Have a balanced 2x4... where to go from here

[RockLeeEV]

*2x4 in-a-box just FYWI

a few suggestions is all i'm wondering

- What should I do about (remote) volume control? Should I just get a receiver or preamp? Or is there anything "MiniDSP" style I could use?

- What should I do about amplification? I'd imagine I want around 20-40W for the tweeters and 60-200W for the midwoofers.

I'm just at a bit of a standstill right now. I know what drivers I will be using, and I know that the 2x4 Balanced will be the centrepiece, so to speak. but what bridges it together? My intended sources all use RCA analog outputs, btw, and do not have volume control built in.

My concerns...

- I don't want to clip the miniDSP inputs with too powerful a preamp
- I don't want to clip the miniDSP outputs with a low sensitivity amp
- I don't want to damage the tweeter with electronics thump.
- I'm not an electronics DIYer like a lot of the folks here at this forum. While I'm sure I could figure these things out, it's not really a comfort zone for me.
- Cost. I'd prefer to keep it cheap!

 

[CharlieLaub]

RockLeeEV,

I am doing very similar things. In fact I am currently building a pair of custom "plate amps" that include the Balanced 2x4's and I am using some outboard unbalanced 2x4s with outboard amps. Let me share my thoughts with you below.

What should I do about volume control? Should I just get a receiver or preamp? Or is there anything "MiniDSP" style I could use?

This depends on your source (what is that?). It might be able to drive the MiniDSPs directly. But a preamp would be a good idea.

- What should I do about amplification? I'd imagine I want around 20-40W for the tweeters and 60-200W for the midwoofers.

For home speakers, 30-60W for midrange and tweeter are probably fine. You can get this using LM3886 chip amps (if you want to build something). These are cheap and easy to purchase and assemble with a power supply. PM me for details and I can point you in the right direction. One plus about the LM3886 is that the distortion is pretty low above 1k Hz, which is NOT the case with many other types of chip amps available today.

Unless you are going to use a high sensitivity woofer, you will probably want more power for the woofer(s). There are options like class-D type amp boards like the L15D and L25D which are based on the International Rectifier IRS2092 driver IC and some MOSFET output devices. These seem to be inexpensive and the design is well vetted. These offer between 150W and 350W of power depending on type of board, driver Re, and power supply voltage. Again, PM me for details or search the forums.

You can build these into the speaker cabinets, or built them as amps and use speaker wire to connect them to the speakers.

I'm just at a bit of a standstill right now. I know what drivers I will be using, and I know that the 2x4 Balanced will be the centrepiece, so to speak. but what bridges it together?

My concerns...

- I don't want to clip the miniDSP inputs with too powerful a preamp

Right. But a preamp is designed to drive line level loads. You won't overdrive the MiniDSP unless you turn up the volume excessively, and at that point distortion increases and the system will be playing at full tilt. I would not worry about this.

- I don't want to clip the miniDSP outputs with a low sensitivity amp

I think that the only way you could have a problem on the MiniDSP outputs is if the amps have too low of an input impedance, but again this will not be a problem with consumer gear or DIY amps.

- I don't want to damage the tweeter with electronics thump.
- I'm not an electronics DIYer like a lot of the folks here at this forum. While I'm sure I could figure these things out, it's not really a comfort zone for me.

I have heard about this problem but I don't experience it. I tend to shut off the amplifiers well before the line level electronics like the MiniDSP, which will prevent this problem. A very helpful piece of equipment that does this automatically is something like the old Adcom ACE-515. It's a sequential turn-on and turn-off unit into which you plug all your equipment. It's also a line filter for the AC mains. Using one main switch on the front panel, the entire system is turned on or off, with a delay for the amps (on last, off first) of about 10-20 seconds. Other manufacturers (e.g. Panamax) make similar units. But the cheap way is to turn things on and off by hand, in the correct order.

Hope that helps one way or the other.

Maybe you can post more details about your system, amplifier preference (DIY versus buying new or used) and source component(s).

-Charlie

 

[Pallas]

Your use here is the SEOS18+TD15 Apollo, right?

I guess the first question is, how many sources? If it's just one, run it straight to the miniDSP. If it's mostly one, perhaps just swap cables. If you'll be using multiple sources fairly regularly (and none of them need external processing, such as a phono preamp) then perhaps an older cheap separate preamp can be used. Lots of great stuff out there, and as long as it's not badged McIntosh, Bryston, etc., the resale value of stereo preamps without remote controls is very low.

I have a wild and crazy idea for the amp: use a top-line "obsolete" (no HDMI, probably no TrueHD/MasterHD decoding, etc.) AVR with 5.1 channel inputs. (Or not; since you have a crossover/EQ that can compensate for FR variations caused by high output impedance, I think a used Panasonic XR55/XR57 is very tempting: plenty of real-world power, very high efficiency, small package.)

But expensive flagship boat-anchor or lithe Class D unit, an "obsolete" AVR will give you six big advantages over any other approach.

First, you can get one cheaply used from craigslist and the like.

Second, you'll get a multichannel microprocessor-controlled volume control downstream of the miniDSP that likely tracks far better than all but the most expensive pots. (I have no problems running a volume control prior to the miniDSP, mind, and driving amps directly off of it. The theoretical issues with that approach don't seem to matter in the real world. But there are theoretical advantages to volume control downstream of the DSP.)

Third, you'll be able to easily adjust relative levels on the AVR if you want to keep the miniDSP relatively hot.

Fourth, because everything's on one PS, you'll have more juice in reserve for the woofers if they need it.

Fifth, you'll more likely than not have a lower noise floor than separate electronics connected by external wires can offer.

Sixth, all the electronics will be in one box.

(A possible seventh is a 12V trigger, though you'd need the separate trigger board for the 2x4; if it were a 2x8 or 8x8, the 12V trigger would be a more compelling advantage.)

Of course, the "high end" snobs will sneer all over this idea for any number of ultimately spurious reasons. But what else is new. AJ seemed to like his Orion-inspired dipoles powered by an AVR downstream of his DCX2496.

As for the RCA-Phoenix adapters, any idiot klutz can make those quickly, easily, and painlessly. Even me.

 

[RockLeeEV]

This depends on your source (what is that?). It might be able to drive the MiniDSPs directly. But a preamp would be a good idea.

Hey; the sources vary. I don't have an issue with getting up to plug in the source but I definitely want volume control no matter what the source. I want to be able to hook it up to the PS3, the Wii, etc. Obviously a receiver seems the easiest way to go, but it's slim pickings for pre-outs and the amps would just be redundant. All the stereo preamps just seem overpriced to me considering the analog signal will ultimately be going through the miniDSP. I wanna keep it simple.

There are options like class-D type amp boards like the L15D and L25D which are based on the International Rectifier IRS2092 driver IC and some MOSFET output devices. These seem to be inexpensive and the design is well vetted. These offer between 150W and 350W of power depending on type of board, driver Re, and power supply voltage. Again, PM me for details or search the forums.

Interesting. As far as cost goes do you have a rough estimate? Currently i've been leaning towards a crown XLS1000 for the woofer (200wpc class D).

I have heard about this problem but I don't experience it. I tend to shut off the amplifiers well before the line level electronics like the MiniDSP, which will prevent this problem.

I'm confident in myself to avoid mishaps, but family members....... not so much.

A very helpful piece of equipment that does this automatically is something like the old Adcom ACE-515. It's a sequential turn-on and turn-off unit into which you plug all your equipment. It's also a line filter for the AC mains. Using one main switch on the front panel, the entire system is turned on or off, with a delay for the amps (on last, off first) of about 10-20 seconds. Other manufacturers (e.g. Panamax) make similar units. But the cheap way is to turn things on and off by hand, in the correct order.

Hey that was some very interesting advice - something I hadn't previously considered.

Maybe you can post more details about your system, amplifier preference (DIY versus buying new or used) and source component(s).

RIght.

Laptop DAC / Wii / PS3 --> ?? -->
MiniDSP --> ??? --> SEOS waveguide + compression tweeter (110db/w/m)
-----------> ??? --> Acoustic Elegance TD15M (97db/w/m), but I may use a bit of LT circuit to boost the 40 - 80hz range from the sealed box until subwoofers are introduced into the system)

Obviously high fidelity at SPLs from 45 to 95db is the most important, but my sister's wedding is coming up next summer.... so these things might just get a REAL workout

The "tedious" switching of sources isn't the issue - just volume control. I feel like all the options are really convoluted.

 

[RockLeeEV]

Pallas, that's a very appealing suggestion. In fact the simplicity of it is pretty much what I had in mind. I'm going to have to give it some serious though.

 

[CharlieLaub]

Laptop DAC / Wii / PS3 --> ?? -->
MiniDSP --> ??? --> SEOS waveguide + compression tweeter (110db/w/m)
-----------> ??? --> Acoustic Elegance TD15M (97db/w/m), but I may use a bit of LT circuit to boost the 40 - 80hz range from the sealed box until subwoofers are introduced into the system)

Obviously high fidelity at SPLs from 45 to 95db is the most important, but my sister's wedding is coming up next summer.... so these things might just get a REAL workout .

Thanks for the clarification on the system. I second Pallas' suggestion to get a used preamp from Yamaha, Adcom, etc. These can be found for under $200 and possibly under $100 if cosmetics aren't super nice.

I wanted to say a few words of caution about the noise floor in your system. I get the idea that many people get super excited to put together a system consisting of high sensitivity drivers, which they pair with a mega power amp, only to be puzzled and frustrated when they can hear hum and noise from their speakers. If you want the speakers to play at even 95dB (moderately loud for home use) you will be using MUCH LESS than 1 watt of power. Power amps perform poorly in the "low power" region in terms of noise (independent of power level) and distortion. Most commercial gear does not publish plots of these versus output power, but if you dig deeper you will find info in general. This is one of the main thrusts behind Nelson Pass' "First Watt" concept. Most of your listening is taking place well within the first watt of power that the amplifier is delivering, so the performance in that power regime should be emphasized. So, I caution you against using high power amps (like the Crown you mentioned) if these speakers are for home use. You really don't need much more than 10 or 20 very clean watts of power with these drivers, and that's no joke! Only if you are going to use a significant LT boost would I consider a 100W power amp, but definitely not a pro amp unless you are using the system outdoors (and then just rent a pro amp for the day).

-Charlie

 

[Pallas]

Just to put some numbers on what I was suggesting, I checked my local CL to see what kind of ballpark pricing you could anticipate.

I found a Denon AVR-5800 for 500 USD. That AVR is rated at rated at 170W/ch, and HTMag measured ~200W/8Ω/2ch, ~140W/8Ω/6ch. That's easily enough power to drive a TD15 and Erich's BA compression driver to outdoor dance floor levels. (Especially if the TD15 is in a closed box, or you run a highpass filter to protect it from unloading below Fb.)

A newer HK 7300 is also listed, at 600 USD. It tested similarly powerful by HTMag, and 190W/8Ω/2ch, 150W/8Ω/7ch.

Also, found a B&K AVP-1000 preamp tuner for $200. I suspect one could get it for quite a bit less, given that the brand's dead and it has no remote (whether it originally had one, I don't know, but the seller states "no remote").

Onto eBay, there is also a Panny XR57 ending very shortly. (No connection to seller, or knowledge of the particular unit for sale.)

But even more interestingly, and more elegantly for your setup, there is also a Harman Kardon AVR-520 listed on eBay right now. (Again, no connection to seller, or knowledge of the particular unit for sale.) This AVR might actually be the perfect box for your needs, because it has something sadly lacking on most AVR's then (and pretty much all of 'em now):

pre-out/main-in loops.

Check it out:

An externally hosted image should be here but it was not working when we last tested it.

That means you can basically bifurcate the AVR into preamp and multichannel amp, with easy remote volume/power/source-switching: run your sources into the AVR, hook the miniDSP up to the preouts, and run all four channels from the miniDSP to four of the AVR's five amp channels. I don't know how much power the 525 has. I suspect, as decent car companies used to list their cars' horsepower, it's "adequate."

I believe some NAD receivers past and perhaps even present have pre-out/main-in loops too. For example, the T773 clearly does, per this pic from the HTMag review:

The picture is small, but the jumpers are clearly visible. (HK has always had internal jumpers with a button, rather than the U-jumpers NAD and others use.)

There may be other AVRs from the early Dolby Digital era that also had pre-out/main-in loops for all channels, but I am unaware them. Perhaps some digging on AVS or the like will turn up other suitable boxes. So I refine my above comments to say that the most cost-effective and elegant solution to your issue is an older AVR with pre-out/main-in loops.

 

[RockLeeEV]

We ended up picking up a local used Marantz SR6300. I'm not sure that it has the Pre-out / Main-in loop you're discussing, but based on playing around with it with some nearfield monitors yesterday it should be satisfactory for home use.

So I'm assuming that it will be

Source --> L / R input 1/2 -> MiniDSP -> Output 1 / 3---> Surround L -10db / Surround R - 10db --> Tweeter
Output 2 / 4 ---> Front Left / Front Right --> Midrange

With the Marantz being able to scale volume for all four channels simultaneously. It would definitely be nice to have the aformentioned loopback feature as I could then go sources --> marantz --> minidsp --> marantz but I don't believe this receiver has this capability, although I would love if it di.

As far as RCa-Phoenix it seems to be a real issue. I keep having wire slip out of the vice. Because of this I'm a bit irritated by the little green clamp connection. Probably shoulda just got an unbalanced miniDSP in the first place. Would be nice if there were a ready-made Phoenix to RCA converter. I'm probably gonna try to find a short RCA Female and then cut that up instead.

I wanted to say a few words of caution about the noise floor in your system. I get the idea that many people get super excited to put together a system consisting of high sensitivity drivers, which they pair with a mega power amp, only to be puzzled and frustrated when they can hear hum and noise from their speakers. If you want the speakers to play at even 95dB (moderately loud for home use) you will be using MUCH LESS than 1 watt of power. Power amps perform poorly in the "low power" region in terms of noise (independent of power level) and distortion. Most commercial gear does not publish plots of these versus output power, but if you dig deeper you will find info in general. This is one of the main thrusts behind Nelson Pass' "First Watt" concept. Most of your listening is taking place well within the first watt of power that the amplifier is delivering, so the performance in that power regime should be emphasized. So, I caution you against using high power amps (like the Crown you mentioned) if these speakers are for home use.

While I understand what you're saying, everything I've read about the XLS Drivecore is that it's a relatively quiet and well-designed PWM amp, especially the XLS 2000 and 2500 even moreso than their lower powered siblings.

I suspect you're giving it an unfair shake due to whatever bias you might have against professional electronics. Especially when you say "Definitely not a pro amp". Unless you've got direct experience with the amplifier in question, I'm not really interested in conjecture based on intended application. Don't get me wrong, I appreciate the advice and it's very valid but it's the same kind of sighted-bias conjecture people make about the miniDSP itself.