What speakers are you using for your ARC tube amp?

[tdh888]

Why would one use them with Maggies? I thought they were meant for tube amps that didn't like seeing low impedances such as that presented by estats. Maggies are a nice 4 ohm load and most tube amps I know have 4 ohm taps.

Because back in 2007 I was able to talked to someone in ARC that he was using his REF 110 w/ the autoformers w/ Maggies 3.3 and Apogee Dueta's . Both were very inefficient speakers he said but because of the autoformers the REF 110 was able to drive them effortlessly using the 8 ohm tap of his REF 110. Maybe somebody else in this forum had tried this already?

 

[MylesBAstor]

Because back in 2007 I was able to talked to someone in ARC that he was using his REF 110 w/ the autoformers w/ Maggies 3.3 and Apogee Dueta's . Both were very inefficient speakers he said but because of the autoformers the REF 110 was able to drive them effortlessly using the 8 ohm tap of his REF 110. Maybe somebody else in this forum had tried this already?

Maggies and Apogees are two different birds. Apogees can be very difficult to moderately difficult to drive because of their impedance curve (that's why Krell and Classe sold well for years!). Maggies OTOH are a relatively easy load to drive. I'm not sure how the autoformer would increase the efficiency?

 

[jadis]

But I recalled JA 30 was at its best when we were using it w/ the Spica TC 50, it was the best amp I heard when partnered w/ this speakers.

BINGO! That night the speakers used were indeed the Spica TC50s. And the consensus then was that the matching of the JA30 and the TC50 was quite fantastic. So maybe in that configuration, the Classic 60 did not fare out too well.

 

[DonH50]

I prefer SS or a big honkin' tube amp on the bottom of my Maggies as the bass is much better. The load is relatively benign but the bass panel benefits from more power and lower amp output impedance (higher damping factor). The tube amps I heard that did best were a big Jadis, a CJ (5, I think? the big one), and a modified Futterman.

The ribbon tweeter in the Magnepans does dip low at HF.

 

[tdh888]

Maggies and Apogees are two different birds. Apogees can be very difficult to moderately difficult to drive because of their impedance curve (that's why Krell and Classe sold well for years!). Maggies OTOH are a relatively easy load to drive. I'm not sure how the autoformer would increase the
efficiency?

There 's no way the autoformers will increase the efficiency of the maggies the way I understand is when he uses his ref 110 he uses the 8 ohm output tap instead of the 4 ohm when driving his 3.3. He uses the 8 ohm output tap of his amp to connect to the autoformer then from the autoformer he connects it to the 3.3 via the 4 ohm output tap or the 2 ohm tap when using his apogee's. He said even w/ 4 ohm or 2 ohm load your tube amp will only see an 8 ohm load. W/c according to some is the recommended load for tube amps and less taxing for the amp. Subjectively the amp will sound more powerful than what the actual output is accdg to some. The autoformer also will give a better grip w/c I think means better control for the speakers.

 

[tdh888]

The ribbon tweeter in the Magnepans does dip low at HF.[/QUOTE]

So this could be the reason why the guy from ARC when using his maggies 3.3 & duetta's w/ the ref 110 insist in using the autoformers of Paul Speltz.

 

[MylesBAstor]

I prefer SS or a big honkin' tube amp on the bottom of my Maggies as the bass is much better. The load is relatively benign but the bass panel benefits from more power and lower amp output impedance (higher damping factor). The tube amps I heard that did best were a big Jadis, a CJ (5, I think? the big one), and a modified Futterman.

The ribbon tweeter in the Magnepans does dip low at HF.

I don't remember that dip off the top of my head. What was the lowest impedance and at what frequency?

 

[MylesBAstor]

there 's no way the autoformers will increase the efficiency of the maggies the way i understand is when he uses his ref 110 he uses the 8 ohm output tap instead of the 4 ohm when driving his 3.3. He uses the 8 ohm output tap of his amp to connect to the autoformer then from the autoformer he connects it to the 3.3 via the 4 ohm output tap or the 2 ohm tap when using his apogee's. He said even w/ 4 ohm or 2 ohm load your tube amp will only see an 8 ohm load. W/c according to some is the recommended load for tube amps and less taxing for the amp. Subjectively the amp will sound more powerful than what the actual output is accdg to some. The autoformer also will give a better grip w/c i think means better control for the speakers.

ok ic.

 

[DonH50]

I don't remember that dip off the top of my head. What was the lowest impedance and at what frequency?

Sorry, I don't recall off the top of my head, either... IIRC, the ribbon itself is only 2 - 3 ohms, dropping to <1 ohm somewhere above 20 kHz, but there is a small (0.5 - 1 ohm) series resistor to bring the impedance up a bit (and attenuate the signal). This is within the crossover inside the speaker, not the optional external resistor you can add. I am pretty sure my old Maggies stated 5 ohms dropping to around 3 at HF.

* Checked the MG3.6/R product manual from the web: bass = 4.7 ohms, mid = 4.2 ohms, ribbon = 3.3 ohms (but that includes that inside resistor)

** Electrostats tend to be much worse, dropping to 2 ohms or below at HF (after all, the panel is just a big capacitor). Full-range ribbons tend to be low everywhere, dropping a little at the high end but not much relative to the bass. Of course, starting with 1 - 2 ohms can be a challenge for some amps, even if it doesn't vary much...

 

[MylesBAstor]

Sorry, I don't recall off the top of my head, either... IIRC, the ribbon itself is only 2 - 3 ohms, dropping to <1 ohm somewhere above 20 kHz, but there is a small (0.5 - 1 ohm) series resistor to bring the impedance up a bit (and attenuate the signal). This is within the crossover inside the speaker, not the optional external resistor you can add. I am pretty sure my old Maggies stated 5 ohms dropping to around 3 at HF.

* Checked the MG3.6/R product manual from the web: bass = 4.7 ohms, mid = 4.2 ohms, ribbon = 3.3 ohms (but that includes that inside resistor)

** Electrostats tend to be much worse, dropping to 2 ohms or below at HF (after all, the panel is just a big capacitor). Full-range ribbons tend to be low everywhere, dropping a little at the high end but not much relative to the bass. Of course, starting with 1 - 2 ohms can be a challenge for some amps, even if it doesn't vary much...

Actually think you're being kind to estats. And it's not that the impedance is low say at HF but that the impedance is all over the place eg the old Quad 63s.

 

[microstrip]

Actually think you're being kind to estats. And it's not that the impedance is low say at HF but that the impedance is all over the place eg the old Quad 63s.

Myles,
May be you are thinking about the Acoustat's? Quad ESL63 are not a difficult low load - otherwise they could not play so well with the Futherman OTLs!

 

[microstrip]

There 's no way the autoformers will increase the efficiency of the maggies the way I understand is when he uses his ref 110 he uses the 8 ohm output tap instead of the 4 ohm when driving his 3.3. He uses the 8 ohm output tap of his amp to connect to the autoformer then from the autoformer he connects it to the 3.3 via the 4 ohm output tap or the 2 ohm tap when using his apogee's. He said even w/ 4 ohm or 2 ohm load your tube amp will only see an 8 ohm load. W/c according to some is the recommended load for tube amps and less taxing for the amp. Subjectively the amp will sound more powerful than what the actual output is accdg to some. The autoformer also will give a better grip w/c I think means better control for the speakers.

The explanation makes sense for the Apogees, but I can not see any reason to use the autotransformer with the maggies. Driving them directly from the 4 ohm tap of the ARC seems a better solution.

 

[Jay_S]

BINGO! That night the speakers used were indeed the Spica TC50s. And the consensus then was that the matching of the JA30 and the TC50 was quite fantastic. So maybe in that configuration, the Classic 60 did not fare out too well.

I remember from some years ago: TC50s with modified Dynaco Stereo 70... not high end by today's standards but very high enjoyment.

 

[tdh888]

The explanation makes sense for the Apogees, but I can not see any reason to use the autotransformer with the maggies. Driving them directly from the 4 ohm tap of the ARC seems a better solution.

Why would driving the maggies directly in the 4 ohm tap will be a better solution if theres an impedance dip in the high frequency? Accrdg. to Don HE ( technical expert of WBF) and some reviews and articles regarding the Maggies they have a 2-3 ohm dip in the high frequency. Maybe it would be easier for a tube amp to use the autotransformer and tap it at 2 ohms to better control the high frequency and your tube amp ( using the 8 ohm output tap) will see an easier load at 8 ohms for better transfer of power & control of the speakers?

 

[tdh888]

I remember from some years ago: TC50s with modified Dynaco Stereo 70... not high end by today's standards but very high enjoyment.

We also tried using the ARC D79B for diving the Spica TC 50 ( associated equipment were Gyrodec MK1, Odyssey RP1-XG tonearm, Koetsu rosewood sig and ARC SP 10mk2) They do sound better when we compared it to the Proac Super tablet back in the day. We should have compared the D79B w/ the JA 30 but never had a chance to do it.This was one of my early experience w/ the high end during the late 80's early 90's.

 

[microstrip]

Why would driving the maggies directly in the 4 ohm tap will be a better solution if theres an impedance dip in the high frequency? Accrdg. to Don HE ( technical expert of WBF) and some reviews and articles regarding the Maggies they have a 2-3 ohm dip in the high frequency. Maybe it would be easier for a tube amp to use the autotransformer and tap it at 2 ohms to better control the high frequency and your tube amp ( using the 8 ohm output tap) will see an easier load at 8 ohms for better transfer of power & control of the speakers?

You wrote " He uses the 8 ohm output tap of his amp to connect to the autoformer then from the autoformer he connects it to the 3.3 via the 4 ohm output tap".

In this situation, from an electrical point of view, the amplifier is experiencing the same load as if the maggies were connected to the 4 ohm tap and you are adding a source of inefficiency and distortion - the autotransformer. Only if you are using the 2 ohm tap you will have a different ratio.

 

[MylesBAstor]

Myles,
May be you are thinking about the Acoustat's? Quad ESL63 are not a difficult low load - otherwise they could not play so well with the Futherman OTLs!

Actually look at the Quad impedance curve. (wish George Kaye was still around ).

http://www.stereophile.com/content/quad-esl-63-loudspeaker-measurements

The 63's impedance rises to to something like 32 ohms in the low end, hence the OTL as I remember puts out more power and sounds more powerful in the low end. The other thing is that the Quads don't need much power; OTOH, they don't have great dynamics, bass or top end. Audiophiles constantly searched high and low for a sub to mate to mate to their 63s (Entec, Gradient, etc). But what's in between is lovely and there was a micro dynamic resolution, esp. back then, that didn't exist in dynamic speakers (the same thing I hear and much better in the present day MLs). BTW, still haven't heard the new Quads sound all that great despite some of my colleagues raves.

 

[microstrip]

Actually look at the Quad impedance curve. (wish George Kaye was still around ).

http://www.stereophile.com/content/quad-esl-63-loudspeaker-measurements

The 63's impedance rises to to something like 32 ohms in the low end, hence the OTL as I remember puts out more power and sounds more powerful in the low end. The other thing is that the Quads don't need much power; OTOH, they don't have great dynamics, bass or top end. Audiophiles constantly searched high and low for a sub to mate to mate to their 63s (Entec, Gradient, etc). But what's in between is lovely and there was a micro dynamic resolution, esp. back then, that didn't exist in dynamic speakers (the same thing I hear and much better in the present day MLs). BTW, still haven't heard the new Quads sound all that great despite some of my colleagues raves.

Stereophile ESL63 impedance curve can be misleading as it was taken a low levels, where current is very low, showing 4 ohms at 20 Hz and around 5 ohms at 40Hz. However ESL63 impedance increases with power as I posted some time ago.

http://www.whatsbestforum.com/showthread.php?2025-Constant-power-tubes-vs.-solid-state-amps-and-wild-impedance-speakers&p=37646&viewfull=1

I have listened to the ESL63 with the NYAL Futterman's, and I share your feelings about the new Quads - it is why I have on my future project list modifying my ESL63's to the SME standards - even got the plans from Mr. Cameron Robertson-Aikman, son of the SME founder.

 

[tdh888]

You wrote " He uses the 8 ohm output tap of his amp to connect to the autoformer then from the autoformer he connects it to the 3.3 via the 4 ohm output tap".

In this situation, from an electrical point of view, the amplifier is experiencing the same load as if the maggies were connected to the 4 ohm tap and you are adding a source of inefficiency and distortion - the autotransformer. Only if you are using the 2 ohm tap you will have a different ratio.

Thanks for clearing up this matter microstrip. By the way has anyone in this forum tried the autotransformer ,any experience ,feedback, etc.

 

[DonH50]

The 63's are a radically different design for an ESL with those concentric rings and delay lines. I'd forgotten what a gnarly load they were! However, they do follow the typical trend of lower impedance as frequency goes up, excepting that wicked spike up around 20 kHz (I used to know what that was from but have forgotten in the intervening decades since I last heard and played around with them). I seem to recall a number of ESL's dropping to 2 ohms and below around 20 kHz but am too lazy/tired to dig up data... IIRC, bass resonance is amplitude-dependent partly since capacitance varies with distance (deflection of the panel) in addition to the usual resonance equations.

McIntosh used autoformers in their SS amps; not sure if they still do (again, have not listened in a while, though technically I did listen to a Mac tube amp driving a pair of B&W 803Ds whilst helping a friend audition). I have never heard an autoformer design I really liked, and they seemed to do best with more benign loads to my ears/measurements (yes, I know that is the opposite of the marketing and various white papers, but that's my experience).

Is Futterman still around?