Passive Crossover bypass – Quest / reQuest

MartinLogan Audio Owners Forum

Help Support MartinLogan Audio Owners Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

JonFo

Super Moderator
Staff member
Moderator
Joined
Jan 16, 2005
Messages
4,916
Reaction score
658
Location
ATL Area, GA
Some members have been asking for help in figuring out how to bypass the factory crossover in the Quest / reQuests so they can use active crossovers.

So here is a short description and attached is a schematic for how to bypass the passive crossover. This applies to most models of first-gen ESL speakers from ML.

Unplug the speakers and let them drain for 30 minutes or so.
Unmount the electronics panel by removing the screws, then once open, carefully disconnecting the woofer leads, and the Panel leads. Pay special attention to the panel leads. Take pics, use labels, etc. you do not want to confuse what goes where.

After you’ve un-mounted the electronics panel, you will be able to work on the process of bypassing the existing passive crossover.

The first thing is, don’t be daunted. It’s not quite as bad as it looks. The majority of the passive parts are simply removed.


Now, if you are looking to do this in a way you could easily reverse, it’s a bit more complex, but not terribly. You just have to ensure things that shouldn’t touch, don’t ;)

Start by studying the before and after diagrams of the crossover. Take some pictures of you board before you touch anything. Make sure you know what is what in the crossover.

Here is a link to the stock request crossover: http://www.martinloganowners.com/~tdacquis/forum/showthread.php?t=126&highlight=crossover+schematic

Once you are sure which leads to cut, go to town and cut the appropriate leads in the high-pass crossover. Put in a new wire from the negative HF post straight to the black lead of the step-up transformer.
For the high-pass, identify the cut points and bypass the existing components.

Please note: you must recover three of the 2 Ohm 20w resistors in the main x-over to build the paralleled set of 3 resistors on the hot lead before the transformer. (or go buy new ones if trying the preserve original passive for reversal). This is to ensure your amp sees a resistive load of some kind, otherwise it’s a fairly reactive load. Some amps will go ‘poof’ if driving a straight transformer (with a capacitive load on the other end to boot).

My Sunfire amps don’t care, they can drive it straight. So if you feel your amps are up to it, you can omit these resistors (they also cause a slight dip at 10K, see my SL3XC build thread for details and graphs).

With your new set of three 2 Ohm resistors, wire them to the red HF post, and their output to the Red feed to the step-up transformer.
The brown lead to the transformer remains with no connection, so cap it off.

Pretty simple really.

Have fun and post pics if you do this ;)
 

Attachments

  • reQuestCrossoverBypass_JPG.jpg
    reQuestCrossoverBypass_JPG.jpg
    49.4 KB · Views: 7,827
Jonathan,

Wow, thanks so much!! This is exactly what I've been looking for. I've been waiting quite some time to be able to actively bi-amp my Quests the right way. Right now, I've got 2 Krell KMA-100s driving the panels(100 watts of pure class A). I think they should continue doing a splendid job even if driving a straight transformer, don't you think? Do you have a pdf of the schematic you could email me? I'd like to see things a little larger and clearer. Thanks again.
 
Last edited:
Jonathan,

Wow, thanks so much!! This is exactly what I've been looking for. I've been waiting quite some time to be able to actively bi-amp my Quests the right way. Right now, I've got 2 Krell KMA-100s driving the panels(100 watts of pure class A). I think they should continue doing a splendid job even if driving a straight transformer, don't you think? Do you have a pdf of the schematic you could email me? I'd like to see thngs a little larger and clearer. Thanks again.

Jedi,

You are welcome, and yes, those Krell’s should have no problem driving the xformer directly. So omit the resistors.

Drop me a PM with your personal email and I’ll send the PDF (or .PNG). Just let me know what format.

Cheers,
 
Thanks Jonathan,
I will definately be doing this, will document and post pics once completed.



Much Appreciated
Cheers
Steve
 
Thanks Jonathan,
I will definately be doing this, will document and post pics once completed.



Much Appreciated
Cheers
Steve


Cool, keep us posted on that.

Also, I sent you the PM with the docs.

Seems I also need to finalize the docs I was writting up on doing the DriveRack 260 set up....

I have that about 50% done. Time to get busy :eek:
 
Thanks again for the schematic,

I will do a write up and post it once I complete everything,
Sorting out my active crossover right now.



Cheers
Steve
 
I have a pair of Quests too that I was thinking of bi-amping. Which active xover are you all using? I've been looking at the Ashly 1001. It has balanced connections which I need. My ARC CL150 are balanced only inputs.
Thanks,
Paul
 
Jonathan,

I got into my Quests with a buddy this past weekend, and we found that there were a few differences from the ReQuest crossover. In fact, he wants to send you some pics and check with you before he snips any wires. Some things on the board are placed differently, some wires are different colors than what they should be, the number of wires vary, etc. His name is Scott and you should be hearing from him on my behalf. My Quests are the Z modification, bought back in 1995.

Thanks,
Adrian
 
Jonathan,

I got into my Quests with a buddy this past weekend, and we found that there were a few differences from the ReQuest crossover. In fact, he wants to send you some pics and check with you before he snips any wires. Some things on the board are placed differently, some wires are different colors than what they should be, the number of wires vary, etc. His name is Scott and you should be hearing from him on my behalf. My Quests are the Z modification, bought back in 1995.

Thanks,
Adrian


Cool, will be on the lookout for that message.
 
I have added a couple of pictures of my un-modified x-overs from my Quest.


I will be modding them very soon.



Cheers
Steve

original
QuestXoveroriginal.jpg


with new music sense power supply
QuestXoverMusicsensepowersupply.jpg
 
I have been in contact with Jim, this is his reply to my email,
asking if I could get a copy of the Quest Cross-over,

================
Since the Quest has been out of production for as long as it has, I
don't mind posting the information. That is not a problem.
Give my best to the ML Club members. I greatly enjoyed meeting some this
past week.
Be well,
jp

=======================

Plus some additional info-
PRODUCT ADVISORY
QUEST
RE: THE ACTIVE BI-AMPABILITY OF THE QUEST LOUDSPEAKER
IT IS POSSIBLE TO ACTIVELY BI-AMP THE ORIGINAL VERSION OF THE
QUEST LOUDSPEAKER AS IT WAS ORIGINALLY BUILT UNTIL THE INTRODUCTION OF THE QUEST Z. ANY QUEST Z MODELS OR LATER DO NOT HAVE THE CAPABILITY TO BE ACTIVELY BI-AMPED.
SN#s AFFECTED:
(ALL QUEST BETWEEN SN# QECA000 UP TO QEEA000-Z) ARE ACTIVELY BI-AMPABLE.
A NUMBER OF INTERNAL COMPONENTS MUST BE RE-CONFIGURED IN ORDER TO ACCOMODATE ACTIVE BI-AMPLIFICATION.
IT IS ALSO NECESSARY TO USE AN ACTIVE CROSSOVER THAT IS DESIGNED TO BE USED IN CONJUNCTION WITH THE QUEST (SUCH A THE KRELL KBX-QUEST).

=========================

As I recall, you will find a series of connections internally that allow
you to bypass the passive crossover. They are labeled as either
connection A or B. Normal single operation uses connection A. The B
(bi-amp) connection remove the filters from the system.
Documentation from that time is limited. I will try to help from my
memory (which is certainly in question these days).
There is a connection change on the input of the large xover board near
where the wires from the binding post attach.
There is a connection change for the RED woofer output wire.
There is a connection change for the audio transformer input wires.

I hope I remember them all.
Good luck.




I have attached the PDF
View attachment quest crossover Schematic.PDF


Many Thanks to Jim for all of this information
Cheers
Steve
 
Well, this kind of sucks for me, since I own the Quest Z. Did Jim tell you why it is not possible for my speaker? Can it really be all that different? I have to believe that there is a workaround for this. Any ideas?
 
Last edited:
If anyone else is wondering about the answer to my last question, Jonathan answered it for me. ML combined high voltage traces with the crossover board, and the stators need that in order to work right. It would take an engineer looking at schematics, and the actual boards in order to reverse-engineer it, and figure out what to do. It sounds like that would cost a lot of money.

I guess I'll just have to settle for running from an external Xover into the internal one. Atleast my woofers are connected directly to the lower binding posts, bypassing the internal Xover.
 
I have older Quest's and am wondering why, and what advantages this would gain? With the right amp and Room, (it plays the biggest factor, I struggled for a year or so until I finally got it right) you can get great bass and great sound. You get plenty of DB with a good 300 wt amp, like a Krell, Classe, Levinson, Bryston, Sunfire. ECT........

With the older Quest you can Bi- Amp with the internal x over. It has a switch that allows that. Why do you want to by pass it and use a external unit? I understand that some designs were poor , but Martin Logan used decent stuff. I know re placing some internal capacitors and supplies and such on the board can help but someone who has done a external x over chime in and tell me. I'm all for better sound per $ spent . I find it a bit over kill for a 15 year old speaker. If I am gonna spend $1000. to $2000 for a external x over I will put that money toward a new set of speakers. Sometimes the old classic sounds of the older designs can be tweaked, like some here have done internally to the x overs. To me its like a car with performance parts, a little tweak hear or there , but pulling the engine out to make a Skylark do 10's in the 1/4 mile is a bit overkill!

Just MY .02 worth !
 
Bi-amping will always produce superior sonic results mainly because of the effect on your amps. An amplifier being asked to drive the entire audio range will work harder than an amp being asked to only do mids and highs, or just bass(even if you have big Krells). Also, intermodulation distortion(I think that's what it's called) is greatly reduced. This kind of distortion happens when a high frequency wave has to coexist with a bass wave, and it loses integrity. When an external crossover splits up the audio spectrum and sends the highs and mids to one amp(or 2 mono blocks, as in my case), while sending bass to another, the speakers sound better because of the more efficient use of the amps. It doesn't have a whole lot to do with the age of your speakers. Well, other than the fact that the Quest are out of production now and there's no chance of voiding warranties by trying this. It's nice that ML is now willing to help concerning this. I ran into a brick wall with them when I asked for help several years ago.

You mentioned the older Quests having a switch that allows you to bi-amp with the internal Xover. Well, that's not really true, as you must have an external active Xover in order to truly bi-amp. The effect is meant to take place at the amps, and there's no way the internal Xover can change how well your amps are working. The switches you're talking about are probably allowing one with an external Xover to bypass the internal one, so they must have a bi-amp label next it. Jim's email to Steve requires some internal connection work to be done on the older Quests in order to bypass the Xover, so I'm even more confused by your comment.

I'm not saying that Quests won't sound good unless you bi-amp them. That would be foolish. I'm simply making a case that if you have the budget, it's worth it to bi-amp them(at any age) because that will allow them to sound their very best.
 

You mentioned the older Quests having a switch that allows you to bi-amp with the internal Xover. Well, that's not really true, as you must have an external active Xover in order to truly bi-amp. The effect is meant to take place at the amps, and there's no way the internal Xover can change how well your amps are working. The switches you're talking about are probably allowing one with an external Xover to bypass the internal one, so they must have a bi-amp label next it. Jim's email to Steve requires some internal connection work to be done on the older Quests in order to bypass the Xover, so I'm even more confused by your comment.

I'm not saying that Quests won't sound good unless you bi-amp them. That would be foolish. I'm simply making a case that if you have the budget, it's worth it to bi-amp them(at any age) because that will allow them to sound their very best.

Jedi, I’m afraid there is an incorrect statement above, as one can indeed bi-amp with passive crossovers. If the speaker (like a monolith passive), which has both high-pass and low-pass sections that are independent, then you just power the HF with one amp the LF with another.

Using an Active external crossover is indeed the preferred method of bi-amping, as it replaces a bunch of power robbing, frequency and phase skewing passive components from the mix. However, it does mean several things must be accounted for:
-The passive crossovers need to be taken out of the loop, either through switches if the unit supports that, or through surgery. Other than the Monolith, whose passives were totally external, all other gen-1 ML require surgery to bypass the internal passive (as far is know, I could be wrong here).
- The phase and EQ that the original passive was engineered to supply, need to be considered in the external active unit.​
The last point is key. While a good active x-over can do a good job at the frequency distribution, the job is only half done if phase and EQ are not accounted for. This why I swear by a good DSP-based speaker processor, as it lets you deal with all these variables, plus time delay, something a passive can’t do. Not quite plug-and-play, but the results are superior.

I would go out on a limb (firmly rooted in my experience with the Monoliths and SL3) and state that a reQuest (or any single-amped, passively x-over ML) could be notably improved by bi-amping and a good speaker processor.
 
Absolutely, Jonathan. Thanks for reminding me, as I had forgotten about horizontal and vertical bi-amping. Forgive me for sounding like a snob, but I guess I didn't think of those methods in light of what I consider to be "true" bi-amping, with an external active crossover. I see greater value in changing the signal that goes into each amp. Passive bi-amping cannot do this, as each amp is still fed a full range signal from the preamp.

Could you tell us more about this DSP-based speaker processor(brand, cost, functions, etc.)? Do you think that ML would share with me all the info about EQ, phase, and whatever else the passive Xover is doing in my Quest Zs? Since the high voltage traces are mixed into my crossover board, I was thinking that maybe I should ask ML if they can swap my internals/back panels for the older Quests cabinet backs, if they have any still sitting around. What do you think of that? Atleast that would give me the ability to bypass the internal crossover. Perhaps they would send them to me already setup for active bi-amping.

In your email to me, you mentioned that it doesn't hurt anything to run from my external Xover into the internal passive one, as long as I stay well enough above the range of the passive so that I don't double up on things and cancel frequencies. 1) Isn't it true that I'm running through 2 Xovers that feature "a bunch of power robbing, frequency and phase skewing passive components"? This means that I'm losing a lot, right? 2) My Quest Zs are crossed over at 150 Hz. You suggested that I should set the external LP at something like 315 Hz. I did try that, and the panels didn't sound too good to me. Bass was weak, but maybe that was because I left the woofers set too low. After several tests, I went the other way and set it below the passive, at about 100 Hz. My woofers, which are directly connected to the Xover, are set at 200 Hz. My panels sound more life-like with these settings, and the bass is quite good. I figure that if my Krell monoblocks don't see anything below 315, then I'm robbing the panels of any chance of seeing signals in the 315 to 150 range, which they should be getting. Setting the woofers at 200 should cover any dips at the Xover point of 150.

As I'm typing this, it occurs to me that what you probably wanted me to do was set both the panels and the woofers to 315, so the woofer would be covering whatever frequencies that were meant for the panels. Having the woofers playing higher than normal would give a warmer mid-bass. I haven't tried that yet, but I will. This setup would have to be pretty darn good, because I love what I'm hearing right now. My Quests sound better than they ever have.

Adrian
 
I have modified the Quest z crossover schematic for those who are interested.

For the bypass,
you only need to take the Green and Black/red stripe out of the connection strip on the Crossover circuit board,
Extend the cables to reach in the input sockets
Green to the positive input socket
Black/red stripe to the negative input socket.

For the woofer, solder positive and negative directly to the input sockets

QuestZforActiveCross-over.jpg



The Quest is very easy,
you change the woofer positive from the A spade terminal to the B spade terminal,
then move the wire link from the A position on the input circuit board to the B position,
then take the green wire out or the A position connector strip, put it into the B position on the same connector strip.

then you are done.
I will post a pic of the changes


Cheers
Steve
 
Yes Bi-amping produce superior sonic provided that by using external active electronic Xover. I have done mine (1992 Aerius ) by using starbuy oldschool car 2-way electronic Xover Macrom 48.22. This active Xover got one lo output, crossover point adjustable from 30Hz to 600Hz and 2 Hi output (hipass) adjustable from 30 Hz to 6 KHz, level -6 dB to + 6 dB.

The connection was done like this , lo output from the above Macrom goes to input amp ( Chimera Lab X100 ) that's drive the woofer ( internal passive Xover bypass ) and the crossover point was set to 400 Hz.
The 1st hi-left output of the Macrom ( internal passive Xover's mod ) goes to input amp's driving the left aerius pannel and the second hi-right output
( internal passive Xover's mod ) goes to the right input of the same amp driving the right Aerius pannel. The purpose of connection as mentioned above, the amp drive the Aerius pannel, the crossover point and the input level of left and the right channel can be adjust individually & acordingly to our taste.
I'm using thi Macrom electronic Xover because for me its easy to adjust and there is one veriable phase allignment for the lo, adjustable from 0 degree to 180 degree and is use to get the right oudible phase between hi/low changes if any.
For me it's worth to bi-amp them (active) because now my amp's that drive the Aerius panell ( Unison Research Triode 20 mod - using 8 Gec kt 66 ) sound smoother and lauder maybe due no more input below 400 Hz..[/QUOTE]
 
Back
Top