[randog]

Curt,

I recently built up an A/V system with emphasis on 2-channel. I also customized an armoire to use to house everything. Well, it seems I'm stuffing myself out of it with my TV, Odyssey Monoblocks, turntable, etc. I've decided to try and downsize and set up the turntable in my bedroom system.

How well do you think the Purest would integrate into an HT application? In other words, if I used one pair of the S inputs from the main speaker outs on the HT receiver, how would I set up the Purest for 0 gain instead of waiting for your pre(s) with the HT bypass? Is that easy and repeatable? What affect will that have to 2 channel listening, if any?

Secondly, I'm assuming you'll say the MB-100's are a great match to the Purest.   I need a stereo amp or MB amps that will be comfortable in the enclosed armoire (I did remove the back completely and put braces in so it does have adequate ventilation altho I assume it will still get warm). In addition, the power switch needs to be located on the front. I'm looking for good, not great integration with the receiver's (Outlaw 1050) internal amp for the surrounds (I'm assuming 'great' integration would require 5 MB-100's which isn't completely out of future possibilities considering their size and price). Does that make it that much trickier to set the preamp up for HT (different power sources)? My main speakers are Ellis 1801's and my cdp is the Norh CD-1. I have GR-R AV-1's for surrounds.

Would the Purest pre along with the MB-100's be a good choice for this application? Any recommendations for other amp(s) to be used with the Purest? And if not the Purest any other preamp recommendations based on my current setup?

Any ETA on the Audiophile and Sabai?

Thanks,
Randog

[Curt]

Just like you said, 0dB gain and a HT pass through are the same thing.

To achieve this "pass through", with the Purist, turn the gain knob to the 1st position (which is 0dB) and turn the volume control up full (position 24), done.  The Purist's step attenuator VC is perfectly repeatable and balanced between L&R channels, great for HT applications. Once set in this configuration whatever goes in any RCA input comes out the RCA outputs at the same level.

This will not effect your 2CH listening in any way, the HT input just becomes one more source, there are four source inputs. Just be sure to turn the Purist's volume down after the movie.

MB-100s sound good with the Purist and they run cool, the heat sink is huge and works very well, not much heat at all (even played hard). The power SW is on the front panel (both units).

To integrate MB-100s with the Outlaw you can use the Purist's VC for SPL level matching    this is a neat trick and has small 1.5dB steps. Once you get it right just write down the VC position (so you don't forget).

I do like all the same type of amps in a HT if possible, including the amp driving the subwoofer. You need a non-powered subwoofer to do it this way.

I think the mix your talking about would not be difficult to integrate, I use a modified CD-1 also (plays well with the Purist and MB-100s).

The MB-100s will drive the 1801s with ease and have more than enough current available for that 2-way system.

The Purist is in a class above the MB-100s, even though they play well together the Purist can be matched to much more expensive amplifiers. It is a very quiet, transparent, and fast preamplifier that will drive any amplifier, even tube types. But, the MB-100 does sound good and it's impossible to beat at its price point.

We have stock in Charlotte now, both MB-100s and Purist preamps.

Hope this helps and thank you for your interest.

[Dozer]

If you want to lessen the risk of accidentally turning on a CD with zero attenuation on your amp, you can crank up the L and R preout volume on your AV receiver and crank down the center and rears, which will let you back off the preamp a little.

I have it set up so my AV receiver L&R are jacked way up, and my preamp will only be REALLY LOUD, but not EXPLOSIVELY LOUD if I accidentally switch sources without turning down the volume.

L +10
C -9
R +10
RR -7
LR -7

Audio preamp -30db from full blast.

Something like that can help you avoid a mishap - unless you don't want to give up any fidelity on your HT (most important to me is that the wife and kids don't blow up the speakers).  I'm sure it results in suboptimal HT performance but can't have everything unless there's a "real passthrough".  Who wants to hold their system hostage for that feature..

[Curt]

The Purist has a "Mute" position on the source selection switch, I always use this when shutting my system down (force of habit).

The mute shorts the preamps input (the inside circuitry only) giving 0V to the amps and leaves all the connected sources looking at 33.2K ohms as usual, of course the sources are NEVER shorted.

So, at shutdown I turn the volume all the way down and select Mute, this makes the Purist ready for the next start-up. Next I turn off all the amps then the sources and then the Purist last (after 2-3min to allow amp PS caps to discharge).

At start-up I turn the Purist on first, then the sources, then the amps, and no pops to worry about.

This is a habit I've developed that has served me well

[LordCloud]

Curt,

If the purist is in a class above the MB-100s, when are we gonna get an amp that can match it? I realize we can always go with another manufacturer but I like the sound of my MBs enough that I would love to see what else you can come up with that's better, especially since your prices are so reasonable.

[Curt]

Curt,

If the purist is in a class above the MB-100s, when are we gonna get an amp that can match it? I realize we can always go with another manufacturer but I like the sound of my MBs enough that I would love to see what else you can come up with that's better, especially since your prices are so reasonable.

Don't take me the wrong way, IMO the MB-100 is the best amp in its class and a superb value. It sounds great in 2-way loudspeaker systems, some 3-way systems, and HT systems.

But, when you get big, inefficient loudspeakers that offer a difficult reactive load, a larger amp is required. One with higher rail voltages (more watts), higher slew rate (to make up for the higher rail voltages), more current (amps) output. These specs do make a difference with larger speakers.

The MB-100 design is already maxed out, I can't squeeze any more watts or amps out of it. This is why were working on the MB-250, the MB-100s big brother.

I know I can get all the MB-250 specs right, I'm just hoping it will sound as liquid as the MB-100. For a SS amp the MB-100 is surprisingly smooth.

Next week I will be testing some hot new bi-polar transistors to hear what they can do.

[LordCloud]

Curt,

I plan on having a pair of subwoofers made to supplement my Meadowlark Swifts. I am an apartment dweller so it won't be the home theater variety, my main goal is to be able to more accurately reproduce an acoustic stand up bass. Soundstage volume is also a goal. since your new amp will be more pwerful than the MB100 should I wait and power the subs with the new amps or will the sound quality be above and beyond the 100s, and I should power my entire system with the new amps. Like I said I live in an apartment so excessively loud volumes are of no use to me, so I wonder if the new amps will sound better or just be more powerful?

[randog]

This is a good question because if I opt for the MB-100's now and decide to get the MB-250's later while moving the MB-100's to surround duty, will I find that seamless integration? In other words, do you consider these two products to be of the same family of design or completely different? This is important to me because my reason for doing so would be if I'm not happy with the integration between the MB-100's for my mains and the receiver's amp for surround duty.

Randog

[Curt]

... since your new amp will be more pwerful than the MB100 should I wait and power the subs with the new amps or will the sound quality be above and beyond the 100s, and I should power my entire system with the new amps.

This is a good question because if I opt for the MB-100's now and decide to get the MB-250's later while moving the MB-100's to surround duty, will I find that seamless integration? In other words, do you consider these two products to be of the same family of design or completely different?

The MB-250s are not finished (not even close), but I can tell you that they will be a totally different design from the MB-100s.

The target design (at this point) is four matched transistor pairs to deliver 125W @8 and 250W @4 at a slew rate of >60V/us, have 80,000uF worth of PS filter caps, soft recovery rectification, and be able to dump 45A within the SOA on demand. The MB-250 will be our top-of-the-line model and sell for quite a bit more than our MB-100s.
 
The MB-100s are designed for medium sized 2-way loudspeakers, bi-amping, and HT applications. To this effect they do a great job. The MB-250s are for larger 2/3-way loudspeaker systems.

I have no idea when the MB-250s will be ready but, with the other components that are ahead of it, I'm sure it will not be until sometime next year.

[Pachom]

Hello Curt,
you wrote, your 125 watts amp would give 45 amperes into a given load, on demand.
This would be a 0.7 ohms load. Therefore, there is no demand. This is about a short on the other side of a speaker cable. I doubt the traces on your pcb would handle such current, and it may smoke the speaker cable too. This is equal to a power of 1,417 watts. Nobody has speakers of 0.7 ohms impedance. But some 3-way, 4-way speakers may require more than 125 watts into 8 ohms. Anyway, if you already know the maximum of output current for your amp, you proof it’s on the way.

[wunderlast]

Back again, eh, SOM.  Don't you have anything better to do?

[Curt]

Hello Curt,
you wrote, your 125 watts amp would give 45 amperes into a given load, on demand.
This would be a 0.7 ohms load. Therefore, there is no demand. This is about a short on the other side of a speaker cable. I doubt the traces on your pcb would handle such current, and it may smoke the speaker cable too. This is equal to a power of 1,417 watts. Nobody has speakers of 0.7 ohms impedance. But some 3-way, 4-way speakers may require more than 125 watts into 8 ohms. Anyway, if you already know the maximum of output current for your amp, you proof it’s on the way.

***** First, for everyone here, this is a known troll, I will allow his post and this one reply. If the tone of his posts don't change he will be banned from this forum. *****

Well Werner, wouldn't it be nice if all that was needed to design a good high-end audio amplifier was basic Ohm's Law. Life would be so simple, everyone could design and build their own amplifier. Unfortunately it doesn't work that way in real life and I'm sorry to inform you that your a bit off track in your attempt to logically discredit a high-current amplifier design.

Perhaps this exhibited lack of understanding is why you restrict your amplifier designs to using off the shelf ICs and the supplied data sheet's sample circuit. I guess this way you to have a much better chance of getting your amps to work with no test equipment and your limited knowledge of circuit design.

** Read This **
I'll answer this post for you, but if your looking to disrupt this forum forget it. I will delete the next post you make that shows any sign of troll attitude. I am the moderator of this forum and simply don't have the time for the games you like to play.
**************

Back to the IRD prototype amplifier design:

Rated at 125W @8 ohms and 250W @4 ohms is the whole story. We never know what impedance loudspeakers our customers will use and some 4 ohm loudspeakers have impedance dips as low as 2 ohms, Thiel speakers come to mind. A good amp needs to be stable and remain low THD over the entire range of loudspeaker choices.
 
At 2 ohms the current demand will reach 15.81 amperes. That's just a resistor, for a reactive load (a speaker) the voltage and current can be out of phase which puts even more complications into current demand.

As the required amperes go up you move up the transistors hFE vs Ic curve, and near the limit of a  transistors output current capability begins a very non-linear region (Read: THD). Therefore the  greater the current capabilities the transistor (or pairs) the better chance it has of staying in the linear region (Read: Low THD).

The Point: An amp that can deliver 45A within the SOA staying within the linear hFE vs Ic region of the transistors rating is much more likely to perform as a true low THD high-end amplifier regardless of loudspeaker choice. Much more likely than an amp that only delivers 5A in the SOA and the linear region.

An amplifier that can deliver 45A not only has a lot of driver control capability but it will also perform very well (Read: Low THD) over a wide variety of load conditions. This is an amplifier design that can be used successfully with even the finest, larger 3-way loudspeaker systems.

Of course this is only a prototype, it can easily can be scaled, to 250W @8 ohms and 500W @4 ohms (or whatever is desired) simply by upping the rail voltage and adding more parallel output transistors.

This is the true benefit of understanding power amplifier circuit design, to design exactly what you want--need, not to work with a manufacturers sample circuit.

EDIT--

On PCB design: Most music peaks last only microseconds and high-current peaks can easily be sustained for these durations by the thick, wide copper traces on our PCBs. We also use heavy ground-bus techniques throughout or amplifiers. Anyone who has looked inside our MB-100s will understand how heavy duty our circuitry is. The ground-bus in the MB-100 can easily handle 40A even though it will never see current higher than 15A(peak). We design equipment that will last a long time under the most demanding conditions. These techniques also keep noise levels at a minimum.

<End Edit>

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