CL Score- Kenwood M1

[thekid]

An addiction is a hard thing to break but even after getting the Luxman a couple of weeks ago I still find myself scanning Craigslist for gear. Yesterday I saw a listing for a Amp and it turned out to be a Kenwood Basic M1 w Dynamic Linear Drive for only $50. Picked up tonight and gave it a quick test with my C2 pre-amp. Sound is very good though I might have to deox it a little as I noted a little scratchiness in the left A channel. Cosmetically it has a few scratches and needs a bit of a cleaning. I have not tried the Sigma drive yet because I am not sure how I should do the wiring. It look like I could use 2 sets of speaker wire and then just twist them into a single strand for the Sigma connection. Anyone have any experience with this unit and could help me with the wiring issue?

[02audionoob]

From what little I've seen on the topic, the Sigma wire was a thin conductor for the Sigma drive and thick conductor for the actual speaker output. The original was apparently 4 meters long, which might have some technical significance if you also knew the gauge of the thick conductor. It does seem like you could replicate the original. Maybe you could try out something like 30 gauge for the Sigma and 16 for the output.

[Mr Peabody]

How many of those do you have now?

Ok, now I'm freaking out. I always thought "Sigma Drive" was just some built in circuit that helped the amp. I didn't realize it had to have extra wire. I worked for a Kenwood dealer and owned the gear, that's why I'm freakin. I had friends that used the M2's in DJ rigs. I don't think any of us must have had that hooked up. I had a very high end Kenwood integrated, KA-3300d, for years and to think i may not have ever heard what it could really potentially do. I know I read the manual but I guess I could have skipped hooking up speakers thinking "any one can hook up speakers: :)

I did some basic searches and the Sigma connection can be made with any thin wire but I found nothing on how to hook it up. If you all turn something up I'd be interested in knowing how this is supposed to work. I can't believe it, even in the literature that described the circuit nothing was mentioned about an extra wire.

[thekid]

02 -Thanks for the suggestion. I might give that a shot after I read up a little more. I want to be careful and not fry an amp and a pair of speakers.

Mr. P

This is my second Basic amp and I have 2 C1 and a C2 pre-amp. Next on the list would be a M2 which come up often enough on E-Pay and still command a premium. Obviously have more than enough gear but if one comes along at the right price I will snag it. I would not beat yourself up too much about not knowing about the Sigma drive. Not all M1's or M2's had it and Kenwood from what I can tell did not put anything on the amp to distinguish models that had it from those that don't. The units that have it just an extra speaker terminal that is grayed out and has a Sigma sign. I am guessing there was a cost associated with those that had it versus those that don't but i have seen anything that would confirm that suspicion.

I have to agree with you regarding info on the Sigma drive. The guy I got it from was clearly not the original owner and when I checked to see if it had it it he was not even aware of it and just had it hooked to the regular speaker channels. (On a side note he had it hooked up to a C1 and a pair Bose 901 Series IV speakers) Even the Kenwood instruction manual for the unit that I got from the owner really only mentions how to hook it up but does not really tell you the benefit of using the Sigma drive versus a regular hook up. From what I have read the Sigma drive help delivers better bass response. The instruction book does say you can make your own "Sigma Cable" using ordinary speaker wire but leave out the mention of using different gauge wire (i.e. thick/thin wire) to do this. It mentions that there is a thinner wire only when describing a factory "Sigma Cable". I am going to look today to seel if anyone sells the original cables and let you know.

[02audionoob]

I copied this picture from thevintageknob.org, which has a section on Kenwood gear. Kenwood's story on this feature doesn't mention bass response, as far as I've seen. It say the wire returns distortion products back into the amp's negative feedback loop for compensation. It claims it provides an extremely high damping factor and optimum control of speaker movement.

As an aside...I used to have an M1 that I think did not have this feature. I sold it on eBay probably 5 years ago with one channel not working and replaced it with a fully-functional M1D for about the same money. In hindsight, I still sort of want that M1 back.

[Mr Peabody]

Controlling the woofer and increased damping factor would lead you to believe the Sigma was similar, or the same, as a servo control.

Over at Audio Karma I saw an old thread where a guy said the gauge of the Sigma wire doesn't matter and I got the impression that any original wires were not to be found for sale but things may have changed since that was written, worth a look.

The concensus around our store was that the M1 sounded slightly better than the M2, but the M2 obviously has more power. I'm almost sure my amp literature said it had Sigma but I would have noticed extra terminals so maybe it didn't. I wish in a way I would have hung onto that KA-3300d. Kenwood was experimenting at the time I think this is one of the first amps I've ever seen with built in DAC. I had the matching 3300d CD player which was as good as the DAC so I didn't use it much, the idea of transports didn't dawn on me back then or I could have used it when my CD player quit working. The amp also had a nice feature in a variable loudness control and a tone bypass switch. It was 150x2 into 8 ohms and a monster. I also acquired the matching tuner and kept it until I ran out of room in my rack and really didn't listen to FM in my main system any more. The KT-3300d was a dedicated FM only tuner and one of the best I've ever owned. I had it side by side with an Arcam tuner and the Kenwood rancircles around it in reception and sound quality was about equal. Well enough nastalgia.

[Kevio]

Controlling the woofer and increased damping factor would lead you to believe the Sigma was similar, or the same, as a servo control.It is servo control but with the servo extended out to the speaker ends of the speaker cables - not just to the speaker terminals on the amp. In theory the amp could then compensate for the impedance of the speaker cables.

[Feanor]

It is servo control but with the servo extended out to the speaker ends of the speaker cables - not just to the speaker terminals on the amp. In theory the amp could then compensate for the impedance of the speaker cables.

Scarey. One would hope the the feedback was used to control only the deep- and maybe mid-bass frequencies. Feedback isn't likely to be fast enough to control higher frequencies.

There is enough controversy about negative feedback within amps themselves without pulling the speaker into the loop. However servo is often used for subwoofers, e.g. the Paradigm Servo 15.

[Kevio]

Yes, to ensure stability of the system, the response of the external feedback would need to be more limited than what you find in a servo-controlled amplifier.

[thekid]

Thanks everyone for your input. It looks like I will have to make my own "Sigma Cables" using a couple of regular wires of different gauge and some spade connectors.

Cleaned out the dust tonight so I thought I'd share a couple of "topless" shots and the speaker connectors. The photo is little blurry but the sigma connections are the gray thatched ones.