VAC Pa100/100 (Valve Amplification Company)

I would love to hear some VAC gear. They look good and I bet they sound even better

By the way what tubes are used in those amps?
 
I feel your pain

I will be pulling the whole main system apart this weekend.
Progress :banana:

Lots of dusting and cleaning, my MC275s are filthy, I'll get those cleaned and then put all the amps back. I'll then play around with amp/speaker match up and resistance, bi-wire, and maybe bi-amping the VAC amps.

Some of what I had will go back the same way like my MC 501s and L250s, but I will try some tubes on them as it's been years since I'v done that. I have speaker pairs staged in rooms, so I can hand truck them in and out of the room for sampling.

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The PA100/100 owners manual says this amp is a "modified Williamson design" with 6 dB global feedback and input sensitivity of .77V RMS. That is astonishingly little global feedback! And yet the specs quote power bandwidth to 50 KHz at 0.5 dB down from reference of 1 KHz. Must be some really well wound output transformers in these amps! Output stage is UL connected and uses 12AU7 small signal tubes (or 12BH7 for "richer sound"), with KT88's or 6550's for power tubes.

The manual says "the output stage is a fixed bias design and operates the output stage in "rich Class AB1 at an idle current of 70 milliamperes per tube, at approximately 535 VDC across the tubes." That's idling the tubes quite hot at approximately 89% of max plate dissipation.

Distortion at 1 KHz at max power (100 watts, both channels driven) is 0.25%. That's an excellent distortion measurement with so little global feedback used.

The manual concludes by cautioning us propeller heads that "In the immortal words of Daniel von Recklinghausen, if it measures good and sounds bad it is bad. If it measures bad and sounds good you've measured the wrong things."

:)
 
The PA100/100 owners manual says this amp is a "modified Williamson design" with 6 dB global feedback and input sensitivity of .77V RMS. That is astonishingly little global feedback! And yet the specs quote power bandwidth to 50 KHz at 0.5 dB down from reference of 1 KHz. Must be some really well wound output transformers in these amps! Output stage is UL connected and uses 12AU7 small signal tubes (or 12BH7 for "richer sound"), with KT88's or 6550's for power tubes.

The manual says "the output stage is a fixed bias design and operates the output stage in "rich Class AB1 at an idle current of 70 milliamperes per tube, at approximately 535 VDC across the tubes." That's idling the tubes quite hot at approximately 89% of max plate dissipation.

Distortion at 1 KHz at max power (100 watts, both channels driven) is 0.25%. That's an excellent distortion measurement with so little global feedback used.

The manual concludes by cautioning us propeller heads that "In the immortal words of Daniel von Recklinghausen, if it measures good and sounds bad it is bad. If it measures bad and sounds good you've measured the wrong things."

:)
Yeah it's a hot little (big for tubes) amp, I think it's pretty much on par with a new mac MC275.
I got music going again but still routing some new cables, cleaning up amps, writing down my changes to the preamp inputs. Then I can play with different speakers with my amps and see what I can fit in the room.
 
Then I can play with different speakers with my amps and see what I can fit in the room.
While I like the tubes and the VAC amps with the IMF and Velodyne sub, they will just take up all the space in the room, leaving with less options. And the IMF sound best with the sub filling in the low end.

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I'm asking because if the monoblocks use 4 KT88's each and are each 100W, and your new amp uses 4 KT88's total and is also 100W/ch, they must be running in different modes?
Well I don't know the differences in the amp designs but to the ear the Mono blocks push the speakers louder than the Stereo amp. They may have the same total output but the Monos are doing it a lot earlier.

Well I finally got your speaker stands in the system, The M3s sound better and less boomy off the floor. As far as amp match up, I got the Pa100/100 hooked to them, very nice indeed, need you to hear this.

I put the monos back on the MLs with the bi-wire of 2 ohm on top, and 4 ohms on the bottom.

The M3s sound really clear and clean with sharp imaging, while needing more gain to push them, the MLs give that airy space with the reflections off walls adding depth. They both sound different and very nice in there own way. Running them together is very nice as you get the best of both worlds, pin point imaging with the wall and room size sounding large.

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It’s always a lot of fun to mix and match gear and see how the various combos sound.

You must be getting a good workout too, moving those heavy speakers in and out of your room. :)
 
I notice in the photos that stereo amp has dummy loads across the 8r output. I assume that was just for testing and they will be removed for use in the system. Also with 775mV input sensitivity, you would be best off using a CD player with a volume control. It makes no sense to take the 2Vrms output from a CD player and boost that in a preamp by 6dB or 12dB (8V) and then attenuate it 20dB to the 775mV which is the maximum input the amp can accommodate. That just adds noise and distortion.

That will leave another hole in the rack that you can populate with something more useful.
 
You must be getting a good workout too, moving those heavy speakers in and out of your room

Hand truck!!!
I have speakers spread around the house, a pair in the bathroom, kitchen, and two spare bedrooms. I just wheel from room to room...:p

The amps are what's a pain in the ass, the Pa100/100 is not too bad at 60 or so lb, the vac monos are my lightest, the MC275s are about 100 lbs, I left the MC501s in place.

I think I might try two more speakers, I have some KEF 104aB in the bedroom, and a very rare pair of Sansui J33 in the closet. I haven't ever tried the J33s in this system as they sounded like crap with my old Sansui gear I used to have. Who knows? maybe they will sound better now.
 
I notice in the photos that stereo amp has dummy loads across the 8r output. I assume that was just for testing and they will be removed for use in the system.
Yes, the amps where on a Variac.


Also with 775mV input sensitivity, you would be best off using a CD player with a volume control. It makes no sense to take the 2Vrms output from a CD player and boost that in a preamp by 6dB or 12dB (8V) and then attenuate it 20dB to the 775mV which is the maximum input the amp can accommodate. That just adds noise and distortion.

My CDP is just used as a transport, the digital signal is sent to my D100 preamp witch is just used for a DAC, so I don't know how you can give advice without even knowing any of the equipment I'm using, how anything is hooked up or output of components. Not to mention the fact my C100 has adjustable line levels.

That will leave another hole in the rack that you can populate with something more useful.
In other words I shouldn't have a preamp? Oh a two box designed McIntosh flagship with supper low noise and stays out of the way of the signal. Ok, thanks for all the info.
 
Bypassing the pre, running the player selfstanding directly to the power amps and controlling level on them.
It'll give a handle on what the pre-prossessor is bringing to the party.
 
Bypassing the pre, running the player selfstanding directly to the power amps and controlling level on them.
It'll give a handle on what the pre-prossessor is bringing to the party.
There is no gain control on any of my amps, I actually have a DAC I like so I really don't know what all this would do other than maybe sounding a bit different, and maybe not better. It would also severally limit me with one input even if I did have gain control. I fully understand signal path and people should maybe read about the equipment I'm using instead of saying some of the comments being expressed.

I bought a power amp to try in my system, I did not buy it to throw out my system.
 
There is no gain control on any of my amps, I actually have a DAC I like so I really don't know what all this would do other than maybe sounding a bit different, and maybe not better. It would also severally limit me with one input even if I did have gain control. I fully understand signal path and people should maybe read about the equipment I'm using instead of saying some of the comments being expressed.

I bought a power amp to try in my system, I did not buy it to throw out my system.
A-ha!
The older Mac amps and some others have level controls for sensitivity. It was just a suggestion for an experiment.
 
A-ha!
The older Mac amps and some others have level controls for sensitivity.
Yes a lot of amp have a gain control, My newer mac amp have a input switch for XLR and RCA that changes the input sensitivity to them as well as well the C100 output is if I use different cables. It also has line level trim. One could call the C100 a fully balanced passive pre as it shuts off switches like volume and has all the preamp in one box and controller in another. It is a preamp that you don't know is there because it doesn't step on the signal.
 
Yes a lot of amp have a gain control, My newer mac amp have a input switch for XLR and RCA that changes the input sensitivity to them as well as well the C100 output is if I use different cables. It also has line level adjustment. One could call the C100 a fully balanced passive pre as it shuts off switches like volume and has all the preamp in one box and controller in another. It is a preamp that you don't know is there because it doesn't step on the signal.
Good!
My past experience has been that preamps are generally where dynamics and nuance dies. In the good olde days, it seems there couldn't be too much stuff in the in the path to sell a preamp, CJ and some others excepted. My benchmatk for a line stage has been a simple bypass parity test thru a high quality attenuator pot. The experimental system is very minimalist, it recently got it's passive controller replaced by a Pass Labs B-1 active unity gain buffer controller. The regular system got a CJ Motif MC-9 line stage control center a few years ago, very minimalist circuitry for the features with high grade parts.
 
Good!
My past experience has been that preamps are generally where dynamics and nuance dies. In the good olde days, it seems there couldn't be too much stuff in the in the path to sell a preamp, CJ and some others excepted. My benchmatk for a line stage has been a simple bypass parity test thru a high quality attenuator pot. The experimental system is very minimalist, it recently got it's passive controller replaced by a Pass Labs B-1 active unity gain buffer controller. The regular system got a CJ Motif MC-9 line stage control center a few years ago, very minimalist circuitry for the features with high grade parts.
Yeah I like a short signal path, and my system dosent have tone controls and extra switches.

You might like to read a bit about this first flagship multi box pre from mac. The shit they did is just awesome.
https://www.manualslib.com/manual/372562/Mcintosh-C100.html#manual

http://audio-database.com/MCINTOSH/amp/c100-e.html

http://www.berners.ch/McIntosh/Downloads/C100_own.pdf
 
My past experience has been that preamps are generally where dynamics and nuance dies.
You may be right as I have not used a high quality passive volume control in my system yet but when I substituted a VTA SP-9 preamp into my system I was floored by all the extra detail I was hearing. Within the first few seconds I was hearing separation of instruments that before was just a blend. Dynamics are great. I have never felt the need to upgrade that part of my system. I believe that preamp is based on the Aikido design and consistently gets rave reviews.

BillWojo
 
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