The best of both worlds? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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

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
Reply
 
Thread Tools Search this Thread
Old 29th August 2002, 11:22 PM   #1
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
Default The best of both worlds?



I've been really interested in the hybrid world, but I can't find many designs out there that do what I want.

I've made a circuit layout of a basic tube driven mosfet amp that I found somewhere on the net. (please not it's not my design so I take no credit - only for the layout).

'As is' this circuit produces 50W into 8 ohms with a THD+noise of 0.64%, which doesn't seem too bad for a valve circuit considering most of this is second harmonic (softer on the ears).

If anyone thinks they may be able to improve upon the design (using bi-polar devices instead of MOSFETs in the output?) give it a go.

Thanks for looking folks!
Attached Images
File Type: jpg hybrid amp.jpg (22.0 KB, 2047 views)
  Reply With Quote
Old 30th August 2002, 03:16 AM   #2
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Hybrid amps

I have built similar circuits. The input tube is in parallel to increase the current available and to lower output impedance I guess.
The output stage you have seems to be a fairly easy load for one triode. If you want to raise the supply voltage (>35V) and want more power output , you would probably have to use a parallel stage as shown. The bias here is not particularly good as it would fluctuate with the supply voltage (on load) . Better to use zener stabilised voltage ( to the bias transistor) for this purpose. For a Hitachi type MOSFET you could use just a resistor instead of the transistor.
You should also note that you would have a fairly high output impedance with just two MOSFET's and no feedback. I found that the no feedback version sounds better than the one with feedback (which had lower measured distortion). So you could build what you have , it should be good. You can modify it later depending on what you think of its sound.

The high output impedance affects the bass end differently on different speakers. You should also remember that a high output impedance will result in a fluctuating frequency response at the speaker terminals due to the inherent variable impedance vs frequency of most speakers .

Build it anyway. It will be fun and is the road to greater fun.
The whole forum is here to help you along!
Cheers.
__________________
AM
  Reply With Quote
Old 30th August 2002, 03:20 AM   #3
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Bias point

I just noticed that you have some errors in the bias section. The bias transistor should go across the bias pot. Your diagram is wrongly connected. Also note that if the MOSFET's have internal protection zeners across gate and drain you only need an external resistor to protect it. Check it before adding more zeners.
__________________
AM
  Reply With Quote
Old 30th August 2002, 09:29 AM   #4
dice45 is offline dice45  Germany
diyAudio Member
 
Join Date: Jan 2002
Location: Munich, Bavaria
Default Pathos amp

annex666,
recently listened to a Pathos amp, was just built like yours, sounded wonderful to me, very musical.

but, please. do not parallel tube sections, eats up detail resolution. Better use one tube for both channels, evcha section for one channel.

If chosen tube is not juicy enoug to drive the SS circuit, use a juicy tube (lower plate resistance, higher transconductance)
__________________
Greets,
Bernhard
  Reply With Quote
Old 30th August 2002, 02:31 PM   #5
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
Thanks for the responce, but as I say the circuit is not my design.

If anyone wants to add pictures of improvements to the amp on this thread I would be more than happy to include them on the final design. Who knows maybe we'll end up with the "perfect" amp some day, lol.

Cheers for the input, keep it coming!



__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote
Old 30th August 2002, 05:16 PM   #6
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
OK, here's the circuit so far, I've added values and corrected some mitakes (it was quite late when I drew the original).

If anyone could design a better output stage then please feel free to post it or email it to me so I can incorporate it into the design. I don't really love the idea of MOSFETs.

Any feedback is good, keep it coming!

Attached Images
File Type: jpg hybrid amplifier.jpg (25.8 KB, 1800 views)
__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote
Old 30th August 2002, 05:23 PM   #7
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
Default Re: Hybrid amps

Quote:
Originally posted by ashok
I have built similar circuits... <BR>
...Better to use zener stabilised voltage ( to the bias transistor) for this purpose.
Thanks for the advice, but I'm quite new to electronics - I understand what you mean pretty much, but a diagram either posted on the thread or emailed to me would be a great help.

I'll incorporate any changes that are popular in the thread to the circuit (until it looses the nice neat simplicity - not to mention build-ability!)

Thanks to everyone who's been posting!

__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote
Old 30th August 2002, 11:21 PM   #8
diyAudio Member
 
Join Date: Aug 2001
Location: Melbourne/Australia
You may already have this, but a great web site for Valves and
Hybrid Amps is http://www.tubecad.com

In particular http://www.tubecad.com/april_may2001/2001_04-05.PDF and http://www.tubecad.com/articles_2002...er_Buffers.pdf

I too am looking towards building a Hybrid amp, but using a BJT output stage.

Regards,
Tim
  Reply With Quote
Old 7th September 2002, 06:19 PM   #9
nar is offline nar
diyAudio Member
 
nar's Avatar
 
Join Date: Apr 2002
Location: near the sea
For the hybrid amp,I would suggest not to use the pushpull output stage.Better drive the output trans with a single ended stage,with its own current source at V+ with same tube as signal.

I would try the Aleph current source with tubes (see http://www.passlabs.com on patents).I guess this would work perfectly,and better than the push_pull

I'd use some IRFP240 instead of the BUZ better sound I guess
__________________
"... Audio needs the thinnest wire ..." Rowan McCombe ... I hear it !!!
"Just 'cause they can't hear or sense it themselves doesn't mean you can't !" Allen Wright Allen was right ...
  Reply With Quote
Old 7th September 2002, 10:28 PM   #10
diyAudio Member
 
Join Date: Jul 2001
Location: Orleans, France
Default :att'n:

Annex666,

BUZ9xx are lateral Mosfets, designed specially for high quality audio, but with special characteristics. If the amplifier operates in class AB with 120 mA idle current, bias of gates must be constant (1.5 v or so between the gates) and needs no temperature compensation. If you use Vbe multiplier as shown in your diagram, crossover distortion will occur if the temperature raises...

If your amp is designed for pure class A operation, you have to experiment some *positive* temperature coefficient bias generator, in order to maintain the drain current approx. constant over the whole temperature range (25...125 C). Or you have to tolerate that sound quality may vary, according to actual power output.

Regards, P.Lacombe.
  Reply With Quote

Reply


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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Worlds smallest amp? Rikard Nilsson Chip Amps 18 9th September 2008 02:37 AM
New JK convertible sub - best of three worlds? rick57 Subwoofers 2 26th July 2005 09:53 AM
Worlds Best Preamp lawbadman Tubes / Valves 45 6th January 2005 11:47 PM
Speaker idea: best of both worlds Nielsio Multi-Way 12 30th November 2002 06:12 AM
The best of both worlds? annex666 Solid State 8 31st August 2002 09:28 AM


New To Site? Need Help?

All times are GMT. The time now is 04:17 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2