ash_dac said:
Can you tell wich ones? Cxxx? And by preamp do you mean the phono stage or is there another preamp section? Do the tone opamp ( NRC ?) upgrade makes any diffrence even if bypassed trough direct mode?
Sorry for the stupid questions, I know nothing about electronics 😉
Malefoda said:
C8, C11
I'm not sure what the other channel of the amp will be C18 C118 extra 1 prefix maybe.
IC1- NE5534 tone controls. (should be two NE5534 on the board)
If you bypass the tone opa627 upgrade would make no difference to the sound.
IC202- NE5532 - is the buffer input, and I have kept this because it's a low noise input.
Like the Stuart, and others have said the 2955 /3055 are slow. They apparently give a warm sound but to me it's more muddy.
read this discussion http://groups.google.co.uk/group/uk...+alpha+NAD+3020&rnum=2&hl=en#a5fcad266dd5bae1
Enough capacitance ?
Hi,
The 30W Arcam alpha uses 6800uf 35v per rail . The power supply is also in the schematic as + - 33v.
Is 35V enough safety margin ?
Is 6800uf enough capacitance per rail ? (my other amp has 15000uf per rail)
Any ideas what the voltage secondary winding would be as my transformer was replaced (1N5403 diode bridge producing +33V / -33V)
Rapid seem to have some very cheap non-ROHS transformers.
Hi,
The 30W Arcam alpha uses 6800uf 35v per rail . The power supply is also in the schematic as + - 33v.
Is 35V enough safety margin ?
Is 6800uf enough capacitance per rail ? (my other amp has 15000uf per rail)
Any ideas what the voltage secondary winding would be as my transformer was replaced (1N5403 diode bridge producing +33V / -33V)
Rapid seem to have some very cheap non-ROHS transformers.
As Eva kindly inform us, our ears will adjust automatically, because we listen with
brain...ears are the transducer...brain is the sound processor...the brain filter, adjust, make it better here or there.
So...to evaluate sonic changes, we have to avoid that time the Brain use to calibrate the sound.
Keeping one channel without changes, and go tweating the other one, you will be able to perceive differences.
Not doing that...maybe we go turning around alike the dog catching it`s own tail...we may conclude that the amplifier turn better when it may be almost the same....our need to perceive it as better, because we have installed better parts, more expensive parts, more pretty parts.....turn us easy to accept that something turn better.
The only method i know not to fool ourselves are the A to B comparison method, of course diagrams, curves, spectrograms, waveforms and all electronic measurement stuff may help a lot...but the decision is connected to your brain and connected to your Will....so...your desire to be a sucessfull amplifier modifier may produce fake results.
I strongly suggest friends to produce always A to B, and taking a lot of care during those tests, as we are very clever to fool ourselves.
There are words that i do not know how to write...fool is one of them...the idea is produce a mistake managed by our own intimate psychological needs....something alike better parts will result in better sound....the reality, sometimes, is terrible, and use to be different than those obvious things.
regards,
Carlos
brain...ears are the transducer...brain is the sound processor...the brain filter, adjust, make it better here or there.
So...to evaluate sonic changes, we have to avoid that time the Brain use to calibrate the sound.
Keeping one channel without changes, and go tweating the other one, you will be able to perceive differences.
Not doing that...maybe we go turning around alike the dog catching it`s own tail...we may conclude that the amplifier turn better when it may be almost the same....our need to perceive it as better, because we have installed better parts, more expensive parts, more pretty parts.....turn us easy to accept that something turn better.
The only method i know not to fool ourselves are the A to B comparison method, of course diagrams, curves, spectrograms, waveforms and all electronic measurement stuff may help a lot...but the decision is connected to your brain and connected to your Will....so...your desire to be a sucessfull amplifier modifier may produce fake results.
I strongly suggest friends to produce always A to B, and taking a lot of care during those tests, as we are very clever to fool ourselves.
There are words that i do not know how to write...fool is one of them...the idea is produce a mistake managed by our own intimate psychological needs....something alike better parts will result in better sound....the reality, sometimes, is terrible, and use to be different than those obvious things.
regards,
Carlos
Malefoda said:
Malefoda,
I've just read your signature, and it says you have an Arcam Alpha one!!! (It's completely different.. sincereley hope you haven't modified it)
old model: - Arcam alpha, Arcam alpha plus, Arcam alpha II, Arcam alpha III
new model:- Arcam alpha one http://www.arcam.co.uk/dealers/alpha/amps/ampalpha1.html The "newer" alpha with Vmosfets !
I have seen this confusion elsewhere on the net in the google groups. I think the thread might need re-naming.
I suppose one is Arcam alpha 1, and the other is Arcam Alpha One
Sorry for the confusion!
Resistior sets bias!!!
Hi,
http://myweb.tiscali.co.uk/nuukspot/decdun/a60powerampcircuit.html
http://myweb.tiscali.co.uk/nuukspot/decdun/a60mods.html
The link is to the earlier Arcam A60 but the biasing is the same in the Arcam alpha using a resistor in the VAS.
In most designs I have seen I see a transistor to in this position (as detailed by the mod on that website).
Could this bias scheme be the cause of the change in sound after warmup ?
Hi,
http://myweb.tiscali.co.uk/nuukspot/decdun/a60powerampcircuit.html
http://myweb.tiscali.co.uk/nuukspot/decdun/a60mods.html
The link is to the earlier Arcam A60 but the biasing is the same in the Arcam alpha using a resistor in the VAS.
In most designs I have seen I see a transistor to in this position (as detailed by the mod on that website).
Could this bias scheme be the cause of the change in sound after warmup ?
Re: Resistior sets bias!!!
Hi Ash_dac,
There should be thermal feedback somewhere to regulate output stage standing current. In designs such as this the temperature of Q14 (the Vbe) affects the current through the output stage. It is therefore normally mounted on the heatsink close to the power transistors in order to compensate. I do not see on the circuit diagram what is mounted on the heat sink - Q14 might be - perhaps I did not read far enough.
In that case it is a bit confusing to also replace R50 with an amplified diode, the purpose of which is to compensate for power stage current by mounting it on the heatsink. The temperature of Q14 will still influence that current, quite as an amplified diode will.
Depending on all this there might well be a change of sound during warm-up, especially at low output. Which of these are mounted on the heat sink?
Regards.
ash_dac said:
Hi Ash_dac,
There should be thermal feedback somewhere to regulate output stage standing current. In designs such as this the temperature of Q14 (the Vbe) affects the current through the output stage. It is therefore normally mounted on the heatsink close to the power transistors in order to compensate. I do not see on the circuit diagram what is mounted on the heat sink - Q14 might be - perhaps I did not read far enough.
In that case it is a bit confusing to also replace R50 with an amplified diode, the purpose of which is to compensate for power stage current by mounting it on the heatsink. The temperature of Q14 will still influence that current, quite as an amplified diode will.
Depending on all this there might well be a change of sound during warm-up, especially at low output. Which of these are mounted on the heat sink?
Regards.
Depending on the output stage configuration, the amplified diode will be mounted either on the main heatsink, or with the driver transistors. In the case of this amp with the CFP output stage, the amplified diode should be mounted in thermal contact with the drivers NOT the output devices or main heatsink. Therefore Nuuk's modification is entirely valid.
Not having seen the amp I can't say if Q14 is mounted thermally, if it is then the thermal compensation scheme may be messed up by adding further compensation, but unlikely as the location is not in close thermal contact with anything. So it will just generate a more stable bias voltage.
Not having seen the amp I can't say if Q14 is mounted thermally, if it is then the thermal compensation scheme may be messed up by adding further compensation, but unlikely as the location is not in close thermal contact with anything. So it will just generate a more stable bias voltage.
Hi Richie,
I agree that two compensating devices would mess things up, especially when they are not tracking the same temperature. From the pictures I do not find any thermal connection to either Q14 and the amplified diode transistor. The latter might be situated on Q19 but the image is not clear.
When the compensating transistor thermally tracks a driver the compensation is more immediate after switching on (see an analysis by Douglas Self), but both a sim analysis as well as practical measurements will show that the power transistors' idling current will not be constant, depending on their characteristics. For this all need to be mounted on the same heatsink. In my case (a high-end amplifier) where I omitted the usuall sub-ohm series resistors in the power emitters (they can cause high-order distortion), temperature feedback became more critical. But it can be done with only Q14 as temp. sensing device.
I have nothing aganst the amplified diode principle, but one would ideally need a constant (VAS collector) current with temperature; not so easy. This will not have much effect in normal designs, but in an optimised one this plays a role. The problem I see here is having three sets of temperature affected devices, each following not exactly related conditions.
My observation of the matter - regards.
I agree that two compensating devices would mess things up, especially when they are not tracking the same temperature. From the pictures I do not find any thermal connection to either Q14 and the amplified diode transistor. The latter might be situated on Q19 but the image is not clear.
When the compensating transistor thermally tracks a driver the compensation is more immediate after switching on (see an analysis by Douglas Self), but both a sim analysis as well as practical measurements will show that the power transistors' idling current will not be constant, depending on their characteristics. For this all need to be mounted on the same heatsink. In my case (a high-end amplifier) where I omitted the usuall sub-ohm series resistors in the power emitters (they can cause high-order distortion), temperature feedback became more critical. But it can be done with only Q14 as temp. sensing device.
I have nothing aganst the amplified diode principle, but one would ideally need a constant (VAS collector) current with temperature; not so easy. This will not have much effect in normal designs, but in an optimised one this plays a role. The problem I see here is having three sets of temperature affected devices, each following not exactly related conditions.
My observation of the matter - regards.
Hi,
I have opened up the Alpha. There is a transistor 'close' to the heatsink but it is not attached (maybe a 4mm air gap). This transistor forms part of the CCS for the VAS.
New book arrived :- IC Op-amp 3rd edition 🙂
I have opened up the Alpha. There is a transistor 'close' to the heatsink but it is not attached (maybe a 4mm air gap). This transistor forms part of the CCS for the VAS.
New book arrived :- IC Op-amp 3rd edition 🙂
Hi Ashley ,
Can you help me ?
Please send me the service manual for arcam alpha one.Arcam broshure don't respond me.
My special thanks , Tudor.
tudor_x19@yahoo.com
Can you help me ?
Please send me the service manual for arcam alpha one.Arcam broshure don't respond me.
My special thanks , Tudor.
tudor_x19@yahoo.com
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