Hi. I was googling this amp and came across a schematic showing headphone socket connections, it is just a potential divider network as you surmise, can't tell you the resistor values but it's out there in the ether.....
Hi abstractjuz. Not the simplest way my any means but one in keeping with spirit of this thread is to build JLH's own headphone amp. It is a split rail version of the 10watter. It can be found in an article on Rod Elliot's ESP site (Elliot Sound Products. Sydney Aust') In the articles section Rod has done the diy community a great service by hosting Geoff Moss's original work which everyone here references. Go to articles and information of ESP. Select Class-A Amp Site. Main TCAAS index. Other JLH amplifier designs. Then JLH Headphone amp.....as the little Russian Meercat on the Australian advert says: "Simples".
Cheers Jonathan
Cheers Jonathan
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In the spirit of DIY I would say go and try a resistive divider as an experiment and see how it sounds, find out if it is to your liking.
Headphones work with mW of power and speakers with W of power so a 1,000x difference which in the voltage domain is a factor of approximately 30. I'm guessing you'll want a divider with a ratio of around that much.
Maybe try a 5W 10R resistor in series with a 5W 0.33R resistor as this will provide a reasonably low output impedance.
You may need to be clearer about a "voltage divider" as not everyone on this thread will be familiar with what is implied. For guitarists using valve (tube) amplifiers in particular, there are also gadgets called attenuators out there for use in practice sessions or at quiet venues and these are similar in principle but use higher rated resistors - as you do when driving loudspeakers directly.
This is a useful intro. and the "get help..." page shows the simple circuit identifying the resistors: LPad Driver Attenuation Circuit Designer Calculator
This is a useful intro. and the "get help..." page shows the simple circuit identifying the resistors: LPad Driver Attenuation Circuit Designer Calculator
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Hi Guru's, just trying to make my first JLH 1969 version amp, almost all the amp components are in place, was now planning for its PSU. I have built Amp Camp Amp before and ran it using Laptop PSU rated @ 19.5V 3.4A...just wondering if I could leverage the same PSU's for JLH test build....has anyone tried before.
Thanks my hopes have increased, what is the amp rating for your SMPS
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My SMPS is way larger than necessary. It was built to supply a battery charger. I think it is 47A. It is made from two HP model DPS-600PB in series. I did it more as an experiment than anything else. The 1969 only draws 2A.
Cool then the laptop brick should be good to power 2 channels....20V 5A one
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It should handle it fine. The only thing I can't know is how clean it will sound. Some switching supplies impart some high frequency hash. I have a Connexelectronic supply that is unusable because of that even though they claim it is purposed for that.
I built Nelson Pass design amp camp amp , runs awesome with laptop bricks....totally quiet
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I'm interested to see how you get on and which version are you building? I'm still in the very early stages of my planning re my build 😕😉
The brand of the laptop SMPS matters. I just struggled with a noise issue on my amp because a low cost $7 19v SMPS that was injecting noise. Finally switched to a good HP ($30 unit) and totally quiet. All the noise spikes that looked like a forest of trees in an FFT went away. Big name computer company supplies tend to be quieter.
Are the advantages of SMPS just cost and efficiency? Linear supply for JLH isn't massive so is there something else I'm missing?
I am running two JLH, one with SMPS and one linear non-regulated. The SMPS has far less noise because the HV is rectified and whatever ripple is on it wont pass through the high frequency transformer. It make for a far cleaner sound overall. With the SMPS you do get ocassional clicks and pops when the fridge turns on but this can easily be treated with some HF filtering.
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Yes this makes a difference, mines is Acer, totally quiet, had bought cheaper one, messed the sound
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Yes, on top of that you can focus on the circuit, rather than power supply
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Thanks Nico. Good point kpsthakur, I guess I was wanting to stick with the minimalist approach, but SMPS seems to be the way to go. I would go with the original 69 too