Hi you all!
I’ve recently finished my version of ZEN Revisited. It worked great first time started and I enjoy its sound almost every day. No hum. Very stable. Sounds good to! Thanks to Mr. Pass I’ve also got rid of that noisy bump in the speakers when powering on.
I‘ve placed the transistors on very large heat sinks, which are at the same time the sides of the Al box. Large enough to comfortably keep my hands on them.
Since there is some extra room for heating I was thinking about adding some power to the amp. Is this possible? And if it is, how can be done?
The stock Zen amp runs the output transistors at
about 25 watts, which is a figure that I have found
over the years to be absolutely reliable. The
manufacturers of these devices tout figures up to 150
watts or so, which I find to result in very unreliable
operation. Somewhere in between is a region where you
might find acceptable reliability with only an occasional
Given good heat sinking, I think you could probably
take the devices up to 50 watts, resulting in 20
watts worth of output for the amp, without seriously
Alternatively, you can parallel (matched) devices and
take the power up arbitrarily, which will be the subject
of a future Zen project.
Also alternatively, you can use the Aleph current source
and double the efficiency of the circuit, which would
double the output with the same dissipation, and if you
also allowed for 50 watts per device, you could easily
get 40 watts. This project has already been done, and
is being prepared for publishing.
There are yet other ways to increase power, many of
which are on a schedule for projects, but we don't want
to overlook an easy and very good sounding one: Build
4 stock Zen channels, and run them as two set of parallel
bridged into the load. This has to be driven balanced,
but it gets you 40 watts and sounds just terrific.
Many thanks for your kind answer Mr. Pass. The idea of balanced driven ZENs is worth giving a try… I can see many of your goodies are still to come. That is good and thanks again for sharing!
Gema, my Zen Revisited does 50W/chan into 4ohm - parallel channels. Nelson (thanks due again) is taking this to the next level - fully balanced - nice :)
I established current and voltage swing requirements into my speakers (by listening to real music & scoping), turned out it needed 50V rail, 4A bias per stage. It'll be less into 8ohm. And (this is the fun bit!) BIG heatsinks. I'm using 250W Exicon MOSFETs from Profusion. These are twin chipped versions of their 125W devices and so far seem happy at 128W - heatsinking is everything with these desgins. The high bias also brings down distortion.
The result manages to both play loud and sound nice. Heating bill will be lower too this winter I'm sure!
Check my site for the rest of the story.
Wait a second. What's this? Balanced Zen?
How many Zens channels did you build to get a stereo set?
probably four....two/ch running parallel,, one big piece of hardware you've got there.....
Yes, but if you look at what NP wrote:
but we don't want to overlook an easy and very good sounding one: Build 4 stock Zen channels, and run them as two set of parallel bridged into the load. This has to be driven balanced,
2 sets of parallel bridged...that sounds like 4 amps for one stereo channel. Parallel one stereo Zen, then bridge another set, right? Is that 8 channels for a stereo setup?
I don't know, someone learn me right here! ;)
I went parallel (still unbalanced) only to drive a 4ohm load - built 4 of the critters - amazing how much quicker the last ones are to build over the first one!
Man. That's what I thought. How's the bridge/parallel sound over a single set? Probably a better lower freq.
You guys ever hear of Bob Lubwig? His main mastering room uses something simular, but his Cello amp's put out 1000w for the neg. side and 1000w for the pos. signal. All going to a set of very large EgglestonWorks monitors. They stand on a concrete slab that goes down to granite. A really sick room!
Some other guy heard about it too.
Thanks for the info.
First of all yeah I think NP means 4 Zens per channel. 8 for a stereo amp. But also I think he meant to bias all of them higher for better quality. I think it´s a great idea. Mr. Pass when is the new website up? I can´t wait for the new stuff. :-)
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