Hi Barry.
Sorry for the late reply, I missed your post.
I lifted the input caps and there was no buzz so its the pre section.
So far I have replaced the following components:
-Local decoupling caps on input selector chip and opamp.
-Preamp supply diodes, caps, and regs.
-Tried a different opamp.
-Tried a different pot.
-Main caps and diodes on poweramp psu.
-Checked ground traces and circuit continuity, all seem ok.
-Checked soldering, all seems ok.
There are details on this thread:
CA 340A SE fault finding.
At the moment my main hunch is the input selector chip. Other than that Im suspicious of a dud resistor somewhere.
Mike.
Sorry for the late reply, I missed your post.
I lifted the input caps and there was no buzz so its the pre section.
So far I have replaced the following components:
-Local decoupling caps on input selector chip and opamp.
-Preamp supply diodes, caps, and regs.
-Tried a different opamp.
-Tried a different pot.
-Main caps and diodes on poweramp psu.
-Checked ground traces and circuit continuity, all seem ok.
-Checked soldering, all seems ok.
There are details on this thread:
CA 340A SE fault finding.
At the moment my main hunch is the input selector chip. Other than that Im suspicious of a dud resistor somewhere.
Mike.
I just had a thought.
Why are the main ps caps often glued to the PCB?
The reason I ask is that when I fitted the Mundorf's I just pushed them in nice and tight and soldered them up, no glue. Is this ok?
Mike.
Why are the main ps caps often glued to the PCB?
The reason I ask is that when I fitted the Mundorf's I just pushed them in nice and tight and soldered them up, no glue. Is this ok?
Mike.
Do I need to glue my caps for any reason or is it a non-issue?
Also I have a question about the volume pot:
Currently there is a 20k pot which I'd like to replace at some point. I would like to use the Alps Blue motorized but I think its only available in 10,50, & 100k values. Which of these would be suitable and why?
Mike.
Also I have a question about the volume pot:
Currently there is a 20k pot which I'd like to replace at some point. I would like to use the Alps Blue motorized but I think its only available in 10,50, & 100k values. Which of these would be suitable and why?
Mike.
The glue may help with flow soldering in mass production.
From my experience hand soldered large capacitors don't need glue.
Never had a failing solder joint with them.
If the pcb is subject to vibration, things may be different.
But I think this is a non issue with your amplifier.
regards
From my experience hand soldered large capacitors don't need glue.
Never had a failing solder joint with them.
If the pcb is subject to vibration, things may be different.
But I think this is a non issue with your amplifier.
regards
Anyone care to comment please?
Why do we get different value pots and what difference do they make to the circuit and sound?
I asked the same question at another forum, but didn't get any usefull answers 🙁
BTW, standart pot is bad, it has awful balance on very low volume (which i use at night)...
BTW, standart pot is bad, it has awful balance on very low volume (which i use at night)...
High value pots will create more noise, but are useful for amplifiers with high input impedance. As a general rule, the pot should be 1/10th of the input impedance.
Why? I don't know, but maybe this will push somebody to elaborate. In your position I'd go for the 50k.
Why? I don't know, but maybe this will push somebody to elaborate. In your position I'd go for the 50k.
If the impedance of the pot is very low it will present a load that the previous stage is likely incapable of driving properly (possibly because it cannot supply sufficient current or the output impedance is significant compared to the pot impedance), so in order to present an easier load a high value pot should be chosen. Unfortunately this brings another problem in that if a high value pot is chosen (100k or 250k say) the input impedance of the following stage becomes significant compared to the value of the pot and this will interfere with the operation of the pot. A happy medium must therefore be selected - impedance matching.
there is aditionally the impact on common-mode distortion and the possible interaction with balance controls.
If I were up to design a preamp, I would use a 10k volume pot.
The 20k may be just right for your circuit or not - how should I know? 😕 (<- kindly asking for a schematic 😉 )
regards
If I were up to design a preamp, I would use a 10k volume pot.
The 20k may be just right for your circuit or not - how should I know? 😕 (<- kindly asking for a schematic 😉 )
regards
Which schematic do you require Juergen?
If I were to bypass the balance pot (I plan to do this) would that make a difference to the value of volume pot required? I'll send you the whole service manual if you PM your email address.
Danke. 🙂
If I were to bypass the balance pot (I plan to do this) would that make a difference to the value of volume pot required? I'll send you the whole service manual if you PM your email address.
Danke. 🙂
Yes, the whole design changes when trying to use a chipamp to feed either a 4ohm or 8ohm speaker.mikesnowdon said:
You can aim for 60W into 8r0 and use two of these to feed the separate terminals on the speaker. That's your next project, to bi-amplify (not go active).
So its something like 'raising the voltage to get more useable power into an 8 ohm load' right? someting like 24/25v with a single LM3886 per channel? This may not be an issue as the service manual states a 24v supply before rectification.
Andrew,
How would I obtain a 60w output? The amp as standard has a manufaturer specced output of 45w/pc. I dont know how accurate this is.
I like the idea of bi-amping. The heatinks allready have tapped screw holes for an additional chip (see earlier pics). Food for thought.
Mike.
Andrew,
How would I obtain a 60w output? The amp as standard has a manufaturer specced output of 45w/pc. I dont know how accurate this is.
I like the idea of bi-amping. The heatinks allready have tapped screw holes for an additional chip (see earlier pics). Food for thought.
Mike.
Hi,
have you got the datasheet?
Voltages and powers and all the other things you need (except de-rating for Tc between 25degC and 150degC) are in there.
Please note I said next project, not trying to uprate the 340A.
have you got the datasheet?
Voltages and powers and all the other things you need (except de-rating for Tc between 25degC and 150degC) are in there.
Please note I said next project, not trying to uprate the 340A.
I read the 3886 datasheet. Claims 50W into 8 ohm @ 35v +/- .
I assume this is suplly voltage at the chips pins.
Where does it say you can get 60w into 8 ohms? And how?
I assume this is suplly voltage at the chips pins.
Where does it say you can get 60w into 8 ohms? And how?
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