Clone ProAC 2.5s and Dynaco Stereo 70

[GaryF]

I built some Clone ProAC 2.5s, (86db Sensitivity) and I would like to power them with tube amps. (I hear that the proacs are tube friendly, sensitivity notwithstanding)

Id like to know if anyone has any experience using the Clone ProACs with Dynaco Stereo 70s. I like the ST70 because of its excellent reputation and upgradability. Is the 35w from the ST-70 enough power to push the ProAC clones? I currently push them with 90W solid state NAD, and it is more than enough power.

If you think it would not be acceptable, would bi-amping them be a better solution? Or should I give up the Dynaco and go with something with more power, such as a VTL or Rogue amp?

Thanks

[sreten]

Wire them in series and run off one channel of the NAD.

If its fine the Dynaco will be more than fine.

sreten.

[cwteoh]

GaryF:
Hi, if you are build your own Dynaco, I wish I can get some info from you, because I am thinking of build 1 for my own. I need some experience expert for guides.

I got the original Dynaco ST70 schematic with me (shown below). With the following tube I could able to start my construction.

4 x E34L quad matched
2 x 7199
1 x GZ34

[Al.M]

I have heard 30W Leak tube amps and 9W 300B and both were OK so the Dynaco should be OK. 9W was able to do only moderate loudness, 30W did higher levels and generally better. Other people I know have used Dynaco 70 well.

The 2.5 clones are best on tubes. Stereophile magazine review interview with Stewart Tyler designer of Proac said he uses Audio Research tube amps to tune his speakers. So the 2.5 clones are voiced for tubes. Other solid state amps will work well but less than most tubes.

[GaryF]

Originally posted by cwteoh
GaryF:
Hi, if you are build your own Dynaco, I wish I can get some info from you, because I am thinking of build 1 for my own. I need some experience expert for guides.

I got the original Dynaco ST70 schematic with me (shown below). With the following tube I could able to start my construction.

4 x E34L quad matched
2 x 7199
1 x GZ34

No, I wasn't planning on building a dynaco. Interesting idea, though. I figure if I go through the effort of building an amp, it will probably be a single ended triode.

[GaryF]

Originally posted by Al.M
I have heard 30W Leak tube amps and 9W 300B and both were OK so the Dynaco should be OK. 9W was able to do only moderate loudness, 30W did higher levels and generally better. Other people I know have used Dynaco 70 well.

The 2.5 clones are best on tubes. Stereophile magazine review interview with Stewart Tyler designer of Proac said he uses Audio Research tube amps to tune his speakers. So the 2.5 clones are voiced for tubes. Other solid state amps will work well but less than most tubes.

I couldn't imagine running 9 watts on my ProAcs. (or should I say TroelAcs?) Maybe in a very small room. Running 30W on my NAD amp is pretty much unacceptable. It really starts having that compressed solid-state sound as the volume goes up. Its good to hear satisfactory reports with such a low powered amp.

I've found that DIY speakers have a great advantage over store-bought because you have the ability to adjust the crossover and frequency response for different amplifiers. Instead of studiously matching speakers to the amp, you can just adjust the speakers to become more or less forward in the voices, or more or less bright.

As for being made for tubes, you are right on the money... Think about it:

If you had an amp that was rolled off in both the highs and lows (like a tube amp), the proac's freqency response is tilted up in the highs and lows.

If you need steady 8 ohm impedance (like a tube amp), the proac does that as well.

However, because of the lowish sensitivity (86db) it needs an amp with some power, which is the trick... That is probably why the Cary 805C is supposedly magical with it. I bet the speaker's frequency response compensates for some of the weak bass and high treble shortcomings of the single ended amp.

On that note, has anyone heard the Antique Sound Labs Explorer 805 with it? I think that is a single ended amp with 40 or 50 watts per channel. I wonder if it is similar in configuration to the Cary 805C.

[Al.M]

I used the legendary old 20W NAD 3020 very well on the Proacs, although this NAD is much better than many other NADs that have more power. Incredible bass and good voice. I mainly use 60W of push pull KT88 tubes and there is plenty of everything. Interestingly tubes give the Proac clones more extended treble and deeper bass with smoother mids, superior imaging and texture, which the opposite to what you may expect. Solid states are generally dull and lifeless, but bass impact is more.

The best match was a Jadis JA30 30w tubes that sounded like 200W+ with liquid gold treble/mids and Krell / Sumo type bass. Very expensive amp unfortunately with 10km or so of silver wire wound transformers!

[markp]

I've used my ST-70 with my version of Proacs with great results. Its not a Who concert but it is usable.

[tktran]

I've tried running my NAD C320 (40 wpc) with my clones, which are sit in a rectangular living area (6x9 metres (WxD)), connected (L shape) to a kitchen and hallway. Low power or volume levels isn't the first that comes to mind when using this amp...

It's a great little budget amp and good value compared to commercial offerings. But compared to one of Al's valve pre/power amp combinations it's really ordinary.

Running the C320 with a valve preamp really improves things. Much more musical and everything seems to be more detail. Whether this was real or perceived (eg. valve adding harmonic distortion may be perceived as extra detail) I don't know how to explain this better, but there was 4 people listening, and we all agreed that the change was for the better.

On it's own the C320 now sounds a bit closed-in, slightly too warm and lacking in detail. The most noticable is an upper bass lump. The difference are not subtle.

But for the last 3 months I use a homemade 90wpc Rod Elliot P3A amp and it's a very good match. Some may argue that it's quite as interesting as some valve amps, but it's a fine amp and sounds very good. When tube afficionados listen to it with the clones, just don't tell them it's a class A/B solid state and they'll stay happy.

I think the ProAc sensitivity is closer to 82-83 dB/W. Power requirements depends largely on size of room and desired volume levels, but I think that the single 6.5" woofer is real the limiting factor.