Jamo Oriel Active Bi-amplification

Preamble

This is an old page – now superseded.  It details the active separation of the woofers and their EQThere is an oversight in the phase alignment of the bass to midrange sections as corrected on the tri-amp page.

An upgrade of the upstairs stereo system to bi-amplification with an ESP P09 active cross-over was so successful that I hadn’t listened to music on the downstairs system in months.  And the downstairs system had the potential to be even better so this project just had to happen.

The downstairs system is a small home cinema setup, but the main front left and right speakers can be used for stereo music CDs without the multi-channel surround processor in-line.  For this, there is a Sony SCD-1 SACD player used as a CD transport, a (C-J) Premier Nine valve output stage DAC,  a C-J Premier Ten valve preamp, a pair of C-J Premier Eight-XS valve mono-blocks and a pair of Jamo Oriel 3-way tower speakers standing about 1.78 m tall.  (UNDER CONTINUOUS OFF-SITE VIDEO SURVEILLANCE, IR DETECTED, DATA DOTTED, ENGRAVED AND GUARDED BY A FIERCE KILLER DOG and Space Enforcer Claudius!) 😯

The bass sections of the Oriels each consist of four chambers and two drivers.  I.e. two pairs of 4th order band-pass sub-woofers in each of which an 8 inch Peerless driver (real Danish ones) separates a sealed chamber from a ported chamber.  The Eton Hexacone midrange crosses over to the bass at 100 Hz and to the Dynaudio Esotar tweeters at around 3 KHz.  The midrange is mounted on a neoprene-clad narrow curved front baffle.  The substantial range of musical frequencies emanate from the midrange drivers for excellent imaging and depth of sound stage.  The bass response is fantastic – fast and dynamic and easily extending below 20 Hz which is deeper and cleaner (for music reproduction at ordinary listening levels) than any subwoofer that I have heard.  It’s like having four small sub-woofers acoustically coupling with each other and complementing two-way main speakers but with their output directly adjacent to the main drivers for near seamless transition to the midrange and with stereo separation of the lower frequencies when called upon.  Some might scoff at that last bit and suggest that bass frequencies are “non-directional” or impossible to localise and settle for a mono subwoofer.  Apart from missing unsubtle things like the discrete left and right cannon shot on the Tchaikovsky’s Nutcracker Soundtrack (Telarc CD) for example, they would miss out on a whole lot of spatial information and 6 to 9 dB of free emphasis brought about by acoustic coupling when stereo sources contain essentially monaural bass content (in this case 6 dB below around 33 Hz due to doubled input power plus acoustic coupling between left and right speakers spaced at a 2.3 metres plus 3 dB right across their pass band due to acoustic coupling alone of the close vertically spaced ports).

In their standard form however (relying entirely on their internal passive crossovers) the midrange and high frequency sound only came to life when valve power amps were added to the system.  Previously several different solid state amplifiers were tried with disappointing results.

Anyway here is a picture of one of the Oriels and a cross section:

CRW_0943

Conventional band pass sub-woofers have a ported chamber that is smaller than the sealed chamber, but the Oriels are different with tight sealed chambers behind each driver.  I guess this was done to limit cone excursion at very low frequencies with some compromise perhaps in the system “Q”.  Pressure mode sound propagation in the listening room seems just as good as with sealed subwoofers, but the bottom end extension is much better.  It’s heaps tighter than most bass reflex designs which seem to lack impact and do unload when called upon to do anything really serious.  The Oriels do not require LF boosting like regular sealed enclosures do, so power requirements are very much lower.  I guess there is a small compromise in group delay response, but this I wouldn’t notice that with the type of music that I like.

So I came up with a combination of ESP project PCBs to actively cross-over the system for bi-amplification and assembled a new chassis which includes a 15-0-15 toroidal transformer, a full wave rectified power supply (P05b), a P09 24dB/octave Linkwitz-Riley crossover set at 102 Hz and a 36dB/octave rumble filter (P99) set at about 15 Hz to further protect the four bass drivers from over-excursion and more importantly, to reduce amplifier power wastage.

Unlike the room upstairs however, there was a “boom” at the seating position at around 25-30Hz which needed taming, so I included a stereo pair of P84 8-band “constant Q” subwoofer equalisers (20-100Hz) after the low-pass outputs of the crossover board and before the rumble filter.

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Here are some photos of the finished chassis:

WholeChassis

The chassis-grounded aluminium internal partition may look silly, but it works very well to isolate the audio circuitry from the 240 Volt AC wiring to  the transformer.  This can be demonstrated by waving an oscilloscope probe around the partition.

PowerSupply

I kept the mid-to-tweeter passively crossing but removed/bypassed the low-pass section of the passive networks to the bass drivers and the high-pass sections to the midrange as I did upstairs.

The crossover inputs receive the stereo signal from the CJ pre-amp.  The high-pass outputs go directly to the upper outputs for the C-J mono blocks.  The outputs of the rumble filter go to their respective output sockets for connection to a more powerful solid state stereo power amp for the bass drivers.  A 4-pole muting relay (powered by an unregulated output of the power supply) shorts the four outputs on powering down.

I decided to stack the equaliser boards (right channel above the left) and used unusual horizontal trim pots extending off the sides of the PCBs with their through-holes aligned to allow a vertical square shaft to pass through and turn two pots simultaneously as though they were dual-gang pots but without the need to tie one board to the other with 17 short wire links!  The equalisers are a set-and-forget arrangement requiring removal of the lid to gain access for re-setting.  And yes – the pots do turn backwards which is a little confusing at first.  🙂

IMG_0996

There was a small problem of chassis height.  I wanted everything to fit in a slim-line chassis and the one I liked had only 46mm internal height.  I figured it could be done with 17mm above each equaliser PCB.  The only real problem was the on-board power supply capacitors and power supply regulators of each board and the usual vertical header pin sockets that would have the wires extending upward, but I carefully mounted the regulators over and under the PCBs with their legs bent in odd directions and was able to source squat Japanese filter caps that fitted straight in vertically.  I also sourced some neat screw terminal headers allowing the connecting wires to extend sideways.

CRW_0960

Here is a side-on photo of the stacked equaliser boards (bit tight eh?).  The diodes at the left in front of the filter caps were removed after the photo was taken.

I was going to raise the crossover frequency slightly (to 112 Hz) so that standard 20 – 100 Hz bands of the equalisers could be used without the top band coinciding too closely with the crossover point, but on the PCB designer’s recommendation I chose the closest possible crossover frequency (102Hz) to the original passive design.  I took his advice that being of band-pass design the sub-woofers might not be very tolerant of out-of-band signals and that with the last pot of each board centred, the equalisers would be almost transparent at the top of the woofers’ pass band.  Also, if the natural 4th order upper roll-off of the sub-woofers happened to overlap with the active low pass slope, the resultant 48dB/octave slope would cause an unwanted dip.  Best hope that the natural roll off is somewhat higher (luckily it was).  And it is probably better to retain the lower range of the midrange drivers for better sound quality compared to that emanating via the ports anyway.

There are plenty of boards and opportunities for unwanted ground loops and mess, so a four-pole terminal block came in very handy for some of the power supply wiring and circuit grounding.

TerminalBlock

The equalisers’ on-board power supplies initially received low voltage AC, but due to slight noise in the low-pass outputs (caused either by the low capacitance value of the on-board filter caps or a duplication in ground references) I rewired them to receive unregulated DC +ve, -ve and GND tapped directly from the underside of the main power supply PCB just before it’s regulators.  The bridge diodes were removed from each equaliser but their regulators were retained.  This obviated any additional burden on the main power supply regulators which already ran warm.  An upgrade of the standard 1W carbon resistors to 3W metal film was all that was needed.   There is now no measurable hum or noise in any output.

The internal signal cabling is thin Teflon coaxial.  I really like this coaxial cabling.  It is easier than using shielded twisted pair and the PTFE does not melt while soldering.  Apart from polypropylene (which melts) it’s the best man-made dielectric too.

I used high grade components throughout without going overboard (say by using esoteric Analog Devices opamps, WBT RCA sockets etc).  The crossover uses LME49720 super low distortion + noise opamps.  The low frequency boards use cheaper OPA2134PAs as they are more than adequate for bass.  The RCA sockets are Neutrik and the electrolytic caps are Japanese Panasonic where available.  The filter caps on the rumble filter are Vishay Dale polyester and the crossover filter caps are Panasonic polyester.  The regular MKT polyester I found to be too inaccurate and imprecise requiring the purchase of about 5 times as many as needed to get the ones you wanted to match at the specified value.  That wasn’t a problem with the equaliser as only a few of each MKT were needed.  The high pass outputs of the crossover have Vishay polypropylene coupling capacitors mounted underneath the PCB.

We tipped the Oriels over to access the passive crossovers:

CRW_1455

Here are the binding posts:

CRW_1460

Looks like a submarine hatch and you practically have to dive to get there!  And they took some cracking after 12 years of being jammed (thank goodness Richard Basehart didn’t step out!). 🙂

CRW_1463

And the passive crossover:

CRW_1461

The board is intended for passive bi- or tri-amping, so there are three discrete filters which were quite easy to modify.  The posts marked “NC” for “Not Connected” are intended for attaching attenuating resistor links for the tweeter in a bright room.

Loaded with horrible (but necessary given their high value) electrolytic capacitors amongst some nice French polypropylenes as well as a couple of nasty iron-cored inductor (distortion) coils:

PassiveHackJob

The under-side photo is flipped vertically so it aligns logically with the top photo.

Two yellow lines indicate new link positions.  Using the above, I drew up the bass and midrange filter circuits.  I nice person later emailed me a factory service manual which confirmed my brilliant circuit tracing skills. 🙂  All but one of the electrolytics were no longer needed and were either bypassed with links, or lifted.  Also, one of the iron-cored inductors was no longer needed.  Great!  🙂

The tweeter sections were untouched apart from replacing the NP electrolytic capacitor with a new one of higher voltage rating, so I didn’t bother drawing up the circuit for it.  The high-pass functionality of the midrange section was disabled as the active crossover does this, but the mid range low pass and Zobel networks were retained of course.  The bass drivers were direct-wired to the input posts (bypassing the low-pass with wire links as the active crossover does this too).

top

links

Calibration was half a day’s work with a tone generator, oscilloscope, SPL meter and ears.  One surprise was that when both amplifiers were turned on together after individually calibrating the SPL with the crossover output trimmers, there was a suck-out at the crossover frequency instead of the expected 6dB gain.  Strange 😕 .  All speaker connections seemed correct – but then I remembered that the original passive filters which crossed the bass to midrange were second order Butterworths each contributing 90° of phase shift for a summed inversion at the crossover point, whereas the 4th order Linkwitz-Riley active crossover is phase-correct (actually a 360° shift) at the crossover point.  As mentioned above, the only output from the bass drivers is via the ports.  Therefore the port tuning of the band pass sub-woofers must acoustically invert the driver phase at the crossover frequency.  Reversal of the speaker cables to the woofer terminals was an easy fix.  The scope was then used to ensure that the levels of both L and R outputs of the crossover were identical.  The 100Hz band of the equalisers were first  carefully “centred” by matching scope traces with the high pass at the cross-over frequency and then all the other bands were adjusted using a tone generator and listening from the best seat.  The calibration is correct only at that seat.  Move just a little bit forward and its all wrong again due to room nodes.

There was a minor buzz in the midrange drivers due to a ground loop,  so I  added a safety ground loop breaker to each of the power amps – which worked.

The performance of the Oriels is much improved.  The midrange has freed up a bit and things seem to be better placed.  I can’t say that the mid and upper frequencies are greatly improved, but the bass is simply astonishing.  Audibly flat to 20 Hz with only slight tweaking of the equalisers.  It’s fast too and without boom at any frequency.  My hearing is only good down to around 20 Hz, but the room continues to shudder silently way down to 15 Hz where the rumble filter cuts input to the power amp sharply (36dB/octave).  Evidence of the response is in what can be “felt” and in sympathetic resonances that develop in various things around the room at different frequencies.

While doing a sweep at about 90dB (about 2 or 3 Watts input) I was able to capture evidence of a 14.3 Hz room response by picking up a vibration around an internal window frame with my digital camera’s microphone.  The SPL meter was still registering 90 dB, but it’s specified lower frequency response is only 20 Hz so the reading can only be considered “indicative”.

Here it is for the doubters (and I know who you are):

The only audible sound in the room was this rattle – i.e. no second or higher harmonic distortions from the speakers which would have been plainly audible had they been present at any significant level.

A highly rewarding project.

🙂

However:

The midrange and treble were still not quite right.  See here for an update.  🙂

30 thoughts on “Jamo Oriel Active Bi-amplification

  1. Hi Ian.
    As you wrote- OMG!
    I greatly enjoy this speakers for the last 10 years(#283 & #284).without Bi-Amp/Wire.
    So I can only assume the improvements, it must be astonishing! (I would love here them..but I’m only 2 hours east of Greenwich Mean Time :)).
    Did you tried to Bi-Amp, using the original passive crossover?
    Thanx.

  2. Hi Yaron,

    Mine are #1263 and #1264.

    I did not try bi-amping with the passive networks, but it would still be an improvement because the high current drawn by the bass drivers would not adversely affect the drive capability of the upper range amplifier(s) by drawing on their reserves. The load of the passive networks could still be a burden on the amps, but the result would still be better than using a single amp to do everything. Be careful though. A few things: Your power amps must have the same electrical gain (say 26dB is typical) or else you would need attenuators on the one with the higher gain to make an adjustment. Also your pre-amp will need two sets of outputs, or you could use some of those brass RCA adapters/splitters. Also watch out for the dreaded ground loops. Nobody tells you about that when you bi-amp and not many power amps seem to have loop breakers in them.

    The Oriels are probably one of the greatest speakers ever made. I have heard many more expensive and more modern speakers including Quad electrostatics, Sonus Faber, Wilson Benesche, Griffon, B & W, Wilson etc, but none come close to the Oriels for pure enjoyment. 🙂

  3. Hi Ian.
    Yours are Young Ones 🙂 As far as I know- only 1000 pairs were made…..
    Many Thanks for your detailed answer.
    If I had a second pair- I would start yesterday! such project.
    But, as the old saying- “if it’s fixed, don’t break it!!” And, as you said (& I more than agree)- they are “pure enjoyment :)” so I have to be satisfied with their basic status for now.

    Also thanks, for revealing to me, at last!! What are the two extra terminals, the N.C ones . (I triad to receive answers from Jamo, but nothing, no reply!!)

    I don’t have any technical paper or user manual for them, if you have…I’ll appreciate if you can share them with me.
    Thanx again.

  4. Hi,

    You would not need to modify your Oriels to passively bi- or tri-amp them using their own standard internal crossovers. All three internal circuits are independent. For bi-amping you could connect a powerful amp (say 150 – 400W at 4 Ohm) to the woofer terminals, then connect a cable from a high quality amp (say of 80 – 120W – 8 Ohm) to the midrange terminals bridged with the tweeter terminals. For tri-amping, you could leave the high quality amp on the midrange alone and connect a low power (say 20 Watt) Class-A amp to the tweeter terminals.

    It’s a shame when companies that once made beautiful products and did so with pride sell out to foreigners that display no regard to anything but profit and therefore sell nothing but low quality Chinese junk these days, spin a load of marketing and not bother to answer emails from a customer of their former name’s sake.

  5. Hi Ian,

    I came across your blog through a search of Jamo Oriel and was really impressed with what you have done to the Jamo Oriels. I live in Toronto Canada and have visited your fine country a few years back doing scuba dive certification in Cairns. I am looking for some help here. I have a Wyred 4 Sound STI 1000 integrated amp and a DAC2 driving the Jamo Oriel. I have been having static electricity problem over the past few months. Very often when I touched the volume knob on the STI 1000, crackling noises can be heard through my speakers. Last night when I touch the volume knob, a loud crack went through my speakers and blew out a midrange driver on one of the channels. So I am now searching for a replacement midrange driver for the Oriel. I am wondering if you know the exact manufacturer and model number of the kevlar 6.5 inch driver (mine has 4 screws) and where I might be able to source such a unit.

    Thank you very much for your help.

    Louis To

  6. Hi Louis,

    They are Eton Hexacone drivers – now long obsolete. I have seen another web site where someone had replaced the early 4-hole version with a six hole model Hexacone with the cylindrical heat pipe at the dust cap area. I think even that one has recently become obsolete. Anyway have a look at the current range of Eton Symphony drivers. I believe they might be available from http://www.europe-audio.com/. I would even consider some of the current ScanSpeak units if they will fit. Your problem is in finding one with the same diameter. And if you are retaining the original passive crossover, you will need to make sure that the new unit is of similar electrical spec. to the old. The four holes are a pain. If you replace the drivers with something different, you will have to drill new holes and that is risky – and especially difficult if you want to do it properly with T-nuts at the back. The MDF is too thin and fragile to anchor wood screws.

    Big warnings:

    1. Do not connect your amp until you find and fix the fault that caused the DC!

    2. The neoprene on the front of the Oriels cannot be replaced, so don’t stick a screwdriver under the edge of the midrange! I would place the Oriels carefully face-down with cushions both ends and let the drivers fall under their own weight to carpet – perhaps with a little encouragement with a flat nail head up through one of the screw holes.

    3. The wires that are soldered to the speaker terminals have aluminium strands that do not accept ordinary solder. You will need a special solder with an alloy of tin and zinc – not lead. The one that I used is called Harris Al-solder 500. Be prepared to trash your soldering tip after using it though! The flux is nasty.

    You are lucky if your tweeters survived the insult.

  7. I really don’t get it! Those fledgling brands of hopelessly under-engineered and over-powered and priced Class-D junk piles actually appear to have a following. They may look stylish and the marketing is glossy, but in reality over 1kW of untamed Class-D filth has no place anywhere near a midrange driver or a tweeter – i.e. in an integrated amplifier like that! Imagine that energy into a toaster – it will TOAST BREAD! And to top it off, they have no speaker protection beyond rudimentary rail fuses. In a fault, the full DC rail voltage goes straight across the speakers until the fuse blows! Completely ridiculous. IMO, Class-D is appropriate for nothing but subwoofers and even then you have to be very careful with it. The forums are full of people raving about it and it just makes me cringe. Try sourcing those orignal Dynaudio Esotar tweeters after toasting them today and you’ll be in for a rude awakening. They may have been extraordinary in their ability to handle a 1 kW impulse for a whole 10 milliseconds but no domestic midrange or tweeter driver will handle that kind of abusive amplifier for long – even without a fault condition that will inevitably develop. AAARGH!

  8. A lot of information, thank you.
    I also bought a Oriel speaker.

    But spike is missing. I do not know how the original looks. Can you send a photo of it?
    Thank you very much for your help.

    László Pap

  9. Mine are non-original. The originals (Jamo part No. 25075) were no good. They were too blunt to penetrate carpet and came with a rubber disc (Jamo Part No. 25076). There was no means of locking the spikes at a desired height to level the speakers. Better ones are available on eBay with a locking disc or nut. I emailed you a diagram of the original from the manual. Cheers.

  10. Hi.

    im building clone´s of Jamo Oriel and I need specs for crossover…I dont have Coil dimensions. I have schesmatic but it does not tell me what is coil specs diametre in and outside and how height… and coil wire how thick is it?

    if you could sent those measurements for me I would be realy happy. Thank you

  11. If I find some time I shall do this as the passive crossovers are sitting here in a box (where they belong). Besides, there are online calculators for that.

    Also watch out. Unless you have the original Eton dual magnet midwoofes, the crossover could require modification anyway.

  12. I don´t have dual magnets yet i have eton 7-360 hex, But… I can glue the backside….

    Dynaudio esotar are same i must glue magnet backside i know…

    but coil measurement if them are different example total resistor are different and delay and that´s why phase behavior are different yes i know calulators but because of those reasons Im not sure if i can trust mechanic specs if I use calculator

    thats why I need orginal dimensions…

  13. No responsibility for any mistakes:

    L1 iron bobbin, OD of rough wound wire 54mm, ID unknown, length of wound part between flanks 32mm, wire dia 1.3mm.
    L2 air core OD 83mm, ID 50mm, height 17mm, wire dia 1.3mm.
    L3 iron bobbin rough wound OD 32-38mm, length 22mm, wire dia about 0.8mm, bobbin dia unknown.
    L4 air core ID 19mm, OD 28mm, height 17mm, wire dia 0.8mm.
    L5 air core ID 19mm, OD 27mm, height 17mm, wire dia 0.8mm.
    L6 air core ID 19mm, rough wound OD 30-34mm, wire 0.8mm.

    My DMM is not good enough to measure the very low DCRs accurately.

    Don’t worry too much about accuracy. This is not an active crossover after all.

    Be careful on midrange section as driver failure is a well known problem due to very high output of this crossover design at low midrange frequencies (around 200Hz).

  14. Thanks for help very much…

    Yes I know I want to make passive crossovers for in case active crossover make someting not good so it don´t destroy speakers elements

    I have active crossover Dbx pa2 Driverack and i use it..

  15. salut i jakko, je vois que vous avez changé le support d’origine pour une eton 7-360 qui a été le résultat? Je veux changer, mais je crains qu’ils sont 186mm de large

    Google/Ian translation:

    Hi jakko, I see you substituted for the original driver an Eton 7-360. What was the result? I want to change, but I am afraid they are 186mm wide.

  16. Hi.
    Anyone here who has diagrams of the external attenuators (for mid and high range termnals) that was enslosed with the Oriel ?

  17. They were just a wirewound resistor with a cheap gold plated tab soldered at each end with a heatshrink covering it.

  18. Greetings.

    I am contemplating on getting Jamo Oriels. I’ve wanted them since elementary school but they somehow just wouldn’t fit my allowance budget back than ;P.
    I am slowly building my sound system and listening room. ( 120 square meters of audiophile orientated space ). Now, I am very adamant in using my Technics SU-V900 Twin Mono amplifier ( maybe I shall get Technics SU-MA10 that is essentially identical to the aforementioned one plus built in DAC ) and the rest of my Technics stuff I have grow up with ( I know, that’s kinda weird but that’s what it is ). I do plan on getting a new Technics SP10 R turntable or at least the new SL 1200G/GR. Here is my thoughts and debates. My amp is only 115Watts RMS into 6 Ohms. Will it be enough for the Oriels? Have you heard any Technics amp driving them? What are your thoughts on all this? I do have quite a few speaker cables to experiment with ( Van Den Hull, Achtung Audio, Cambridge Audio, Kimber…) and I can only do a single cable or bi-wiring. I do have very good high end interconnects as well a s power cords ( Kimber Select, Achtung Audio Silver, Nymak Iggy ). I should mention that amplifier has been tweaked by previous owner, and audio engineer and audiophile so it is a really a worthy amplifier. What are your thoughts and advice regarding all this? Many thanks and kind regards,
    Bojan

  19. Power is enough. Try to find late production Oriels – not early ones (originally had midrange with just 4 bolts). The late production ones are identifiable by 6-bolt midrange drivers. The crossover circuit is slightly different. And please don’t waste money on those audiophile cables! They offer nothing over standard cables and are just a rip-off. Get some medium gauge speaker wire from your local electronics supplier (not a hi-fi store). The only advice I can offer about turntables is “don’t bother”. 🙂

    Cheers.

  20. Thank you for a prompt and informative replay, Ian. I was looking to get the late models, I believe those are from 1996/97 up to 1999, right? Cables I just happen to have, so as mind as well try to utilize them. So far, the ones I have found ( 3 of them on HiFiShark.com ) seam to be an early models. Two of them are about 3K euros and one is 18K!? The ones for 3K Euros that are in Russia seam to be 1999 though. Gonna try to contact the seller. 😉

  21. Not sure of production dates. Just look for ones with original 6-bolt mids. The last Oriels sold in my country (Australia) went for around AUD4K but they were early ones. I believe that mine might be the only late ones in the country.

  22. There is not many late models out there. I shall ( try ) to be patient and wait for the right ones. Many thanks. BTW. This blog of yours is great. 🙂

  23. Hi…

    Ian do you have review articles or test where Oriel`s are tested ?

    Or where I could find test or review

    Because I have one pair and I have deal one pair more… for hometeater of course 😉

    And that`s why Im curious to know what have been written about these

  24. The answer to that is on the tri-amp page. The only article I know of is in the August 1992 issue of Electronics Australia magazine. It’s a stupid article with editorial errors, but it does include anechoic measurements that you will not find anywhere else. Polar measurements and all – and from 1992!

  25. Hello Ian

    I just got the Oriels few months ago, and the connection is really weird for me, the tri amp connection down there in the speaker is connected with copper bridges except the + pole of the woofer is bridged to the + pole of the tweeter with a 0db connector , and i dont know how to connect the amp to this tri amp connection, can you please advice?

  26. Just connect standard speaker wire from amp to Woofer +ve and -ve and then bridge woofer +ve to both mid and tweeter +ve. Also connect woofer -ve to both mid and tweeter -ve. Leave NC (Not Connected) alone and discard the tweeter attenuator resistor. The original bridges are gold plated brass. You can find the Owner’s Manual online for exotic connection strategies, but if you are just using a single stereo amp then you don’t need to bi-wire or tri-wire. That was a pointless (and stupid) marketing fad of the 90’s and achieves only tangles.

  27. Hi.
    My request is the same as a previous one, see below. I bought my Oriels second hand and the external resistor network didn’t come with it. Anyone here who can send the schematics with values (ohm’s + wattage) and connections to my email?

    Thanks in advance.
    /Poul
    Mail: [email protected]

    ———–
    Hi.
    Anyone here who has diagrams of the external attenuators (for mid and high range termnals) that was enslosed with the Oriel ?

  28. Neither the owner’s manual nor the service manual reveals the tweeter level adjustment resistor values. The wirewound resistors were in heat shrink tube, so the resistance values (and poor quality) of the resistors were obscured. The heat shrink was labelled optionally as “0dB” for standard treble, “+1dB” and there was also a jumper for “+2dB”. So for standard response you needed a resistor of a value to attenuate by 2dB. You’re simply forming a voltage divider with the existing tweeter network resistors. The tweeter has an 18 Ohm resistor across it and a 10 Ohm resistor in series with it. The tweeter is nominally 8 Ohms so at the relevant frequencies you’re basically looking at around 9 Ohms to “ground”. Use any online L-Pad calculator to determine standard values of 2.2 Ohms to attenuate by about 2dB, or 1.2 Ohms to attenuate by about 1dB and see what sounds best. Use 10W parts. The midrange section does not want any adjustment resistor. But really, you’re barking up the wrong tree. The passive crossovers in the Oriels let them down. You could transform the speakers into something really quite remarkable by removing the crossovers in favour of a decent active front-end. DSP would be the easier way to go these days, although it wouldn’t rival what I’ve done with analogue active as detailed on the tri-amp page.

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