Impedance ratio and T-amps - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 15th February 2007, 01:09 AM   #1
diyAudio Member
 
Join Date: Aug 2004
Location: Alabama
Default Impedance ratio and T-amps

I have been registered with this forum for a while but have only started posting in the last couple of weeks, so forgive me for just jumping into the discussion.

I love the sound of tube amps and bought the Tripath SI on a whim based on the laudatory reviews. I thought the sound was clear and far better than solid state, but thin and without good bass. Being a tweaker, I immediately removed the circuit board from the case and installed it in a different chassis with bigger and more adequate input caps, a switching power supply to provide adequate current, and high quality bypass caps. I added a 50,000 mike Sprague reservoir cap that can run the amp alone for .5-1.0 sec for slam. The sound was better but still a little thin in the midrange. FTR, I like a big, fleshed out "organic" sound with good dynamics.

After looking at the schematic (and confirming this on a multimeter), I realized that the amp has a 20K input impedance but has a 50K (in my case 100k) pot in front of it. Thus, voltage distortion should be unacceptable by common design standards.The optimal impedance ratio ought to be better than 1:10 (first to second stage). So, I built a resistor loaded tube buffer after the pot and before the amp. This is a stupid amount of circuitry in front of that little circuit board. Nonetheless, the sound was superb--better than any tube amp I have built. This has been the greatest pleasure I have had in audio. The true measure of great audio is whether your shoulders slump within 5 seconds of listening. Nothing else matters. If you don't relax, it's not good. This configuration does it with only the slightest hint of improvement needed (nothing's ever perfect)

Well, after looking over reviews of these amps, I noticed a pattern. People who don't like the amp usually don't report having preamps. People who love the amp, do. They turn the volume control to max and then use their preamp to control the volume. This means that they have supplied the board with a good impedance ratio.

I submit that the major factor in the appreciation of this wonderful chip is the impedance ratio driving the chip itself. And adding some tube distortion may help matters.
  Reply With Quote
Old 14th April 2013, 11:14 AM   #2
diyAudio Member
 
Join Date: Mar 2009
Default schematic

Could you show us your full final schematic.Thanks
  Reply With Quote
Old 14th April 2013, 02:40 PM   #3
ATAUDIO is offline ATAUDIO  Austria
diyAudio Member
 
Join Date: May 2011
Location: Wien
Quote:
Originally Posted by Sasquatch View Post
I realized that the amp has a 20K input impedance but has a 50K (in my case 100k) pot in front of it. Thus, voltage distortion should be unacceptable by common design standards..
What you say *might* have a meaning in subjective/audiophile sense, but it is meaningless in an electronics - scientific POW.

Resistors, by definition are linear components and do not carry distortion with the notable plus of not influencing the phase. And even if you have massively unmatched input iimpedance (that is NOT your case) this would affect power transfer between the two devices, NOT distortion.

In general having a source (including the input pot) with an impedance realtively higher than the input (the T-amp) is NOT a problem when you consider it as a Voltage amplifier. You have just a sub-optimal Power transfer, but since we are speakig about voltage signal, this should not be a problem.

Note that this is valid also when considering the impedance given by capacitive (usually) or inductive components in the input network. In fact inductors and capacitor as referred as linear devices in electronics.
As long you have only linear devices in your signal path (and of course that would be great, but it is not the reality) you have none distortion.

How this rhen applies in general to T amps, it is also something that i cannot understand from your post. For the few that I know. in T-amps (i.e TA2020 stuff), as usual, the input inmpedance is greatly the result of the rf/ri network used to estabilish the closed loop gain.
__________________
@Audio
  Reply With Quote
Old 14th April 2013, 06:44 PM   #4
diyAudio Member
 
Join Date: Aug 2004
Location: Alabama
Funny. The original post is six years old, and I have long since gone onto other things. At the time I had a faulty understanding regarding impedance ratios and distortion. I know now that impedance matching is critical for power transfer or insuring adequate current deliver to the second stage, but couldn't affect the signal fidelity as described here.

Still, I have always thought a tube (in this case, I think it was a resistor loaded 6bl7 or something similar) to sound nice following a digital source. No theory as to why. Pleasant harmonic distortion? But it does seem to flesh out the sound and enhance the sense of presence.
  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
Tube amps, power and speaker impedance Klimon Tubes / Valves 3 11th January 2007 07:32 AM
Speaker impedance too low for amps! paulj Multi-Way 6 18th May 2004 12:58 PM
Hi-Fi amps....an impedance question rossco Multi-Way 4 25th March 2004 04:26 PM
High impedance out amps VS as low as possible. Brian Guralnick Solid State 57 31st October 2002 07:47 PM


New To Site? Need Help?

All times are GMT. The time now is 09:54 AM.


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