input tubes for rm10 mk2

banquo446 · « **on:** 12 Dec 2011, 06:54 pm »

I've been playing around with different output tubes for the rm10 mk2, and now I've set my sights on the input tubes. Do they make a significant difference to the sound of the amp? Are people just using the stock tubes? If not, what are some recommendations? I see that Roger sells different 12ax7 tubes rated for noise (standard, low, super low). Does anyone know which are the stock ones? I sent Roger an email asking but it must have been lost because I've gotten no reply. My amp is basically as quiet as a mouse--except for a very annoying transformer hum--so whatever the stock tubes are seem fine (from the perspective of noise).

Thanks.

pehare · « **Reply #1 on:** 12 Dec 2011, 09:01 pm »

Sal at Ram Labs tubestore said he thought the Ei's were the best sounding so that's what I bought as a backup pair. (my new RM10 came w/Ei's) Hopefully Roger will chime in & give his opinion which'd be interesting to know.

Oh & by the way a different powercord makes a big difference (I can see Roger rolling his eyes now

). I tried a cheap used JPS Labs GPA cord & it was a real discernable improvement so I'm having Joe at JPS build me a new PAC Lite cord w/shurter IEC plug so it fits happily since there isn't room for the Power AC+ (which is really good too) Happy Holidays & cheers!

tubegroove · « **Reply #2 on:** 13 Dec 2011, 08:00 am »

I havent changed the EIs that got with the amp since Roger said they were amongst the best sounding and also reliable and silent for the $$. For input tubes, be careful to select replacements with low noise in the section that matters (depending on whether its the 1st or second input tube). I believe Roger also offers services to test and grade tubes that he doesnt sell
What sort of hum are you referring to? Is that audible in your speakers or is it a vibration when you touch the wood chassis? if its the latter, a little bit of that is normal per Roger and no cause for worry
I am curious what output tubes you changed to?

banquo446 · « **Reply #3 on:** 13 Dec 2011, 08:39 am »

Thanks for the responses so far. The Ei tubes are stock (as opposed to Mullards, etc.) but are they the standard, low noise or super low noise yugos (Roger sells 3 different grades)? Have I answered my own question and they are the standard yugos? My owner's manual doesn't say which came with the amp.

Pehare: what differences are you hearing with the new cord? I haven't dared consider cords as there are plenty of other little things to worry about (like the cursed ground loop I have).

tubegroove: I've tried gold lion reissues (from McShane) and now NOS GE's (from Vintage Tube Services). The former sound more or less like the stock tubes (whatever those are) but the GE's are a true winner. More natural, more space and better bass among other characteristics.

The transformer hum does not go through the speaker (that would be intolerable), but can be heard from 3-4 feet away. I have it on the bottom of my rack and I can easily hear it while changing records. I used to have the amp in my listening room and the hum was very annoying. I could barely hear it from the listening seat but to know it's there forced me to move my rack. I put isolation footers under the amp and that helps some. Some days it's quieter than others; it mocks me that way.

tubegroove · « **Reply #4 on:** 13 Dec 2011, 09:00 am »

Good question on the EIs - I think they are the standard but I am not sure. I assume there would be an upcharge for the better ones
Did you face any difficulty in biasing each pair of the GEs since the amp has only one pot per channel?
That hum sounds too loud - perhaps worth asking Roger to take a look

tubegroove · « **Reply #5 on:** 13 Dec 2011, 09:11 am »

Btw, I also use an after market power cord. Overall, compared with unbranded shielded cable or like a computer cable, an overall greater ease in the presentation (think space and timing), more controlled LF and somewhat cleaner highs (though the amp is so quiet that I anyways hear more detail than I did before).
Its easy enough to try
FWIW, YMMV

Ericus Rex · « **Reply #6 on:** 13 Dec 2011, 01:01 pm »

Ground loop hums are easy to fix...usually. You just have to float the ground on all but one component. You can use one of those cheater plugs (you can get them anywhere these days) into a power strip or power conditioner, then plug all the components except your amp into that strip. Be sure to have one component grounded!!! I recommend the amp since that's where your high voltages are. In the event of a catastrophic meltdown, the floated components would then ground out of the amp via the interconnects.

rbwalt · « **Reply #7 on:** 13 Dec 2011, 01:54 pm »

when i bought my Rm9se from roger i had him put a EC connector on it( pig tail). i started with the JPS GPA2 power cord and that made a nice difference. then i used a AC+ a bigger improvement(smoother, quieter, etc). i was using them on my equitech power conditioners( gone now in favor of a running springs Jaco). now i have a JPS kaptovator PC on my amp. much better than the AC+( smoother again, better dynamics, more articulated, more open sounding, more definition in the bottom end with more authority).

might i suggest trying a cardas Clear M PC. i am using one on my line stage. i also tried it on the amp and was dam good. that might be the way to go with your RM10 but allot depends on the kind of PC's you are using on your other gear.

rob.

PS. i had a nice long chat on PC's with roger. it was entertaining to say the least. he even got on the phone and had a chat with the fellow that told me to try a different PC on my amp. wish i could have heard that one. that is our roger.

banquo446 · « **Reply #8 on:** 13 Dec 2011, 05:02 pm »

Quote from: Ericus Rex on 13 Dec 2011, 01:01 pm

Ground loop hums are easy to fix...usually. You just have to float the ground on all but one component. You can use one of those cheater plugs (you can get them anywhere these days) into a power strip or power conditioner, then plug all the components except your amp into that strip. Be sure to have one component grounded!!! I recommend the amp since that's where your high voltages are. In the event of a catastrophic meltdown, the floated components would then ground out of the amp via the interconnects.

Oh, I wish it were that easy for me. I just bought the jensen isomax hum/buzz killer and the only thing it killed was my hope that I can defeat the problem.

rbwalt · « **Reply #9 on:** 13 Dec 2011, 11:51 pm »

how far back from the amp is your listening seat? i had a Rm9MkII that hummed when i got close to it. now if you are not hearing any humming coming from your speakers then do not worry about it.

r.

Ericus Rex · « **Reply #10 on:** 14 Dec 2011, 02:04 am »

Search 'hum' here and you'll come up with lots of great suggestions for tackling it (ground loop hum, not transformer hum)

rbwalt · « **Reply #11 on:** 14 Dec 2011, 02:23 am »

yea ground loop hum poses another problem. i had hum like that and i tried all sorts of things such as floating grounds( didn't help much) playing around with cable placements( helped some). in the end i ended up with a equitech balanced power unit. solved that problem. now i have a Running Springs ( Jaco). no hum at all!! i get protection from power surges and other noise that creeps in.

Roger A. Modjeski · « **Reply #12 on:** 14 Dec 2011, 05:09 am »

Quote from: banquo446 on 12 Dec 2011, 06:54 pm

I've been playing around with different output tubes for the rm10 mk2, and now I've set my sights on the input tubes. Do they make a significant difference to the sound of the amp? Are people just using the stock tubes? If not, what are some recommendations? I see that Roger sells different 12ax7 tubes rated for noise (standard, low, super low). Does anyone know which are the stock ones? I sent Roger an email asking but it must have been lost because I've gotten no reply. My amp is basically as quiet as a mouse--except for a very annoying transformer hum--so whatever the stock tubes are seem fine (from the perspective of noise).

Thanks.

Allmost all RM-10s go out with Yugo drivers and we select a v1 and a v2 for you putting the low noise section where it counts.

Transformer buzz presents many challenges. I have reduced it in several amplifiers by removing the transformer cover and tightening the 4 bolts that go thorough the laminations (not the mounting screws) though some people put grommets on those to decouple the chassis.

Another good thing to do is get a square of thick, heavy commercial 12 inch floor tile at home depot. Not the thing stuff with the adhesive. Cut several panels to fit the inside surfaces of the transformer cover and glue them firmly and all over with silicone or caulking. Also run a bead of silicone in the inside seams of the cover.

Roger A. Modjeski · « **Reply #13 on:** 14 Dec 2011, 05:16 am »

On the subject of ground loops. I cannot recall a time when I could not conquer them. First try floating each component separately, floating a strip or multiple outlet does no good. Let the power amp ground remain. Make sure you don't have any TV cables, grounded televisions or ANYTHING else.

The true test of the hum output of an amplifier is to put shorting plugs in the inputs and listen to the speaker. RM-10s have exceedingly low noise of 300 microvolts or less. When you remove the shorting plugs now connect the preamp. Any increase in hum or noise is obviously from the preamp. If it is still quiet with the preamp start adding your signal sources one at a time.

For those technically inclined, I have to face this situation on my test bench and it's all floating except the amp.

banquo446 · « **Reply #14 on:** 14 Dec 2011, 08:50 am »

I've tested the amp with shorting plugs and it's more or less dead quiet. Shorting plugs on passive preamp, more or less dead quiet. Add phonostage: hum and buzz from hell. I've floated the phonostage and that did nothing. The three other pieces of equipment I have (passive preamp, dvd player and turntable power supply have two pronged plugs), so there's nothing to float there. Plugging into different circuits doesn't help either. And like I mentioned, I bought a Jensen transformer and I was praying it would do the trick but alas no such luck.

I don't own a tv so no issues there. There is an internet cable line hooked up to my dvd player, but during testing I've unplugged it and moved it away--with no effect. To top it off, when my wife turns on the space heater in her office, it emits a buzzing through the speakers that's intolerably loud

I'm going to try breaking the circuit of everything else in my house except the one for the electronics and see if that does anything.

The transformer hum I can live with, especially now that the amp is far away from my seat.

At any rate, back to the question at hand. Sounds like no one has experience trying out different input tubes and that the main consideration is noise. So, one low noise tube 'where it counts' and one standard one. Right?

tubegroove · « **Reply #15 on:** 14 Dec 2011, 11:07 am »

Banquo446, your ground hum issue sounds similar to what a friend of mine experienced. After trying many options including an AC power regenerator, what completely solved it was the use of a large (3kVA) balanced isolation transformer. Not familiar with Jensen, but I believe Equi-tech makes something like this. Basically the way I understand it, the xformer takes in 2 live lines, eliminates the neutral and then steps down the voltage. Worked really well for him.
Another aspect I noticed in my own set up is that sometimes pops, clicks buzz sounds from heaters, micro ovens, flourescent lights are air borne. I have tested that by running my entire rig on batteries through an AC regenerator with no power cable connected to a wall socket. For airborne noise, I found no solution but to replace/limit use of those appliances/switches etc
On the input tubes, both need a specific section of the dual triode to be very low noise. Best to check with Roger which requires which though its also mentioned on the MR website under "RM10 Design Philosophy"

rbwalt · « **Reply #16 on:** 14 Dec 2011, 01:32 pm »

Banquo446 i suggest that you try a very good power conditioner. i had the hum issue and i tried floating grounds and it did not totally get rid of my hum. i bought a equi-tech power conditioner and that solved my problems. i now use a Running Springs Jaco conditioner and no hum at all and no noise. if you have things plugged into a power strip that is NG.

banquo446 · « **Reply #17 on:** 14 Dec 2011, 06:14 pm »

"Another aspect I noticed in my own set up is that sometimes pops, clicks buzz sounds from heaters, micro ovens, flourescent lights are air borne."

Good grief, I never thought of that. This errant noise is as elusive and as difficult to kill as a bed bug.

Thanks for the suggestions everyone.

rbwalt · « **Reply #18 on:** 14 Dec 2011, 09:00 pm »

i take it that all of your cables and interconnects are shielded.where is your system located in your house? have you tried your system in another room of the house? if that is possible. can you give a list of your gear? have you checked all your interconnect connections? they will snap, crackle and pop if bad. start at the top of the system and work your way down to the amp. have you wiggled the input tubes around a bit on the amp. sometimes that will help if they are not seated correctly.

just more ideas for you to look at if you have not thought of them already.

banquo446 · « **Reply #19 on:** 15 Dec 2011, 12:22 am »

Quote from: rbwalt on 14 Dec 2011, 09:00 pm

i take it that all of your cables and interconnects are shielded.where is your system located in your house? have you tried your system in another room of the house? if that is possible. can you give a list of your gear? have you checked all your interconnect connections? they will snap, crackle and pop if bad. start at the top of the system and work your way down to the amp. have you wiggled the input tubes around a bit on the amp. sometimes that will help if they are not seated correctly.

just more ideas for you to look at if you have not thought of them already.

I've checked my connections about a 1000 times already. Swapping cables does make a tiny difference but the noise persists regardless. I've tried plugging into different circuits but no change. The gear is in my office which is adjacent to the living room where my speakers are.

Equipment:
1. technics epa 100 mk2 tonearm: this has an rca plug at its base with separate grounding input. I have the original ic's for it, but use rca's with a separate grounding wire (banana to spade). The connection is difficult to secure because of the pod I have the arm housed in, but I don't think it's the arm because I have another (din to rca) arm I use and the same noise is present.
2. technics sp10 mk2: separate power supply that uses a 2 prong plug
3. allnic h-1200 tube phonostage: 2 input (mm and mc); I use both and I've tried just using one or the other with no difference to noise; 3 pronged plug
4. lightspeed passive pre: 1 input; wallwart 2 prong plug
5. rm10 mk2 amp

I'm pretty sure it's the Allnic causing the trouble because when I take it out and use my dvd player, there's no noise. But I don't know what to do about it--other than buying a different stage and hoping it has no issues. For the price of these power conditioners, I'd just as soon sell the stage and buy a different one.