KEF iQ70 Upgrade

[albertshi]

I bought a pair of KEF iQ70 in 2012 when they were on sale. They used KEF proudly new Uni-Q® point source drive for High and mid-low plus a 6.5" bass driver. After enjoying them a few months, I realized some weaknesses of these speakers. they gave some level of details but were a bit dry. their bass was less appreciated. I would be not involved enough when I was listening classical symphony. However, what would you expect hundreds bulks speakers could do? They were still great value but I hoped they could gave me more. That was why this upgrade idea started!
It was planned and being held for years because I had been very busy and/or lazy. I had searched over internet for some simple references but I found nothing. I had to start a brand new project. I had spent months for analysis, learning, sourcing/purchasing and hand craft works. Fortunately It has been done recently. I like to share here for people who owns these speakers and like to upgrade them like me. I also like to hear from your expertise opinions in this great audiophile community.

 

[maty tinman]

[Polish] KEF iQ70 - Zespoły głośnikowe | Testy w Audio.com.pl

more pictures: [PDF] https://audio.com.pl/files/2/6/7/267-kef-iq.pdf


Do you have a picture of the crossover?

 

[albertshi]

Open the speaker:

 

[albertshi]

The Uni-Q driver:

 

[albertshi]

The woofer:

 

[albertshi]

The crossover mounted inside:

 

[albertshi]

Crossover circuit:

 

[albertshi]

All the value come from their labels and verified by precision measure.
The components used in this circuit: Aluminum bi-polar caps, core inductors, air core inductor for High frequency filter. That was expected from a mid-class speakers:

 

[albertshi]

That's it for today. I was very curious for the usage of series capacitor (1500uF) in Low pass filter. The good thing is to prevent any DC current from bad amplifier, the bad is to reduce the bass extension for low frequency audio signals. Could that be a reason that this speaker doesn't produce heavy bass?
Because the high value of the capacitance, KEF could not use high quality film cap but MDL brand aluminum bi-polar caps the low end "N" series. It will be terrible cost and size if I upgrade them all to Film caps.

 

[maty tinman]

Bennic resistors and M.D.L. (Jantzen) electrolytics as my KEF Q100. I suspect that both are very bad because after changing the resistor and adding a bypass cap the sound has improved dramatically in previously improved (by hard and soft) loudspeakers.

Looking for a new pair of 0.22uf coupling caps.

Resistors with very low inductance -> speaker crossover and in others places

[IMGDEAD]http://maty.galeon.com/WP-imagenes/kef-q100/KEF-Q100-crossover-Miflex-KPCU-01-001uF-capacitor-Mills-06R8-5-watts-resistor.jpg[/IMGDEAD]

You have to decide if you rebuild, modify the filter or do like me (hard+soft), for now.

With soft:

* Minimum Phase vs Linear Phase | Page 7 | Audio Science Review (ASR) Forum

* Minimum Phase vs Linear Phase | Page 16 | Audio Science Review (ASR) Forum

 

[maty tinman]

What amplifier do you use? In another forum I just posted the impedance and phase graph of the Klipsch Forte III. The phase does not appear in the Polish graph. Maybe the problem is the same:

Klipsch Forte III Upgrade with Pictures!

The minimum value is 3.65 ohms at 125Hz. However, the electrical phase angle (dotted trace) is sometimes extreme, and there is a current-hungry combination of 5 ohms and –49° phase angle at 90Hz. Despite its high sensitivity, the Forte III will work best with amplifiers that are comfortable driving 4-ohm loads.

 

[albertshi]

I use Denon 5800 main channels to drive KEF speakers.

 

[maty tinman]

Denon AVR-5800 A/V THX Ultra Receiver Made in JAPAN For Sale - Canuck Audio Mart

Dynamic power: 390 watts x2 at 2 Ohms! Modern AVR wrinkle long before.

Denon AVR-5800 A/V receiver Measurements | Sound & Vision

Denon AVR-5800 - Manual - Audio Video Surround Receiver - HiFi Engine

Speaker load impedance: 6Ω to 16Ω

Must be with the other speakers. Only in stereo it can with 2 Ohms.

 

[albertshi]

The simulations done for the crossover High frequency:

Simulation for Mid and low frequency:

 

[albertshi]

I do think the multiple series capacitors can be combined to one then the value will be reduced. In that way the crossover board can be smaller and I am able to apply better caps. However, I was a little afraid of risks with big modification. So I just increase the first series cap to be 2200uF with makes LF decay slower, supposed to improve low frequency response without much risk.

 

[albertshi]

I replaced the bi-polar Al caps with Solen film cap for HF Crossover.
For the mid-low I replaced single cap with multiple small value in parallel. So 2200uF=125uF*16+50uF*1+75uF(Film)*1; 500uF=125uF*3+50uF+75uF(Film). The 120uF and 50uF are MDL Bi-polar Al cap B05 series (Their best Al cap). Film cap is KEMET C4AQCBW5750A3NJ.
Inductors are Madisound brand.
Resistors are better precision WISHAY parts.
The box is BUD Industries when they are sale, nice product!

 

[albertshi]

This is how I made cable:
I bought Silver plated copper wires, twist them clockwise and then anticlockwise 3 pairs. After that apply cotton cloth ribbon wrapped twisted cable, finally wrapped by cable braids.