rjp

I tend to agree. Every amplifier has a characteristic sound. It seems that the question comes down to do you which sound you like better, the preamp, or the power amp? From what I'm reading it appears most of the big money is invested in preamps to get a super great sounding but very fragile signal, and then the power amp is just about making this louder and strong enough to drive speakers. So using a path into the power amp that is as transparent as possible only has value if indeed the power amp is what you want to hear.

Fair enough. I meant they were 100% out of the signal path. I wonder, can the additional path to ground make any difference in the sound? The attenuator Bob supplies is 100K. The VTA board itself has an input impedance of about 270K I believe. So the (full volume) input impedance at the RCA jacks with the stepped attenuator in place must be down to about 75K. The output impedance of an iPhone 6S is 3.2 Ohms, so even 75K seems huge in comparison. A higher resistance attenuator could be used to keep the input impedance up, but that would potentially introduce another more significant problem. Loss of high frequency content due to Miller effect. I assume this played into the 100K choice.

Technically speaking 100% correct. Zero NEED for a preamp. But preamps (good ones, I'm told) add a host of magical musical qualities and gonads (a.k.a., dynamics). I have recently been involved in extensive research and technical discussions on this matter, and though I could uncover no good technical reason for the preamp, I just bought two of them so I can find out for myself if they really make the VTA70 sound better (compared to the 21-step attenuator direct approach). I purchased a Dynaco PAS 3X from ebay and a VTA SP12 kit from tubes4hifi. I am really looking forward to building the SP12 kit! If I realized I could get the basic board for under 200 bucks I would have skipped the PAS option. Well, it will be fun to try both. I'll keep the one I like and sell the other. They will both be in super amazing condition when I'm done owning them. So...I intend to be in serious preamp mode shortly You know what's the dumbest thing? Calling a simple potentiometer or stepped attenuator a "Passive Preamp". Well, actually, that's just a misnomer. The dumbest thing is paying 800 dollars for "really good ones"

Ok, so the amp you have is a Bob Latino ST70. Most people call it a VTA70 (Vacuum Tube Audio) to distinguish it from the original Dynaco ST70. This is an amp I am very familiar with. The input level required for full power out is 1V rms. I bench tested mine and was able to get 38W rms per channel before I started to see clipping. This was with both channels driven into 8 Ohms at 1KHz. The input voltage required to achieve this was just slightly over 1V rms (i.e., 1.4V peak). Any modern input source can easily provide the required voltage swing to get the full 35W rms out of the VTA70 without an active preamp. It could be that the Kenwood is boosting the input signal more so that the overall output is louder but the peaks are clipped. SO it could appear louder but there might be distortion present. Just a guess. Are you saying that if you set the volume to full on both amps your VTA70 is still not as loud as your Kenwood?

Emile, Are you running an original ST70 or a modified version? Where is the attenuator you mention installed? BOTH a stepped attenuator and ANY volume pot of ANY taper will be effectively out of the circuit at full clockwise rotation (well, unless it's wired up wrong). What is you input source?

Emile, I think I know what you are talking about, but after reading some of the interveaning replies I am a little unsure now, so I will just speak about my experience with stepped attenuators. I had a "regular" volume pot on my VTA70 before I installed a 21 step attenuator. My first reaction was, "Why is there so much less volume now?" There is not less volume. It has just been redistributed. The difference was entirely due to the taper of the designs. The stepped attenuator (at least the most common ones) have steps that are roughly 3dB each. This means that just 2 steps down from full volume is half power. This is known as a logarithmic taper (a.k.a. Audio taper). The potentiometer I was using was a linear taper. So even though the two devices spanned a total resistance of 100K Ohms, they did so in very different ways. Most volume controls on consumer stuff are linear taper, and consequently that's what a lot of us are used to. Most audiophile stuff, however, tends to be logorithmic. WIth a linear taper control the volume initially increases quickly as you turn the knob clockwise, and then slows down. I prefer linear personally. You can get a stepped attenuator in linear as well if you like the "advantage" of discrete steps rather than continuous adjustment. Same price on ebay. Drop in replacement.

Thanks for your consideration Mike, but I don't think of it as "my" thread. It is for all of us. Besides, after 11 pages I think there were only a hand full of posts actually discussing the HIII's. Which, btw, I am liking more and more lately. Ultimately, I decided to return the Monitor Audio Silver 100's and keep the HIIIs. I may put L-pads in them some day

picoBells rule!

I like tone controls as much as I like L-pads. And we all know I like L-pads, right? I see no problems as long as when they are set to zero I hear absolutely no change in the signal compared to a direct path. I auditioned and ultimately returned a product called miniDSP HD for this reason. I rigged up an A/B switch on the line level inputs and with all EQ functions on the miniDSP set to off I could still hear a definite degradation in the sound quality. I assume this was due to the A/D - D/A stage itself which is essential for any digital tone control product of course. It was subtle but consistent. I performed the same test on a Schiit Loki 4 band EQ and it passed with flying colors. I may have already mentioned this above. I forget what thread I'm on sometimes. My advice is if you have to have tone controls, get the good Schiit http://www.schiit.com/products/loki Speaker placement is effective. Many people roll tubes as a method of tone control as well. All methods have one thing in common: they emphasize some frequencies more than others. It's all "tone control".

I know you try to help members. Thanks for your contributions. Let's just move on for now and put this behind us.

Back on Page 3 we had this conversation. I told you I like L-pads. I even told you I bought the same L-pads as you from Parts Express for just this purpose.

Do they make analog versions?

Me too. I learned to love the PEQs from working sound for bands. But where can one buy a nice *analog* 2-band PEQ for home use that doesn't look like a guitar stomp box?

It depends on the room I suppose. Maybe "too hot" is not the right word. It's just that sometimes I want them to calm down and be mellow for a while It's hard to describe musical stuff with words.

Westcoast, perfect! This is why I like parametric EQ the best. Find the "annoying" frequencies and cut them out. It's hard to do this with a graphic even with 1/3 octave sliders. Give me to good PEQs any day!

wdecho: I had made up my mind I wasn't going to respond to any more of your posts after the way you have abused everyone, including myself, trying to help you. But for the sake of other readers who might be confused by your latest missinformation I want to set the record straight. (1) The Klipsch HIII is the best speaker I have heard in all of the speakers I have auditioned, but yes, it is still a little harsh on my ears at times. I plan to keep them because they do so many other things well. (2) I believe L-pads are an *excellent* way to tame "too hot a driver". I explained this to you in this thread and months ago in a similar thread. The point of all the math was to demonstrate to you that the L-pad will change the load the crossover sees (an assertion you seem unwilling or unable to recognize). I never made the claim it was "the wrong way to do it", just that it wasn't totally inert as you claimed. Hear this. I believe that although the L-pad will change the load, this change is *very likely not significant* enough to ever be heard, This means I agree with you that L-Pads are good!!!!!!!! Get it yet? (3)L-pads may in fact be the best approach to too hot a driver. Equalization is another very good approach. I like and use them both. (4) I don't want to change the crossovers in my new speakers. (5) Please stop telling people with way more education than you that they need to go to electronics school. Here is the simplified version of the above: (1) L-pads are an excellent choice for taming too hot a driver. (2) L-pads will effect the crossover slightly but you probably wont hear it. (3) Stop being rude.

What was this thread about?

You have the resistance part right but are missing the point we are trying to make about the frequency dependency of the speaker. The diagram you posted above may help illustrate this as follows. Let's call the impedance of the speaker be Z3. Now the input resistance to this network that the crossover sees (on the left side) is Zin = R1 + (R2 * Z3)/(R2 + Z3) Now using the values indicated in the diagram for R1 and R2 we get Zin = 2.34 + 19.39*Z3/(19.39 + Z3) Now if we let Z3 be exactly 8 ohms, solving for Zin gives Z3 = 8 >> Zin = 2.34 + 19.39*Z3/(19.39 + Z3) Zin = 8.0034 Which is almost exactly 8 ohms. Which is the goal of this properly designed L-pad,. (This is your point I believe) But this speaker is not always 8 ohms. Its actual impedance changes with frequency. Let's suppose that at a certain frequency the speaker's impedance is 16 ohms, then re-evaluate the same equation setting Z3 to 16. Z3 =16 >> Zin = 2.34 + 19.39*Z3/(19.39 + Z3) Zin = 11.1063 Now we see that the load the crossover sees is approximately 11 ohms, but if the speaker was connected to the crossover without this L-pad it would be 16 ohms. Hence the introduction of the L-pad changes the load presented by the speaker on the crossover. Hopefully this helps clear things up.

Mike is right. The combination of the speaker's complex and frequency dependent impedance and the resistor's real and constant impedance will add to produce something different than what the crossover was designed for. I doubt anyone could hear any ill effects of the L-pad, but yes, it is definitely going to be a different load.

For anyone on the fence about tone controls. One thing I like about the Schiit Loki 4 band tone control is that is is completely transparent to my most critical listening. And I listen very critically. In general, I don't favor EQ or messing with the sound, but I have got to give some praise to this little device. It greatly exceeded my expectations. By "transparent" I mean that when it is in the circuit and all 4 knobs are at zero I hear absolutely no difference between a direct path and the path through the equalizer. I performed this test using an A/B switch box on the RCA lines to instantly bypass the unit. I can not hear any difference between the direct path and the path through the zeroed out Loki box. That is a good starting point. First do no harm! EQ later. For comparison, I did the same test with the miniDSP HD unit (also with all EQ functions defeated) and I could definitely hear a difference. When the miniDSP was in the circuit (even though it was set to no EQ) it degraded the signal quality slightly. Very slightly, but I could hear it. I sent it back. The miniDSP HD is an amazingly powerful device, but I didn't really need the full blown room EQ, and didn't want any degradation whatsoever that I could hear. When I begin to turn one of the knobs on the Loki away from flat I hear it smoothly and almost imperceptibly begin to effect the sound, and with a simple turn back to zero it is invisible again. The Loki is fully analog. This makes a big difference. There is no added A/D - D/A stage to mess things up like some other EQ boxes. So if you are looking for just a little more bass at low volume or moving the mids a bit back in the mix when you get a recording that is not so well recorded, but are not sure you want to "mess up" the sound with tone controls I suggest giving the Loki a try. You may find it as sonically transparent as I did. It also has it's own built in bypass switch. I dare anyone to tell me you can hear when this thing is in the circuit.

Sound bar EDIT: With L-pads

The music we are playing back has already passed through an awful lot of Op-amps and equalizers before we ever get it.

I have two of those same L-pads from Parts Express at home. I didn't realize the speaker backs were screwed on. I didn't notice screws.

Agreed. If I built speakers I'd put an L-pad on each tweeter and mid just because it's easy and cheap (and I like tuning stuff). Will the mid horn in the HIII respond well to an 8 Ohm L-pad without it messing up the crossover frequencies? There seems to be a lot of debate about such things.

The closer I sit the better these sound. I am really enjoying what I am hearing lately. I think that when too far away the room messes up the sound. Right now the HIIIs are about 6 feet away and 6 feet from each other, on the floor on their original risers and it is very nice.