micaddict

Comments, Please
« on: August 22, 2017, 06:24:31 AM »
Hi guys and gals.
The video in the link has Aspen Pittman talking about the (discontinued) Groove Tubes Vipre preamp.
It runs about half an hour, but boring it is not IMO.
Although it's all certainly not unfamiliar to me, I'd like to hear your thoughts about what he says.
Some topics that stand out are (truly) balancing, impedance (loading) and rise time.

So please discuss.  :)

https://www.youtube.com/watch?v=B33N5zuHRn8


Heikki

Re: Comments, Please
« Reply #1 on: August 22, 2017, 12:37:01 PM »
I'm afraid to watch it out of fear it might make me dumber.

ruffrecords

Re: Comments, Please
« Reply #2 on: August 22, 2017, 12:57:02 PM »
I only got as far as impedance but much of what I heard was techno bull.

Cheers

Ian

micaddict

Re: Comments, Please
« Reply #3 on: August 22, 2017, 01:36:36 PM »
LOL

Could you guys be a little more specific?

Or is it that hopeless?

ruffrecords

Re: Comments, Please
« Reply #4 on: August 22, 2017, 04:16:59 PM »
LOL

Could you guys be a little more specific?

Or is it that hopeless?

IMHO it is not worth listening to.

Cheers

Ian

micaddict

Re: Comments, Please
« Reply #5 on: August 22, 2017, 04:27:33 PM »
Should I feel sorry for asking?

ruffrecords

Re: Comments, Please
« Reply #6 on: August 22, 2017, 05:39:42 PM »
Should I feel sorry for asking?
No, there are lots of videos like this on the net. For regular folk it is very hard to differentiate between fact and folklore.

Cheers

Ian

Re: Comments, Please
« Reply #7 on: August 22, 2017, 07:17:17 PM »
I had a look at this ,and yeah it does seem like his explanations are a bit of a mix of fact and fiction.
Seems like an input transformer with various impedence tappings , as he lowers the impedence the step-up ratio is increased .
the rise time control just sounds like its a passive top cut .

Re: Comments, Please
« Reply #8 on: August 22, 2017, 08:07:43 PM »
He sorta gives the impression that the fully balanced topology solves all ills ,he's right from the point of view that balanced is less sensitive to interference from power supply  and induced noise ,a single ended stage will require quieter ht rails .
One potential downside to balanced is if your tubes are badly matched or drift due to age, performance will be affected., not  much of an issue with single ended topologies.
The other thing , and this has as much to do with personal taste as anything else, is that a  balanced transformer coupled output stage will tend to cancel 2nd harmonic distortion making 3rd dominant, where in the case of single ended 2nd harmonic will always be dominant and mask the higher order stuff . When your signal levels are well within the capabillity of the unit this wont make much difference ,on transient peaks I favour the a-symetrical clipping of the single ended stage.
NFB also has a bearing on an amplifiers abillty to recover quickly from transient over load ,high feedback tends to be clean up to a certain point then over the space of a few db gets dirty very quick ,where no feedback tends to have a much more gracefull overload .

ruairioflaherty

Re: Comments, Please
« Reply #9 on: August 22, 2017, 08:40:05 PM »
...where in the case of single ended 2nd harmonic will always be dominant and mask the higher order stuff ...

This is the opposite of my experience.  Our ears are very forgiving of relatively large amounts of 2nd harmonic but 3rd, 5th ,7th ,9th even in small amounts are much more audible, even in the presence of significant 2nd.  I have never experienced the "masking" you mention.



Re: Comments, Please
« Reply #10 on: August 22, 2017, 09:42:43 PM »
I agree with you Ruari, moderate second harmonic amounts only to a slight brightening of the sound, and even relatively large amounts of it often arent even percieved as distortion by the ear . Back in the good old days of single ended tube topologies specing outputs to 5% thd with triodes was normal enough . Of course as you get up into the higher harmonics ,the percieved anoyance factor increases exponentially , What I was saying is that  in simpler topologies the ratio of second to higher order harmonics is large .As you go towards high gain high feedback circuits  the ratio of say 2nd and 3rd to higher harmonics gets smaller ,in the case of balanced push pull second harmonic tends to  cancel in the output transformer and at the same time a higher proportion of ugly upper harmonics is produced .

moamps

Re: Comments, Please
« Reply #11 on: August 23, 2017, 04:07:06 AM »
Should I feel sorry for asking?

No. Thanks for pointing to it. Nice design. Does anybody know where and for what price I can buy the input transformer (Cinemag CM-9955-T), Europe preferred?
More discussion about the preamp:
https://groupdiy.com/index.php?topic=30267.0

micaddict

Re: Comments, Please
« Reply #12 on: August 23, 2017, 04:28:46 AM »
No, there are lots of videos like this on the net. For regular folk it is very hard to differentiate between fact and folklore.

Cheers

Ian
Don't know if I'm regular or non-regular myself, but I think I can spot where he loses objectivity. The guy is obviously repeating his old promotion act, which he even confirms himself. Nevertheless or maybe because of this, I somehow remained interested until the end. And I still feel it's a nice handle for discussion in this preamp section. But I've been wrong before.

 

Tubetec, thanks for biting.  :)
Quote
One potential downside to balanced is if your tubes are badly matched or drift due to age, performance will be affected.
This is exactly what came to my mind first.


Quote
The other thing , and this has as much to do with personal taste as anything else, is that a  balanced transformer coupled output stage will tend to cancel 2nd harmonic distortion making 3rd dominant ...
And this is the sort of discussion you'll find when people discuss single ended versus push-pull amps. Strong advocates on both um ... ends.

Anyway, seems like we have a discussion.  :)



« Last Edit: August 23, 2017, 04:37:41 AM by micaddict »

micaddict

Re: Comments, Please
« Reply #13 on: August 23, 2017, 04:30:44 AM »
No. Thanks for pointing to it. Nice design. Does anybody know where and for what price I can buy the input transformer (Cinemag CM-9955-T), Europe preferred?
More discussion about the preamp:
https://groupdiy.com/index.php?topic=30267.0
Hey, thanks for the link!
I did do a search, but apparently in the wrong section.

abbey road d enfer

Re: Comments, Please
« Reply #14 on: September 05, 2017, 01:53:58 PM »
Aspen Pittman is a musician-turned-entrepreneur; his scientific knowledge is shaky at best. He should let a real designer do the tech talk. He must be praised for investing money and time in tube manufacture, though.
The ViPre is a nice piece of gear, but its price prevented it becoming popular.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
"The important thing is not to convince, but to give pause for thought." (B. Werber)
Star ground is for electricians.

deuc224

Re: Comments, Please
« Reply #15 on: September 09, 2017, 06:09:39 PM »
I wish someone would recreate this preamp.  One of the most elusive ones made. 

micaddict

Re: Comments, Please
« Reply #16 on: September 10, 2017, 06:28:46 AM »
I wish someone would recreate this preamp.  One of the most elusive ones made.
Well, if the bright minds here team up, I wouldn't know a better place.  :)

mjrippe

Re: Comments, Please
« Reply #17 on: November 14, 2017, 06:17:13 PM »
I wish someone would recreate this preamp.  One of the most elusive ones made.

Ridiculously overblown piece of $#!+ in my opinion.  Of course my clients who have them LOVE them.  I hate working on them and they are at that age where problems are not infrequent.  Take a look at the available schematics to see why nobody in their right mind would DIY one.