REL Subs with ARC Ref series amps

This is basically a public service announcement, etc. I recently finished off my ARC quest by purchasing an ARC Ref 5se to go along with my Ref 2se Phono and Ref 250 mono blocks. I have used a REL sub via low-level connection with my preamps in the past as I had a Rowland 302 class D amp that 'didn't like' the REL via high level neutrik connection.

When going to the Ref 5se, I knew from previous threads that the ARC preamps were optimal at their impedance loads with REL via low level connections. One way around this is to have a custom impedance box made to insert between the REL and the ARC preamp. I didn't want to do this so I still used it via low level connection with marginal results and 'tubby bass.' When trying to connect the REL to the ARC mono blocks via high level Neutrik, I got into quite a bit of noise/ground issues that couldn't be resolved.

Then a quick email to Paul Greene at Sumiko and I found out that the ARC Ref series amps are different than most amps. Here is how Paul had me set this up and said it comes straight from ARC:

R monoblock:
0 ohm tap - negative loudspeaker cable
4 ohm tap - positive loudspeaker cable
8 ohm tap - red REL cable
16 ohm tap - nothing

L monoblock:
0 ohm tap - negative loudspeaker cable
4 ohm tap - positive loudspeaker cable AND black ground from REL
8 ohm tap - yellow REL cable
16 ohm tap - nothing

When doing this, everything got tons better with tight bass and superbly integrated with the loudspeakers - just like it was before with a Rowland Synergy using low level.

What I learned was the following:

1. The rumor is absolutely true - ARC preamps don't like REL subs hooked low level due to impedance matching. From other threads on the forum some even say that it shortens the life of the preamp.

2. The REL to ARC Ref amps high level hook up via Neutrik is not like other high level hook ups to REL subs. Apparently this is for the REF amps only.

Thanks a bunch to Paul Greene at Sumiko for a quick and very helpful response!
Phil ... glad to read that you were able to hook up your sub with good results. Your tale is somewhat similar to my situation when I tried to hook up my self powered Paradigm sub woofer to my former Ref 3 (now 5 SE). I went the impedance buffer route. Actually, had no choice. My sub is not set up to be driven off my Ref 150 amp.

Just curious. Why did you contact Sumiko rather than ARC tech support??
Since they are all part of the Fine Sounds Group, I figured these issues would be shared by all. I actually contacted REL first via their website and I'm guessing REL forwarded it to Sumiko since I was a US customer.

Your thread on impedance and subs/ARC Ref preamps was very helpful, otherwise I would have never known. The sound I'm getting without strapping both outputs of the Ref 5se is startling. I wasn't expecting much difference, but frankly I'm shocked.

I had initially tried the High Level set up with the REF 250's but had some ground issues. I followed REL manual set up recommendations. When Paul from Sumiko said 'trust me, this will make no sense hooking the ground tap to the 4 ohm positive loudspeaker tap, but it's the only way for ARC REF amps, ' I thought I should share this with other people in my potential situation.

Again, bifwynne, thanks to you are I may have never known and tolerated less than maximal sound quality.
Thanks and glad to read that you're having such a great result.

You may want to share your story with Kal or Chris at ARC. Your REL/Ref 250 tap hook-up is an interesting solution and other ARC owners may benefit if Kal and Chris learn about your hook-up solution, if they aren't already aware of it.

I surmise that our shared experiences are not unique and no doubt others can benefit from what we have learned.
Thanks for publicizing this excellent info.

I recall seeing schematics on the web for two or three older (non-REF) ARC power amps which showed the 4 ohm tap as being connected to the amp's circuit ground, with all of the other taps (including the 0 ohm/common terminal) outputting signal voltages relative to circuit ground. And, as might be expected, circuit ground being connected to chassis ground/AC safety ground through a low value resistor.

So I suspect that a similar approach may be used in the REF amps, which would explain why connecting the black (ground) wire from the sub to the 4 ohm terminal makes sense.

Also, I would think that if connecting the positive wires from the main speakers to the 8 ohm taps, rather than the 4 ohm taps, results in better sonics from the main speakers there would be no reason not to do that, while leaving the REL connections as stated. And I would think that connecting the REL's red and yellow wires to the 16 ohm taps rather than the 8 ohm taps should also work fine, with the black wire continuing to be connected to the 4 ohm tap of one of the amps.

Best regards,
-- Al