Audeze LCD 4 - Which amp?

[Deke609]

Hi all - what Bottlehead amp would you recommend for the Audeze LCD 4 (200 ohms)?  I think I saw a post from Doc B. suggesting that the Crack, with a 5998 in place of the 6080, can be paired with cans having a input impedance as low as 70 ohms.  But I've read on other forums that the LCD 4s are power hungry - so I'm not sure if this would be a good paring.  I built a heavily modded Crack w/Speedball (w/ Tung Sol 5998) and love it, and so will try it with the LCD 4s for sure, but do others think another amp would be superior - e..g., S.E.X.? - perhaps even a Kaiju or Stereoamour if they can can be modded for output to cans?

I have no technical or theoretical knowledge about audio circuits and the like - just a guy that loves good sound and DIY soldering projects

thanks in advance,

Derek

 

[Doc B]

S.E.X. is a sure bet. Mainline might have enough power, but I have not tried it with the LCD4. Another sure thing would be the Neothoriator. I do have one available.

 

[Deke609]

Many thanks Doc.

The Neo is intriguing but outside my price range. So the S.E.X. it is.  But I am still concerned about driving the LCD 4s to their full potential. 

What do people think about running dual S.E.X. monoblocks, one for left channel and one for right?  Is that doable? Maybe with gross and fine attenuators on both to get matching volume?

If the dual monoblock approach makes sense, my next question is: Do I get and build 1 S.E.X. now in stereo configuration to see how its sounds, and then convert to monoblock if I think the headphones need more power, or just build the dual monoblock configuration from the get go?  Would the conversion from stereo to monoblock be an entire rebuild with newly sourced parts? If yes, I'd rather just start with the dual monoblock project. 

many thanks again,

Derek

 

[Doc B]

Start with one. It's probably plenty of power. If you feel you must have more power you could build a Stereomour II with DC filament supply and make up a binding post to whatever-your-headphone-connector-is adapter

 

[Deke609]

Thanks Doc.  Order for S.E.X. placed.

 

[Doc B]

Thank you!

 

[Deke609]

Doc - Apologies for belaboring the issue, but I know myself: even if the S.E.X. sounds great paired with the LCD 4s, I'll always be wondering what they would have sounded like driven by the Stereomour.  So I'm almost decided on replacing my S.E.X.order with an order for the Stereomour with all upgrades.  The only thing holding me back is a question about noise floor.  In a 2015 thread, Paul B. stated that the Stereomour should not be used drive headphones with an input impedance of 62 ohms b/c the noise floor would be too high.  I don't know if Paul B's answer predated the the DC filament upgrade or whether he would have given the same answer in respect of the LCD 4s.

The LCD 4s, to which the amp I build will be dedicated, are a different beast: 200 ohms impedance and sensitivity of 97dB

For comparison: the LCD 3s (which I will not be using) have an input impedance of either 100 or 50 ohms and sensitivity of 102dB

The BH description of the DC filament upgrade includes the following:

"This supply will reduce the already exceptionally low noise floor of the AC heated Stereomour II amplifier to levels acceptable for use with the most sensitive horn speakers. Its installation is recommended in particular for use with speakers above 96dB@1W@1M sensitivity. "

That sounds like a good match for the LCD 4s with their sensitivity of 97dB.  Am I wrong about this? I can live with a faint hum at quiet spots in the music in exchange for greater dynamics. 

many thanks in advance,

Derek

 

[Doc B]

Yes, the Stereomour II with the DC filament supply will work well and be very quiet. The comments from 2015 are about an earlier version of the kit that did not have the DC filament upgrade. You will of course have to make up some sort of adapter to connect the speaker cable binding posts to your headphone cable. Your best bet is to contact Eileen tomorrow (queen at bottlehead dot com or 206-451-4275) when she is back in the office and she can help you with upgrading the order from S.E.X. to Stereomour II.

 

[Deke609]

That's great.  Thanks a million, Doc.  I will contact Eileen tomorrow as you suggested.

 

[Paul Birkeland]

Those comments I made were indeed about the Stereomour I, which would work OK on a very power hungry headphone like the K1000, but would be too noisy for much else that was on the market.

The Steremour II with the DC heater upgrade will be significantly quieter and capable of driving just about any headphone you can think of.

 

[Deke609]

Thanks Paul.  I've put in my order for the Stereomour II with all 3 upgrades. 

Even if there is noticeable hum, I think it will be worth it just to hear what the LCD 4s are capable of when there is tons of power on tap.

Worst case scenarios: either (a) I thereafter engage in endless modding/tweaking in search of an even lower noise floor (which would be fun - so not that bad of a scenario); or (b) I have an excuse to get a nice pair of bookshelf speakers.

And who knows, maybe you guys at BH will come up with an upgrade that lowers the noise floor even further, or, dream of dreams, converts the SII into a headphone amp for power hungry cans. 

 

[Paul Birkeland]

The modifications to allow something like the Stereomour II with all the upgrades to work on a headphone like a Grado would involve adding two resistors per channel to pad the output down and keep the amp loaded.  I generally recommend a pair of 16 ohm and a pair of 1 ohm resistors to accomplish this.

For what you're doing, you may not need any resistors at all.

 

[Deke609]

Many thanks Paul. I'm really looking forward to the Stereomour II with the LCD 4s.  Once I've got the amp running and settled in, I'll be sure to post about the results. 

 

[Deke609]

Paul - Just following up about using resistors to lower output and keep the amp loaded.  Is there an optimal range of load that needs to placed on the amp for it to sound its best?  I.e., does the amp need to perform a minimum amount of "work" before it comes into its own?

Not an urgent question - I'm simply trying to educate myself about what all the "stuff" in the amp actually does.  At present, I have only a very rudimentary knowledge and am trying to improve on that.

many thanks in advance,

Derek

 

[Paul Birkeland]

If the resistor values get too large, you'll lose damping of the headphones and the bass will get lumpy on you. If the resistor values are too small, you'll load the amp down and it will distort.

Using about twice the intended load seems to be a good trade-off between these issues.

 

[Deke609]

Many thanks again Paul.  The damping vs distortion issue is very helpful. I'm doing a bit of self study about these and other issues and hope to get back to you in a few weeks with what I hope at least will be the right questions. 

By the sound of things, finding the right damping/distortion balance is matter of "try and listen" experimentation.  But it also sounds like that, with enough experimentation, I should be able to get the amp nicely dialed in for the LCD 4s. My current working idea is to create a box with stepped attenuators that would plug into the binding posts and then allow connection of the headphones - so that the load at the output could be adjusted to see what sounds best.  I think this might be a bit of construction challenge as the resistors for the attenuators would probably need to be rated for 4W or so to cover off the 3.5Wpc? and would therefore be quite large and possibly expensive.  But the ability to switch loads would allow for quick A/B comparisons.  I'd try to get less expensive (and consequently noisy) resistors for the attenuators. Once I find R values that worked best for me, I assume I should get some low noise resistors (e.g., Vishay naked bulk foil?) for the final implementation?  Does that make sense? 

many thanks in advance,

Derek

 

[Paul Birkeland]

I would try wiring the amp for 2 ohm output and driving the headphones straight from the speaker jacks first.  There's no need to spend money on a problem that you aren't certain you will have.

 

[Paul Joppa]

I see that PB posted while I was writing. He's right; comparing the 2-ohm and 8-ohm outputs will give you two data points on the power/distortion tradeoff, at essentially zero cost, and you are likely to be happy with either. The rest of this post is in case you (or someone else reading this) wants to go into more depth to explore these variables.

You can get adjustable L-pads for loudspeaker crossovers. They are not expensive, handle plenty of power, and have wirewound resistance elements (the good kind!). If you load the output of an 8-ohm L-pad with an 8-ohm power resistor (also widely available and inexpensive), it will present an 8-ohm load to the power amp no matter the setting, and still provide an adjustable signal to the headphones (which are in parallel with the 8-ohm load resistor). As long as the phone impedance is much larger than 8 ohms, it will be dominated by the paralleled 8-ohm resistor.

This way, the damping will be excellent no matter the setting, and you can explore the distortion vs. power tradeoff in a fairly clean experiment.

Once you know your sweet spot for power/distortion, you can separately explore the damping issue. We can get into that another time - there are actually two in the case where an output transformer is involved: 1) headphone damping affected by source output impedance, and 2) parafeed circuit resonance affected by amp load impedance. The latter is usually a smaller effect, and often can be ignored, but if you want to explore all the relevant variables it might be interesting.

I recommend this approach because the results are more easily perceived, understood, and communicated.

 

[Deke609]

Many thanks to you both.  I agree that it makes no sense to problem-solve a problem that may not even materialize.  But curiosity is getting the better of me and I "just want to see what happens if ..."  This is all quite new and fascinating to me.  I've tried numerous times over the years to learn the basic principles of electronics from texts that taught the principles in the abstract or only provided boring experimental applications -- in both cases, that part of my brain that asks "Who cares? So what?" would kick in and I'd close the books after a short time. I've probably relearned "how to calculate voltage between two resistors" at least 10 times by now and never cared, and it wasn't until last night that I had an "Aha" moment when I saw that a volume pot acts as a variable voltage divider - the simple beauty of it! ... So maybe I'm getting the bug.

Regarding the premade L-pads for power amps - that is very helpful.  I will look into that.  My idea of putting together large step attenuators was my attempt to solve the (perceived) problem of how to determine the required resistance values (they could be read from the position of the attenuator). I came across a lot of discussion about the use of L-pads for guitar amps, and assumed that such devices would use a potentiometer and that this would making it difficult to determine the "good sounding" resistor values b/c I'd have to estimate the position of the knob as a point on the resistance divider range of the pot - but maybe that's not an issue.  I'll look into it.  But perhaps you (Paul J.) are suggesting that the L-pad could be part of the "permanent solution" -- i.e., that it would be good enough sonically and not need to be replaced by a fixed value resistor setup?

I had also planned to ask you (Paul J.) about capacitors, as I came across an earlier post of yours that mentioned tweaking "parafeed capacitors" and I did some initial online reading about that last night.  But I will wait until I understand more about it before asking questions.

Again, many thanks to you both for having taken the time to respond so helpfully. I really appreciate it.  I'm not sure what I'm looking forward to more: good sounding music or the learning/experimentation   But why choose between them?  Hopefully I can have both (barring a major screw-up that melts my amp or blows up my cans).

 

[Deke609]

Oops. I misunderstood the L-pad point.  I think you are saying that it presents a fixed and not variable resistance load to amp - e.g., so that on the 8 ohm tap the amp "sees" an 8 ohm load.  I had in mind a device (perhaps non-existent) that could vary the load that the amp sees.