How is this possible? (a bit long)

I started a similar thread in the General Audio forum but received no comments (maybe because I asked no questions?), so I figured the Tube forum would be the proper place to go.
I've had a German-made AudioValve RKV MKII headphone amplifier for over 5 years now, and for headphone usage it has been a superb performer. However, for speaker usage, the specs didn’t look none to good, particularly the wattage rating, as I'm used to thinking "the more watts the better."
Here’s the specs:

OTL - transformerless tube amplifier
double mono construction
Alps volume control
1 pair 6,3 mm stereo jacket for headphones
tubes: 4 * PCL 805
power output: each channel 3 watt SINUS, ( between 100 to 400 ohm loads )
bandwide: 15 - 100 000 hz
damping 3600
distortion 0,002 % at 1 Watt-200 Ohm load
max. output voltage 80V
sens. 0dBm
IC – full autom. - controlled bias
class - a
power consumption 40 watt
size 360*200*120 mm (d.w.h.)
weight 10kg

I've always wondered, at 3 watts, what it would sound like with some high efficiency speakers, in particular my Frazier Black Box II (horn mid/tweeter with 8 inch woofer in a slot loaded enclosure- 96dB/1W/1M efficiency). I’ve read quite a lot about those flea powered tube amps being wonderful with those kind of speakers and was curious enough to try it out for myself.
When I purchased these Fraziers (late 60’s), I was using Dynaco tubed equipment, and, to my ears, the sound was wonderful. But as the Dynaco equipment began to age and need repair and maintenance, I moved on to SS equipment and was never really satisfied with the sound (with the Fraziers). My ARs, on the other hand, really came alive with the additional wattage, and seemed to thrive on SS.
With the Fraziers, there always seemed to be a glare, particularly on brass, that was not there when I was using the Dynaco gear. And the ever-present hiss, at close range, even with the volume turned all the way down was an annoyance.
Enter the RKV Mark II and the Impedanzer, a device that allows the amp to be hooked up to speakers or low impedance headphones. It has settings for 8/6/32/64 ohms.
Recently, I switched out a (circa) 1987 Onkyo TX-890 (around 100 watts per side) that I was using. I was happy with it driving Rectilinears , but not so thrilled with its synergy with the Fraziers. The CDP is nothing special, and probably not even mid-fi, but it serves the purpose for these old ears………a Sony 200 CD mega changer.
I put on some Ella Fitgerald and settled back for some serious listening. I was immediately struck by the effortless, smooth sound emanating from the speakers. Ella’s voice remained rock solid between both speakers and seemed to be in the room. The transparency was incredible. And when horns appeared, they had none of the glare or harshness I found so irritating with SS equipment…..just a nice “bite.” Granted, this amp isn’t going to rock the house, but at moderate or slightly above average listening levels, the sound is quite delicious, with a smoooooth top end and nice, punchy bass. The mids are extremely tasty. I don’t feel I’m missing anything. As a matter of fact, these speakers now sound as I remember them.
I then listened to some Louis Armstrong, Gillian Welch, Dave Van Ronk, Ray Charles, Johnny Cash, and Joan Baez. I was struck by the realization that I didn’t miss tone controls………..I felt no need to boost or cut anything. With the Onkyo, I was usually playing with the treble to cut the glare, or bringing up the bass a bit, depending on the recording. Also, the stereo image is rock solid.....vocals are dead center, thus no need for a balance control.
After some extended listening, I switched out the RKV and hooked up a few SS amps......a Kenwood KA-8300, a H/K430, and an Advent 300 receiver. It only took a few minutes (seconds?) with each to realize that none of them could match the musicality of the tubes, although the H/K came closest. With all the amps, there was an ever present hiss between tracks when I pressed my ear up to the horn. And the horn glare was damned grating, as well. I found myself reaching for the treble control quickly. With the RKV there was nothing but silence between tracks (even with my ear pressed to the speaker), and just smoooooth sound when the music began.
Now, I have some vintage Dynaco gear (SCA-35 integrated, PAS-3x/ST70 combo) that I've had since the late 60s and is in need of refurbishment.
If I refurbed these, would I get an improvement in any way sonically (other than being able to play louder)? The sounds these old ears are hearing from this RKV/Frazier combo would be tough to beat (IMO). It just sounds so "right."
How is it possible for something like this to happen?
Here are some pics of amp and Impedanzer:

I think it's difficult to answer questions like these because the "sound" is so personal. Someone else's music taste and sonic preferences may be completely different to yours. What is to lose in bringing the Dynaco's up to spec and giving them a good comparative listen for yourself? If you don't like them, you could sell them to recover refurb cost.

joelongwood said:

I started a similar thread in the General Audio forum but received no comments (maybe because I asked no questions?), so I figured the Tube forum would be the proper place to go.
I've had a German-made AudioValve RKV MKII headphone amplifier for over 5 years now, and for headphone usage it has been a superb performer. However, for speaker usage, the specs didn’t look none to good, particularly the wattage rating, as I'm used to thinking "the more watts the better."
Here’s the specs:

Click to expand...

Of course peoples opinions vary. Myself I have found tubes and headphones a very nice combination. And I have heard some of the worlds finest.

But no phones have ever competed with my current system in the sense of size as I prefer life size imaging and placements in space. In fact I get bored.

As to the dynaco's The SCA35 has the best transformers even better than the 70 by far IMO.

Also the HK gear has always been pleasantly warm sounding and your comments don't surprise me as I have owned a couple of their power amps which are competitive with many other manufactures @ 5-10 times the price.

Its pretty amazing when I think of it, how I have went from 400 watts/channel in my younger yrs to just 10 watts today and I venture to say these 10 watts are as dynamic or even more dynamic as anything I have owned through the yrs and the harmonics are far more interesting as well.

Its all in the Design :yes:

SET12

Sometimes you just find "the match" and all the pieces come together. More isn't always better.

RKV mk2

Hi Joelongwood


I have an Audio Valve RKV mk2 and impedance matcher. I have never used it as an amplifier for speakers. I first read about it in an issue of Hi-Fi News an English/UK magazine. Ken Kesseler wrote about it and raved about it being used with the impedance matcher as an OTL integrated amplifier. I guess it could be used as a power amplifier too if you had the right pre with the right output voltage.

3 watts with a normal transformer coupled valve amplifier can give excellent results as long as you are not trying to fill a huge room with sound. In a medium sized room you could get away with speakers at 90 db or above with a flat 8 ohm load. Floor standing speakers will be better, than stand mounts. However if you want to rock out in a big room you will need very easily driven speakers of 8to16 ohm and probably 100 db...this means horns or something similar. I have yet to hear any horn speakers I could live with the midband colourations are just to intrusive IMHO.

With an OTL even with the impedance matcher you need to pick speakers with more care than transformer coupled amps (they are a wee bit more forgiving).

I should give my RKV a go as an amplifier....I have thought about it but never got round to it. I once listened to some Atmosphere OTL amps and they were very good (a lot more power than 3 watts) but they ran to hot for the small room I was using at the time.



Regards D S D L----Neil