605-ALTEC N-1600-C Crossover help!!

Hi to all,

i have a pair of 605a altec speaker with the n-1600-c crossover.

The problem is that someone "modified" the crossover by taken out the hf-attenuator.

So what i have in the crossoverbox is a 12db slope (1mh+20uf) for the woofer and a 6db slope (5ohm+5,3uf+4ohm) for the tweeter.

Do have someone the original schematic or can advice me to complete the hf section?

Or,what crossover do you use with your 605?

Thank you very much,
frank

Hi Frank

I don't have the schematics you seek ( I see you tried Todds' Altec Site ) - but maybe with a bit more info from you - your concerns can be addressed here. So , in that spirit ;

(1) What sonically bothers you about using your modified crossover ?

(2) Are you simply seeking an "L-pad" / attenuator control wired into the circuit so that you can determine & adjust for yourself the balance between horn and woofer ?


(3) Are you getting too much, +/or enough of the top upper octave with the present crossover design ?


(4) Are you handy with a soldering iron ?

(5) Do you have a multimeter than can measure the DCR ( resistance ) of that compression driver ?

(6) Do you have access to DIY speaker parts wherever you are ?

(7) What types of music do you mostly listen to ?

regards <> Earl K

Hi Earl,

thanks for your reply!

Here are the answers.


(1) What sonically bothers you about using your modified crossover ?

Too much high frequency and no magic in the mids

(2) Are you simply seeking an "L-pad" / attenuator control wired into the circuit so that you can determine & adjust for yourself the balance between horn and woofer ?

This would be a solution


(3) Are you getting too much, +/or enough of the top upper octave with the present crossover design ?

I think too much


(4) Are you handy with a soldering iron ?

Thats no problem

(5) Do you have a multimeter than can measure the DCR ( resistance ) of that compression driver ?

Yes,the compression drivers have 10,5ohm

(6) Do you have access to DIY speaker parts wherever you are ?

Here in Germany it is easy to get speaker parts in all qualities.

(7) What types of music do you mostly listen to ?

I mostly hear newer jazz and worldmusic and my girlfriend is listening to classic music.


I have seen the mastering labs crossover schematics but i am not really sure if its work for the 605 because its designed for the 8ohm 604.

Diy would be no problem.

THanks again

frank



regards <> Earl K

Hi Frank

Here's a jpg ( screen-shot of my software ) that shows the values one would use for a 1600 hz crossover point for perfectly well-behaved components. The values given are obviously quite different from what you find in your crossover. I'm sure the original crossover values have been derived empirically through observation and therefore closely complement the real electrical needs of the transducers' Response Curves and AC ( motional ) Impedance Signatures

This jpg is just for reference to show the futility of designing crossovers from simplistic formulas.

regards <> Earl K

Hi Frank,

Here is another jpg showing the AC ( Motional ) Impedance Values that would "agree" with the 1st Pole ( or element ) position for each of the High Pass & Low Pass sections of your crossover .

These could in fact be the AC impedance values ( as measured around 1600 hz ). I never know - because I don't actually have your components to measure .

NOTE:
(a) The second element ( C2 ) in the low pass leg doesn't agree with what you have.. More on that next installment .

(b) You need an L2 - we'll eventually get to that .

regards <> Earl K

Hi Frank

This jpg shows a ( guessed at ) new lowpass point that would specifically agree with that one C2 value that you find in your crossover. As you can see the #2 element in the lowpass leg starts its reactive duties about an octave below your idealized 1600 hz crossover point .

Is this 20 ohm value a mistake ? I don't know without actually plotting a mid-band response curve.
It's more likely original and meant to "flatten" a rising midband response anomaly / . Substituting in a 10 uf capacitor would tell you quickly ( if you have any RTA capabilty ) & if you saw/hear the 800 to 1600 area "spike" up.

regards <. Earl K

Hi Earl,

thank you so much for your work!!

I received an other schematic from an altec crossover and recognized that it was a series crossover.

I opened my N-1600-C again and made a schematic-it was a series crossover too.

The part are original but someone put the hf-attenuator out.

What is missing?

Best wishes ,

frank

Hi Frank

Well here's what I think your crossover does based on your latest info.
( I would love to actually measure those components - that way I might really have a clue as to what's needed ! )

I seems the circuit design is qute a hybrid. Most of it is acting in a series crossover topology . But that single 5.3 uf capacitor isn't part of the series circuit. It's acting in the "normal" manner as a high-pass filter. It's actual turnover frequency is likely in the 1600 hz area - but I need to know more about the AC impedance curve of the compression driver to really "know" that .

The 5 ohm resistor "pads" the driver a little bit but obviously not nearly enough. Together with 16 ohm value ( just guessing ) of your compression driver in the crossover area they form the 21 ohms that my little Crossover Calculator used as the working impedance for the HF section .

The 15 ohms for the woofer vale at the crossover frequency is just a "convenient" guess for the calculators sake .

Here's a jpg of your circuit as I understand it .

regards <> Earl K

Hi Frank

Here's what I believe is a workable solution.

Remove that 5 ohm resistor and wire in one 8 ohm Lpad into it's place - placed ( according to my included jpg). I've never wired a Lpad into a series crossover circuit before so I spent sometime this afternoon checking out where that Ground/ Drain-Wire works best. Wire it in as I have shown on the jpeg. If you are tempted to attach the ground/drain, say to the standard ground side of the circuit ( as I was ), it does quite bizarre things . Everything is fine " full-up" but as you attenute or turndown the tweeter - the "self-balancing" nature of this circuit type rises up and bites one in the proverbial behind: :biting:
- Frequencies below the HF cutoff are actually significantly BOOSTED into the compression driver at full Lpad attenuation. :no: :scold:
This would of course, drastically shorten the lifespan of the diaphragm and it really thows the spectral balance out of whack when the Lpad is used in the middle of it's rotation area .
The position I've shown gives stable attenuation without moving the crossover point ( blasted self-balancing circuits !)

If it was my compresson driver - I'd play around with the value of that 5.3 uf capacitor. Making it smaller has the "realized" effect of slowing a drivers topend roll-off by starting its' highpassing action at a higher frequency. I'd play around with values between 3 uf to the stock 5.3 uf value . Because this alters the balance of "Midrange to HF" frequencies you would have to do this ( if at all ) to suit your own particular musical tastes .

Here's the jpg

If anyone out there sees a "train-wreck" occuring here, please speak up.
( Afterall - I electronically crossover everything - so what do I really KNOW ? ) :yes:

regards <>Earl K :)

Hi Earl,

thank you again for your very helpful information!!

I think i try your second circuit with the l-pad!

I will play around with the value of that 5,3uf capacitor too.

If your crossover simulator has a database-I think the 605 is a 416 woofer and a 806 tweeter.

For your interest i attached a received schematic from an altec N-1500 crossover-do you think i can use the attenuator part (15ohm+25ohm adjustable)with my tweeter?
(Have no l-pad handy,but can buy it on weekend)

Best wishes from germany,

frank

Hi Frank

Quote:

---

do you think i can use the attenuator part (15ohm+25ohm adjustable)with my tweeter?

---

Yes, those values will work just fine. You might see if you can find a 30 ohm Lpad instead of the 25 ohm . I ran motional impedance checks this afternoon on my series circuit setup and found the Lpad didn't register a measurable change when either "wired in or out" of the circuit . My setup was a 16 ohm Lpad along with an 8 ohm shunt resistor, using the same ratios as the N1500 pic. - but with 8 ohm drivers and appropriate LC combinatons.
- This also means those pics that I posted earlier with greater than 16 ohm values are now really just bunk.

It seems the value of the Lpad doesn't effect the crossover circuit operation much at all.
The added 15 ohm shunt resistor likely offers the crossover region a little better dampening. This is likely very important when the LC ratio ( or damping factor) becomes very low .

When using an Lpad that's TWICE (ie; 25 to 30 ohms ) the value of the AC impedance of the driver (15 to 16 ohms at the crossover area ) with a 15 ohm resistor wired into the shunt wire, one gets 10 to 11 db of maximum attenuation( from the Lpad.) Meaning - you can never completely turn the compresson driver "off" when that shunt resistor is wired in place. I measured this 11 db range on my circuit mockup this afternoon ( after looking at that N1500 circuit you posted). The 5.3 uf capacitor adds a sliver more attenuation when put into the high pass portion of the circuit.

So , in total there's about 12 db of available attenuation from the Lpad. That's a reasonable range when blending a compression driver with a high effiency woofer . If that range isn't great enough then simply swapping out the shunt resistor ( presently equaling the impedance of the driver ) for a smaller value - will allow a greater amount of attenuaton from the LPad. The Lpad will also work fine without any shunt resistor - but I imagine that the resistor offers some extra damping in the crossover region. With no shunt resistor , there's a bit of energy "blow-back" from the crossover frequency region that's never completely attenuated. The amount of this blow-back energy is proportional to the damping factor ( or LC ratio ) used in the initial design stage. I discovered this when I purposely compromised the LC ratios ( damping factor )

That 5.3 uf high pass capacitor offers some opportunities for highpass slope tailoring. By having two caps provide the capacitance choices one could make create 2 or 3 different highpass slopes. The slope would depend on the value of the cap chosen. Wiring up an appropriate swith that offers the choice of one value or the other or both in parallel might be a worthwhile feature.

Let me know how this works out for you.

regards <> Earl K



ps - Here's a pic of the N1600 with more appropriate "guesstimated" values. ( I left out the rest of your circuit because a case of ADD just kicked in.)
(Okay - ADD attack is now over ,,,, see posting below for a more accurate pic )

Hi Frank

Here's a more accurate representation of what I believe that crossover is all
about.

- As you can see, my software believes the circuit is slightly underdamped.
( I wouldn't know without actually listening to the whole setup. )

- I'd speculate the consequences of that judgement - would be that this circuit will be somewhat sensitive to amplifier selection, as well as, enclosure sizes.

regards <> Earl K

Hi Earl,

Quote:

---

As you can see, my software believes the circuit is slightly underdamped.

---

what can i do to correct it?

(Sorry i know only a little bit about crossover)

Best wishes,

frank

Hi Frank

My suggestion;

Purchase the necessary Lpads and Resistors, intall them , and take a listen. If your amplifier has a good damping factor or if your enclosure size isn't on the "too large" size then this crossover with its' slightly low Zeta factor will probably sound just fine.

If it doesn't ( say the bass is electrically boomy and uncontrolled as opposed to the acoustic space ) then the cheapest thing to do is wire up another crossover with a higher damping factor . Then take another listen. If things are still on the wild and uncontrolled side then you have more expensive fixes looming into your future. Ie; an amplifier that suits this system more and/or - a different enclosure size with a different tuning ( if its a reflex style ). ( What is your enclosure and what is its' size and tuning ? )

- The software calculator defaults to .707 damping factor when it's opened up. I'll post another drawing ( for .707 ) with new LC values tomorrow. That way you'll have a reference to use when shopping for parts.

- The LC values from that N1500 crossover drawing that you posted, give it a damping factor of .65 ( if I remember right ).
Someone must of thought it important to raise that value - maybe it was a redesign.

- If the woofer in your 605 was actually a 515 magnet assembly ( and not a 416 type ) then I'd say not to worry about this crossovers Zeta factor. The deep gap / short coil of the604 / 515 offers a lot of inherent motional control ( damping ) . That's why the 604 can get away with being thrown into overly large boxes ( compared to what the software suggests ).

- Please take a measurement for me of the 806 driver portion of your 605 . The measurement needed is from the bottom ( or top ) of the silver top-plate - down to where the 806 driver is joined to the woofers magnet. Millimetres are just fine. Thanks !

regards <. Earl K

Hi Frank

Here's the pic as promised with a damping factor of .707 . This is what the software defaults to when opened up. The suggested LC values appear in the picture.

regards <> Earl K

Hi Earl,

i take your advice and purchase the components tomorrow and then take a listen.

I think my amp (3w single ended 6B4G without feedback))is very sensitiv with the original crossover.

Maybe i need an other design.

You asked me about a measurement of the 806 tweeter-it is yet not possible for me but maybe in a month.A guy which i know has a proffesional measurement system,but he is very busy now .
When he take the measurement i will post it.

Best wishes,

frank

Frank,

Have you heard about the special 604 crossover designed by Doug Sax of Sheffield Labs. It meant to improve the 604/605 performance?

Ian