SMPS powered JLH 69 - quick and dirty results

I just wanted to share some things I found today while playing around. I recently bought a connexelectronics 48V SMPS500R-single to power a Pass Zen v1 amp that I have. Unfortunately when i tried the SMPS on the amp my outputs shorted internally(I am still not sure what happened) so no more Zen V1 until I figgure out the issue.

Today I decided to try my SMPS on a JLH 69 amplifier I assembled using MJ15003 outputs and an unregulated linear supply. With the linear supply the amp sounded good but it never sounded like something special. It was easily bested by my Decware Zen select when A/Bed on multiple occasions. It also always had a slight hum on my parker audio 98s (96db/watt/m) but you couldn't hear it from the listening position.

With the SMPS I had no hum and no noise from the speakers and it sounded better in every way. The soundstage was bigger, the sound was clearer (less veiled) and the bass was improved. The amp now sounds like a real high end amp to me. I have not A/Bed it with the Decware Zen select but if I were to make a guess I would bet they are now close to the same level but just different "flavors". I think I may order another smps with the proper voltage for my JLH and make this a permanent addition.

BTW i tried adding a 1mh coil between the smps and the JLH to clean up any noise from the smps. I previously tested this unloaded and the coil did lower the noise output on the smps. I found however that this had a negative impact on the sound of the amp. The bass seemed to be reduced and it gave the amp an overly forward sound. If I were to play with this again it would be with an inductor made of a much higher gauge wire. Honestly I really don't think it is needed.

I put this up so that any of you who still think SMPS is not for hifi. I think the technology is here and could be used to push some current amplifier designs even further. If you haven't played around with SMPS I suggest you give it a try.
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One problem with an SMPS over a linear supply is its reaction to driving the amp too hard.
A SMPS will reset itself if too much current is drawn and you will need to power down then up again.
A linear supply will keep trying output current until eventually its fuses blow.
The linear supply will react better to short bursts of peak power.

This is what I have found in use.
The SMPS I am using can output 10A into 48V and the circuit I am using is class A so I haven't run into any reset issues. I will say that it seems like a SMPS seems to make things burn up quick if there is a problem and it doesn't see it as a fault/short. I believe this may be due to their ability to provide a large amount of amps in a very short period of time.
I would guess it is down to the over current setting.

The SMPS I built used a 2 volt limit across the lower mosfet to determine when reset mode occurs. This along with the mosfet Rdson determines reset current trip.

If your 10 amp supply is well inside what your amp needs to destroy itself then thats what will happen.

An SMPS will not give much 50Hz out as the switching frequency will be a 100KHz or so.
If the primary side smoothing is a bit poor then 50Hz can get through.
I'm always fascinated about SMPS usage for pure class A amps, assuming it is done right (not for skimping purpose, as most SMPS are).
One important note is that SMPS shouldn't run between loaded/unloaded state. On average, it wants a rather constant load. For class A, this isn't much of a problem. For class A/B or Gainclones, tho, it means no good.
For class A/B and Gainclones, you can bleed SMPS output for about twice or three times the bias current, so that SMPS won't go unloaded.
Some SMPS's don't like big capacitive loads. They may have several hundred uF on the output for filtering, but regulation might be upset if too much is added at the point of use. Does your amp have a big cap near the output transistors?

What's really needed is a regulation and stability test where frequency sweeps are run through the amp at several power levels and the output of the SMPS monitored.
I just finished 5200-based JLH 1969 this morning, using 30V-8A SMPS. It might be premature, but the sound is pretty satisfactory.

I have a few questions:
1. There is absolutely no noise when I use Ipod as the source, but there's some high-pitch noise when I use DAC. It is not 60Hz AC noise. The frequency is higher. What can this be?

2. I used very cheap parts for the construction, but still sound quality is very good. Is there anyone who uses JLH 1969 as their main amp? Then what are the input and output capacitors?

3. How's 1969 version compared to other versions such as PLH, 1996, etc?


I'm also looking into using an SMPS with one of the ebay JLH 1969 kits.
Looks like a "fast" way to have an experiment with Class A amps, as reports seem this circuit works quite well driven by SMPS, and it will simplify the build for me.

For my use it will be for the HF amp an an active system (crossover @ 600hz), so not much bass energy, so lack of power for bass is OK as long as it doesnt affect the basic operation of the amp.

Will I be able to get away with a smaller SMPS, rated @ 4A or 6A?
One example I'm looking at is:
Altronics - M8410 Switchmode Power Supply DIN Rail - 120W 24VDC
which looks like it has quite good specs, if my intended use for non-bass lets me work with the lower power.
I realize I'm a bit late in answering this question but.....:p

1. There is absolutely no noise when I use Ipod as the source, but there's some high-pitch noise when I use DAC. It is not 60Hz AC noise. The frequency is higher. What can this be?

This is what's called 'common-mode noise'. You don't get any with your ipod because that has no connection to mains, but I take it your DAC has a trafo and a mains cord. The noise is the switching frequency generated within the SMPSU and travels down the amp's input connecting cables back through the DAC's trafo (inter-winding capacitance) and returns to source via the mains. This form of noise the biggest bug-bear of using a switching supply.

Solution is fitting a suitable common-mode choke, sometimes more than one. Your switching supply will already have one internally but its inadequate when being used in an audio application (as are practically all because switchers aren't designed with audio in mind).
JLH with SMPS sounds incredible. I use it with a 27V 10 amp Meanwell supply, no noises of any kind with anything as input, even a PC. I also changed from typical transformer supply to SMPS. What a change it was, like chalk and cheese! Mine has been running for 3 years and I do not turn the power off, ever.


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I'm thankful for the dented dust cover and the repaired tear in the other woofer. Because of those, these speaker were given to me for free. I repaired the tear and they play perfectly. How many guys do you know who have a set of vintage JBL's that they use for their "test" speakers? :D If the amp works on those I move on to my better JBL's.

Blessings, Terry