Kinki studio EX-M1, EX-M1+ differences... vs Denafrips Hestia/ Hyperion combo?

The only one I am aware of that has had both the Kinki and Denafrips pieces in house and for review is Srajen with 6 Moons.  Reach out to him through the contact on his website and see what he says.  He currently has the Kinki EX-M1 and the B7 monos in his personal systems.

Couple years ago looking for summertime ss amp to replace my 845SET tube amp/space heater. Had both Musical Fidelity  M2si and Hyperion in for audition, much preferred MF. In my setup the Hyperion was overtly dark, closed in, small sound stage, images, one of the most disappointing audio purchases ever. I'm willing to entertain the thought Hyperion just not sympathetic with my Coincident Statement preamp, Based on specs, no impedance mismatch.
I did hear Hyperion matched with Hestia at sellers residence, not familiar enough with his system to make informed impression. Perhaps its informative to mention it was his third choice system out of three systems in his house.

Thank you jackd, I will check out 6Moons and see if I can get a hold of
Srajen!

sns, all feedback is good feedback and I thank you!

Sarjan, by the way, is in the middle of moving from his old digs in Ireland to another location (still in Ireland) that will occupy him for the next few weeks. He said he'll be back as soon as he can, but he won't be answering any emails, do any reviews or updates until then.

In the meantime, you can scour his reviews and thoughts at his site as he always references the components he uses and he uses several, all in different combos and systems to get a proper handle on the sound of things.

All the best,
Nonoise

Can you just give me his cell phone number, I’m sure he won’t mind. hahahaha Thanks for the heads up. I’m already leaning toward the M1+ now, but would still like to get as much feedback as I can before I spend more money.

The EX-M1 is a pure integrated amplifier without the capability of preout and power amp in ( home theater bypass), meaning it is impossible in future if you want to add another power amp to bi-amp your speaker or you want to make it to use as a power amp. While the EX-M1+ had the capability to become a power amp or preamp.

https://www.youtube.com/watch?v=qw1K76Ki69A

https://www.youtube.com/watch?v=W94mpTZhAA0

The original EX-M1 was introduced in 2017. The newly updated EX-M1 — without the “+” — costs $2398 and includes, among other things, changes in the power supply, capacitance, and the volume control, the latter now using a MUSES72320 controller instead of the previous relay-based control. The EX-M1+ is essentially identical to the upgraded EX-M1, but adds a preamp-stage output and a home-theater bypass to entirely bypass the preamp stage.


This seems pretty clear to me the latest version of the EX-M1 has those updates to the power supply capacitance and volume control. The + version has those updates but also adds a preamp out and a home theater bypass. The preamp out allows you to use an outboard amp and the bypass allows you to run an AVR  or something to control multiple speakers in a HT setup.

Hestia and Hyperion r the choice for my Zu DW’s.  Let ‘em run n, they gotta lot of caps; so for a good month.  The pair is smooth, organic, open, dynamic and powerfully musical.  The midrange is excellent.  If you’ve played around with tube and ss amps for a while, you may find the Denafrips sound to provide that ‘just right’ sound.  Organic and dynamic, with a wide soundstage and plenty of air the duo may give up a tad of resolution but easily resolves the quality of your music collection.  They’ve an analog character in a good way, open and balanced, powerful and confident.  
My sense is that the Kinki gear is voiced towards a faster, leaner sound.
A set of different listening priorities, the ‘you are there’ presentation that prioritizes detail retrieval and micro spatial cues along with tight fast transients.  
If these two were coupling capacitors, the Denafrips house sound is Jupiter or Dueland copper foils, the Kinki is CuTf V-Cap built around speed and resolution.  If you’ve familiar with the differences, you know one must be very careful when mixing them as it is easy to introduce anomalies in the frequency response, a hardness or sluggishness is introduced by often times a component mismatch or speaker selection.  They may really both potentially be very good, but perhaps not together.

Horses 4 courses… (-;

jond,

After you said it is pretty clear to you, I re-read the sentence, slower this time and it is pretty damn clear.  haha 

Thanks!
jwlaudio

regismc,

Thank you for your impressions.  I'm getting a similar impression, albeit without any real-life experience with either system.  I'm told youtube's audio is heavily compressed so I take all the videos I watch with a grain of salt, reviewers included.    

Damn, I am getting into this price territory now, where if I spend a little more, I can get the Pass Labs INT25 or the PS Audio BHK 250 power amp (I have the opportunity to buy it for 30% off right now).  This is seriously an addiction.

jwlaudio

Not really sure with the M1+ priced at $2895 with free shipping how you are getting anywhere near the price territory of either the Pass or BHK with both at $7250 plus without shipping included.  I own a BHK 250 and even at the old heavily dealer discount prices it wasn't close price wise. Also as I own or have owned an original EX-M1 and the current M1+ and M7 I have a pretty good idea about the house sound after almost four years.  Lean it is not and I have used them with over a half dozen different speakers from Spatial, Verity, Nola, Reynaud, Harbeth and Fritz.

jwlaudio, can I ask what speaker you will be using?  Both those products you mentioned, the Pass and PS are nice amps.  If I’m going low power I’m going SET.  So I’d pass on the Pass though I’ve heard the 60wpc sound great with a pair of Ryan’s.  I like the BK amp very much though.
When I mentioned the Kinki as being ‘leaner’ it was in relation to the Denafrips.  All three would be leaner in comparison.  Perhaps I should have simply said more neutral, less warm, cooler.

jackd any comparison of Kinki vs PS amp?  I’ve only read about the Kinki stuff.  U certainly roll through a bunch of speakers, nice ones too…

@regismc 

Two my ears with multiple speakers the Kinki house sound is pretty much neutral and allows the character of the particular speaker in use to set the tone.  Amps that I have owned that were similar were the Nuforce STA-200 and the Job 225, both based on the same circuit design owned by Goldmund.  The BHK is just to the slightly warmer side of neutral and it can be tailored slightly by the choice of input tube.  I have tried Gold Lion, Tungsram, Mullard and Matsushita in it and the sonic character only changed slightly and not by the great lengths i have seen described by others.  Both are great amps but with the BHK you still need to drive it and using a DAC to do it was not for me as I tried it with the DS SR.

jackd 

Nice.  I can relate to the small tube rolling and the subtle differences imparted.  I did the same with Amprex and Mullards years ago.  Still use a pr. of Bugle Boys in my EAT Petite phono pre as the Mullards go a bit too soft.  Did you go with the BK preamp in your setup?  After years of going dac direct, I like the Hestia pre also, just a bit more tonal body driving the Hyperion amp.  ‘Sides I like the footprint of the duo.  I’ve got an Athena pre here also, and she’s a beast, big and heavy.  I picked it up from a fella moving to an ARC Ref 6 because he felt the added active drive helped control his speakers woofers better.  It’s ‘almost’ too much in my modest system.  Like moving from the 10th row to the front row.  Added magnification, better separation, bigger soundstage, but the same tonal qualities as its smaller sister.  I’m unsure on weather to get the dac or a larger amp next as I think any step up will force another speaker purchase.  The new Zu Soul’s would be terrific with the top Denafrips gear.  A bargain too!  The endless chase, as really the Denafrips duo, driving the DW’s w/Jupiter caps is a nicely balanced system and I quite like how easily the entry duo makes me forget about the several tube amps I’ve collected.  Are those 6922’s in the BK or ???

@regismc 

The BHK amps will take any tube from the 6dj8 or 7dj8 family.  The Matsushita's I ended up staying with are 7DJ8's.  I have tried the BHK 250 with the Modwright LS-100, Sonic Frontier Line 2 SE+, the BHK preamp and the Supratek Chardonnay.  In the end the Supratek won out. Not as many convenience features but much better sound and less noise.  

Wow!  Those r cool preamps.  Must sound really nice.  Did u settle on a speaker?  I’ve some of those 6dj8 around as I once had a Dodd battery pre that required such.  Think I sold it on to a fella in Eastern Europe.  Sure was a good looking piece of kit though…

@regismc 

For now the #1 speaker is the Verity Otello but I still have all of the others between two houses in two different states.  The Verity's are driven by either the BHK 250 or the Kinki EX-M7 with the Supratek Chardonnay. The Nola KO's give the Otello's a good run for the money. 

jackd 

I bet they do!  You’ve got an audiophiles dream going on.  Tough problem, the BHK on tone, finesse, the M7 on pure grunt?  I bet both sound great.  Thnx 4 sharing, b well…

Jackd,

Thank you for your impressions with the kinki and bhk!  I have the opportunity to buy a BHK 250 for about 5k.  I was actually comparing that price with the Denafrips stack, which I'm also considering. 

I've love to hear more of your impressions comparing those 2.  I've been reading that my DirectStream DAC benefits greatly from a pre-amp, so initially I wanted to buy a power amp and live with the volume control on my DAC until I get the motivation to spend even more money on the BHK pre amp.

This is real dilemma. Is the BHK that much better? Is it better?

Regards,
jwlaudio

regismc,

I'll be mating this amp with the Klipsch RP-600M, but I see an upgrade in the near future, possibly the Heresy IVs.  I ordered a Decware tube amp, but it's still like a half a year out, if not more.  I've been hesitant on the BHK 250, not only because it ups the price so much, but also because I'll have a tube amp coming sooner or later, I was planning on adding a full solid state amp to the collection.

jwlaudio

jwlaudio 

Anything Klipsch will not need the kind of power or sophistication you r considering.   The Decware will serve u well, when it arrives.  If it were me, and I’m biased cause I own the stuff, I’d buy the entry Hestia/Hyperion and settle in.  Will take about two weeks to get to your doorstep and won’t break the bank.  Good luck…

Hell even better, pick up the Rotel Tribute integrated and settle in for a few months.  $800 bucks I think.  They sound really nice and even do Bluetooth.  I own the matching CD player and like it very much…

Take a look at the Norma Audio integrated amps.
Norma Audio | AudioThesis

jwlaudio, you're on the right track with Decware amp. I used the Hyperion with my modded Klipschorns, not a good match. I'd stay with tube amp for Klipsch. And you don't need that much power anyway, if you want ss amp try the Musical Fidelity M2si, now that is a sweet sounding ss amp for Klipsch, won't break the bank.

@regismc and @sns 

Thanks for the feedback.  These Kilpsch are currently my speakers but I will probably venture out into other makes and models in the future.  As you mentioned, the Decware will probably drive these pretty well.  I've watched reviews about some of the models you mentioned and I was considering them as well.  I don't mind spending a little more now if I can future proof, if that is even possible.  With all the "synergy" talk with components, I know it will be difficult.  I guess part of the fun is upgrading and trying new things.  At one point, I thought about building those Pass Labs Amp Camp Amps to get a taste of that sound before I spend too much.

@mboldda1 I've never heard of those Norma amps before.  I'm going to have to check those out as well.

@jwlaudio  here is a recent review of the norma entry level integrated.
https://www.thesoundadvocate.com/2021/08/norma-hs-ipa1-integrated-amplifier-analysis/

@mboldda1  - Thank you.  It was nice to read about something else besides what all the reviewers are taking turns reviewing.

I've decided to go another direction due to a sale that brought an item down into my price range.  I wish I would have seen the sale sooner, but oh well, I learned a lot during that time.

Thanks everyone!

jwlaudio

@jwlaudio don't just leave us hanging what did you get?

@jond 

I didn't know you cared!  hahaha

I ended up with a First Watt F8 (Picked up 30mins from me =) and I was able to get a 30% discount on a new PS Audio BHK Preamplifier.  I found out about the PS Audio sale after I bought the First Watt F8.  I could have ended up with the PS Audio BHK 250 + BHK Pre, for about $1k more.  The BHK Pre is getting built right now, so we'll see how it sounds.  So far, the First Watt F8 is getting better and better as it burns/breaks in... it is also on the bottom shelf, but near my thermostat and my place is freezing in every room when it's on. This amp runs HOT! lol

@jwlaudio that's great I've heard First Watt amps a few times at shows always sounding great you basically can't go wrong with a Nelson Pass amp. And a tube pre and great SS amp is a fantastic combo for many listeners. And yes those class A amps do need extra ventilation get it away from that thermostat lol!

@jwlaudio 

Just a bit of info that may or may not be important to you from an owner of the BHK preamplifier for over three years.  As the F8 is a single ended amp and the BHK is fully balanced you are likely to run into two small issues.  One is you are likely going to half to lift the ground on either the amp or the preamp and secondly the BHK preamps in general are not fond of SE amp connections as it tends to cause an increased level of clicking with their unusual volume control.  I tried mine with well over a half dozen SE amps and the increased clicking occurred with each one.  A friend tried two different samples of the BHK and ran into the same issues and this includes SE amps with convenience XLR connectors.  Another issue that may limit your tube choices is that the BHK needs input tube with matched triodes to keep the volume control noise in check which is much harder and more expensive to find in NOS variants than in new production tubes.  But in the end if you have an amp that the BHK "likes" then it is a very solid choice.  

@jackd 
Thank you for the info. What does "lift the ground up" mean? I've read about all the quirks of this preamp, but it seemed to be a trade off people were willing to deal with because it improved their sound.

I was looking into the Decware zbit to increase the voltage to my F8 because right now with the DAC controlling the volume, I can max it out and it's loud, but nothing too crazy.  I'm just not used to having my volume at 75 to 90% all the time.

I don't plan on tube rolling any time soon, so I'll have to cross that bridge when the time comes.

Like you mentioned, since the F8 is SE, I've wondered if it's worth connecting everything else with XLR.  

What amp have you matched the BHK Pre with?  Do you have an experience with mating it to the BHK 250?

@jwlaudio

By lifting the ground I mean using a cheater plug preferably on the preamp and if you are plugging into a grounded conditioner it won’t make a difference anyway.

In the 3+ years I owned the BHK I tried it with the following amps all from memory. Mystere PA-11, Music Reference RM-10, Granite Audio 861 mono’s, Nuforce STA-200, Nord One, Nuprime ST-10, Mivera Purepower, Odyssey Kismet, Kinki EX-M7 and the BHK 250. The best match was obviously the BHK which I still have and swap in and out with the EX-M7.

Sticking with the stock tubes or the Gold Lions is a good place to stay as finding NOS as quiet will be hard and expensive in most cases. When you get the preamp I would suggest you take the tubes out and re-seat them after their ride with FedEx.

As to the cables for a start use what you have especially if you don't have a long distance to run or noise issues.  

@jackd

I take it "lifting the ground" removes noise?  Worst case I can just return the BHK Pre, or sell the F8 and buy the BHK 250, I guess.... hopefully I don't run into too many quirks.

Thanks for this info, I know what to expect.

It's for if you have a ground loop which with that combo is likely.  Like I said if you are plugging the components into a conditioner that itself is grounded then that will be fine.  If the problem does occur try the cheater on the preamp first. Not the end of the world if you like the sound from the combo.  The BHK only has about 4db gain from the SE outputs so you still may borderline on gain.

@regismc  &  @jackd 

Very interesting reading your comments/experiences on the Kinki and Denafrips gear as I'm considering heading that way.

I'm currently running Auralic G1 > Holo Spring L2 > Herron VTSP-3 > Rogue Stereo 100 > Silverline Sonata III floorstanders (8ohms, 93 dB sensitivity) & Rythmik sealed sub.

Sound is excellent but a few factors are driving me toward some changes: wifey doesn't like the big Rogue sitting on top of the hifi cabinet, the Herron is only single ended but the Spring DAC is best from its balanced outputs and the Rogue is best via its balanced inputs, there is too much gain in the system, I want to try something new. Room is 19' x 22' x 8' and acoustically treated.

My preferred sound is reasonably neutral and "in the middle", not fast/lean/ultra detailed/analytical and not overtly tubey/schmaltzy/euphonic etc. Even though the Herron and Rogue are both tubed, neither is particularly tubey sounding.

In an attempt to downsize last year I tried a Kinki EX-M1 integrated for a while and loved its low noise floor, dynamics, detail and PRaT but it lacked a touch of warmth (partially alleviated by discrete opamps) and there was something in the sound that I couldn't quite live with. Somehow it seemed excessively damped like harmonics were being truncated (sorry if that doesn't make sense but I'm not sure how to properly explain what I heard/sensed) and there was way too much gain, even on the low gain setting. As much as I loved 99% of what it did, something in my subconscious kept telling me that there was something very slightly unnatural about its portrayal. I don't know if this issue stemmed from the pre-amp or power amp section of the EX-M1 (there was no pre-out to test on another amp) so I had to sell it and my subconscious was then able to fully relax again and enjoy the music with my tube gear again.

I'm thinking that step one may be to replace the single ended Herron with the Denafrips Athena which is unity gain and fully balanced (allowing me to get max performance from my current DAC and amp) with a slightly warm and full bodied persona that might maintain much of the sound qualities I get from the Herron tube preamp, and with a lower noise floor that may convey more detail and dynamics.

Step 2 would be the power amp. Once the Athena was bedded I'd know whether I needed to go for an amp that is slightly faster/leaner (Kinki EX-M7 if it doesn't have the same issue I heard with the EX-M1) or slightly more full bodied (Denafrips Thallo). Either of these amps would fit in my cabinet with 2 or 3 inches space above for ventilation (the back of the cabinet is also open). 

I would try to get loaners to try out in my system but I'd be very grateful for your thoughts on whether you feel this strategy makes sense given my stated goals/preferences.
  

While I can't say anything specifically in regard to Athena, my experience with Hyperion leaves me skeptical that any Denafrips product would be to my liking. The extreme darkness, closed in voicing of Hyperion leads me to believe company doesn't voice their products towards the neutral. Perhaps they balance out end sound signature with darkness in one component, lightness in other, not my cup of tea. I want all my components voice towards the neutral, I can flavor myself.
I also hear this overly warm characterization from some Denafrips Terminator users. Seems the new + series has improved greatly upon this. Perhaps the Athena will reflect this new voicing at Denafrips, in which case it may work well for you.

@dkerr -- I've been experimenting with some different gear lately in my second system. I picked up a Kinki EX-M1+ last week, and I must say my experience is almost the same as yours. It is a good competent amp and does all the 'modern' tricks of neutrality, detail, dynamics, etc. quite well. But just like you, I can't help but feel that something is amiss. I'm impressed but not moved.

I have been helping a family friend build his system based around tube amps. We bought a used VTL I-85 and it is an excellent amp. I'm so impressed that I'm thinking of buying one for myself now. It's not 'modern' sounding per se but it draws you into the music in a way that Kinki can never even dream of.

@sns 

The extreme darkness, closed in voicing of Hyperion leads me to believe company doesn't voice their products towards the neutral.

After everything I've read on the Hestia/Hyperion/Athena, I don't think that there is any doubt that these units are all more full bodied than the Kinki gear which is (comparatively) cooler/leaner/quicker and more overtly detailed. 

Srajan, who prefers the cooler/leaner/quicker "Swiss" sound, makes this point in his comparisons but notes that the delta is small and that his preference would depend on which speakers were in use or even how lively the room was, that it was a case of fine tuning. His testing of the Hestia and Hyperion together indicates that they are both similarly voiced (and the Terminator too) but he doesn't seem to indicate that even using them together takes these traits too far.  

Obviously it also comes down to personal taste as well but I think that you are the first person I've seen to go so far as to use "extreme darkness and closed in" to describe the Hyperion. I do prefer a touch of warmth, full bodied-ness and organicness to overtly detailed, lean or analytical but extreme darkness makes me think twice about purchasing a Denafrips preamp or amp.

Can I ask what amp(s) you compared in that system that made the Hyperion sound extremely dark and closed in? And the speakers used?
 

So after I started this post I went bonkers.  I now have the First Watt F8, a Yamaha B-2 (Vfet), built the Nelson Pass Amp Camp Amp and have a BHK Pre on order.  I have to say the F8 and the B-2 are amazing amps.  Comparing the characteristics of these amps vs the $100 Class D SMSL SA 300 that I also have, I learned that I really enjoy the forward midrange presentation... or vocals that are more forward, if that's what forward midrange presentation means.  I'm still very curious about the kinki and denafrips offerings but need to calm down on the spending.

@dkerr For amps I have Coincident Turbo 845SET,Art Audio Carissa Signature 845SET,  custom built 300B SET monoblocks, Prima Luna Dialogue Four (modded with Takman resistors and Miflex and Mundorf capacitors, use exclusively with EL34 these days), Coincident Statement line stage, Klipschorns (extensively modded, only bass enclosure stock).
I also had Musical Fidelity M2si ss integrated amp in for audition at same time as Hyperion, MF sound signature light and lively compared to Hyperion. All my amps more modern sound SET in nature, not rolled off on top, tight bass. Klipschorns, and all Klipsch generally thought of as bright speakers, mine far more refined, but definitely not dark.
I really dislike criticizing equipment, but I have to say, Hyperion had perhaps the most apparent sound signature I've ever encountered in an amp. I've also been through many other push pull tube and class A ss amps over many years, none, with perhaps a Conrad Johnson MV-55 were quite this tilted towards the warm. It wasn't just the sound signature that bothered me, it didn't resolve very well either, smaller soundstage, less dimensional imaging, obscured lower level details. I actually thought the amp broken or no burn in at first. Both were accounted for, no issues here. For what its worth, guy I purchased from had perhaps seven, eight amps in house, this was the only one selling, and he didn't keep long.
 The only way I could see Hyperion working is in extremely up tilted system and/or for someone who enjoys warm syrupy sound. For context, In spite of my preference for SET tube amps I prefer slightly to the analytical side of neutral, Hyperion on far end of warm in my system and for my ears.

I've recommended the MF2si any number of times to those seeking a nice sweet sounding ss integrated. Don't let the $1k price fool you, relatively low powered ss has always worked best for me. I'd for sure check into the First Watt, would be my first choice for low powered ss, many flavors available Still, based on your stated sound preferences, I'm not sure any ss will deliver the full measure on those.

@sns  Wow, thanks so much for the detailed response. It provides great context and much for me to think about. 

I've never heard a First Watt amp class A amp but can't go for a class A amp given that one of the justifications for a new amp is that it will fit inside my low profile cabinet (shelves are only about 8" high). I had a big Plinius SA100 mk3 many years ago and liked it but it seemed to have a slight haze that masked detail.

based on your stated sound preferences, I'm not sure any ss will deliver the full measure on those.

That thought has been in the back of my mind too. But the Kinki EX-M1 integrated came VERY close to dislodging my tube preamp AND tube amp. A different sound ... more dynamic, punchy, detailed (but smooth and not bright or aggressive), robust, exciting ... but I wanted for just a touch more organicness, palpability, harmonic completeness ... I love tone more than hyper detail.

Overall my system is fairly neutral but just a little closer to the "full bodied  and relaxing" end than the "faster and exciting" end. I want to move it slightly toward the faster and exciting side but without any brightness, glare, leanness or analytical sound.

Maybe my tube pre with say the Kinki M7 would achieve this ... and get the amp inside the cabinet ... the M7's input sensitivity of 1.45v (as opposed to my Rogue's 1.0v) would help with the gain issue (the Rogue has 29dB gain, I'm unsure of the M7). This setup still wouldn't enable me to use balanced out from the Spring DAC but maybe I could live with this given the potential benefit from the M7 *IF* it doesn't have the truncated harmonics (for want of a better description) that I heard in the EX-M1 integrated.

@arafiq 
 

I've been experimenting with some different gear lately in my second system. I picked up a Kinki EX-M1+ last week, and I must say my experience is almost the same as yours. It is a good competent amp and does all the 'modern' tricks of neutrality, detail, dynamics, etc. quite well. But just like you, I can't help but feel that something is amiss. I'm impressed but not moved.

I have been helping a family friend build his system based around tube amps. We bought a used VTL I-85 and it is an excellent amp. I'm so impressed that I'm thinking of buying one for myself now. It's not 'modern' sounding per se but it draws you into the music in a way that Kinki can never even dream of.

Funnily enough, the guy that bought the EX-M1 from me preferred it to his VTL ST-150 & modded Audionote M3 combo and sold them.

Different strokes ...

@jwlaudio 

If all of those new amps in your stable are all single ended you may be disappointed with the BHK preamp.  Both myself and several friends found that when run single ended the volume control makes a great deal of noise when used in either direction.  The only way to mitigate it at all is to have fully gain and triode matched 12AU7 tubes which pretty much limits you to new production.  I had no luck at all with 6 or 7 volt tubes over the four years I owned mine and found it's best mate to be the BHK amp and I tried many. 

@jackd 

Thanks for that.  Why do you think this is the case?  I have thought about buying an XLR to RCA that boosts the voltage a little bit so I can use the balanced interconnects.  If I build another Nelson Amp Camp Amp, I could have an amp with balanced outputs in dual mono configuration, but the F8 and this Yamaha is noticeably better, at least to my ears.  I hope they send me new tubes, PS Audio is building my BHK pre right now, so at least the unit is new production.  It's been like 3 weeks already, hopefully they will finish building it and send it out to me soon.

@jwlaudio 

Not sure but something in the way Bascom designed the volume control circuit.  Just know that between a friend and I we tried three different units and almost a dozen SE amps.  If it causes a problem at least you have the 30 day return.