KEF 102 Reference Kube question

[John Parkey]

Greetings everyone. I am the original owner of KEF 102 Reference speakers and Kube. My question is whether it would be OK, without any loss in fidelity or sound quality, to hook the Kube between the pre amp and power amp? I am not sure of the max voltages out/in of a Tape loop vs a Pre Amp/Power Amp. My tube pre amp does not have a tape loop. If that is not recommended, same question to hook up between my source (Cambridge Audio DACMagic Plus) and Pre Amp.

Thank you for your help with this question and I hope this is the right place/forum for this question.

John

 

[RossW]

Between the preamp and the power amp is pretty standard, the only real advantage of the tape loop is that it allows you to switch it out.
If anything the tape loop is probably slightly worse for sound quality (more connections, etc.).

 

[Pyrrho]

It has been a while since I owned a pair and looked at the manual, but I seem to recall that KEF recommended using it in a tape monitor, but that it would be okay to put it between the preamp and power amp. So, I think it will not hurt anything, but will be less than ideal.

 

[swechsler]

Voltages in tape loop and preamp output are pretty similar, to the point that in a pinch you could hook the preamp outputs to a tape deck's inputs and record a tape that way (assuming you kept the volume constant while doing so). The only disadvantage is that any noise from the Kube will be amplified at maximum volume rather than at the volume knob's setting. You'll want to hit the controls with some Deoxit and make sure they are completely quiet before running the system this way.

 

[Pyrrho]

I see my memory is correct:

https://us.kef.com/explore-kef/kef-museum/1980s/reference-series-model-102-1986-90

Here is the manual where it tells you it is best in the tape monitor:

https://us.kef.com/pub/media/pdf/Reference_Series_Model_102_Installation_Instructions.pdf

 

[Pyrrho]

... If that is not recommended, same question to hook up between my source (Cambridge Audio DACMagic Plus) and Pre Amp.
...

If you have only one source, that is probably better than putting it between the preamp and power amp, because the level should be pretty close to what you would have in a tape monitor loop. The reason they don't suggest this as an option is that they are thinking most people will have more than one source, and you want the Kube for all sources, whenever you are using the speakers, or it will not sound right.

 

[Pyrrho]

One more thing: Those are really nice little speakers.

 

[John Parkey]

Thank you everyone! I am listening to them now and really enjoying it. I had the Kube rebuilt because several of the larger capacitors split open. The technician used op amps which have a much lower noise floor than the originals and the speakers have never sounded better. Love AudioKarma.

 

[canuckaudiog]

Thank you everyone! I am listening to them now and really enjoying it. I had the Kube rebuilt because several of the larger capacitors split open. The technician used op amps which have a much lower noise floor than the originals and the speakers have never sounded better. Love AudioKarma.

Good call. I did the same thing in the KUBE for the 107s I used to have, and the difference was astonishing.

 

[Blue Shadow]

The level of the preamp output is Variable from very low to a volt or two. When the kube is between the pre and power at low listening levels the signal going into the kube might be just barely above the noise in the kube. Unless you use most of the preamp output you wil have better signal processing using the tape loop and that standard voltage for the most part. The signal will be well above the kube noise in the correct operating range of its electronics.

I would always us a tape/signal processor loop unless I needed it for another input before I would stuff the kube between pre and power.

 

[John Parkey]

The level of the preamp output is Variable from very low to a volt or two. When the kube is between the pre and power at low listening levels the signal going into the kube might be just barely above the noise in the kube. Unless you use most of the preamp output you wil have better signal processing using the tape loop and that standard voltage for the most part. The signal will be well above the kube noise in the correct operating range of its electronics.

I would always us a tape/signal processor loop unless I needed it for another input before I would stuff the kube between pre and power.

Thank you. I checked with a repair tech and he told me the same thing. 0 to 1.5 volts out of preamp and 0 to 5 volts in tape loop and also out of most source components.

 

[Laurence C]

I recently rebuilt a pair of Kef Reference 102s for my father, to go with a Quad FM4/34/306 (also rebuilt). With this particular combination, the 34 has a low output and the 306 high sensitivity so definitely the best route was to go via the tape loop so that the gain structure was better and the noise floor was pre-fader, as per KEFs recommendation in the manual. To make things easier, in this arrangement I lifted out one leg of C55 in the Quad 34, and the 34 will power up with tape monitor activated. A few other notes along the way:-

1. My T33s were really down on output (12dB!). The original specification APG512 ferrofluid for the T33 is no longer available. This was low viscoscity (120MPa) with flux density 250 Gauss, and I had trouble finding a suitable equivalent - most are too viscous. The ferrofluid in this design provides very little if any damping and appears to have been for cooling only. I was able to make a proportionate mix of two other commonly available fluids to get to a similar specification.
2. The Kube is of course very much necessary as it forms part of the crossover in this design. Since I had to rebuild mine and test it, I have attached a few images of the frequency response since I've seen this come up a few times with folk who no longer have the Kube and want to replicate it using DSP, or check the Kube they have is working correctly!
3. Recapping was worthwhile. I used Solen caps and replaced the 600uF in line with the LF driver with a wire link. This would probably have created a 3rd-order LF rolloff instead of a natural second order, and I suspect mostly protected the LF driver against excessive excursion due to vinyl warp - not an issue for the system they'll be used in.

Its is reasonable to go further and replace the voltage regulators with something quieter - the 78/79 series are particularly noisy (especially the negative rail), and replace the op amps if I was also doing those in the Quad 34.

Next project is an LED replacement display for the Futaba 6-LT-06 vacuum flourescent display in the original Naim NAT-01, but retaining the original OKI MSM 5525 frequency counter and driver.

Hope this is useful.

 

[kuene]

I’ve had a pair of KEF 102 in near perfect condition for a couple years now. Did the ferrofluid in one tweeter that was very dull and brought it back to life. (Will do the other one when I get a chance). Of course there was no KUBE when I picked these up, and I’ve been messing with loudness and eq to get that bass sounding better. Last week I finally scored a very nice KUBE on eBay for fairly cheap (was missing plastic button covers for the two switches, but otherwise clean and mint).

All I can say is WOW. I thought these 102s sound great before, but I’m now firmly in the camp that insists on having the KUBE or nothing. These things sound absolutely amazing now.

I tested out the KUBE via the tape ins/outs, but since I only have one clean digital source, and to avoid extra cables and the extra tape circuit of a 90s era amp, I’m just running the KUBE in line between my streamer and my Denon PMA 560. Sounds the same as tape in/out.

 

[Massive Lee]

I just purchased a Kube 102 to run on my KEF C60 (I also have a set of R102 for which that Kube was designed).

I find the sound awfully dull with the Kube in the loop. Is that how it is supposed to sound when used on an R102, or am I in for a recap job?

PS _ I have had several Kubes over the year, and currently running a KEF KUBE 200 prototype on my 107/2. None of the Kubes sounded as bad as that one.