Bi-Amping Altec Lansing Model 14 with Driverack PA2 - Project and Questions

[Sam08861]

I've decided to give this a try, follow the example here, although with different amps. Don't have much experience in speaker building, bi-amping or using crossovers, so have some newbie questions.

https://www.audiophilenirvana.com/a...ws/altec-lansing-model-14-part-4-ultimate-14/

Components I'll be using:

Technics SU-9070 Preamp (and source selector/phono stage) (+ RTR, CD, Streaming and Turntable as sources)
Luxman R-115 (amp section only to drive L/R Horns - Highs)
Luxman R-117 (amp section only to drive L/R Woofers - Mids)
Velodyne Optimum 8 Sub (Powered servo sub - Lows)

As far as parts needed to accomplish this:

2 47uf 250V Dayton Polypropylene Capacitors (to be place inline with the horns)
8 binding posts (existing posts will stay in place, but be disconnected, along with the internal crossovers)
6 XLR Female to RCA Male Cables (Output L/R Pairs for H/M/L, 3',3' and 10')
1 XLR Male/Female Cable (for RTA Mic)
2 XLR Male to RCA Male Cables (Preamp, being used as a source selector to Crossover)

In addition, for the Active Crossover, I've obtained a Driverack PA2 and RTA microphone.

Costs are as follows: Binding Posts and Caps ~$70USD (tell me about it)
XLR Cables (16 GA Monoprice premium, ~$60)
Driverack PA2 & Microphone (Used, but never used) ~$370 shipped
----for a total of----> $500

This will take about 3-4 hours for me, since i'm OCD and cautious, to do the following:

1. Remove Woofers, Horn, Crossovers and all internal Wiring
2. Tap in High and Mid Binding Post Pairs (parts express)
3. Solder Wire to Binding Posts, Solder and strap down Capacitors and add spade connectors for speakers
4. Reinstall Woofers, Horn and Crossover with new High and Low Connectors
5. Run Cabling from Preamp to Crossover
6. Run Cabling from Crossover to amps and powered subwoofer
7. Run Speaker wire from Amps to H/M/L Drivers as appropriate
8. Configure and Dial in the PA2.

Some questions:

1. I am assuming the Technics SU-70 is at -10db output, being a consumer model? (as opposed to pro/PA gear, which is at +4db) Just making sure since it's rack mounted and marketed as 'professional'

Specs are here and I can't quite make out how to figure this out... https://www.hifiengine.com/manual_library/technics/su-9070.shtml

2. In looking at the Driverack PA2, it has a facility to limit the output to the amplifiers and is in dBu units. Any suggestions on how to determine the max dBu at the inputs for each of the 3 amplifiers?

(as the 2 receivers do not have gain controls and clipping indicators as a professional amplifier would, I cannot use the procedure outlined in the setup procedure.

The sub has a gain control, but no clipping indicator)

The Driverack can output up to +20db. From reading I am thinking to set the threshold at -16db with a soft knee as a starting point?

Any suggestions on how the various amplifiers' input thresholds can be determined? Is there a suggested maximum dBu for consumer line level inputs I could use as a safe starting point? Can the gain be calculated from published specifications?

Will be glad to post the published specifications and reviews of the 3 amps in questions.

3. Assuming the capacitor should be place in line between the + input of the horn and the + binding post? (or does this matter since polarity is always reversing to move the voice coils?, or does this need to bridge the input terminals?)

The remainder of the setup seems straightforward so far, but I am hoping to figure these things out.

So far, I've received the PA2 unit and RTA Microphone and had on hand already the XLR cables to run from the preamp to the crossover. Binding Posts/Caps should be here Saturday and the remaining XLR cables next Wednesday.

Will post the how to pics and thoughts on if this ends up being worthwhile if anyone's interested.

Save 4 1/4" holes for the binding posts, all else will be modified in a way as to be completely reversible. The binding posts I am thinking to mount on the bottom as well to keep the veneered surface intact. (since these speakers are veneered everywhere except the bottom and the small strip of Altec's special MDF between the horn and woofer boxes. (and insides, of course!)

 

[bowtie427ss]

2 47uf 250V Dayton Polypropylene Capacitors (to be place inline with the horns)

Why?

As high as the crossover point is on 14's, i'd choose a safety cap value that would give a knee point about a half octave below XO.

At 47uF that gives a knee point of around 425hz, it will do very little in the way of protecting the HF driver as the signal will get well into the bass range at only 12 db of attenuation.

 

[Sam08861]

Unfortunately, I cannot say. Not knowing much about audio electronics or design, I'm somewhat blindly following the recommendations in the article, which specified this cap.

Perhaps I've interpreted them incorrectly?

---
We began by ordering more Dayton Audio BPP-G Premium Binding Posts, a pair of Dayton Audio DBPP-BK Double Binding Post Plates, and a couple of 47uF capacitors from Parts Express to allow for bi-amplifying the speakers. The original crossovers were completely disconnected. The new capacitors were placed in-line with the wiring to the Mantaray horn to protect from potential DC offset from direct coupled amplifiers.
---

 

[Zonker92]

The original article cited those 47s as a means of blocking any stray DC voltage.

Following...

 

[bowtie427ss]

Perhaps I've interpreted them incorrectly?

No. It was a bad assumption on my part. I assumed the purpose was to protect the HF drivers from an improperly set network accidentally sending lower than intended frequencies to them.

47uF would be very good for DC protection as their effect will be totally below the HF pass band.

However, if i were using an amplifier that is known for, or likely to output harmful levels of DC i would probably take a different course for a means of protection.

 

[toddalin]

Actually, it is more than dc voltage that the caps can protect.

BION sheet happens and in a bi-/tri-amp setup it is possible that the input plug to the HF amp, after the crossover, can come out. And, if the hot lead on this plug is subsequently touched..., HMMMM right though the horn at full volume. BTDT, luckily without harm.

 

[Sam08861]

Thank all, learning as we go.

Is my assumption to place the cap somewhere between the + binding post on the cabinet and the + tab on the horn's compression driver correct?

 

[Sam08861]

Also, thinking that -16db threshold for all of the amps should be a good safe starting point with enough headroom? I'm not a crank it up all the way kind of guy and the size of the room would make it a painful experience anyway, if I did.

(threshold would limit the output of the crossover into the amps inputs)

For more information, the speakers with crossover in place are rate for 75 watts @8 ohms and 250 watts with speaker protection circuit in the crossover. Since this will all be out of circuit, I'm not sure what the individual 'capacities' are for the drivers.

The sub has it's own amp (1200w)
The low amp is rated at 160w continous @8ohm
The mid amp is rated at 70w " "
The low/mid receivers apparently have a lot of 'dynamic headroom'

So I'm not worried about clipping but am worried about sending too much power, if that's a possibility?

 

[62caddy]

10 watts per channel applied to a pair of Model 14s would have me running out of the room.

I would think your hearing is more likely to become damaged long before the speakers are overdriven.

 

[Sam08861]

62 caddy, I agree completely. The 14s behave a bit like PA speakers that way and are one of the few speakers I’ve found that sound good in the outdoors. I’ve had then out on my deck and they easily powered past 50 loud drunk folks. (Including me)

My bigger concern was a guest when might turn the Sys on with the volume cranked for some reason.

As an aside, Interestingly, there’s no on off switch on the PA2 crossover.

 

[damacman]

62 caddy, I agree completely. The 14s behave a bit like PA speakers that way and are one of the few speakers I’ve found that sound good in the outdoors. I’ve had then out on my deck and they easily powered past 50 loud drunk folks. (Including me)

My bigger concern was a guest when might turn the Sys on with the volume cranked for some reason.

As an aside, Interestingly, there’s no on off switch on the PA2 crossover.

I used mine for my backyard pool parties numerous times - MC2300 driving them at 80Hz and up with a Crown MT2400 driving (16) subwoofers ...

 

[Sam08861]

Binding Posts and Caps arrived Saturday, but I spent my time an money not catching fish and having beers outdoors.

Here are they are. Caps are about the size of D batteries for scale.



First removed the horn, crossover and woofer.





Drilled Holes on the bottom, inboard of the existing binding posts. I have stands I made, so will use a hole saw in the stand base, where the binding posts will be installed.



Posts hammered in. (and correction to 1st post, these are even veneered on the bottom and partially on the inside.)



And threaded ends screwed back on. The posts on the left of the picture will be for the woofer, and the ones on the right will be for the tweeter.



Made up the internal wiring, soldering binding post tabs to 14 ga speaker wire. Shorter pair are woofers. Made each set about 1 foot longer than I needed to make them easier to reassemble. Hate it when speaker leads have to be disconnected/connected without any wiggle room. I know that's a longer path, but convenience wins over performance for me in this case. Will have to make sure they don't interfere with the woofer excursion.

Copper colored side is + in all cases. Red + on tab side and used yellow for negative on tweeter (like tweety) so I can tell them apart in the cabinet. Crimped then soldered to ensure good connections.



Spliced in capacitors on tweeter positive leads. Hooked, soldered then heat shrinked.



Next step will be to connect the leads and reassamble the 1st speaker and then breakdown the 2nd speaker, drill holes, tap in posts, connect wires and reassemble. Should go much quicker now that I have the leads all made up.

Also, need to figure out where and how to mount the caps so they don't interfere with the horn fitment. Thinking to use double sided 3m silicon tape to mount them onto the horn itself, to be strong yet reversible and also keep them from vibrating. Will also have to zip tie the crossover cables so they don't interfere and are safely out of the way. Thinking to also cover the crossover boards/cables with a pair of socks, to prevent any accidental electrical contact.

Open to all critique and suggestions. XLR cable are due to arrive tomorrow or Wed, so can start the setup then.

Thanks,

Sam

 

[Sam08861]

A few zip ties gets the (now truly passive, lol) crossover under control. No need for the socks, lol.

 

[toddalin]

Hot glue works well to mount the caps/stuff and is easy to remove.

 

[Sam08861]

Posts from inside.. Order (outside to inside) is washer, nut, solder tab, washer, nut. Use a 10mm deep socket and try and contact the fiberglass matting as little as possible, unless you like that kind of itch.



Mounted Cap:



Test fitting stand and labels to keep me out of trouble...



Finished right speaker on stand.

 

[Sam08861]

Just dawned on me I'll need to make up another pair of speaker wires, lol. Will edit the 1st post, if possible.

 

[Zonker92]

Good fun and write-up! Please keep updating it; I'm fascinated.

 

[Sam08861]

Thanks Zonker92,

Cables have arrived.



Large 15' is for the RTA microphone.
Remaining 2' are from PA2 crossover to the 2 receivers. (high and mid outs on the pa2)
10' Items are to the subwoofer. (low out on the pa2)
The open item were XLR to RCA that I already had on hand and will go from the preamp into the PA2

Close of up of the monoprice cable ends.



Good news: since I previously ran the sub from the 117s B channel, I don't need to make another set as these can be used for the horns and the old existing ones to the woofers in the Altec. The sub will receive it's input via RCA from the PA2s low l/r outputs.

Not so good news: The 115 doesn't have an amp in like the 117, so will be fed either through the pre-processer in or the CD direct in, whichever has a more direct path to the amp section. I suspected this, but got too lazy to check! Not too worried as tone defeat option is there too.

Re-arranging the "rack" and cleaning up the dust while I'm at it.



Now the fun part begins... running all those interconnects and speaker wires!

I must say the XLRs are a pleasure to connect. Wish the amps and pre all had balanced connectors, as it's an incredibly satisfying and positive engagement! I also like the slap of an SLR mirror or the fake click on my phone's camera, so am weird like that, lol.

 

[Sam08861]

Looks like on the Luxman R-115 CD straight is a more direct path and with tone defeat only passes through the loudness control and volume control. Loudness I can turn off, will have to figure out what to do with the volume knob. I can use this as a gain knob, I think and dial in using the PA2s wizard.

Now to make the connections...

 

[Sam08861]

All hooked up except at the Altec speaker terminals. Lots of Zip ties are in order here to clean up the rats nest.



Thinking I'm going to get one of those 8 outlet Furhman power conditioners from CL to complete 'rack' since the PA2 doesn't have an on/off switch and my plastic power strip feels like a fire waiting to happen.

From the front, I tried to put the heaviest item on bottom (r-117) and the PA2/Pre together and in between the 2 amps to minimize interconnect lengths.



Going to take a pause here until I get the skinny on the -10/+4db and pin 1 lift questions and how to best deal with the r-115. Have an email into Harman support, so will see what I hear back. Might try some of the pro-sound forums also.

Once these questions are answered, I'm 10-15 minutes away from a 1st listen. Cautious but excited!

Welcome any input/suggestions from the members here.