Hi, I have an ARCAM delta 90 amplifier that needs help. The r58 and R59 resistance of the last stage triode emitter is 0.22 ohm. It is tested that the voltage at both ends of r58 is DC voltage of 1mV. Is the real standard 23.1mv? Is the adjustment adjusted through rv1? Attach the circuit diagram,
The manual says it runs with 30 milliamps flowing in the output transistors so that means you adjust for 6.6 millivolts across (be sure to measure across) either of the 0.22 ohm resistors.
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The manual mentioned that R42 has rv1 to provide bias fine adjustment. At present, the voltage at both ends of R46 is 2.085v. I think this is safe. Then measure that the voltage of r58 is only 1.5MV. What's wrong?
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Minor thread resurrection;
I have a Arcam Delta90 that I've used daily for the last 35 years. Unfortunately, it's just blown the internal 1.25A slow blow fuse. I've taken the top off and poked around with a multimeter and determined that the output transistors on one channel have failed. Not quite sure why. I have replaced these with new transistor and the amp appears to work OK.
However, it now get very host quite quickly, so I checked the quiescent voltage across R58/R59. For the good channel, it is approx 3mV presumable set by Arcam along time ago. For the channel the blew the output transistors, it measures 25mV and rising to 50mV after 5 minutes. I tried to adjust RV1 to reduce it, but there appears to be insufficient adjustment available.
Anyone have any suggestions what to check next?
I have a Arcam Delta90 that I've used daily for the last 35 years. Unfortunately, it's just blown the internal 1.25A slow blow fuse. I've taken the top off and poked around with a multimeter and determined that the output transistors on one channel have failed. Not quite sure why. I have replaced these with new transistor and the amp appears to work OK.
However, it now get very host quite quickly, so I checked the quiescent voltage across R58/R59. For the good channel, it is approx 3mV presumable set by Arcam along time ago. For the channel the blew the output transistors, it measures 25mV and rising to 50mV after 5 minutes. I tried to adjust RV1 to reduce it, but there appears to be insufficient adjustment available.
Anyone have any suggestions what to check next?
Most likely is that the replacement parts have differing characteristics to the originals. You need to also make sure both drivers OK as these often get taken out with output transistor failure.
You could try reducing R42 in the diagram in this thread from a 68 ohm to either a 56 ohm or 47 ohm to get a lower current.
Frankly: Burn it ! Or simply drop in it to your Trash bin.
Bought a Delta 290... Based on StereoPile recomendations.
Only to discover that it's a Piece of Shite.
Muddy sounds .. No soundstage and dull.. everything. A really poor design.
Shame on me for being so Gullible /Naive.
Walk yours out to your trashbin and Never look back. Thank me later.
Not worth the time nor the effort to waste yet More Time and $$ on the excreable thing.
True .
Bought a Delta 290... Based on StereoPile recomendations.
Only to discover that it's a Piece of Shite.
Muddy sounds .. No soundstage and dull.. everything. A really poor design.
Shame on me for being so Gullible /Naive.
Walk yours out to your trashbin and Never look back. Thank me later.
Not worth the time nor the effort to waste yet More Time and $$ on the excreable thing.
True .
So, why doesn't everyone eliminate the Vbe multiplier and vary the VAS current like this to set the output stage bias? I don't think I've ever seen this done before, so there must be some disadvantage?
I'm not keen on it either. The VAS current is now a variable determined by the preset and 'significant' current now flows in the preset wiper. I would have thought Q6 would need to be in some kind of thermal contact with the output stage.
So, I replaced R42 with a selection of lower values and settled on 56Ω to match mV across R157/8 on the blown channel to R57/8 on the good channel. The mV changes quite considerably as the amp warms up and Q10/110 and Q11/111 getting pretty warm. Anyway, it works for now. Thanks for your help.
By the way, Delta 90 is quite a bit different to Delta 290, so I'm not sure sound really compares. Delta 290 has MOSFETs and a PIC controller for the input selection (?) where as the Delta 90 has plain old analog switches and BJTs. Not saying either is high-end audio or anything, but my Delta 90 has served very well for background music in my office for the last 15 years.
By the way, Delta 90 is quite a bit different to Delta 290, so I'm not sure sound really compares. Delta 290 has MOSFETs and a PIC controller for the input selection (?) where as the Delta 90 has plain old analog switches and BJTs. Not saying either is high-end audio or anything, but my Delta 90 has served very well for background music in my office for the last 15 years.
Q10 and 11 in post #7 are for current limiting and they should not even come into play here. They are maybe just warming from other surrounding parts. You would need about 700mv across those 0.22 ohms for them even to begin to come into play.
Drift of the value is pretty normal. Set it correctly when the amp is warmed up properly and at a uniform temperature.
Drift of the value is pretty normal. Set it correctly when the amp is warmed up properly and at a uniform temperature.