Hi,
When building a power supply for an audio amp with a transformer that has a center tap, or better yet dual secondaries, and using two bridge rectifiers, I get that you can use one bridge for the positive and one for the negative rail, and then share the split rail supply with both channels, as in this standard Pass DIYaudio design, from the Aleph J build guide:
:
Alternatively, Rod Elliot suggests this "dual mono" design where you have a center tap transformer and two bridge rectifiers and you use one bridge rectifier for each channel, as in this link:
rod elliot power supply
I'm wondering what the pros and cons are of each of these approaches.
I get why you would want to separate the channels, to avoid 'cross talk', but what's the advantage of separating the pos and neg rails?
When building a power supply for an audio amp with a transformer that has a center tap, or better yet dual secondaries, and using two bridge rectifiers, I get that you can use one bridge for the positive and one for the negative rail, and then share the split rail supply with both channels, as in this standard Pass DIYaudio design, from the Aleph J build guide:
:Alternatively, Rod Elliot suggests this "dual mono" design where you have a center tap transformer and two bridge rectifiers and you use one bridge rectifier for each channel, as in this link:
rod elliot power supply
I'm wondering what the pros and cons are of each of these approaches.
I get why you would want to separate the channels, to avoid 'cross talk', but what's the advantage of separating the pos and neg rails?
I guess in theory the second way each channel is mostly independent and wouldn’t affect each otier. Ie with supply one, if the left channel pulled full amps but the right channel didn’t, the rails for the right channel might end up sagging a bit since they share the same reservoir capacitors.
In the second approach they each have their own reservoir capacitors so they don’t interact with each other. The downside is for the same board space you now have half the capacitance for the rails, so likely more ripple on each channel compared to the first.
Most people put a fuse after the rectification on the DC rail, so in the second case you now need four fuses. I think in the real world where the left and right channel are usually correlated with most types of audio (standard music etc), I’d prefer the first version.
In the second approach they each have their own reservoir capacitors so they don’t interact with each other. The downside is for the same board space you now have half the capacitance for the rails, so likely more ripple on each channel compared to the first.
Most people put a fuse after the rectification on the DC rail, so in the second case you now need four fuses. I think in the real world where the left and right channel are usually correlated with most types of audio (standard music etc), I’d prefer the first version.
That's a good point above > mentioning music.
Most modern music is mixed with BASS being essentially mono. This means that 'pull' of bass energy from the power supply is the same for Left & Right.
It is my opinion that for most amplifiers, having a somewhat over-rated VA transformer, ONE bridge rectifier + plenty of big uF caps. is really all you need.
The price of high value capacitors is now very affordable >
This means you can have a very low impedance & high current power supply with just one bridge rectifier. [ esoteric designs will tell you another thing ]
Most modern music is mixed with BASS being essentially mono. This means that 'pull' of bass energy from the power supply is the same for Left & Right.
It is my opinion that for most amplifiers, having a somewhat over-rated VA transformer, ONE bridge rectifier + plenty of big uF caps. is really all you need.
The price of high value capacitors is now very affordable >
This means you can have a very low impedance & high current power supply with just one bridge rectifier. [ esoteric designs will tell you another thing ]
Actually. I think if the channels are the same, this is true. But in the hypothetical example where the left channel is pulling full amps and the right isn’t, then the ripple on this is worse as the capacitance is half. Stated another way, the left channel can’t use the right channel reservoirs to get more juice in the second configuration.
But for standard music where each channel is pulling 50% of the power I agree it’s about the same.
That's funny > I'm 'hopeless' without my morning coffee.
I've always wondered about > other people > in different places > at different times 🙂
[ off topic ]
If you live on the equator, you are moving through space at approximately 1600 kilometers per hour >
So hang-on for the ride 🙂
If you live on the equator, you are moving through space at approximately 1600 kilometers per hour >
So hang-on for the ride 🙂
Years ago I visited Ushuaia, Argentina, which is the southern most city in the world. It was weird looking at it on a 3D map, as it's feel like you're standing upside down.
Hi. In my understanding, using two diode bridges, one for each stereo channel, is better than one bridge for positive and one for negative voltages. Why? Because of voltage drop on diode bridge. When using transformers CT configuration, midpoint grounded, you get capacitors charged at higher voltage ( one diode less ), that's about 0,5Volts. So regardless the fact, that if one channel pulls more current, and capacitors are no longer shared, you have higher initial voltage on capacitors stored, so more time needed to discharge them same level as if it would be two diodes in series. For transformer load is almost unchanged, as same total capacity is charged at same time.
The 'accepted standard' here seems to be a transformer with dual secondaries. I suspect this is a function of availability and cost. Antek seems to have what most hobbyists want.
Regards,
Dan
I understand that dual secondaries are better than a center tap, for several reasons, including that you have more options in how to use the transformer. So let’s say you’ve got that. If your amplifier uses a split rail supply, is there any way to separate the two channels or do you need two transformers to do that?
Agreed to dual secondaries, but absent that I would use the 2nd circuit in the OP, not the Pass circuit.
The Pass circuit isn't an option if you don't have dual secondaries. The two rails aren't tied together at the center tap. So let me rephrase my question. Suppose you have a transformer with dual secondaries. Then which is preferable - the Pass circuit or the Elliot? Opinions seem divided.
With excessively large capacitor banks, it somewhat makes sense to use more rectifier.
They are getting punched in the face at startup.
Although in normal practice, soft start up would be considered if excessive cap banks are used.
Good way to weasel around soft startup, I guess.
What I thought of using dual recs for.
Of course 330 VA is considered more than good for home use.
Little wimpy for live sound.
The idea crossed my mind for current surges rectifiers would expect from maybe 800 to 1000va transformers
with normal capacitor banks not excessive capacitor banks
I believe this trend became more acceptable when National Semi/ TI published a high power supply example for bridged
chip amplifiers. They also mentioned overpriced transformer brand in that paper too. So they became cool then too.
Basically paying more markup makes the same transformer wire gauges more special.
You could of course sell normal 10 dollar rectifiers for 100 dollars too. This trend never caught on apparently.
American 120 is half tapped 240 so your already getting those harmonics from the AC
might as well rectify a half tap on a half tap. Be interesting if or how much additional noise is added
They are getting punched in the face at startup.
Although in normal practice, soft start up would be considered if excessive cap banks are used.
Good way to weasel around soft startup, I guess.
What I thought of using dual recs for.
Of course 330 VA is considered more than good for home use.
Little wimpy for live sound.
The idea crossed my mind for current surges rectifiers would expect from maybe 800 to 1000va transformers
with normal capacitor banks not excessive capacitor banks
I believe this trend became more acceptable when National Semi/ TI published a high power supply example for bridged
chip amplifiers. They also mentioned overpriced transformer brand in that paper too. So they became cool then too.
Basically paying more markup makes the same transformer wire gauges more special.
You could of course sell normal 10 dollar rectifiers for 100 dollars too. This trend never caught on apparently.
American 120 is half tapped 240 so your already getting those harmonics from the AC
might as well rectify a half tap on a half tap. Be interesting if or how much additional noise is added
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I've been puzzled a bit by the Pass circuit myself, wondering what it's advantage is. I thought I read somewhere that it helped in situations where the current draw from the two polarities weren't equal. With a single bridge rectifier, the imbalanced current draw would lead to transformer core saturation, which was avoided with the dual rectifiers. Does this sound familiar to anyone?