?

Alan

[Radio Wrangler]

Multiple revisions of a power amp is a sign that the manufacturer had problems with it.

Looking at the schematic there seem to be a few gotchas. Things that bitten designers have learned to avoid.

Switched speakers and no catching diodes across the power devices to keep the output voltage within the rails.

Darlingtons without resistive pull-downs on the first emitter

no capacitor across that series pair of bias diodes

Nothing to protect the darlingtons from reverse b-e voltage on transients.

I'd EXPECT these to keep blowing up

0.5A seems an awful lot. As Alan says, the bias should be rather low. Notice the darlington bases are separated by two 1N4148 drops, yet the darlingtons will need four Vbe drops to start turning them on, so there really isn't any bias voltage at all left to appear across those emitter resistors. By rights it should be showing poor crossover distortion.

So, you still have a deeper fault left in this amp.

From that schematic I would not consider such a unit to be a 'keeper'. I'd have doubts about whether it was worth fixing to be honest.

David

[mole42uk]

Originally Posted by snowman_al

Are you sure that is the diagram for your amplifier.

I am quite certain that it is not the circuit for this amplifier, there are detail differences. But Creek sent me six circuit diagrams for their 4040 amplifier none of which bear a closer resemblance to the unit on the bench.....

Also, upon retest I note that the quiescent current is 10.88mA, I don't know from where I got the earlier 500mA reading.

Before I attempt another full test I think I'll pull the output caps and test them.

[dave cox]

What are the output devices in this amp ?

I think that schematic is the one they send out to put any wanabee 'clone' makers off the scent !

dc

[Radio Wrangler]

Seeing that circuit would have me putting people off buying anything from Creek.

Looking at it, it could well be intentional... it ought to sound bad and have poor reliability.

However, if you take the opposite direction of logic, if that's what they think an amplifier ought to be like, their produce shouldn't be touched with a barge pole.

Deliberately putting out misinformation can easily backfire.

Anyhow, whichever way it is, having several revisions suggests they have had prolonged trouble with the thing.

It amuses me that these audio companies keep acting as if they had the formula for some secret rocket fuel and have to protect it from spies. Their competitors probably got one of the first units sold and took it apart. Most certainly their analysis and costing would be right on the money. It's all a game to make their products look more precious. Building an isolated research lab, surrounding it with electrified fences and rabid guard dogs would appeal to them.

How to design a good audio amplifier is no secret. Buy a copy of Douglas Self's book. It's all out there in the open.

What does interest competitors is the costing and an analysis of serial numbers to get an idea of sales. They're also interested in marketing claims. Have they discovered a new imaginary parameter?

I think Richard's going to have to trace out the circuit of the thing before him to make any progress so he can discard all the distractors. Then a sensible diagnosis can be planned. It's likely to turn into an impulsion to do a redesign.

David

[dave cox]

I just found a schematic for the 4040S2 V2 dated 1988 on DIY audio.
This has TIP3055 / TIP2955 with BC639 / BC640 drivers.

dc

[Ted Kendall]

And Haymarket praised it to the skies...

[audiomm]

I had to fix one of these amps quite a few years ago and wasn't impressed with it at all. I can't remember exactly what I did but I do recall replacing the darlington output devices. I got circuit diagrams from somewhere or other and these are attached for your information. No doubt there are other diagrams as well for 'other versions' which in marketing speak usually relates to their ...ahem... 'continuous improvements'

[Radio Wrangler]

Ah, the top one is where the diagram up-thread came from. Completely execrable as one would say in polite company.

The second one shows it now has grown discrete output Darlingtons and an emitter pulldown
Oh, look, it's got a proper adjustable Vbe multiplier AND a pair of current limiter transistors. Ooh and split rail power supply and DC coupled output. AND a diff pair input stage.

This isn't the same amplifier! Still not thrilling, but it's lost a few schoolboy howlers. I see they still bootstrap the collector load of the voltage amplifier stage. And like the first one, it still lacks the series element of the zobel arrangement in the output. I guess they didn't know what that part did. Don't put this one anywhere near silly speaker cable

Now, what about the third one?

Looks rather like the second one... still no series Zobel network, just the shunt part. No wild differences. Still no catching diodes. Still not much of a clue, by the evidence.

So the first one is a bit of a joke. The second and third ones are nothing special.

They got praised to the skies in print? Ye gods and little fishes! Well, the first one ought to have offered a lot of 'character'

David

[Silicon]

Richard, what are the output devices and where did you get them?

Could they be fakes?

[mole42uk]

Originally Posted by Silicon

Richard, what are the output devices and where did you get them?

Could they be fakes?

A good point! They were from a supplier on eBay, they have believable markings and give test results similar to the ones from the working channel but they could be fakes. If this second pair fail I might try some from RS before giving up altogether.

[mole42uk]

Originally Posted by audiomm

I had to fix one of these amps quite a few years ago and wasn't impressed with it at all. I can't remember exactly what I did but I do recall replacing the darlington output devices. I got circuit diagrams from somewhere or other and these are attached for your information. No doubt there are other diagrams as well for 'other versions' which in marketing speak usually relates to their ...ahem... 'continuous improvements'

Thank you, I have all three of those from Creek themselves. None is the same as the amp I'm working on. For RW's amusement I attach part of the v1 circuit for the 4040 amplifier.

There's also an image of the amp on the bench. Those of you who care will note that there are significant differences between the physical and the theoretical. Personally, I am not far away from throwing it into landfill.

[Herald1360]

Don't do that, just enjoying WEEEing all over it......

[bikelectro]

I would persevere, I have owned the early version from 1984 which has played loud for years with no problems! a superb performing amp.

[dave cox]

From the photo it looks more like the 1st version (transistor count alone) but there are 3 diodes in what appear to be the bias chain - that might be barely enough to have some standing current in the output stage

If your replacement transistors are of modern manufacture there could be RF instability due to them having a lot more gain at higher frequencies.

Given it's such an early design I don't think I'd bother to fix it unles I had some LM3886 going spare !

dc

[bikelectro]

Can you find any date code - this looks like a later version to me. These are great amps, and Creek are very helpful.

[bikelectro]

On my diagram, for an early one I repaired it states something about capacitors needed removed if you fitted other than Phillips transistors, or vice versa, it caused the output pair to blow on the one I was fixing, I think it was BD139 that had to be philips - I can look it up this evening. This was over 10 years ago, but it caused the output pair to instantly blow on switch on.

[mole42uk]

Originally Posted by bikelectro

Can you find any date code - this looks like a later version to me. These are great amps, and Creek are very helpful.

There's a test label dated 12 March 1988 from a London dealer - Grahams Hi-Fi Limited on Pentonville Road.