[Eric M.]

I had some general amplifier questions I was hoping I could get help with. I just purchased Bobs (thunderbrick) Forte Audio #3 and ran these questions by him. He thought it would be a good idea if I posted them here.

I was heavily into audio back in the 80s but got out of it as business and family responsibilities took precedence. I had collected quite a bit of professional and vintage JBL raw drivers and misc. solid state equipment. I never had a chance to build the system I had collected equipment for. In fact, all of my gear went into storage until earlier this year when I finally pulled it out and decided to put it together. I am wrapping up construction of my listening room, under the disguise of a home theater (gotta keep the family happy!) and now have a few questions about configuring it.

My system is actively split 5 ways (probably over kill, but was all the rage in 1985 when I came up with this idea)

The split goes as such:
Below 100 Hz (driving JBL 2245)
100 Hz- 500 Hz (driving JBL 2225)
500 Hz to 1200 Hz (driving JBL 2204)
1200 Hz to 4K Hz (driving JBL 2445 w/ 2382a horns)
4K Hz and above (driving JBL 2404)

My question is which amp is best for which frequency range. My collection consists of:
Threshold 4000
Threshold 400a
Forte Model 3
Hafler 500 with Musical Concept upgrade from 1987
Hafler P500
BGW 250D
Hafler 220
Yamaha M-4

All speaker enclosures were designed using BassBox 6 Pro. Although I'm sure as I get back into this, some of the electronics will change, all of the speakers are built into the room. I can't see myself changing these.
The active crossovers are Rane AC23. I have a Yamaha CX-A5000 preamp I will be using for the surround sound but also have a PS Audio 4. I'm going to start with the Yamaha and maybe compare to the PS 4.

For now I'll leave out the details of the center, side and back surround setups as those will only be used when the family is watching movies (JBL drivers and Sansui intigrated amps from the 1980's)

Any thoughts?




Thanks,
Eric M.

[G Georgopoulos]

My question is which amp is best for which frequency range. My collection consists of:
Threshold 4000
Threshold 400a
Forte Model 3
Hafler 500 with Musical Concept upgrade from 1987
Hafler P500
BGW 250D
Hafler 220
Yamaha M-4


Any thoughts?




Thanks,
Eric M.

Hi Eric

what i would do is select the more powerful amplifiers with the lower frequency speakers
these have lower Zout and are perfect for high power (low freq)

cheers...

[SteveFord]

I can't be of much help but I know my Hafler has pretty good low end.
Can you hook the amps up to a full range speaker and see how each one sounds? 
George has the right idea, too, about power.

[Eric M.]

That may be a good idea. I can run each amp to the side speakers (4 ways w/ passive crossovers) and judge which reproduces what range best.

Thanks,

Eric

[Johnny2Bad]

Am familiar with most of your gear; my recommendation is based on Sound Quality. Use the Thresholds and the Forte for the upper three frequencies, the Forte on the highest. Use the most powerful remaining amps for the lower two frequencies; I would try the BGW for the lowest frequency and see how that sounds; if it lights the clipping indicators then move it to the second lowest but no higher. The Hafler P500 might work well in the lowest frequency in that case.

The Thresholds will probably never move out of Class A, should sound pretty sweet.

The BGW, if you don't like it on the bottom end, is expendable. Try the Yamaha in the 2nd lowest or another Hafler. Sell what you don't use.

You might want to invest in a variac and slowly increase the power (5 minutes, then up about 20V, 5 more minutes, etc), if these amps have not been powered up for years (goes between the wall socket and the amp's power cord; allows you to start at almost 0V and adjust until you are at the full 120V). Wear eye protection; remove the plug from the wall socket when it's not in use.

This unit will work fine, since you won't actually be driving the amp with a music signal:

http://www.amazon.com/Variac-Variable-Transformer-300va-Output/dp/B006NGI8VS/ref=sr_1_1?ie=UTF8&qid=1431361925&sr=8-1&keywords=variac

You want to slowly form the power supply capacitors; they degrade with age and un-use. After you've powered each amp via the Variac, plug it into the wall for 24 hours. It should then be ready to install into the system.

If for some reason you decide not to use the Threshold 400a and want to sell it, PM me!

[Eric M.]

I like the idea of the class A amps on top, but considering the Yamaha is only 80 watts a side and the BGW 250 is 125 watts, I'd be building my system upside down with the smaller amps driving the bass. Maybe I put the 2 Hafler 500s at sub and low, the Threshold 4000 at Mid and the Forte 3 and Threshold 400a at the top(not sure which should be where)

Thanks,

Eric

(Don't hold your breath for the Threshold 400a!)

[Johnny2Bad]

I like the idea of the class A amps on top, but considering the Yamaha is only 80 watts a side and the BGW 250 is 125 watts, I'd be building my system upside down with the smaller amps driving the bass. Maybe I put the 2 Hafler 500s at sub and low, the Threshold 4000 at Mid and the Forte 3 and Threshold 400a at the top(not sure which should be where)

Thanks,

Eric

(Don't hold your breath for the Threshold 400a!)

I suspect that Hafler/Hafler/Threshold/Threshold/Forte is probably your best bet.

But you have more amps than you actually need, so there's value in trying out what you have before you decide to sell which. Your JBL drivers are all very efficient, which is why 80 or 120 watts in the lowest position might still work fine, and I would be very surprised if 80 watts was not enough in the second-to-lowest position.

So you owe it to yourself to try them and see what sounds best to you.

The thing is you have quite a few vintage amps, and broadly speaking the newer the amp design, the more likely that the top end is done right. So that's why I suggested that the Forte3 might work best on the highest registers.

[Eric M.]

Good point.
I think I'll start with that arrangement and then try a few other options based on what I'm hearing.

Thanks

[MaxCast]

Hi Eric, be sure to post some pics when done.  I'd love to see it.

[RDavidson]

I'd definitely run the Forte and/or Thresholds from the low mids through the highs as was suggested earlier and arrange them per your preference as I'm sure they each have differing qualities. They'll likely stay in Class A the whole time which = lowest distortion. So you'll have the lowest distortion sounds being produced in the range of human hearing that we're most sensitive to.

[Eric M.]

Hi Eric, be sure to post some pics when done.  I'd love to see it.

I will. Carpet is going in tomorrow. After that I can start moving in the equipment.

Eric