Does anyone care to ask an amplifier designer a technical question? My door is open.

Hello Roger, I've purchased your tubes several decades and liked the quality and longetivity.  

Funny how people denigrate my Marantz 7T although I only use it for 78 rpm phono stage.  It sounds much like a 7C.

My Dynaco ST70 on my second system has magnificent bass as it was modified from its ultralinear design to a voltage regulated design (taking off the 2nd transformer tap).  Added very large storage cap, ss rectification but kept the tube for soft start.  Just a wonderful low powered amp.

My friends and I have found some early ss receivers with low power are superior to higher power receivers in the same line.  E.g. Yamaha CR 620 is superior to the CR 1020 and higher power receivers.  The Sherwood 7100 is superior to the 7200 and 7300.  They have fewer stages on the low powered units.  I use the Yamaha for video/audio systems although a friend uses them on his Legacy Focuses.  Even the Sherwood brings out great low and tight bass on Legacy Signature IIIs (its shocked the seller when I used it to audition them).

I really like your answers on many of this forums questions.  

There only place where I strongly disagree is in the use of premium fuses.  My amps had standard fuses replaced by SR Blue fuses.  The difference in SQ was very substantial.  The manufacturer of my big amps went one step further and replaced his fuses with circuit breakers.  Now his amps sound nearly identical (we can't tell the difference) from my amps with the SR blue fuses.  He is a huge skeptic and this is his only tweak to his system.  

I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers.  They sounded great wherever I heard them and they appear to be conventional designs well executed.  They must have good impedance outputs to make them adaptable to drive many types of speakers.   

I heard those Jadis amps on new Magico speakers (maybe the S3 or Q3).  I wondered why the highs were rolled off and soft sounding.  Probably due the loss of power in the highs.  Terrible sounding.  

Funny that the latest ARC amps I've heard sound greyish, muted dynamics, etc.  My friend has an ARC 75 which is no match for his Classic 60s or my voltage regulated amps.  Worse, his amps, Ref 5 preamp and $10K CD player all have had significant break-downs after only a year or two.  Yuk!

My question remains, I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers. They sounded great wherever I heard them and they appear to be conventional designs well executed. They must have good impedance outputs to make them adaptable to drive many types of speakers like your own amps.

Thanks for answering me. I noticed that the continuous bias VAC 200IQ sounds better than the manual bias predecessor Phi-200. The improvement is claimed on the continuous bias. I also own a backup amp, the 70 watt EAR 890 which runs really hot in Class A with autobias. It is not sonically in the VAC ballpark. It doesn’t control 3-12" woofers in my main system with 2.8 ohm low impedance but sounds fine in my second system controlling 3-10" woofers with a 3.7 ohm low impedance.

I now remember my own experiences with an ARC SP-14 preamp where the central cap melted in the middle of the circuit board and the need to replace output tubes after maybe 1000-1500 hours in a pair of Classic 60s. That’s also what worries me about the VAC 200IQ as they get 100w 8 ohms out of a pair of KT88s. Based on your lecture, it appears they are being driven too hard. The worst tube life experience I’ve had were the Dynaco Mark IIIs. 9 months and I had to replace the output tubes-bad design.

That's interesting information concerning the 6SN7 tube.  My power amps use them (NOS 1948 Raytheons) as cathode followers and the 6CG7 as a pair as input tubes.

Now if the 6SN7 is not really a good audio tube, why does VAC use it on the entire line of amps as input tubes?   He could have used a 6SL7 or 6CG7 or variant.

I’ve tried a dozen 6SN7s for my amps’ cathode followers. What a huge range of sound characteristics.

The worst (thinnest,brightest) were Russian 80s or 90s ones under the Sovtek label, which looked identical to the Counterpoint branded ones and an English branded one. NOS GEs were generally noisy/distorted sounding.

The best were Raytheons for my amps, with the older VT-231 my favorite for its huge dynamics and warmth. Raytheons from the GT era can be more neutral sounding and harmonically thinner than the VT-231.

Sylvania’s Chrome dome had too tipped up sound for my amps but very clean and dynamic too.

RCAs, for decades of production, were warm sounding but less dynamic. My amp manufacturer uses 60's RCAs to great effect in the same amps but with very different speakers.

Ken-Rad was similar to VT-231s.

Any of the NOS tubes are superior to the 80s/90s Russian made tubes. I haven’t tried the latest tubes. In my application, the tubes can last possibly 10,000 hours (I know it’s lasted 5,000 hours already).

Maybe microphonics are not an issue with cathode followers.

I just don’t understand VAC using only 6SN7s in all their current amplifiers if they are worse than 6SL7s.

My pre-amps are unusual in many ways as they use only six subminiature tubes, are a voltage regulated design with no fuse/breaker necessary and have the stepped attenuator out of the signal path but operates by bleeding off voltage to ground to attenuate the volume. That’s what the manufacturer told me. Sounds as good or better than an EAR 912 with tubes rated for 100,000 hours and non-microphonic. The phono pre-amp is similarly designed without the attenuator.

ramtubes   I poorly wrote that line about the EAR 912-  My pre-amp has subminiature tubes rated for 100,000 hours, the EAR 912 can use 7DJ8s or 6DJ8s rated for 10,000 hours as you stated.  My old EAR 864 NOS 12AX7s and 12AU7s only lasted about 3,000 hours before replacement.  However the EAR Acute has 6DJ8s at over 7,000 hours and going strong.  Depends on the tube and design of course.  My Audio Research gear back in the 90s had power tubes last about 2,000 hours or less, not really good but better than my Dynaco IIIs which lasted about 9 months, 1,000 hours or less.

I had the Acoustat Xs back in the early 80s.  They sounded very good with their built in high voltage amps (dangerous things).  However, they looked like coffins (my late wife's terms) and had lost all its highs above the speaker height, about 4' high.  Stand and you would hate the sound.  I replaced them within a year with Acoustat 2&2s, very superior overall.  

ramtubes - So, you don't believe power cables make a difference other than connectors and isolation transformers are worthless?  Is that correct?

Well ramtubes, we have 100% opposite opinions concerning the necessity for well designed power cords.  I am a beta tester for a boutique manufacturer.  I've sampled at least 50 designs and tested them against all types of high end cables.  When substituted at audio shows, they were the equal of or blew away the comparable high end and expensive cables.  The worst power cables were from High Fidelity with their patented magnet design.  (I've have 8 friends and two high end homeowners who did testing on their equipment as well and the latter two dumped their HF cables).  Two posters have thought HF cables are supreme.  We (10 of us), have found them to be hard, bright, forward sounding and harmonically thin on a wide range of tube Class A, A/B SE and SS amps, pre-amps and phono pre-amps.  

I don't have any electrical engineering degree or knowledge concerning transformer design or household current.  Basically, after auditioning so many PCs on so many high end systems, it appears that you could conclude that all the auditioned equipment was faulty do to poor transformer or power supply designs or implementation.    I disagree.  My own various custom made Class A/B tube equipment are greatly altered based on the power cables and I do not believe they are poorly designed.  They sound magnificent.  The chassis and transformers remain cool to the touch (maybe 80 degrees) after hours of use at sound levels averaging 90 db with challenging impedance speakers (Legacy Focus) with 6 - 12" woofers in a 5,000 cuft room.  The EAR 890 amps Class A chassis and transformers are burning up trying to drive those speakers (no problem with the Signature IIIs at 1 ohm higher impedance and 6-10" woofers).  

ramtubes you stated " My stand on power cords is entirely intellectual from an amplifier designer and transformer makers point of view. I know what is inside a transformer and how it works. When you know
about transformers, house wiring etc. we can further discuss this interesting topic."

 Caelin Gabriel of Shunyata Research Inc. knows much more than I do and he is an electrical engineer with a high pedigree in the audio industry. Whether his cables and noise suppression equipment are correct or not, I don’t know. However here are three of his quotes concerning power cables and sonic degredation due to faulty power supplies in equipment.

" Misconception #3: There is up to a hundred feet of wire in the walls, so the last 6 feet of power cord can’t possibly make any difference.

Answer: “The power cord is not the last 6 feet, it is the first 6 feet from the perspective of the component. As stated in #1 the local current and electromagnetic effects directly affect the sonic performance of the component.”

So, he feels that the upstream house wiring all the way the transmission towers are not as relevant as the Power Cables leading to the equipment.

Misconception #4: There is a tremendous amount of electrical interference and EMI coming from outside the home that we need to protect our equipment from. This implies that we need some sort of power conditioner or filter to protect the equipment.

Answer: “Most of the EMI that affects the audio quality of a system is generated by the audio components themselves. Electromagnetic waves that traveling through space dissipate in power at the square of the distance from the source. Further, very high frequencies that propagate through the power circuit do not survive for long. Power lines present a high impedance to MHz and GHz signals due to the relatively high inductance of power lines.

"A primary source of audible sonic degradation is caused by the power supplies in our audio/video components. Most components use FWBR (full wave bridge rectifier) power supplies that generate an incredible amount of transient noise when the rectifiers switch off. The design of a power cable can significantly affect the reactance of these signals within the power supply. The power cable is effectively part of the primary winding of the power transformer. The transition between the various metals used in a power cable and its connectors can cause electromagnetic reflections and diode-like rectification of the noise impulses as they propagate away from the power supply. If the power cable presents a high impedance to these signals they will be reflected back into the power supply where they will intermodulate, thus increasing the high frequency noise levels of the component. Most power supply filters are ineffective at blocking very high frequency noise components and much of it is passed through to the DC rails. The sonic effects of this include: high background noise levels, blurred or slurred transients and a general lack of clarity and purity of the sound or visual image.”

Here he is stating that the equipment power supply creates the sonic degradation.

Misconception #5: There is some sort of conspiracy among audio designers that keeps them from producing a "proper" power supply that is not affect by power cable quality.

Answer: “This concept is like saying that if a speaker where properly designed, you wouldn’t need to use a good quality speaker cable. PowerSnakes have been tested with the most modest of mid-fi equipment and the most exotic state of the art components. We have yet to find a component that cannot be improved by replacing the power cord.

"As long as power supply design is based upon FWBRs or switching supplies, the power cord will always be significant.”

Basically, he is stating that power supply design generally is at fault resulting in power cords making a significant difference.

Are your RM series amps and pre-amps designed to prevent all of these problems? Are most equipment designers not designing their equipment correctly? You would know as I don’t.

Okay, does atmasphere believe that power cables can make huge differences in an amplifier’s sonic performance and why?

I’m not picking a fight, I just don’t understand the rationale behind what is so obvious to many audiophiles and my personal experiences with testing cables on high end equipment (limited to about 2 dozen systems). Is it because our equipment is all faulty due to poor design or poor implementation?

Is Caelin Gabriel wrong to suggest that the first 2 meters of wire connecting the equipment is the most important compared to the upstream wiring?

Does most of the EMI come from the equipment and not from in the air contamination?

These are relevant questions, especially for me, a non-engineer. Only one of my friends is a manufacturer, the others are famous mastering engineers so most of my friends are non-technically knowledgeable audiophiles.

I 100% agree that there are many more excellent sounding lower power amps than higher power amps.  Most appear to be between 20 and 40 watts.  I have a voltage regulated (non-ultralinear) 35 watt Dynaco 70 that is superb sounding.  I have also have the Macintosh MC 30s, Yamaha CR 620 and have heard the Macintosh 225 and 240 and several Marantz 1970s receivers.  Some favor the tubey sounding Fisher 400 and 500 receivers (I own them but don't find them as resolving as the above mentioned Dynaco, Macintosh and Yamaha units).   

I forgot the great Leak and Quad amps, low powered but wonderful.