Audio source . Model Amp One . In protect mode ?

[michael dranfield]

Hi Guys , I am struggling to find the fault on this Audio Source Model Amp One as I dont have a circiut diagram .
The amp seems to be in protect mode and the speakers are switched off by a relay, however if I ground the collector of the relay switching transistor the relay clicks in and the amp is working perfect with no DC in the speakers and on both channels so there is not too much of a fault.

The strange thing is some of the protection circuit seems to be connected to the bulbs in the VU meters which are not lit up , its almost as if the amp is designed to go into protect mode if the lamps go out, I have tried a resistor to simulate the lamp current but the relay still wont click in .

Any ideas ot a diagram would do ?
Many thanks in advance .

[budm]

Re: Audio source . Model Amp One . In protect mode ?

It may be helpful if you upload good clear pictures that will show all the boards and the pictures of each board.
BTW, is it Model AMP One?


I do not see VU Meter.

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

I am still a bit new to these forum things how do I add the photos ?
Many thanks for the reply. Was

[ReeceyBurger123]

Re: Audio source . Model Amp One . In protect mode ?

Press go advance and you will see the button that allows you to add attachments.

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

Many thanks for that , I will try in a few mins .

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

Pitcures of Audio Source AMP ONE.
The protection circuit is the 5 transistors where the pen is pointing , the 6 th transistor is the relay driver.

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

That was pretty easy , many thanks for that RB.
Michael.

[stj]

Re: Audio source . Model Amp One . In protect mode ?

why arent the meters lit?
that may be relevent.
also, there may be an "anti-thump" timer on the circuit that has failed.

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

Hi Guys , I am struggling to find the fault on this Audio Source Model Amp One as I dont have a circiut diagram .
The amp seems to be in protect mode and the speakers are switched off by a relay, however if I ground the collector of the relay switching transistor the relay clicks in and the amp is working perfect with no DC in the speakers and on both channels so there is not too much of a fault.

The strange thing is some of the protection circuit seems to be connected to the bulbs in the VU meters which are not lit up , its almost as if the amp is designed to go into protect mode if the lamps go out, I have tried a resistor to simulate the lamp current but the relay still wont click in .

Any ideas ot a diagram would do ?
Many thanks in advance .

I forgot to add , two of the bulbs in the VU meters have gone but I dont have replacements to hand.

[Longbow]

Re: Audio source . Model Amp One . In protect mode ?

The strange thing is some of the protection circuit seems to be connected to the bulbs in the VU meters which are not lit up , its almost as if the amp is designed to go into protect mode if the lamps go out, I have tried a resistor to simulate the lamp current but the relay still wont click in.

Some equipment like this can use panel lamps as convenient power supply dropping resistors, which puts the unit out of service when the lamps fail. Not my favorite design, but possible. Time to look for a manual.

[budm]

Re: Audio source . Model Amp One . In protect mode ?

So the model number is AUDIOSOURCE AMP TWO? Not AMP ONE

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

Hi , Many thanks to everyone who replied to this thread , it was STJ who gave me the clue suggesting the anti thump circuit , I drew the circuit down on a piece of paper as best I could and it turns out the anti thump and dc detect both operate the relay, the anti thump is effected by a simple time constant circuit charging a capacitor through a high value resistor which is connected to cathode of a zener diode D005 , when the cathode of D005 exceeds 6.9v the diode avalanches and turns on transistor Q4003,however the cathode of D005 did not reach 6.9v , I traced this back to the power supply where a half wave rectifier and single capacitor produce the charging bias, the capacitor in question is C010 10UF 50V , and had 37 volts across it , when I took C010 out it measured 5.62 Uf with and ESR of 4.2 Ohms at 100Khz , I replaced this and the voltage across it rose to 47Volts instead of 37v and hey presto after a couple of seconds the relay clicks in and the fault cured , I think the connection with the VU meter lamps to the protection circuit is they only light up when the relay clicks in and the amp produces an audio output.

[michael dranfield]

Re: Audio source . Model Amp One . In protect mode ?

So the model number is AUDIOSOURCE AMP TWO? Not AMP ONE

Hi BUDM , I see where you are coming from but strangely enough no, its Amp one , I will post photo .

[egmike]

Re: Audio source . Model Amp One . In protect mode ?

Thanks for the Info on this thread, I had same problem on my AMP ONE/A (no Vu meters) replaced C010 cap and back in action.

[Longbow]

Re: Audio source . Model Amp One . In protect mode ?

It is funny to hear about an anti-thump circuit. I'm not getting what the difference is between thump and d.c. on the output. The protection circuit waits until the output line is near zero volts, then energizes the relay. D.C. on the output is what causes thump. I've never heard it called that, but no matter.

It is possible that they also include a muting function in the pre-amp, so you don't get instant high volume music. Also, some of the early equipment that used panel lamps did actually use them in the protection circuit in order to insure that the relay would open the moment that the power switch was turned off. Its worth checking out.