Hello all.
I have just built this jlh kit from ebay.
2pcs JLH 1969 A CLASS A amplifier kit sc | eBay
Its sounding ok its a great quality kit for price.
I have used the supplied 2n3055 ,but I have a pair of original motorolla 2n3055 and was thinking of using them .
I understand although it uses 2 per channel one is acts as load? and other is the one that amplifies.
If so which one amplifies as I am thinking of using the original ones I have.
I have 2 of these kits so I can see which sounds best.
I have just built this jlh kit from ebay.
2pcs JLH 1969 A CLASS A amplifier kit sc | eBay
Its sounding ok its a great quality kit for price.
I have used the supplied 2n3055 ,but I have a pair of original motorolla 2n3055 and was thinking of using them .
I understand although it uses 2 per channel one is acts as load? and other is the one that amplifies.
If so which one amplifies as I am thinking of using the original ones I have.
I have 2 of these kits so I can see which sounds best.
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I really like this design but mine (not a kit though) is not finished yet. I can point you to a good sources of information
The Class-A Amplifier Site - Excellent site !
I'm not sure if it's worth swapping the parts, but if you do it's recommended to use the one with the highest performance for TR1. The best performance might be the parts that came with the kit, I can't say. If you have an old milt-meter with an hfe test you could measure the devices and us the ones with highest hfs (or 'beta' = current gain) for TR1.
The Class-A Amplifier Site - Excellent site !
I'm not sure if it's worth swapping the parts, but if you do it's recommended to use the one with the highest performance for TR1. The best performance might be the parts that came with the kit, I can't say. If you have an old milt-meter with an hfe test you could measure the devices and us the ones with highest hfs (or 'beta' = current gain) for TR1.
That is a good site. I am using an unregulated 30,000uf psu at moment as I have tried to build the one using lm338 on that class a site but I am having problems .
I have destroyed 2 lm338 !!with 2 different circuits.
I thought Tr1 was the one as its runs at 113c and tr2 78c
thanks for your help
I have destroyed 2 lm338 !!with 2 different circuits.
I thought Tr1 was the one as its runs at 113c and tr2 78c
thanks for your help
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And you might want to read the existing JLH thread - most of your questions will have already been discussed
JLH 10 watt class A amplifier
JLH 10 watt class A amplifier
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I'm not planning to regulate my supply, I'd lose too much voltage in the process. If you don't have a big problem with the dreaded HUM then maybe you are just fine as you are. If I remember from the last time I read it - in the 1970 letter from JLH he said that the regulator circuit wasn't needed - either for the power supply or the idle current.
This version with the single ended supply won't mind the supply voltage varying slightly as mains voltage varies.
The dual polarity version will have output offset variation that WILL change when supply voltage changes.
Even a regulated dual supply will allow a small variation in output offset.
The dual polarity version will have output offset variation that WILL change when supply voltage changes.
Even a regulated dual supply will allow a small variation in output offset.
No chance - that heat sink must blister your fingers already with one amplifier running.
Andrew my unregulated psu is a single ended .
I have a 100nf across the ac going to bridge ,3 10,000uf in parallel then another 100nf after them then it feeds amp.
I am still wanting to quieten the hum though.
I have a 100nf across the ac going to bridge ,3 10,000uf in parallel then another 100nf after them then it feeds amp.
I am still wanting to quieten the hum though.
You could insert a low value resistor before the bridge rectifier.
That might attenuate hum a little.
You can also insert a low value resistor between cap1 and cap2 of the PSU.
Don't add a resistor after cap3, nor between cap2 and cap3.
A 1Vdrop across both resistor might be about right, i.e. for 1.4Adc passing to the amplifier a 0r33 + 0r33 would drop ~924mVdc
If that seems too much to lose, then you can substitute an air core inductor (for the Cap to Cap2 R) with a lower "r" try 100 Turns in 10layers 10Turns wide on a 15mm to 20mm diameter bobbin
1.2mm diameter enameled copper will give a resistance between 0r1 and 0r2
That might attenuate hum a little.
You can also insert a low value resistor between cap1 and cap2 of the PSU.
Don't add a resistor after cap3, nor between cap2 and cap3.
A 1Vdrop across both resistor might be about right, i.e. for 1.4Adc passing to the amplifier a 0r33 + 0r33 would drop ~924mVdc
If that seems too much to lose, then you can substitute an air core inductor (for the Cap to Cap2 R) with a lower "r" try 100 Turns in 10layers 10Turns wide on a 15mm to 20mm diameter bobbin
1.2mm diameter enameled copper will give a resistance between 0r1 and 0r2
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Sorry to say but I also have a suspicion that your heatsink is too small - however, that's just a guess from looking at it. You can significantly improve the thermal situation by arranging for good airflow over the heatsink. A couple of 'silent' computer fans could provide a low cost solution.
Agree with Andrew - for less ripple on the supply without a lot of voltage drop you could try an inductor. If you can afford some voltage drop then maybe try making a capacitance multiplier - you have some spare 2N3055's that would suit the purpose. Use a smaller transistor as a base driver, in a Darlington configuration. The capacitance multiplier does not rely on an i.c. regulator and you can use it to achieve a slow start for the amplifier too. It will dissipate heat and will need a small heatsink of it's own.
Agree with Andrew - for less ripple on the supply without a lot of voltage drop you could try an inductor. If you can afford some voltage drop then maybe try making a capacitance multiplier - you have some spare 2N3055's that would suit the purpose. Use a smaller transistor as a base driver, in a Darlington configuration. The capacitance multiplier does not rely on an i.c. regulator and you can use it to achieve a slow start for the amplifier too. It will dissipate heat and will need a small heatsink of it's own.
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I have been out in the rain making a bigger heat sink.
I am recycling as much as I can,its 2 heat sinks bolted to 3m aluminum plate. The amps will be mounted either end horizontally
I can spare a few volts as its running at 28.8v
thanks everyone
I will polish the contact surfaces and apply heat sink paste.
The transformer is from an Arcam alpha a.
I am recycling as much as I can,its 2 heat sinks bolted to 3m aluminum plate. The amps will be mounted either end horizontally
I can spare a few volts as its running at 28.8v
thanks everyone
I will polish the contact surfaces and apply heat sink paste.
The transformer is from an Arcam alpha a.
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Looking better - the more heatsink you can use the better your chances it'll survive. You can still add a fan like the KRELL amplifiers people love.
You may not have the voltage headroom you think you have if you are measuring it without a load connected. Two channels drawing, say, 3A total will pull down the voltage of that transformer by a few volts.
The cap multiplier should have a fair bit of real capacitance after it to provide a return path for signal current or it'll adversely affect the sound. And you want enough capacitance before it to ensure the rectifiers have plenty of filter/storage to provide maximum voltage. Maybe simply split the capacitance 50:50 before and after the capacitance multiplier.
As you add more capacitors you'll put more stress on the rectifiers when power is first applied - no free lunch so be prepared to up the mains fuse 🙂
You may not have the voltage headroom you think you have if you are measuring it without a load connected. Two channels drawing, say, 3A total will pull down the voltage of that transformer by a few volts.
The cap multiplier should have a fair bit of real capacitance after it to provide a return path for signal current or it'll adversely affect the sound. And you want enough capacitance before it to ensure the rectifiers have plenty of filter/storage to provide maximum voltage. Maybe simply split the capacitance 50:50 before and after the capacitance multiplier.
As you add more capacitors you'll put more stress on the rectifiers when power is first applied - no free lunch so be prepared to up the mains fuse 🙂
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The 28.8 is with the amp connected under load.
The transformer has a 1amp fuse on mains side at moment just for testing.
The transformer has a 1amp fuse on mains side at moment just for testing.
Hi,
Death of Zen - A new Class-A power amp
Capacitance Multiplier Power Supply Filter
Minimalist Discrete Hi-Fi Preamp
Are a good read.
rgds, sreten.
Death of Zen - A new Class-A power amp
Capacitance Multiplier Power Supply Filter
Minimalist Discrete Hi-Fi Preamp
Are a good read.
rgds, sreten.
Change C1 from a lonely capacitor to a snubber using a series pair of capacitor+resistor.
Delete C5
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