Impedance Matching - Tube Amp/Speakers

Just connect your speakers to the 4 ohm taps onyour amp. Will work fine. I use a VTL ST-85 to drive 4 ohm Maggie 3.6's with no problems

I have Legacy Focus 20/20 and have only used tube amps with no damage. From Conrad-Johnson MV-52, to Conrad Johnson Premier 11a to now Wyetech Topaz monoblock. The question to answer is not is a tube amp a problem with four ohm speakers but how low does the impedance go. If it stays above say 3.5 ohms in general that could be fine. The Legacy's dip below that in a few spots but in areas where there is not a lot of need for energy from the amp in those spots. So while your friend is right, a solid state amp would give you more power and probably work better finding out the impedance chart for the VTL-ST-85 would provide you with the information you need.
Stereophile had a review back in February 1999. That might answer your questions.

Thanks alot. Stereophile review is saying "VTL-85 is optimized for a load of around 5 ohms (85Wpc)" so 6 ohms Dunlavy SM-1 speakers (with a 3-10 ohm range) should be no problem, is it right? But why my friend's multimeter measured 4 ohms on Dunlavys when they should be 6 ohms? Or this multimeter checking is not optimal and values are only approximate?

What you are reading with the multimeter is the speaker's impedance at a frequency of zero Hertz, or in other words its DC resistance. That will differ significantly from its impedance at audio frequencies, which is what matters.

According to this review "impedance is shown as 3 to 10 ohms, with 6 ohms nominal, which should be an easy load for most amplifiers to drive." I don't think there is any cause for concern, especially given that the amp is rated to drive 4 ohms continuously, and is specified for a recommended load of 3 to 8 ohms.

Regards,
-- Al

You should try the speaker with both the 4 ohm and 8 ohm tap to determine which sounds better. Using either is entirely "safe" in terms of not damaging gear.

The 4 ohm tap will deliver less power, but, it will increase the damping factor, something that may improve the frequency response (typically, tighter, better defined bass).

Once again, Al offers excellent advice.

It is worth mentioning that the impedance of the speaker will affect the sound and control the amplifier has.

You may notice a bit of extra bloom in the bass or loss of control.

Not a big concern but you could try the different outputs on the back of the amp (presuming they give you a choice) and use the one you like best.

fwiw...

Guys, according to the Stereophile review linked to above there is only 1 output tap, "optimized" for 5 ohms, with power output being specified for 4 ohms. Some photos of the rear panel that can be found via Google's image search function appear to confirm that there is only 1 tap.

Unsound, thank you most kindly!

Regards,
-- Al

Thank you guys, alot of useful infos for me. I can confirm that my version of ST-85 has only 1 output tap, and also there is no triode/tetrode switch as on newer model. When I was comparing sound of Dunlavys with tubes (VTL) and with some solidstates (Teac ABX-10, SAC Mediatore monos), I noticed that SS has better bass control, speed and transients, but I expected that. Maybe better preamp could cover this area.

FWIW, in my conversations with the late great John Dunlavy, he had a strong preference for ss, and especially Class D amplification.

SS has better bass control, speed and transients, but I expected that. Maybe better preamp could cover this area.

While I am a big proponent of building a system around a great pre-amp, IMO, you are not going to get significant improvements in the areas you mentioned unless you change amplification. V. good tube amps can provide all of those elements, w/o sacrificing the good things that tubes do. This is all theoretical. I've never heard your amp and the speakers only once. YMMV.

Is there someone who has experiences with some Dunlavy speakers and tube amps? I did buy ST-85 with EL34 tubes Electron (made in China), I dont know if they are good ones or not, so maybe some tube rolling could improve dynamics and bass, if preamp not. I also read that valve amps with EL34's will always struggle with bass.

You’re safe…

Back in the day, I had Duntech Marquis and had lots of fun using QuickSilver Silver 60’s (KT88’s) and the Silver 90’s but those were big 3 way, time aligned speakers that really needed solid state to sing. They sounded very good with tubes but they were unstoppable when bi-amped with 2 McIntosh 7270’s .

The bass coming out of the ST-85 should be very good, although EL34’s are considered leaner than some other tube types (i.e. 6550’s), however there is always a trade-off. I currently have a VTL IT-85 (same amp section as the ST-85 using EL34’s) driving Dynaudio Special 25’s ( 4ohm, 88db) and the bass is killer.

It could be the source and or wiring.

If the load is right, bass will not be a problem- that has nothing to do with the amp using EL-34s!

Hi, Ts0711, I think source and wiring is respectable (Bryston, Cardas, Kimber), only preamp is a little behind (Hitachi), but I want change tubes. Which brand tubes are in your IT-85? Do yout think better tubes can improve bass and speed?

I believe I'm using Electro-Harmonic EL34, that were sourced from VTL. In my experance different brands of tubes (in the same family - i.e. EL34) will have an impact on bass, but not speed. For my main stereo I use NOS Mullard XF2's (EL34's from the '60's / 70's) which have a fantastic bass rendering however they cost as much if not more than the amps they are in (VTL Compact 100's).

For speed and dynamics I strongly recommend "Crimson Music Link" speaker wire and interconnects... Start with the speaker wire and you will be blown away. Switching from Harmonic Tech Pro 9+ speaker wire to the Crimsons was like buying new speakers. I was amazed at the difference in PRAT that my Dynaudios delivered.

Good luck.