Tube amp design parameters (distortion) - 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 16th August 2002, 04:22 PM   #1
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Default Tube amp design parameters (distortion)

What is a reasonable target for distortion in a Push-Pull tube amp of 4-8W? At the moment, I am excluding any OPT-induced distortion from the discussion as that will be very device dependent.

In some simulations I was able to achieve something like 0.2% at 1W rising to 1% at 5W. Is this par for the course, or are better figures achievable? I haven't seen distortion figures quoted much for tube amps, possibly because they are so often high.

FYI spice simulations when I was designing my tube line stages matched reality extremely closely, so for the moment I'll also pretend the simulations will match the real-world devices.
  Reply With Quote
Old 16th August 2002, 05:36 PM   #2
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Distortion

Hello Tiroth,
I think you need not be too worried about the tube amps distortion figures when they are in the region you mentioned. Amps with much higher distortion figures at full output still sound great. I didn't quite understand why you are designing to meet a distortion figure target. Most people cannot hear the difference between 1% and 0.1%. You should try to achieve good sound. This you can confirm only by building the unit. IMO go ahead and build it and listen to it. You can tweak it after that.
Best of luck .
__________________
AM
  Reply With Quote
Old 16th August 2002, 05:47 PM   #3
tiroth is offline tiroth  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Basically I'm just wondering what is considering "average" for a hi-fi tube amp. (i appreciate the irony) I would consider 1% to be far too high for a SS design, but I wasn't sure what was reasonable for a valve amp. Thanks for the input!
  Reply With Quote
Old 16th August 2002, 06:06 PM   #4
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Distortion

Hi Tiroth,
I did a quick check with my ( tattered) RCA Tube manual. They have some circuit diagrams for 'Hi-Fidelity' amplifiers. There is a 50 watt amp with 0.1% harmonic distortion and 1% intermod distortion. A 30 watter has 0.7% distortion ( harmonic) and 1.5% intermod distortion. You could check the web for data on the Dynaco ST70 or the Willimason or Marantz tube amplifiers. All generally considered good.
I once built a tubed amp with no feedback with something like 2% distortion at full output ( 40 watts) and also with negative feedback with less than 0.2% distortion. I liked the no feedback version for midrange and highs but the feedback version had better bass ( tighter and deeper). This would most probably have been due to reduced output impedance and wider bandwidth due to feedback.
You should be OK. Go ahead and try out your circuit.
__________________
AM
  Reply With Quote
Old 16th August 2002, 08:32 PM   #5
diyAudio Member
 
Gabevee's Avatar
 
Join Date: Feb 2002
Location: Richmond, VA.
Hi Tiroth,

Your figures are pretty typical. It is hard to reduce the distortion further for lack of gain overhead.

As Ashok mentioned higher power amps have lower distortion ratings. If you do a search on tube amps in Google or your favorite search engine, you will find that the manufacturers of high powered tube amps have rated their high power amps at 0.05% and lower. But the power is 300 and more watts. That with transformers.

I have heard solid state amps with upwards of 10% distortion at full power and they sound OK. My own design, before NFB, had a rating of 4%, and to me sounded superb. Of course, NFB brought it down to 0.01%, and still sounds as good.

So, as another said, put it together, give it a listen, and tweak as desired. Because even a "golden ears" can barely hear the distortion of a pure sine wave of 1%. For music it is impossible to hear.

My additional 2 cents.
Gabe
__________________
Gabe CGV Electronics
Home of the CGV-300B amplifier on a budget
  Reply With Quote
Old 16th August 2002, 10:07 PM   #6
diyAudio Member
 
Join Date: Sep 2001
Location: Fairbanks, Alaska
Default Distortion, levels and types need to be considered.

When looking at amplifier distortion it is important to look at the type of distortion produced. Even order products are generally less disturbing while the odd order products are always more noticeable and thus more objectionable. Also out of band intermod caused by high harmonic levels of the primary signals causes in-band beat notes to be produced. There is also the issue of phase cancellation when various harmonics add or subtract from each other amplitudes in the wrong relationships. This causes the original harmonic structure of the input signal to be significantly modified.

Distortion measurements can provide a rough guide of the performance of a amplifier and it can be deduced that amplifiers with no negative feedback will likely have distortion figures that are likely between 1 and 5 percent at close to maximum output levels. The same amplifier with moderate feedback will likely run around .1 to .5 percent. If the amplifier has enough gain and the negative feedback is increased substantially the distortion figures may reduce to .01 to .05 percent. The output impedance of the amplifier will decrease with each increase in feedback and also there will likely be some changes in phase cancellation levels of the harmonic structure versus output amplitude.

Single tone distortion measurements are truly hard to analyze subjectively. It used to be a rough guide that Hi-Fidelity sound amplification required a 1 percent or less distortion level when using single tone harmonic distortion tests. These days with lots of amplifier gain available before the application of negative feedback while maintaining stability can produce distortion figures that are hundreds of times lower. Many say that the negative feedback levels required to produce such low distortion figures have undesirable side effects that are hard to measure but can be heard when reproducing music. One of the primary differences between most solid sate circuits and old tube technology is gain. The solid state units have in general much more gain and thus run at much higher levels of negative feedback.

Perhaps this is a little off the subject but perhaps worth considering when looking at distortion figures.

John Fassotte
Alaskan Audio
  Reply With Quote
Old 17th August 2002, 04:31 AM   #7
diyAudio Member
 
Gabevee's Avatar
 
Join Date: Feb 2002
Location: Richmond, VA.
Very well said. However....

My SS bridged amp sounds so much like a tube amp... and its distortion product is all odd order since as has been repeatedly been told to me, virtually all the even order harmonic distortion is gone.

So... it can be truly said that listening is the best determining factor, IMHO.


Gabe
__________________
Gabe CGV Electronics
Home of the CGV-300B amplifier on a budget
  Reply With Quote
Old 19th August 2002, 12:22 AM   #8
SHiFTY is offline SHiFTY  New Zealand
diyAudio Member
 
SHiFTY's Avatar
 
Join Date: Jul 2002
Location: New Zealand
With a Class AB PP amp, you have some crossover distortion where the waveforms are "put back together" or something. To minimise this in mine (PP 6v6) I used a small amount of NFB.

With virtually no NFB there is a little bit of noticeable distortion at mid-volume, but when you adjust the level (I use a 10k variable resistor in series with a 4k7 resistor in the loop) you can pick a level that sounds cleanest. The amp sounds very nice now, accurate and clean but still with warmth.

The added bonus with NFB is that it removes any last traces of hum and noise, the amp is dead silent now.
  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
Design parameters for SE OPTs' Richard Ellis Tubes / Valves 2 3rd September 2007 01:20 AM
TL design vs driver parameters Henkjan Subwoofers 0 20th September 2006 11:03 AM
Calculating Tube Parameters +SPICE jackinnj Tubes / Valves 3 19th November 2005 01:23 PM
How to design port without driver parameters jedcrocker Multi-Way 2 27th December 2004 03:24 PM
What program will allow you to input the T/S parameters and make a speaker box design kehi Multi-Way 3 11th December 2003 02:05 PM


New To Site? Need Help?

All times are GMT. The time now is 09:13 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