[amplifierguru]

550K Zin - that's worth having! 

[Steve Eddy]

550K Zin - that's worth having! 

Well sure. Bigger 'n 100k, innit?

se

[Daygloworange]

Ok, so this got me curious so I dug up my owners manuals, to see what the impedances were.

Pre-amp : Adcom GFP-345
Output impedance    100 ohms    (normal and LAB)
Output level            2.0 V          (normal and LAB)
Input impedance(high)    22,000 ohms
Input sensitivity(high)     210 mV

Power- amp : ATI 1202
Input sensitivity       1.3 Volts
Input impedance      28k ohms (nominal)
Gain                      24 db (voltage gain)
Slew rate               50 V/microsecond
Damping factor        greater than 400 from 10Hz to 100kHz

I don't have the owners manual for my CDP, but I'm wondering if the pre amp/ amp specs are a decent match impedance wise?

Also, My pre-amp has 2 sets of outputs, normal and what are called LAB. The difference being that the normal outputs are capacitively coupled using high grade metallized film capacitors, they say it's ideal for use with amplifiers which require a bandwidth-limited signal which does not extend to DC.

the LAB outputs are direct-coupled with no capacitors, described as an extremely broadband circuit which responds down to DC. It also describes that it is designed to drive amps with input sensitivities ranging from 500mV(0.5V) to well above 2.0V.

I've got the normal outputs hooked up to my power amp, and the LAB outputs hooked up to my subwoofer's plate amp inputs.

Should I leave it as it is or use the LAB outputs to drive my amp speakers?

Any thoughts?

Cheers

[Bob Reynolds]

I believe the general rule of thumb is that the input impedance of the amp should be at least 10X the output impedance of the preamp. 28,000 / 100 = 280 so it looks like you're well covered impedance wise.

Regarding the capacitor coupled outputs on your preamp. My understanding is that is a mechanism to block DC voltage from appearing on the output. I believe the other common approach is to use a DC servo. I'm sure other's here can expand on this.

I do have one comment regarding your sub hookup. Rather than running your main speakers with a full range signal, have you considered inserting a high-pass/low-pass filter between the preamp and amp? The high-pass signal would go to your amp (taking the bass load off the amp and the main speakers) and the low-pass signal would go to your sub (you would set the sub's internal low-pass filter to by-pass or as high as it will go).

You might find this article of interest: http://www.mkprofessional.com/bass_mgmt.htm

[Daygloworange]

Hey Bob Reynolds,

No, it had never occurred to me to try what you're suggesting. Thanks. That sounds interesting. When you suggest a high pass filter, what roll off point/rate are you suggesting? If indeed we have the same understanding of a high pass filter. My main speakers are full range transmission line types that go down to an -3 db point of 40 Hz. My sub is crossed over at 50 Hz. A lot of times I don't even turn the sub on, the mains load the room that well. It's almost redundant.

Cheers

[Daygloworange]

Bob Reynolds,

Thanks for the link. I'm not sure if he mentions whether or not they are using active crossovers and/ bi-amping. I think perhaps he's taking in to account that the majority of home video is played on " theater in a box" systems, and perhaps mixing from that perspective. Personally, I have an extreme dislike ( more like, hatred ) for movie audio. I think it's atrocious. I watch movies on a "theater in a box" system. The lows are rolled off, and the dynamic range control is set to full, as I find they exaggerate the dynamic range way too much.

As far as my 2 channel set-up, I guess to roll off the low end to the mains and have the sub crossed over higher would have the effect of making the L+R amplifiers job of driving the speakers easier. As well as being less taxing on the mid/bass drivers of the L+R speakers, with the effect of lower distortion as a result.

Theoretically, this sounds interesting. I'd like to discuss this with Danny from GR Research, as my system consists of his AV/3 speakers and PR sub. I guess I would ask him what his thoughts are as far as phase coherency, time arrival issues and so on. ( incidentally, my sub isn't ported either, but rather has a passive radiator, and works quite nicely )

I do enjoy contemplating the possibilities however!

Cheers

[Bob Reynolds]

Hey Bob Reynolds,

No, it had never occurred to me to try what you're suggesting. Thanks. That sounds interesting. When you suggest a high pass filter, what roll off point/rate are you suggesting? If indeed we have the same understanding of a high pass filter. My main speakers are full range transmission line types that go down to an -3 db point of 40 Hz. My sub is crossed over at 50 Hz. A lot of times I don't even turn the sub on, the mains load the room that well. It's almost redundant.

Cheers

You are using your sub, as many people do with "full range" speakers, in a bass reinforcement manner. There's a few points to keep in mind with this configuration: 1) multiple bass sources in the room may interact in ways you do not desire, 2) woofers in full range speakers begin to distort when pushed in either SPL or lower frequency and 3) it's somewhat of a trial and error thing to set the low-pass filter on the sub so that it blends reasonably well with the main speakers.

The typical high-pass/low-pass (bass management controller) uses 80Hz as the crossover point and many don't specify the order of the filter. I use M&K bass management controllers with an 80Hz crossover point and a 2nd order filter for both high-pass and low-pass. As you know, it's important to set the sub's level correctly so that it does not call attention to itself. M&K provides test tones (you can download them from their web site) for setting the level correctly. Their more expensive LFE-4, that I use in my main system, provides level adjustment on each channel so that you can compensate for acoustic issues in the room like furniture placement.

Hsu Research has this: http://www.hsustore.com/high-pass.html and this: http://www.hsustore.com/highendcrossover.html

Using this approach takes the bass load off the amp and the main speakers, lessens (essentially eliminates) woofer distortion, makes setup very easy, allows the mid/treble to be positioned completely independently of the bass.

[Bob Reynolds]

Bob Reynolds,

Thanks for the link. I'm not sure if he mentions whether or not they are using active crossovers and/ bi-amping. I think perhaps he's taking in to account that the majority of home video is played on " theater in a box" systems, and perhaps mixing from that perspective. Personally, I have an extreme dislike ( more like, hatred ) for movie audio. I think it's atrocious. I watch movies on a "theater in a box" system. The lows are rolled off, and the dynamic range control is set to full, as I find they exaggerate the dynamic range way too much.

Yes, the crossovers are active and biamping with the amp in a powered subwoofer, but not with the main speakers. Just a guess regarding dynamic range of movies on DVD is that the dynamic range is not exaggerated, but is actually much wider than CD and movie audio takes advantage of that. I'm not sure what you mean by the lows are rolled off. I listen to movies on DVD through my 2.1 music system and film audio is quite good. It may be that your HTIB has given you a distorted view of film audio.

As far as my 2 channel set-up, I guess to roll off the low end to the mains and have the sub crossed over higher would have the effect of making the L+R amplifiers job of driving the speakers easier. As well as being less taxing on the mid/bass drivers of the L+R speakers, with the effect of lower distortion as a result.

You are exactly right.

Theoretically, this sounds interesting. I'd like to discuss this with Danny from GR Research, as my system consists of his AV/3 speakers and PR sub. I guess I would ask him what his thoughts are as far as phase coherency, time arrival issues and so on. ( incidentally, my sub isn't ported either, but rather has a passive radiator, and works quite nicely )

Sounds like a good idea.

[Daygloworange]

Bob Reynolds,

I agree with you on being carefull with multiple sound sources and them not causing more issues than they solve. I've carefully set my sub up. The sub plate amp has a variable crossover that's variable between 40Hz to 160Hz with a 12db/octave slope, and variable phase, 0 to 180 deg. Both continuosly variable.

I will admit that I have not set this up with an SPL Meter and test tones, but tweaked on it over weeks with critical listening with CD's I am very familiar with as references. I've been a semi-professional recording engineer for over 20 years, so I'm very confident that I've set it up well.( I'm not a bass junkie, by any means ) I really strive for neutral. I don't like hyped up highs or exaggerated bass. But, eventually will get a new SPL meter and do the test tone thing just for kicks. ( Mine died years ago, along with my tape de-magnitizer, and de- gausser, Ahh, the good ol' days!  )

BTW, how long ago did you start using these high/low pass filters in your system? Can you describe how different it is now as to the way it performed before you added them?

Cheers

[Daygloworange]

Bob Reynolds,

Sorry, I described that poorly. I was describing how I had my " theater in a box" system set-up. I rolled of the lows, and squashed the dynamic range. I don't like it when a car door closing sounds like a giant thud that rattles my fillings loose! And when you're listening to very quiet dialogue, and then the next scene has an explosion or gun shot or door slam at 120db's.....you know, in a effort to make you jump out of your seat. That's why I have it set up like that. I want the story line to do the drama, not foley effects and exaggerated dynamics.

Cheers

[Bob Reynolds]

BTW, how long ago did you start using these high/low pass filters in your system? Can you describe how different it is now as to the way it performed before you added them?

Regarding speaker evolution, I was on the path for full range floorstanders. I started with B&W 601 bookshelfs, then Meadowlark Kestrel Hot Rod (transmission line) floorstanders, then Spendor S8e floorstanders. I still wanted a full range speaker, but the 3-way floorstanders I was considering were in the $5K range and beyond my budget.

So after quite a bit of research on subwoofers I bought an M&K MPS-5310 and an M&K LFE-4 bass management controller. I added the sub with out the BMC initially to get accustomed to the change. I ran it that way for several weeks. Then I inserted the BMC and the impact on the Spendor was dramatic. It seemed to be more transparent and detailed. Still had the Spendor midrange, but cleaner sounding. At the suggestion of Barry Ober at M&K I plugged the rear port of the Spendor and that made a difference, but much less than the BMC had. I then used the test tones and an SPL meter to set the level balance and that made a nice improvement again. Our living room is such that a fabric love seat is near the sub and right speaker, both needed a little boost to match the left channel. That was over two years ago and it has sold me on subs and BMCs.

I recently swapped the Spendors for M&Ks S-150 reference monitors and the change in soundstage was startling. A/B-ing between the two the soundstage would just shrink to almost nothing with the Spendors. I use a pair of M&K CR-2401 ($600/pair) nearfield monitors in my office system and I A/B'ed them with the Spendors and that convinced me to get the S-150s. The little $600 monitors were almost indistinguishable from the $3K Spendors when used in the 2.1 system. I have since become a fan of sat/sub systems in general and M&K specifically.

-- Bob

[G Georgopoulos]

CD Player Output Impedance and Opamps
---------------------------------------
hi everyone
whats so important about this topic, all cd players have standard
o/p impendances that are capable of driving other equipment

suppose o/p impendance is low enough the performance of the
cd player and the equipment driven by it should be free from
any noticable effect on specifications

given i/p impendance is high in cd player driven equipment i dont see
any significant effect in their perfomance

noise performance could be affected only when there is an effect on
the source-cdplayer therefore cdplayer noise should be as low as possible

cheers
George