Hi Pros,
I'm an absolute noob. I've just bought this amp.
Question: In the Arcam Diva A85 service manual the quiescent current setting voltage at the measure point is suggested to be 8.5 mV cold and 12 mV hot BUT on the schematics itself the suggested value is 16mV. What value should I use?
It was set to 15 mV now I set to 8.5 mV (I think it's a bit better but might be placebo).
Reason: I think this amp sounds s.. dull with bad image and a lot of strong but muddy bass(this can be party the rooms fault tho), sounds like a cheap hifi tower. I had a Rotel RA-970BX 5+ years ago and imo that's sounds 10 times better. As all the reviews say the diva is a super amp I assume it must be faulty/"worn". Can the quiescent current misalignment cause this? Or the old caps? But visually the caps look ok to me.
I know it's not really a diyAudio topic but all the experts are here
I'm an absolute noob. I've just bought this amp.
Question: In the Arcam Diva A85 service manual the quiescent current setting voltage at the measure point is suggested to be 8.5 mV cold and 12 mV hot BUT on the schematics itself the suggested value is 16mV. What value should I use?
It was set to 15 mV now I set to 8.5 mV (I think it's a bit better but might be placebo).
Reason: I think this amp sounds s.. dull with bad image and a lot of strong but muddy bass(this can be party the rooms fault tho), sounds like a cheap hifi tower. I had a Rotel RA-970BX 5+ years ago and imo that's sounds 10 times better. As all the reviews say the diva is a super amp I assume it must be faulty/"worn". Can the quiescent current misalignment cause this? Or the old caps? But visually the caps look ok to me.
I know it's not really a diyAudio topic but all the experts are here
Lower bias is "worse". I'd pick the 12mV value.
The "cold" and "hot" values means when the heatsink is cold (when you've just turned it on) adjust for 8mV. Wait about 10-20 minutes, then re-measure - you will find the bias has increased. Trim it back to 12mV. You can also speed things up by warming the heatsink (JUST the heatsink, not the capacitors or other parts!) with a hair dryer.
The "cold" and "hot" values means when the heatsink is cold (when you've just turned it on) adjust for 8mV. Wait about 10-20 minutes, then re-measure - you will find the bias has increased. Trim it back to 12mV. You can also speed things up by warming the heatsink (JUST the heatsink, not the capacitors or other parts!) with a hair dryer.
The A85
I repair it
I listened to him
then I took it apart and put the rest in the trash ...
resells it...
I repair it
I listened to him
then I took it apart and put the rest in the trash ...
resells it...
Thanks I re-trimmed it to 12mV.
One thing I've noticed is that the left voltage is fluctuating 0.2-0.4 mV up and down in quick transitions(so stable for a couple of secs then goes up/down stable again), other is stable. Is there any obvious reason what can cause it?
@huggygood I planned to resell it but now I want to re-cap at least as a practice and see what happens if I fail then... well it was an expensive practice 😀
I've never done recaping, are there any tricks? I can pick the proper replacement caps but some are with 10% tolerance so is there any tuning I should know how to do or if I pick the right caps it should be fine and only the quiescent current needs to be set?
So if a cap is 10% it is 10% because that's enough precision there and no tweaking is needed...?
One thing I've noticed is that the left voltage is fluctuating 0.2-0.4 mV up and down in quick transitions(so stable for a couple of secs then goes up/down stable again), other is stable. Is there any obvious reason what can cause it?
@huggygood I planned to resell it but now I want to re-cap at least as a practice and see what happens if I fail then... well it was an expensive practice 😀
I've never done recaping, are there any tricks? I can pick the proper replacement caps but some are with 10% tolerance so is there any tuning I should know how to do or if I pick the right caps it should be fine and only the quiescent current needs to be set?
So if a cap is 10% it is 10% because that's enough precision there and no tweaking is needed...?
The newer Arcam amps have gone to class G. It is a matter of taste if you like them or not. Personally I think they are awful.
@ chinpok
honestly, I would not put a dime to upgrade this thing that I hardly call "amp".
for me it's a bit like want to upgrade a battery charger or a garden trash, it does not really make sense.
resell it and buy a good, well-known and well-documented base to make your experience and learn.
honestly, I would not put a dime to upgrade this thing that I hardly call "amp".
for me it's a bit like want to upgrade a battery charger or a garden trash, it does not really make sense.
resell it and buy a good, well-known and well-documented base to make your experience and learn.
@chinpok
Recommended operating conditions for Sanken SAP15N/SAP15P
➀Adjust the forward current flowing over the diodes at 2.5mA.
➁Adjust the idling current at 40mA with the external variable resistor.
Ad➀ Measure voltage over each R338/R339 (R438/R439) resistors...it should be ~375mV
Ad➁ Measure voltage between TP305 and TP306 (TP405 and TP406) test points...it should be ~17.6mV
All the above will indicate recommended bias settings from Sanken datasheet.
As for how it sounds...well I think amp is crippled by poor choice of opamps IC300/IC400. They use the very same opamp for different duties.
Please read the following patent, it is a grandpa of all amps with the same concept.
US5097223A - Current feedback audio power amplifier
- Google Patents
Recommended operating conditions for Sanken SAP15N/SAP15P
➀Adjust the forward current flowing over the diodes at 2.5mA.
➁Adjust the idling current at 40mA with the external variable resistor.
Ad➀ Measure voltage over each R338/R339 (R438/R439) resistors...it should be ~375mV
Ad➁ Measure voltage between TP305 and TP306 (TP405 and TP406) test points...it should be ~17.6mV
All the above will indicate recommended bias settings from Sanken datasheet.
As for how it sounds...well I think amp is crippled by poor choice of opamps IC300/IC400. They use the very same opamp for different duties.
Please read the following patent, it is a grandpa of all amps with the same concept.
US5097223A - Current feedback audio power amplifier
- Google Patents
Thanks.
First I want to clean it as it is very dirty and for that I need to take it apart.
What is a safe way to remove the heatsink from the mosfets? They are kinda glued there... I'm not sure if it is because of time or it's some sort of adhesive thermal paste.
Btw I see the fluctuation(left side) on output terminal too, not too much but might be enough to ruin the image.
First I want to clean it as it is very dirty and for that I need to take it apart.
What is a safe way to remove the heatsink from the mosfets? They are kinda glued there... I'm not sure if it is because of time or it's some sort of adhesive thermal paste.
Btw I see the fluctuation(left side) on output terminal too, not too much but might be enough to ruin the image.
Are you sure the fluctuation you see is not that of the DMM? Not all digital instruments are capable of stable, precise measurements, so what is the voltage and the amount of fluctuation you are reading?
BTW, don't try to disassemble the amplifier before you are certain that it is working properly. Otherwise, you will almost certainly end up with a bin full of scrap or a non-working amplifier. Unless you are experienced with the assembly of electronic equipment, this will end in having nothing of value to sell.
BTW, don't try to disassemble the amplifier before you are certain that it is working properly. Otherwise, you will almost certainly end up with a bin full of scrap or a non-working amplifier. Unless you are experienced with the assembly of electronic equipment, this will end in having nothing of value to sell.
There are no mosfets in this amp, output stage is pure BJT darlington.
I second Ian regarding disassembling amp...do not take it apart!
The readings you see on DMM is amplifier output DC offset and is normal (a few +/-mV depending on amp construction and opamp used in DC servo roll.
Fluctuation: It happens only on one side. I tested it with both multimeters I have and the oscilloscope(all cheap but it's not the multimeter's fault). But if you say it's normal then I believe you and consider the amp working correctly and then it is just a bad sounding amp(no other obvious problems).
Disassembly: I've already done the preamp but that was easy, I'll see how brave I am with the rest(probably not worth the hassle anyway).
Disassembly: I've already done the preamp but that was easy, I'll see how brave I am with the rest(probably not worth the hassle anyway).
TI TL072CD datasheet says intristic Vio (input offset voltage) for is +/-3mV typ. up to +/-10mV max. so your amp is ok regarding output DC offset.
Please, do not be brave...be smart-)...choose battle you can win.
😀
Alrighty then.. you won this time Arcam Diva A85 but next time... no there will be no next time bye.
Arcam Diva A85 for sale in perfect condition, one of the best amplifiers ever made based on multiple trustworthy reviews, don't miss it!
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