TRIODE Voltage amp + Power OP output follower

lineup · 16th August 2010, 03:36 PM

It is quite easy to build a good and simple 'tube amp'
if using a triode (like 6DJ8) as voltage amplifier
and add one Power Op-Amp as output stage, follower.

Getting 50 Watt RMS into 8 Ohm with less than 1% THD distortion is not difficult.
The dist that is there will be totally of TUBE characteristic
as the Op-Amp gives practically no dist at Unity Gain.

It is a bit like Tube-Buffered Gainclone.

But problem with LM3875 and LM3886 is they can not work at Gain=1.
They are not true Op-Amps in this respect.

OPA541 can be used as a 'normal' opamp, at unity gain = 1.
And so easily work as output follower.
Power supply can be 70V for plastic models and 80V for metal package.
See images ...
Output current is 10 Ampere, so it drives 4 Ohm speaker, too.
Precision Amplifier - High Output Current - OPA541 - TI.com

My idea is very simple and works very good in SPICE.
I will post more detailed circuits later.
Here is the concept:

Bigun · 16th August 2010, 04:02 PM

I think this is a good looking approach, you could do a search to see what else might be helpful,

e.g.
Synthesis Magnum, commercial tube-chipamp hybrid...

Connecting tube gain stage to LM3886 for guitar amplifier??? How can this be done???

Tube with Power IC Output Stage - JLTi

pedroskova · 16th August 2010, 05:28 PM

The JLTi is kind of the opposite of the OP. No gain from the tube, and all of the gain provided by the chip. The tube is pretty useless if a decent preamp is present in the system.

Lineup - could the OPA544 be used as a substitute, i.e., is it unity gain stable as well?

SemperFi · 16th August 2010, 09:52 PM

Sorry mate, the distortion will not be tube b/c it is driving an easy load (the IC). The IC is driving the difficult load and the distortion will be like a SS amp.

Wavebourn · 16th August 2010, 09:56 PM

The distortion will be like a tube is driving SS amp, and SS amp is driving a complex load.

tinitus · 16th August 2010, 09:59 PM

isnt amplification from the tubes just about 20 or so
thus still needs some amplification from IC too

would be interesting to reverse it, IC driving tubes

or maybe IC driving IC, with tube interstage trafo

tinitus · 17th August 2010, 07:23 PM

would it have more interest in ChipAmp forum ?

I can move it over if you want ?

SemperFi · 17th August 2010, 07:35 PM

Maybe. point is u're assumption is wrong, shouldn't matter which forum u chose. But that's the whole point about this site, discussing ideas.
The concept of a tube doing voltage gain and transistors doing current is fine, but the distortion will be just as Wavebourn said.

teemuk · 18th August 2010, 08:40 AM

Circuit and method for a ... - Google Patent Search

16th August 2010, 04:02 PM	#2
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	I think this is a good looking approach, you could do a search to see what else might be helpful, e.g. Synthesis Magnum, commercial tube-chipamp hybrid... Connecting tube gain stage to LM3886 for guitar amplifier??? How can this be done??? Tube with Power IC Output Stage - JLTi __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

16th August 2010, 09:56 PM	#5
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	The distortion will be like a tube is driving SS amp, and SS amp is driving a complex load. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
four transistor emitter follower (diamond buffer) as power output stage?	capslock	Solid State	99	14th September 2010 09:17 PM
Choosing rail voltage in Class A, Power Follower Amp	ervinl	Solid State	1	5th August 2010 11:26 AM
Mosfet Power Follower with 1:1 Output Transformer questions	AudioGeek	Solid State	0	23rd February 2010 01:22 AM
N-channel only output devices in a power follower.	x-pro	Solid State	23	6th August 2009 01:50 PM
Low Voltage Plate Follower 6DJ8 Buffer Power Supply	mwl6m	Tubes / Valves	50	3rd August 2007 07:50 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

16th August 2010, 05:28 PM	#3
pedroskova RIP Join Date: Dec 2002 Location: C'ville VA, USA	The JLTi is kind of the opposite of the OP. No gain from the tube, and all of the gain provided by the chip. The tube is pretty useless if a decent preamp is present in the system. Lineup - could the OPA544 be used as a substitute, i.e., is it unity gain stable as well?

16th August 2010, 09:52 PM	#4
SemperFi diyAudio Member Join Date: Jan 2002 Location: nowhere	Sorry mate, the distortion will not be tube b/c it is driving an easy load (the IC). The IC is driving the difficult load and the distortion will be like a SS amp.

16th August 2010, 09:59 PM	#6
tinitus diyAudio Moderator Join Date: Nov 2005	isnt amplification from the tubes just about 20 or so thus still needs some amplification from IC too would be interesting to reverse it, IC driving tubes or maybe IC driving IC, with tube interstage trafo

17th August 2010, 07:23 PM	#7
tinitus diyAudio Moderator Join Date: Nov 2005	would it have more interest in ChipAmp forum ? I can move it over if you want ?

17th August 2010, 07:35 PM	#8
SemperFi diyAudio Member Join Date: Jan 2002 Location: nowhere	Maybe. point is u're assumption is wrong, shouldn't matter which forum u chose. But that's the whole point about this site, discussing ideas. The concept of a tube doing voltage gain and transistors doing current is fine, but the distortion will be just as Wavebourn said.

18th August 2010, 08:40 AM	#9
teemuk diyAudio Member Join Date: Nov 2004 Location: Suomi, Finland	Circuit and method for a ... - Google Patent Search

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)