It's been raining here in Santa Barbara relentlessly for the last week. I measure about 10 inches in various flower pots and buckets around the place. Since our average annual rainfall is 13 inches this is unusual, though welcome. Following is the solution to an important technical problem most of you are putting up with, a diatribe (I like the archaic definition see Webster #1 and #3) of my view on boutique parts, and a little
audiophile nervosa I hope to cure or at least allay. Oh, and there's some of my humor thrown in to keep things lively. It's intentional.
Wouldn't it be nice to switch inputs and not have to make a big change in the volume control? Wouldn't it be nice to be off the bottom of the volume control where the steps are so large, the tracking poor. It is a fact that the higher you can run the volume control the better. If this is news to you then read this carefully as your view may change.
If you are short on time you can skip the following two paragraphs (I'm just bragging a little) and the one about "botique parts". Skip that one especially if you like those kind of parts, it will just make you mad. I do have two reasons for these asides. 1. I get to get some things off my chest. 2. It gives you ammunition if you get into a battle with one of those guys who believes in such things. Choose your battles carefully, I find that the "believers" will not bend to logic or any information that is contrary to their belief. Well that's what a belief is supposed to be. isn't it?
Here's how I solved this problem 28 years ago, before CD players were even commercially available. Part one was in the RM-5 by making the line gain adjustable down to unity. The only thing I would do differently now is to have more and adjustable phono gain to bring phono level up to the level of the CD. Part 2 was in the RM-4 with its wide range of gain modules. So this wasn't so hard 28 years ago. Sadly too many preamps made after the arrival of CD still stick to the old standard of 40dB phono and 20dB (or more) line gain. If you have such a preamp which was designed after the advent of CDs I'd love to hear why the designer did what he did. The most common answer is that the line gain comes from the tube chosen as if the designer has no idea how to reduce the gain of the tube. That's also why you see 12AU7 and 6SN7 tubes used for line gain where they are totally unsuitable due to noise and microphonics.
Common problem, simple solution. One of the features I put in the RM-5 MK IV was the ability to attenuate the CD input since its always the loudest. Many of you are unable to get past 9 o'clock when playing CD but can run the volume control much higher with Phono. Therefore lowering the preamp gain is not the best solution. The proper thing to do is to attenuate the CD input to the point where it matches the phono.
Now I already know (because I hear it all the time) that many audiophiles assume this will degrade the sound. I use Dale precision resistors or any you might want though Vishay (not the water) are expensive and have no sonic value. Oh, Vishay bought Dale in 1985. In any case the company is now called Vishay/Dale. As often happens in audio a resistor that is expensive because its was made for some special industrial purpose gets to be boutique part for no sonic reason at all. I'll say one other thing about those Vishay foil resistors, they are very delicate and fall apart if you barely touch them. FYI, the Vishay power resistors are packaged in TO-220 (plastic transistor packages) so they can be mounted on a heat sink just like a transistor. They offer high wattage in a small package and no inductance making them preferable to bulky wire-wound resistors that Dale has made for years and still makes. Made sense to combine the products, but has nothing to do with audio although Vishay lists "high end audio products" as an application along with electronics that goes down in deep wells! Feels nice to be noticed along with the oil drilling business. I did a little research on Vishay and found they have also bought BCcomponents, Sprague, Spectrol, Sternice, Siliconix, Vitramon and has a big line of their own semiconductors. This a facinating mega component company. Here's the link
http://www.vishay.com/company/about/. They even own Telefunken. Maybe can get them to make 12ax7's again... just kidding. Given that I suppose I am using Vishay resistors since Vishay owns Dale, though the resistors haven't changed. I've used the brown Dale RN-55 and RN-60 series in all my products along with Roderstein (which I later found out weren't as relaible as the Dales). Another time that I bent to the part of the day and which I hadn't. BTW I don't do that anymore. I buy the best part that is reasonably priced. If I made a preamp with all Vishay Plate resistors the resistors alone would add about $3000 to the price. Oh yea, and they would be breaking all over the place, so there goes my reliability. I can't even remove the dust anywhere near them for fear of breaking them. They are very very fragile and stick up above the board just asking for trouble.
Now, if anyone thinks adding 2 resistors per channel will degrade the sound there are hundreds of other resistors (likely of lesser quality) in the signal chain, are we going to loose sleep over those? There is this irrational fear that if the customer adds anything it must be of the utmost quality to preserve the sound of significantly lesser parts already in the unit.
There are lots of places to put this attenuator. I am offering several. I can put it into the plug on an interconnect. This option, with good quality connectors and cable I can do for $300 a pair. A less expensive solution is to put 4 gold jacks in a small shielded can. That requires 2 pair of cables which I assume many of you have.
I have several ideas about the physical embodiment of these ranging from under $100 to several hundred $ depending on connector choices and "looks". The one that I prefer is a 2x2x1 inch die-cast aluminum box with the custom made gold RCA jacks I use on the RM-10 and my all my products. These are nice gold jacks that grip the hot securely with 4 fingers and have a robust outer shell. The box has 4 screws in the bottom so resistors can be changed by you or me. Once the proper attenuation is determined this box sits permanently between your CD (or other hot source) and its input jacks on the preamp. You will soon forget it's there, while you enjoy the expanded range of your volume control.
To determine how much attenuation you need, here is what I have found by measuring a number of volume controls and you may find this very interesting. Starting full up on a 22 step volume control the first 11 steps are about 2 db each and whether stepped or not 12 o'clolck is -20 dB. From there to 9 ocllock the stept get bigger and at 9 you have -30. Now heres the rub. From 9 on the clock to the last step before off one must go another 40 db in just 5 or so remaining steps. These steps are big, the last 2 being about 10 dB each. No wonder you have trouble setting volume. Its been this way ever since log pots were invented. Unfortunately we use them all wrong. If we used them properly full volume would be nearly all the way up and we would have great control of the lower volumes. For anyone who thinks its good to play loud at 9 o'clock is missinformed. Sadly, I have been told by many dealers and especially foreign distributors that if it doenst play loud at 9 they won't buy it. I fixed a lot of table radios in my after school repair job (I was the audio guy in a TV shop) and as i recall there was never a problem playing the softly and full up was pretty much full up. I would say those engineers at Zenith, Motorola and RCA knew what they were doing. Sadly as time went on two things happened. Marketing stepped in and screwed things up as usual and DJs started using compression to make their station the loudest on the dial. Doesn't that seem like what has happened to CD's today. How many of us have CDs that play too loud and are obvioiusly compressed. The other day I was listening to Willy Nelson's Stardust on CD. We used the vinyl at Beveridge till we wore it out. Great sounding record. I was jolted when I heard the CD of the same album (re-mastered of course) clip badly on the drum strikes. I put it on the scope and there is was. Visible clipping right at 2 volts where CD's run out of numbers. There is no excuse for re-mastering that hot. The signal to noise of the original tape is well within the usable range of a CD without compression or clipping. I wonder if this is one of the reasons for the vinyl comeback. I agree vinyl sounds better and this is just one of the reasons to add to the list.
Ordering informationIf your CD player output impedance is higher than 1 K ohm (many are less than 100 ohms) and your preamp input is less than 47 K ohms (50-100 K is pretty standard) then a standard unit is what you want.
If you think it degrades the sound you can send it back for a refund less shipping ($4 each way courtesy of USPS Priority mail) and a modest $5 return fee. I'm taking orders now for the first run. Contact me via ramtubes@gmail.com.
Your suggestions are welcome.
