LE15A/375/075 Box Design

[Val]

I have been wanting to tri-amp these speakers for a long time but have never been able to scrape together enough mad-money to buy 6 channels of amplification and an active crossover. A few weeks ago I picked up a non-operational Marantz SR7400 AVR at a garage sale for $20 including 5 working ProCinema speakers. I was able to repair the AVR and I noticed that it had something called 7.1 Mode which accepts output of an external 7.1 multichannel decoder. After looking at the manual and doing a few tests I now realize that when in 7.1 mode I basically have 7 channels of 105 watt/ 0.08% THD amplification into 8 ohms. Once a volume level is set in 7.1 mode, the AVR "remembers" the volume and mode even after the AVR is unplugged for several hours. So my thought would be to run this in 7.1 mode and plug it into switched power.

Now I'm trying to think of what can go wrong with using the AVR as my 6 channels for tri-amplification. Clearly, if the AVR gets flipped to any non-7.1 mode where signal is present, my tweeter and mid-range could blow. I'm thinking that I need to install shorting RCA plugs in all inputs and short across both FM antenna inputs. That way, if somehow if gets into a non-7.1 mode it will not have any signal to amplify and blow my speakers. What else could go wrong?

As for an active crossover, I'm thinking of an Ashly XR4001 - 4 way stereo active crossover. I like the XR4001 as I have the option of running my sub in addition to the LE15A/375/075, and one pair of channels can go beyond the 8kHz limit of the other models (it goes to 24kHz). The down side it that these are no longer in production and so I will need to buy a used one. My backup plan would be two XR1001s. Thoughts?

[Val]

I have been wanting to tri-amp these speakers for a long time but ...

...life happened...Father, I have sinned, my last post was 8 months ago...

I've collected my active crossover (Ashly XR-4001) and amps (JBL 6320 for the LE15A and Emotiva UPA-500 for the 375 and 075). I'm building cables and a guard to keep busy fingers off of knobs. I've put together a diagram because I'm stuck in a hotel room on a business trip. As always, open to input...

[Mr. Widget]

A couple of thoughts...

That's not a lot of power on the LE15As, but if you aren't into loud, that won't be s problem. What horn do you have for the 375s? Even though vintage JBLs frequently used this frequency, very few horns will pull this off if you don't want the squawky-honky sort of midrange common to vintage systems.


Widget

[grumpy]

I'd be tempted to also try it the other way... don't use the lowest filter band
unless you bring in subs, leaving the tweeter high end unfiltered and using
the 'response' knob to get into the 40's as much as possible. Not a huge
effort to try it both ways and your personal preference and listening may
nudge you back to your original idea. Just a thought.

May be possible to modify the unit's lowest crossover range to use a "divide by 20"
rather than by 10 (20-400Hz), but that would require a schematic and some EE know-how.
Seems like someone here may have done that on this or a similar unit.

[Val]

That's not a lot of power on the LE15As, but if you aren't into loud, that won't be s problem.

You have a point with the 6230 as it's only rated at 75watts. I got is for a song and may end up swapping it out.

What horn do you have for the 375s? Even though vintage JBLs frequently used this frequency, very few horns will pull this off if you don't want the squawky-honky sort of midrange common to vintage systems.

I'm pretty sure my components were bought in the mid-1970's as a S8 Component Series so the horns are HL93's and the slant plate diffusers are L91's. I totally have the squawky-honky issue you mention. Once I have the tri-amping in place I plan to move up the crossover as much as the LE15A will go...which sadly is likely not very much. Would replacing the HL93 with a smith horn help with the squawky-honky issue?

[Val]

I'd be tempted to also try it the other way... don't use the lowest filter band
unless you bring in subs, leaving the tweeter high end unfiltered and using
the 'response' knob to get into the 40's as much as possible. Not a huge
effort to try it both ways and your personal preference and listening may
nudge you back to your original idea. Just a thought.

May be possible to modify the unit's lowest crossover range to use a "divide by 20"
rather than by 10 (20-400Hz), but that would require a schematic and some EE know-how.
Seems like someone here may have done that on this or a similar unit.

I've wanted to do just as you say as the highest band let's you crossover up to 24k. There is a bit of harshness in the 075 that I would like to address. The other bands max at 8k. I had not thought about a hardware hack. With the stock XR-4001 if I use the upper bands then I would be rolling off the LE15A at 40 hz. I do have my 2245H sub down there though.

[Mr. Widget]

I totally have the squawky-honky issue you mention. Once I have the tri-amping in place I plan to move up the crossover as much as the LE15A will go...which sadly is likely not very much. Would replacing the HL93 with a smith horn help with the squawky-honky issue?

You can go to 800Hz and use the JBL 2397 horns and you will hear a marked improvement. Be aware of the fact that the 2397 has a very wide horizontal pattern so side reflections should be controlled for the best performance.

As to Grumpy's suggestion... if you plan on going with your 2245 sub then a 40-80Hz crossover between the LE15As and sub should be fine.


Widget

BTW: I see you are in Palo Alto... if you want to borrow a pair of 2397s, mine are not currently in use.

[ivica]

You have a point with the 6230 as it's only rated at 75watts. I got is for a song and may end up swapping it out.



I'm pretty sure my components were bought in the mid-1970's as a S8 Component Series so the horns are HL93's and the slant plate diffusers are L91's. I totally have the squawky-honky issue you mention. Once I have the tri-amping in place I plan to move up the crossover as much as the LE15A will go...which sadly is likely not very much. Would replacing the HL93 with a smith horn help with the squawky-honky issue?

Hi Val,

I have 2231A & 2441&(with Radian 1245-16) & 2311 & 2308 and 2405 what would be almost equivalent with
136A + 375 + HL93 with "slat plate diffusers" +077 (075), using cut-off frequencies about 800Hz, and 8kHz sounding quite acceptable.
It seems to me that bass section has to be stopped about 600~700Hz, while VHF section has to start from about 800~1000 Hz.
Owing to the relatively short horn ( about 11cm) and internal-driver horn (about 7cm) honky effect is not so 'pronounced', or better to say much, much less then on 2312/2307&2420 combo.

regards
ivica

[Val]

You can go to 800Hz and use the JBL 2397 horns and you will hear a marked improvement. Be aware of the fact that the 2397 has a very wide horizontal pattern so side reflections should be controlled for the best performance.

As to Grumpy's suggestion... if you plan on going with your 2245 sub then a 40-80Hz crossover between the LE15As and sub should be fine.


Widget

BTW: I see you are in Palo Alto... if you want to borrow a pair of 2397s, mine are not currently in use.

So cool that the 2397's can improve my situation. I would love to borrow your 2397's when the time comes, very generous, thanks.

[Val]

Hi Val,

I have 2231A & 2441&(with Radian 1245-16) & 2311 & 2308 and 2405 what would be almost equivalent with
136A + 375 + HL93 with "slat plate diffusers" +077 (075), using cut-off frequencies about 800Hz, and 8kHz sounding quite acceptable.
It seems to me that bass section has to be stopped about 600~700Hz, while VHF section has to start from about 800~1000 Hz.
Owing to the relatively short horn ( about 11cm) and internal-driver horn (about 7cm) honky effect is not so 'pronounced', or better to say much, much less then on 2312/2307&2420 combo.

regards
ivica

You are right, there are similarities between our component sets with a few notable differences. I think the 2231A rolls off around 2k and the LE15A under 1 kHz and the 2405 is a much better tweeter than the 075. I like my old LE15A's and 075's but the 2231 and 2405's are better drivers.

[Val]

Forgive me if this is off topic, but, I fear sticky fingers turning knobs. So, I decided to make a locking cover for the bottom portion of my DIY equipment rack. I bought some "Union Jack" design decorative metal from Amazon and a skeleton key lock (the family is very excited to have a skeleton key lock in the house). I knocked together a frame and now can lock my tri-amp gear.

Next up on tri-amping...finish making cables!

[grumpy]

Looks nice. Prudent idea

[Val]

The slowest tri-amp project continues.

Awhile back I bought a Smart Strip to control the power for my crossover and amps. The idea is that is senses power draw on the control plug (I plugged in my AVR) and it turns on the amps and such. Turn on the AVR, all the amps go on. Great idea. Even has a sensitivity control. I could only get it to work some of the time. So it falls into the "don't waste your money" category.

I ended up buying a solid state relay and some parts and made my own 12v triggered power. One plug is always hot, one is triggered by my AVR's 12v. Now it works every time. The SSR was only 12 bucks for 25A. Came with a big heat sink. Who doesn't like heat sinks? Anyway, it was a fun sub-project. About $25 in parts. You can't see it in the pics but there is a 3.5mm plug for the 12v trigger input just under the power cable.

[ivica]

The slowest tri-amp project continues.

Awhile back I bought a Smart Strip to control the power for my crossover and amps. The idea is that is senses power draw on the control plug (I plugged in my AVR) and it turns on the amps and such. Turn on the AVR, all the amps go on. Great idea. Even has a sensitivity control. I could only get it to work some of the time. So it falls into the "don't waste your money" category.

I ended up buying a solid state relay and some parts and made my own 12v triggered power. One plug is always hot, one is triggered by my AVR's 12v. Now it works every time. The SSR was only 12 bucks for 25A. Came with a big heat sink. Who doesn't like heat sinks? Anyway, it was a fun sub-project. About $25 in parts. You can't see it in the pics but there is a 3.5mm plug for the 12v trigger input just under the power cable.

Hi Val,

Why not to use standard (electro-mechanical) relays, that can be controlled by 12V or 24V or.... supply.

regards
ivica

[Val]

Hi Val,

Why not to use standard (electro-mechanical) relays, that can be controlled by 12V or 24V or.... supply.

regards
ivica

I actually started with looking at those and they would work fine. The SSR was only $12, is silent and didn't require a cap for emf suppression.