rotel 820 stan curtis - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 7th July 2007, 12:37 PM   #1
diyAudio Member
 
Join Date: Dec 2003
Location: earth
Default rotel 820 stan curtis

I read somewhere that curtis explained how he tweaked teh bass end of this amplifier in the power supply.

Anyone any idea how precisely?

a specific time constant of the caps and the load? ( however, that load will vary depending on what speakers are used)

or a combination of resonance between the transformer and smoothing caps?

thanks!!
  Reply With Quote
Old 7th July 2007, 02:40 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the relationship I use (but not universally accepted by other builders) is:-
Set input filter time constants to about, Low pass 0.5uS to 1.5uS
High pass 80mS to 100mS for sub-bass or 20mS for universal amp that does NOT pass bass signals.
Set the NFB time constant at least half an octave lower i.e>140mS
Set the PSU time constant at least half an octave lower than the NFB. i.e.>200mS.
This last recommendation may be something similar to what S.Curtis was referring to.

My interpretation of those RC time constants leads to +-20mF for the PSU in an 8ohm single channel amp or +-40mF for 4ohm.
That has led to considerable disagreement between builders on what affects bass performance.

Read other's and decide/experiment for your self.
__________________
regards Andrew T.
  Reply With Quote
Old 7th July 2007, 03:15 PM   #3
diyAudio Member
 
Join Date: Dec 2003
Location: earth
thanks andrew, where also would RC power rail decoupling come in that scheme?

best wishes
  Reply With Quote
Old 7th July 2007, 03:38 PM   #4
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally posted by AndrewT
Hi,
the relationship I use (but not universally accepted by other builders) is:-
Set input filter time constants to about, Low pass 0.5uS to 1.5uS
High pass 80mS to 100mS for sub-bass or 20mS for universal amp that does NOT pass bass signals.
Set the NFB time constant at least half an octave lower i.e>140mS
Set the PSU time constant at least half an octave lower than the NFB. i.e.>200mS.
This last recommendation may be something similar to what S.Curtis was referring to.

My interpretation of those RC time constants leads to +-20mF for the PSU in an 8ohm single channel amp or +-40mF for 4ohm.
That has led to considerable disagreement between builders on what affects bass performance.

Read other's and decide/experiment for your self.

Andrew,

This is quite interesting. I know Stan Curtis did 'something' but was not aware it involved tweaking time constant ratios. Is there any other stuff available on the net where this is addressed that you know of?

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 7th July 2007, 04:01 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by lt cdr data
where also would RC power rail decoupling come in that scheme?
What I do and it may not be correct, is find the current fed from a particular decoupling and calculate the equivalent R to match the current with the supply voltage. Then check that the RC time constant is below the frequency I am interested in. I suspect it should be more complicated than that but it appears to work or at least identify if the cap has significant ripple and then investigate it's purpose.
__________________
regards Andrew T.
  Reply With Quote
Old 7th July 2007, 04:10 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by janneman
I know Stan Curtis did 'something' but was not aware it involved tweaking time constant ratios. Is there any other stuff available on the net where this is addressed that you know of?
Hi Janneman,
I have seen a few papers that use the RC ratios suggestion. The main purpose is to guarantee avoidance of motorboating that used to be more common in valve circuits, but I can't see why the same logic should not be applied to SS circuitry.

Once one accepts that the staggered ratios are important, it follows that the HP turnover is directly related to the capacitance fitted into the smoothing of the PSU. This of course only applies to the simple unregulated PSU.

There are many that laugh at my recommendation of +-20mF for an 8ohm amplifier and point to the thousands of amps that work "perfectly" well with 25% to 50% of this level of smoothing. Few seem willing to even experiment.
__________________
regards Andrew T.
  Reply With Quote
Old 7th July 2007, 05:02 PM   #7
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
No, your numbers make perfect sense. I once read a story by Stan Curtis that he was able to "tune" an amp so that it didn't measure particularly well on the testbench, but boy it sounded good!

He didn;
't give details but I read between the lines that it had to do with the interaction of real loudspeakers with 'time constants' in the amp.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 7th July 2007, 05:07 PM   #8
diyAudio Member
 
Join Date: Dec 2003
Location: earth
well, I recall the 'tuning' of the rotel was to do with bass guitar, so if you look at the fundamentals and harmonics of that instrument and work out the frequencies.

also, say the rhythm of music, say 120bpm, you may be able to coincide the discharge current and values of smoothing caps

problem is like I mentioned is that it will vary obviously depending on the speaker used.

its a particular interest of mine how so things are 'tuned'/voiced, I am sure its very simple, basic equations, but there are really no references to it.

there may be a way to do it with possible compression things like attack and release times, and also phase manipulation, as that changes bass character, too, but I havne'e mangaged to fit any of the pieces of the puzzle together yet properly

I don't know if you could use cap values to resonate at a certain bass frequency with the secondary inductance of the mains tx ( likely to be small, but that's isolated by the bridge rectifer??)
  Reply With Quote
Old 7th July 2007, 05:23 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
try to find Dr Cherry's article on tuning the high pass filter in the NFB loop.
It produces a hump (Q>0.7?) in the low end response just at the turn over frequency.
This frequency could easily be chosen to coincide with audio signals and thus become very audible.
Much the same as tuning a speaker to have a bass hump to mimic bass notes and what they are doing is exaggerating the second harmonic to trick the ear/brain into hearing the bass.
__________________
regards Andrew T.
  Reply With Quote
Old 7th July 2007, 05:39 PM   #10
diyAudio Member
 
Join Date: Dec 2003
Location: earth
I once heard julian vereker, of naim, say that he increased the time constants in the power supply to put a hump in the bass.

I am sure there is no 'magic' to it, just a posh way of saying he increased cap values. I think they try to camaflauge it in posh words to make them look cleverer than they really are, and there is a simple explanation for it.
  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
Service Manual/ schematic for Rotel ROTEL RHCD-10 Michi CD player Staykov Digital Source 5 16th May 2012 12:24 AM
stan curtis 60w class a jamesfeline Solid State 16 6th May 2008 02:47 PM
Stan Curtis' 60W Class A Amp Audiofng Solid State 13 14th January 2006 02:52 PM
Curtis Mathis TUNER AUT-8300E Sam Odom Analogue Source 8 14th May 2005 01:15 AM
HELLO from SOMERSET STAN(ski) Stanski Introductions 0 14th July 2004 04:36 PM


New To Site? Need Help?

All times are GMT. The time now is 09:32 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