Tubes matching & volume control question?

[Shannon Parks]

I'm in the process of building the Eiclones which is my first project. Does the tubes for both mono blocks have to match? Do I need to get a quad matched EL34, matched 12AX7, etc?

Matched pairs are OK. I would stick to four tubes that are generally the same construction and from the same manufacturer.

Is it possible to add a volume control to the Eiclones similar to the ST35? Help on the wiring?

Does putting a volume control lower the perfromance of any amps? Would it be better to use a preamp?

I would recommend a preamp with these guys, but using a audio pot on each unit is possible. You could use one of the Xicon/ALPS 100K audio pots, wiring pin 1 to the RCA, pin 2 (wiper) to P1-1, and pin 3 to ground.

Shannon

[pro_crip]

If you're using a cd player as your source, you could use the volume control on the headphone jack as your system control. You'd need a 'y' jack from rat shack, but that's what I did until I built my foreplay and it worked just fine for me.

[Thermion]

I have tried putting a volume control between my CD player and my Dyna MKIII's and always prefer the sound with a preamplifier versus the volume control. With a preamp, the music sounds more dynamic and involving. I think it must have something to do with the impedance matching between components. (The EE's out there can chime in on this) I once had a PS audio pre-amp that had a 'Straightwire" mode. Essentially the straightwire mode bypassed the gain stage and just routed the signal through the volume and balance control. However, I also think that it buffered the signal somehow. The straightwire mode sounded as good or better than the regular mode. I tried to recreate this feature in a tube preamp but never really liked the sound.

If you have a CD player with outputs that are controlled by a volume pot, that would be OK. My CD player only has a volume control for the headphone jack in the front. I once bought an adapter from Rat Shack that plugged into the headphone jack on one end and had two female RCA jacks on the other. The results were terrible. Even my tone deaf brother could tell it sounded bad. Again, I think that it is an impedance matching problem.

JT

[Shannon Parks]

I played my workbench ST35 with a portable CD player for a long time and only just recently put a NAD preamp with it. For a time, I also used a hacked Harmon Kardon CD player in which I had installed a Radio Shack stereo ALPS pot. There's no problem with that, and I liked the direct connection with 'less in the chain'. The high impedance inputs of these tube amps will work well with any source.

One caveat - and I think this is where Thermion's thinking comes in: If you have to crank that portable CD player or Ipod all the way to eleven to drive the amp, the source will probably be adding a lot more distortion. An el-cheapo portable CD player I had was like this - actually, it could barely output above 10kHz.

I guess I'm just getting lazy and like having the computer, turntable, CD player and tuner all hooked up at once. Yellow_Light_Colorz_PDT_02

Shannon

[erichayes]

Hi All,

There's a nasty little gremlin that lurks in the shadows of (primarily) triode tube electronics known as Miller Effect or Miller Capacitance. Jones has a very concise, lucid description of its cause and effect in Valve Amplifiers, but the Cliff Notes version is that it raises Hell with your high frequency response. This is especially true when adding a gain, or volume. control to the input of a power amp--which is why I bring it up.

For those of you who've used the typical 500K or 1 Meg pot as a gain control in the past and were less than satisfied with the results, try a 100k, or even 50K pot and see (hear) what happens. It might help; it might not. One of the many experiments I intend to conduct now that the lab/shop is on the verge of completion is the effect on high frequency response different values of input level controls have.

Stay tuned--but, as you've all probably figured out by now, don't hold yer breath.

[EWBrown]

The headphone output on most CD players has reallhy terrible sound when piped into an amp (amplified computer speakers notwithstanding).. The "line" output is much better for this purpose.
The "phones" output goes through a ten cent chip, and is designed to fed a relatively low impedance (32 - 300 ohms) set of phones. Also, some headphone outputs play around with "equalization" and bass boost, which really sounds horrible straight into an amplifier.

The next best step beyond a "passive preamp" is a volume control or step attenuator, into a simple cathode follower stage. The CF does not supply any voltage gain, in fact it has a slight loss, but it does help with impedance matching, and it supplies greater signal current (not voltage) to the amplifier that it feeds.