[PaulFolbrecht]

Steve,

Seriously, what did you mean by these two thigns:

1) The IM distortion is 3-4 times the HD, at low signal levels.

2) SET damping is different than PP damping if one examines the entire cycle, depending on which class the PP amp is operated at.


Please elaborate.  Thanks!

[Steve]

Hi Paul,

    
I stand corrected by the RCA Radiotron Designers Handbook (27 engineers). Here is what they state:

"If all harmonics are within the frequency range of the amplifier it may be shown that---

1) If only second harmonic is present (a condition which never occurs in practice), the ratio of total intermodulation distortion to second harmonic distortion is 3.2

2) If only third harmonic is present (another condition which never occurs in practice), the ratio of total intermodulation distortion to third harmonic distortion is approximately 3.84 at low values of distortion."

3) If the distortion is small, the intermodulation sidebands are approximately given by
     Modulation percentage of first intermodulation sideband} approx 2 times second harmonic distortion percent-
     Modulation percentage of second intermodulation sideband} approx 3 times third harmonic distortion percent.

Thus intermodulation distortion is automatically weighted by the order of the distortion.

As a very rough approximation, the ratio I.M./H.D. may be taken as:

3.2 for single-ended triodes and 3.8 for PP (triodes or pentodes) where I.M. = total intermodulation distortion (r.m.s. sum)
and H.D. = total harmonic distortion," provided that the operation is restricted to the normal low-distortion region." The ratio tends to increase as the distortion increases."

As one can see, it is advantageous to keep the distortion as low as is reasonably possible.

--

The output Z of a tube varies with plate current. It is hard to find pictures or graphs showing Rp changing with changing plate current but imagine a snow ski jumper on the ramp. Near the bottom of the ramp is the normal plate Rp at idle current and tends to level off.

At the top of the ramp is tube cutoff, Rp is very very high.

In SET operation, the positive portion of the cycle is marked by a slightly lower Rp as the tube conducts more heavily. During the negative portion of the cycle, Rp increases dramatically as less and less current flows through the tube (at cutoff, infinite). It is similar to a perfect amp with a resistor in series with the speaker. Near constant Rp in the positive portion of the cycle, and constantly changing value during the negative portion of the cycle. So the output Z of the amp varies depending on the signal applied.

In PP, this radical change is much less (though not perfect) as one tube is conducting more as the other tube is conducting less.

Added: The sound quality of both SET and PP can vary alot, depending on quality of design and parts quality, price point. I just try to present views for better understanding.

Hope this helps to explain your two questions, Paul.  

[Les Lammers]

I just posted this on the Yahoo SET forum:


Gentlemen,

The last 20 minutes of my life has been the first 20 minutes listening to a SET amp and I do believe it will be far from my last.

Don't know if I mentioned, but I'd ordered a used Dared VP-845 on agon as an experiment and possibly for a 2nd system (I'd really prefer monos for the main system).

Anyway, it's really true.  I don't know what it is, but I've just not heard (recorded) music quite like this before.  "Immediacy" - yes, that does a  ...

Paul,

Your choice of SET amps is pretty limited with your speakers, unless your budget is unlimited. There are many great PP amps too. A well designed amp is just that, it can be PP or SET. You can go nuts with theory. Trust your ears. Make one change at a time or you will enter the 'black hole'
of audio.

Les

[eagertrader]

I just ordered a brand new, 2006 Dared VP-845, with a couple of mods, a SUB-OUT on LINE-3, and a PRE-AMP BYPASS on LINE-4, other than that is the stock items, which I'm being told has a number of upgrades over the earlier models. Next year, $$$ and wife permitting, I plan to connect pa pair of Dared monoblocks using 845 tubes as well. In the meanwile, on the integrated amp I plan to use the stock 845's, and once I get used to them, roll in a pair of 845M's that people are raving about (what the heck! isn't good enough good enough?).

Just for the occasion, I also bought a pair of Hyperion HBS-938's (To replace my Dali Grands) which are discussed in detail on a speaker thread in this forum. They are called Watt Puppy/7 killers at a fifth their price, so of course I gotta find out...

Since neither has arrived to my abode yet (which is OK as it buys me some more time alive as my wife hasn't found out yet...), I cannot report on the validity of any claims and the sonic virtues of neither.

I'm writting on this thread because 1) it references the Dared VP-845, and 2) my previous integrated which I just sold was a very fine ASL AQ 1001-DT PP which I upgraded w/EH KT88's and NOS RCA 12AU7's, and used exclusively in the 29w triode mode. I was much in love with this amp, which makes it just about right time to upgrade. The only reason for changing is to find out what all this SET fuss is all about, and like I said before, gotta find out...

PS: If anyone has a good recommendation on replacement tubes or mods for the Dared that will take the sound to the next level, I'd like to hear it. TNX

[PaulFolbrecht]

Well, eagertrader, interesting that you found this old thread of mine.

We have some things in common.  1st of all, the Dared VP-845 was also what started the SET craze for me - my 1st SET amp.  I currently have a pair of Consonance Cyber 845s which I am very happy with.  And - the Hyperion 938s! 

You are going to find that the 938s play very well with SETs and with 845s especially.  You are going to be really happy with this setup.

The Dared 845 is a pretty nice amp.  It is a very sweet-sounding amp and shows off the 845 pretty well.  There were a few things I could complain about:

- It is not completely silent.  There is substantial mechanical hum especially from the power tranny.
- It runs VERY VERY HOT.  Simply too hot than an amp should, even a class A amp.  It runs so hot that you cannot put your hand on the VC for more than a couple seconds.
- The VC pot on my unit at least had a low-quality feel to it.

However, the amp is well-built and the parts are very good.  And it does sound good as I said.

[mrtlaf]

Has anybody ever heard of "Kailin"??

http://cgi.audiogon.com/cgi-bin/auc.pl?ampstube&1149642730&auc&3&4&

I purchase a Kailin K-6L6 about 9 months ago on a whim on AudioGon auction thinking I would not win with the bid I gave.  Well I did.  I had a Sophia Electric Baby amp driving Omega 6 speakers w/Cary 303/100.  The Kailin produces a larger soundscape with a little more punch in the lower end.  But it is twice the power of the Baby amp (20 versus 10 watts/channel)

I've been searching for a new integrated tube amp to use here in the office that has remote control volume.  Complaints with the Kailin are:

1. power switch is on the rear of the unit
2.  volume pot must be dirty.  Every once in a while, I get a hum/static that is easily fixed by moving the volume control up/down

Hope this helps.

Mike

[eagertrader]

Paul,
 
This is what the Dared US importer responded as I ask him to respond on the issues of the Dared VP-845's excessive heat and hum you brought up on your post following mine:

"If the VC was that hot as he said, then I think there might have been be some problem with the amp. Otherwise, I do not think so."
and
"All 845s transformers have some sort of mechanic hum because of the huge amounts of current that goes through a class-A tran. Some are better. You may get very little mechanic hum. Usually, people added sound deadening materials (soundcoat) to the bottom cover and it greatly reduces the transformer hum. Many types of materials are available from speakerparts.com."
 

[PaulFolbrecht]

Paul,
 
This is what the Dared US importer responded as I ask him to respond on the issues of the Dared VP-845's excessive heat and hum you brought up on your post following mine:

"If the VC was that hot as he said, then I think there might have been be some problem with the amp. Otherwise, I do not think so."
and
"All 845s transformers have some sort of mechanic hum because of the huge amounts of current that goes through a class-A tran. Some are better. You may get very little mechanic hum. Usually, people added sound deadening materials (soundcoat) to the bottom cover and it greatly reduces the transformer hum. Many types of materials are available from speakerparts.com."
 

1) I believe the 6moons review of the Dared 845 said about the same thing about the heat.

2) All power trannies, big or not, do *not* have mechanical hum.  The Art Audio Carissa 845 stereo amp I owned did not.  The Consonance monoblocks I have now do not.  This isn't the end of the world.  It's just something worth noting.  The Dared is a good amp for the money.  In fact, I run a Dared 2A3 amp in my 2nd system.

[mcrespo71]

NAIM

[eagertrader]

I apologize as I keep bringing up the Dared VP-845, my first foray into SET, as this thread is about SET vs. Push-Pull and not the Dared. Since I'm still waiting to get it, I cannot defend nor critique the merits or flaws of this amp, and I'm just passing along what I get from the technical experts that know the product intimately, as they import it and service/mod/work on it regularly.

Here's the last bit of info I've got from the Tech performing a couple of minor mods before I take delivery (SUB-OUT & PRE-BYPASS).

"This amp has evolved over the past couple years. Joe has added excellent capacitors: Blackgate and Auricap.
The power supply and transformers are very high quality. Build quality also is top grade. Comes down to how you like the 845 sound. Most find the midrange outstanding. This one also has solid bass too. Should be a keeper from day one. Be prepared to lift a very heavy amp!  845 glass gets very hot very fast - be careful. Only upgrade I would try are some old stock (NOS) 6SN7's and different 12AX7's. Supplied Chinese are good, but there are better old tubes still out there.   
The supplied 845's are just fine."

This is the last comment I will make on this thread regarding this amp as I should start a thread on the Dared once I have acquainted myself with it well pass the break in period. Thank you Paul for your insights that force me to ask questions on this integrated amp.

[PaulFolbrecht]

eager,

I agree with ALL of that! 

The new stock Chinese 845s are indeed REALLY good and they are so cheap.  I still run them (Shaugung B's).

I also noted that Dared uses very good parts.  And I did not mean to imply that the trannies are 'bad' in any way due to the hum - what matters is how they sound - and they sound good.  The amp is very extended on both ends (could not be if the output iron was not good stuff) and does show the 845 for what it does best.

Have fun.  You'll enjoy it.