Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

David Berning's zh-230 - whats going on here?
David Berning's zh-230 - whats going on here?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 19th September 2012, 02:42 AM   #1
JZatopa is offline JZatopa  United States
diyAudio Member
Join Date: May 2003
Location: Chicago
Default David Berning's zh-230 - whats going on here?

I had the ZH-230 pointed out to me in this thread Contemporary tradition breaking amp schematics it looks like nothing I have seen before. From reading what he says about the amp it almost sounds like he has built a tube based class D amplifier of some kind. Am I close? Could someone explain this amp and how it works a bit better for me?
Knowledge is Power & Applied Knowledge is Freedom,
There is no higher religion than truth
  Reply With Quote
Old 19th September 2012, 04:40 AM   #2
smoking-amp is offline smoking-amp  United States
diyAudio Member
smoking-amp's Avatar
Join Date: Dec 2001
Location: Hickory, NC
Its not a class D amp. Its basically a square wave inverter from LV (like 50V) to HV (like 400 V). (high frequency square wave through a ferrite xfmr) Now put a tube across the HV side and control its current draw with the audio signal. As the HV side current varies, so does the LV side current (but at a higher current level).

So then you just put the speaker in series with the LV side. Two such units (from +50V and - 50V say), each with its own load tube, are used to generate LV bipolar current draw through the speaker on the LV side.

(like the totem pole complementary follower output transistors in a SS amp from + and - LV supplies, ie, just replace each output transistor in a SS amp with a square wave inverter going to each tube, and the speaker runs off the center point like a normal SS output. You just drive the two tubes like a conventional P-P amplifier to control the currents from + and - LV sides. )

The two HF inverters effectively become impedance converters for the tubes, so you can substitute the tubes right into the SS totem pole circuit. Any type of DC to DC converter can be made to work. You could use a HF capacitance voltage multiplier instead for example. The switching frequency must be high enough to support the audio bandwidth without intruding into the audio. The ferrite xfmr version(s) can actually work (in theory anyway) with switching freq. right in the middle of the audio band if you can null out the glitches. In practice it has to be well above the audio band, with low pass filters on the output to the speaker to elimnate the HF noise.

The HF switching frees the audio from the magnetic hysteresis of the ferrite xfmrs in the audio band. The penulty however is that the xfmrs suffer the usual leakage inductance effects at the HF rather than at audio freq. This leads in turn to using rather high impedance ratios to overcome the leakage inductance losses, which look like series resistances at the audio frequencies. Feedback becomes mandatory to control the output impedance to the speaker, and the HF filtering is a problem then for the feedback bandwidth needed. You win some, you lose some.

Last edited by smoking-amp; 19th September 2012 at 05:07 AM.
  Reply With Quote
Old 19th September 2012, 05:46 AM   #3
smoking-amp is offline smoking-amp  United States
diyAudio Member
smoking-amp's Avatar
Join Date: Dec 2001
Location: Hickory, NC
The Berning approach trades off one set of OT issues for another complex set. The tubes still have to drive the full load too.

A far simpler and better performing impedance converter approach is to just use the tube with a HV SS device in a Darlington or Sziklai pair. The tube still sees the load voltage and current (but is more lightly loaded for good linearity), and the bandwidth is phenomenal without all the problems from switching frequencies (high output Z, global feedback, switching noise). The lowered impedance then allows an easy to make, low primary Z, OT possible, which will have good audio bandwidth.

Certain further refinements can eliminate the need for an OT altogether, while keeping the output Z very low. Feedback is only used in the local pair. These approaches have been discussed extensively in various threads over the years by members here. The main objection to these approaches are that they look superficially like a typical Hybrid amplifier to the uninitiated, but there is a big difference in functionality. Most Hybrid amplifiers are just a SS follower pair stuck onto the end of a tube pre-amp.

Last edited by smoking-amp; 19th September 2012 at 05:58 AM.
  Reply With Quote


David Berning's zh-230 - whats going on here?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
For David Michael Bean Chip Amps 3 22nd September 2011 06:59 PM
David forthharmonic Tubes / Valves 1 10th January 2011 03:19 PM
wanted some Rubycon ZL/ZH Stefanoo Parts 5 10th November 2008 10:08 PM
Rubycon ZL/ZH NEEDED Stefanoo Swap Meet 0 8th November 2008 10:35 PM
David and Goliath Bgt Class D 7 1st October 2005 08:02 PM

New To Site? Need Help?

All times are GMT. The time now is 02:03 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio