Hi EM7 owners and potential owners.
Here is the latest. I just got a Canon Rebel and it’s time to take some new pictures. The current introductory price is still $850 for the next 6 amplifiers which are the same as batch 2 as photographed by Jeffreybehr. When those are gone it will be $925.
As to the power question: The first batch of these amplifiers had fixed output set around 4 ohms. Into an 8 ohm load they had more damping but less power, about 2.5 watts so we called it at that. The second batch and third we are selling now have user adjustable Hi and Lo Z. The high is 12.5 ohms which works well with the Druids and FE 103 speaker we are releasing soon. Some people will prefer the low Z as it has a different sound. The low Z is exactly 1/4 the impedance, or about 3.2 ohms, a handy number we all know. For 8 ohm speakers go either way. Acually you can go HI-LO Z with any speaker. You can't hurt the amplifier or your speaker so try them both. The difference will be similar to or greater than listening to a cable change. The power difference is only 1.4 dB from 2.5 to 3.5 watts, not enough to make much difference. BTW, a power rating is rather useless without a distortion number to go with it. The standard amplifiers(the ones you can buy now)are currently producing 3.5 watts iat clipping, 3 watts at 10% THD and 2 watts at less than 2.5 %. The amplifier is also very quiet hum coming in at 0.3 millivolts at the Hi Z output. Many SE amps are advertised at 1 mV or worse. Those will certainly be audible on sensitive speakers. In some systems the dominant noise can be from the preamp. When you turn the preamp volume all the way down, the line stage is still at full gain sending its noise to be amplified by the power amp. Shorting plugs will confirm this. If your preamp has this excess noise, it can be reduced by 6 dB by using the Lo Z configuration
We are getting custom orders running about one for one with the stock units. We have done a mono pair producing 10 watts/side for $1600. We did a stereo “anti-tweak” (that means, no power switch, no IEC, minimum input/output connectors of common brass, volume control , no stain, two layers lacquer vs. the normal 7. If everyone wanted these I could offer them for $800 all day long. We added a volume control for $50. The volume control lets you go direct from your CD player to the amp.. no preamp needed. If your CD player has a volume control already, as mine does, then you don’t need one in the amp.
The third custom we did is for a reviewer from Finland. Since he needed a custom 240 volt transformer I raised the B+ about 50 volts and run the tubes a little hotter (9.5 watts dissipation vs. 7.5). That gives an output of 4 watts to clipping. The power transformer is twice the rating of the standard. These sell for $990. Sorry, no introductory price on the custom amps.
I would love to get some feedback from owners and potential owners as to what features they find important. We are offering Cardas input jack upgrades and output post upgrades to our beefy RM-200 binding post. (See the back panel shot of the RM-200 at
www.ramlabs-musicreference.com.
I have done many SE designs over the past 25 years. I did what everyone does, choose a tube, look up an application, build the application, see what you get. My first go was a 6L6 selectable triode- pentode- ultralinear. I didn’t produce that because 25 years ago there were no takers. Next I did a parafeed EL-34/KT-88 triode or UL switchable. The pentode needs feedback to even be decent and I needed the pentode too get 6 watts. Still not enough power for those days.
I fooled around with the 6C33 (a pass tube from a Russian MIG jet power supply (but unsuitable for audio due to bias drift), the 6080/6AS7 (same problem) and finally got to the tubes that were designed to be bias stable triode amplifiers (45, 2A3, 300B). Those are all good tubes but expensive to apply due to their directly heated cathode.
I started buying 6EM7’s 15 years ago to make a 250 milliwatt headphone amp that I never produced. With all the interest in low power triode no feedback amplifiers I went right to that tube and designed a circuit to produce some reasonable power. FYI, the EM7 possesses both high performance and stable operation. It had to because it was designed to be a vertical amplifier in a color TV. Turns out the vertical amplifier is a class A, single ended, cathode biased amplifier, with gapped output transformer driving a deflection coil. This tube is just as happy swinging audio as it was swinging the electron beam from top to bottom. It had to be stable and linear or else I was going to come back and readjust the bias and gain. Low gain would show black bars top and bottom, high gain would cut off peoples heads and feet. If it wasn’t linear, people would be stretched or shrunken like the mirrors in a fun house. Something that others have missed is the fact that this tube was aged at the factory many times longer that other tubes. My 1970’s price list reflects this additional cost and my memory as a 16 year old TV repairman supports this characteristic as I never had to wait more than a minute for the set to be warmed up enough for that tube to be stable. This means the EM7 amp gets going in the first few minutes and stays there. It also stays there over the life of the tube. The power supply has enough stored energy to play for half a minute after turn off. Actually the filaments get cold before the B+ is drained. This allows the amplifier to have stable characteristics in the face of an unstable line voltage. You don’t need any fancy power conditioners.
I would love to get some feedback from listeners who are considering or already own a SET. Answer any or all the questions below.
The questions: You can just use the question # and your reply.
1. One pair of input jacks or two pair with a high pass 6dB/octave input filter on the second pair?
2. Output: High Z, LowZ, as we do it currently on the back. You just move some jumpers. If we reduce the speaker posts from 4 to 2 per channel that will bring the price down. With 2 per channel, the high/low Z would be changeable with a soldering iron.
3. Limited bandwidth. Pick a frequency that would be the lowest you would need to reproduce.
4. 4 watts for $XXX dollars over the standard 2.5 watt model.
5. The option of having your amplifier with whatever resistors and capacitors you supply. You send them, we put them in for a nominal fee of $5 per part, $50 minimum. This is better than having someone make a mess of something that is done nicely.
We might as well discuss it here so everyone gets to see the desired applications. You might briefly state your application.
I am committed to making these amplifiers available for a long time and have adequate parts and tubes on hand to do so. For those of you who don’t already know Music Reference and Ram Tubes, we have been doing this for 30 years now. The RM-1,2,3,4,5,9,10 and 200 are highly sought after and retain their value better than any tube gear I know. We have used, factory reconditioned units available, call for information. 805-687-2236.
