TRL Dude or Joule 150 MKII for Major Pre Upgrade

Atmasphere, I have not tried to run the Jensen with rca's as yet. I am so thrilled with the sound right now. Seems my amp really sounds best through the xlr inputs. All I know is my system has never sounded better plus is now very quiet.

So simple impedance of the source is partially ruled out- we are OK with a relatively high impedance at the input, so long as it is balanced. What happens if we use the same source to drive the RCA single-ended?

Grannyring, are you able to use the Jensen running single ended? How you would do that is to use the RCA input of the amplifier by using an adapter with the Jensens, one that ties pin 3 and pin 1 of its XLR output together.

This is still pointing to an issue with the input wiring where it is able to pick up noise from inside the amp. I suspect that it is common mode to the inverting input and so is not picked up when the amp is driven balanced.

Al, a couple of things I pointed out to Grannyring were that I did in fact speak with Bill Whitlock back in Aug, 2010, and posted about my conversation in another thread that you too were involved in. I hadn't remembered that thread, but I found it in a search. I was using a Lamm LL2 Dlx at the time, which has a rising output impedance at low frequencies and my concern was bass roll-off. My post is at the end of the thread here;
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1280795210&read&keyw&zzbill=whitlock
Bill basically told me the Jensen posted specs apply to the "worst case" scenario where the load is 10K ohms. Good news for Grannyring is that the input impedance of his Atlas amp is enormous at 940K ohms! Here is what JA at S'phile had to say;

The Atlas's voltage gain into 8 ohms was the same for balanced and unbalanced drive, at 25dB, which is lower than normal. Both inputs preserved absolute polarity (ie, were non-inverting), the XLR jacks being wired with pin 2 hot. Specified at a very high 470k ohms for the unbalanced input and twice that for the balanced, the amplifier's input impedances were at least those values at low and midrange frequencies, dropping slightly but inconsequentially at 20kHz. (With such high impedances, there is inevitably a large error in measuring the exact figure.) The Crossover inputs behaved identically to the main inputs in these respects.

I suspect with such a large input impedance, Grannyring is good to go with the transformers.

Ralph, thanks for the info about 100 ohms. I would not have suspected that such a low value would generally be effective.

Regarding the effects of the transformer on the source impedance seen by the amplifier, though, I don't think that is the explanation. For two reasons:

1)It was reported that the problem was still present when the amp was driven by several different low impedance sources.

2)The Jensen Isomax "input transformers," such as the one whose data sheet I linked to in my previous post, do not provide a low output impedance. That presumably being a major reason that they are only recommended for use with short low capacitance cables on their output side. As you can see in the data sheet I had linked to, that particular model has an output impedance spec of 4.65K (typical) when it is driven from a balanced impedance of 300 ohms per leg. Also, the DC resistance of its secondary winding is spec'd at 1.9K (typical). When driven by a source having high output impedance, such as the Dude, the 4.65K figure would presumably be even higher.

So as I see it the mystery remains unsolved.

Best regards,
-- Al

Hi Al, in practice 100 ohms can be quite effective. We use that value a lot. It does not seem like much in the face of the higher impedances that tubes employ, but it can make the difference between RF oscillation (resulting in hum) and absolute stability.

So right now I am thinking that grid stops are not the issue.

Its interesting that using the Jensens sorted it out. This would be a way of reducing the output impedance of the source. If the amplifier is having troubles with AC line noise at its inputs, this would be the sort of thing to shut it up. I suggested that this might be one of the explanations back on the 13th; that theory has now gained some juice.

Thanks Al. I will check into the cable capacitance to be sure I am doing all I can for best sound.

Success, at long last. Outstanding! Although I guess we'll never really be able to be sure of exactly what was causing the problem, given the bizarre results of some of the experiments.

The key thing with the XLR cable is that its capacitance has to be kept very low. I suspect that you are using the PI-2RX transformer, for which the datasheet indicates a maximum acceptable load capacitance of 100 pf. That would be for the sum of the cable capacitance and the input capacitance of the amp (which is unspecified). I suspect that the main consequence of driving the transformer from an output impedance that is significantly higher than the 2K recommendation will be that the load capacitance becomes even more critical, excessive capacitance potentially affecting the highs particularly.

For most purposes the capacitance of Mogami's Gold Studio or other Mogami 2534-based cable (if that is what you are using for the time being) is reasonably low, but it may not be low enough in these circumstances. I don't know what kind of cables you are awaiting, but if they do not have very low capacitance you might want to consider say a 1 foot length of inexpensive Blue Jeans/Belden 1800F, which would be only 13 pf plus the capacitance of the connectors.

Best regards,
-- Al

Update. The use of a Jensen input transformer under the brand Iso Max completely removed the buzz to a dead silence. Simply place the input transformer between the amp and preamp. Single ended preamp into the Jensen Iso Max using my RCA ic's and out from the Jensen Iso Max into my amp using xlr connectors. So the Jensen receives RCA in and xlr out. I am now able to use my amp in it's fully balanced mode.

The xlr ic's going from the Jensen to the amp must be 2 feet or under to avoid any signal deterioration.

The down side is the cost of the unit plus the cost of an extra set of ic's. Not sure as yet if then Jensen changes the sound as I am using some pro sound Mogami xlr's for now. The sound does seem a little more polite or less alive, but this my be the new set of IC's?

I will soon receive a set of xlr ic's of the same brand that I use throughout my system. I will update all as to wether the Jensen input transformer changes the sound.

The sound is very good with the inexpensive Mogami cable however. A little less top end sparkle is what I notice thus far.

I also left Jensen a message to clarify the compatability of the unit with a higher output impedance preamp. The site suggests the preamp should be no higher then 2k ohms , but other threads I have read seem to suggest this may not be the whole story.

Acck! I now have to say hold everything cos I just looked at my NP220PG and the grid stops to the 6SN7 (also in diff amp config) is 100 Ohms. They are place after the grid leak which is 100k to ground.
So if my NP100PG is so darn quiet and EM free even with crappy cables whats up with Grannyring's Aesthetix?
My NP has very low gain though, my speakers are 89-90dB efficiency.

Ralph, the present (original) value is 100 ohms. Do you still feel that is not the problem?

Best regards,
-- Al

The 1000 ohm value on pin 1 (grid) represents the grid stop resistance at the input. That is not the problem.

No, don't solder a resistor between the RCA and pin 1 of the tube socket. That would put the 1K in parallel with the 100 ohms, resulting in an overall resistance of about 91 ohms.

Hopefully you can unsolder the wire that is presently connected to the RCA jack, and put the resistor in series (i.e., connected between that wire and the RCA jack). That would result in an overall resistance of 1100 ohms.

It might be a surer bet, though, to use a resistor having a higher value, such as the 3K or 4K values I mentioned. The main constraint on how high a value should be used is, I believe, that if it gets too high the bandwidth of the low pass filter formed by that resistance and the input capacitance seen looking into the grid of the tube, based on the Miller Effect, will reduce the overall bandwidth of the amplifier (which is spec'd at 150 kHz). Calculating from the 6SN7 data in my tube manual, I believe that 4K would still be low enough to not have a significant effect on that bandwidth.

Best regards,
-- Al

All depends on how long that curcuit trace is from the RCA hot pin to pin1.
If its less than 3 inches then a 1k grid stop in series ie
UNSOLDER RCA hot and put 1k inline.
SOLDER Socket-hot-->1k-->wire to grid@6sn7.
But if its any longer then you will need help from Aesthetix.

I agree completely. 100 ohms sounds way too low. And as the link you provided indicates, too low a value for the grid stopper resistor of the input stage could very conceivably result in rfi problems.

According to some quick calculations, 1K strikes me as a reasonable value. I believe that a value up to around 4K or 5K would not adversely affect anything, the overall bandwidth of the amp in particular.

Kudos to Johnsonwu.

Best regards,
-- Al

Jognsonwu, thanks for your insight. I am not sure how to wire such a resistor as my amp has a circuit board for each input tube/channel. Hard, if not impossible , for me to wire in a 1k resistor. Wish the amp was point to point wired!

It may be possible for me to simply solder an additional 1k resistor from the RCA to pin one and not undo anything else. Is this what you are suggesting?

Correction the grid stop resistor should measure over 1000 ohms and often is a very high value.

Ok, did one additional measurement per the instruction Jognsonwu above.
I measured the ohms reading from the RCA center to each of the eight 6sn7 socket pin numbers.

I did this to check the input grid stop resistor.This grid dropper resistor is used to form a low-pass filter to get rid of RFI/EMI. For more reference, please see the following link:
 
http://www.aikenamps.com/InputRes.htm

Pin one should measure 1000 ohms, not 100 according to two individuals that are helping me. Love input from Atmasphere or Al or others who may know something on the this subject.
 
Here are the measurements,
 
Pin 
 
1.   100 ohm
2.    3.9 mohm
3.    1.45 mohm
4.   .527 mohm
5.    3.9 mohm
6.    1.45 mohm
7.   .527 mohm
8.   .527 mohm
 
Checked and recheck.......before I call Aesthetix I could use some confirmation. I am not the most tech savy and must say I have a hard time thinking they would miss such an "obvious" thing? My amp is not under warranty and wonder if this is something that should be made right, or simply just one way to build an amp?

I greatly appreciate the help I have received from all and this is the last request I will make for help before calling Aesthetix again.

Grannyring, that info weakens my theory about the specific malfunction, but strengthens the idea that the amp is at fault. If the amp is in warranty I would return it for repair.

Grannyring,

I have no experience with the Bel Canto but when your passive lightspeed is set to vol = 0 can you measure zero ohms at the output RCA relative to ground, much like the shorting RCA jack you tested? If it's zero ohms then I see no reason why connecting to the lightspeed would be different than shorting the inputs with a shorting RCA.

Recently I spent many hours tackling an interesting project on a previously modified Jolida which gives a buzz similar to what you are hearing. Turns out that power amp uses an AC filament for the gain stage and the center tap of the power transformer is faulty and I had to create an artificial center tap w balancing resistors.

Highly unlikely with your hybrid power amp cos judging from the build ($$$) it would likely use DC filament for the 6SN7s.

Check the input grid stop resistors again, it might be as simple as adding a 1k resistor inline with the signal input to the 6SN7s grid.

Atmasphere,

What about the fact that a Passive Lightspeed pre, cd players and a Bel Canto pre with average to low output impedances caused the same buzz with this amp? Does this rule out the high preamp output impedance theory into the Atlas?

grid stop resistor on the 6SN7 of the Aesthetix
OR less likely...
RCA connector on the Aesthetix shorted audio ground to chassis.

From the descriptions above, IMO the preamp is off the hook- this is a problem with the power amp.

Also based on these descriptions, its my theory that the amplifier has a problem with noisy rectifiers, which is getting picked up at the input if the source impedance is too high. This is why it is quiet with a shorted input and a 1K resistor, but not with the Dude (which has a relatively high output impedance as the volume control is at the output of the preamp), and likely a few other tube preamps as well.

Noisy rectifiers can be tricky as the commutation noise they produce acts very much like RF (which *is* part of their noise component), in that it can easily get to other parts of the amplifier, and use input connections as an antenna.

However this is only a theory, another possibility is a layout problem where the AC power is somehow too close to the audio input. Either way though- things are pointing at the amp.

This was extremely bizarre to me...

To me as well.

Have the preamps been located close to a possible source of emi/rfi, including perhaps the amplifier itself? If that seems like a possibility, try moving the preamp to different physical locations.

Beyond that, I'm out of ideas at this point.

Best regards,
-- Al

Vett93 summed it up very well. My speaker and other cables really did not change position. My speaker cables are simply solid core copper runs and very straight forward. Changing power or ic cable brands did nothing to change the hum.

Grannyring, what kind of speaker cables are you using, and how long are they? If by any chance they are one of the kinds that has extremely high capacitance, such as Goertz or Ocos, and you are using them without a Zobel network, I'm wondering if that may be resulting in the amp being on the edge of having some sort of low level oscillation, that could somehow be put over the edge by conditions at the inputs.

Also, did the positioning of the speaker cables change significantly when you changed speakers? Perhaps they are picking up rfi/emi which is entering the feedback loop of the amp, if it has one.

Just some shots in the dark.

Best regards,
-- Al

I wouldn't expect that shorting the preamp inputs would make any difference, since the problem occurs even when the preamp is turned off and unplugged from the AC.

Sure is a baffling problem :-)

Best regards,
-- Al

I found a bunch of unused RCA cables and connected the ground and center wires to short the jacks. I places these on my 3 sets of unused preamp inputs. Still have the buzz. Still think this may be a good idea however.

Granny has put an integrated amp in place of Dude preamp and Atlas amp, with the same CD player, ICs, power cords, and speakers. It was quiet. No hum.

The Atlas amp has balanced differential input gain stage and followed by driver and output stages in bridged configuration. We measured the RCA ground to the IEC ground pin to verify that signal ground is connected to AC ground.

We also tested the RCA and XLR inputs and concluded they are correctly wired, by measuring the resistance of pins to the ground and RCA center to XLR Pin-2. We got new XLR connectors, short pin 1 and 3, and connect them to the amp.

Then we use a pair of RCA sockets to simulate inputs. First, we shorted the RCA sockets. With ICs between shorted RCA sockets and amp, the system was quiet. So we changed the RCA sockets from being shorted to being loaded with 1K ohm resistors. This was to simulate if the amp could pick up noises and then hum/buzz. But it was quiet too.

Then strange thing happened as soon as we connected anything else to it. They don't even need power cords to cause hum. We also measured Dude preamp and concluded that it was also wired correctly too. On the Dude preamp, if we adjust the volume all the way down, it is like shorting the output. (We verified it by measuring the output with a multimeter and got 0.3ohm.) But the system would still hum, without power cord. This was extremely bizarre to me...

What was even more bizarre to me was that we connected CD player to the amp directly, without any preamp. One channel was humming loudly and one was humming a little. When we switched cable the hum pattern stayed.

Thanks Al. I just inserted two shorted RCA jacks on the unused crossover inputs on the amp. Still have the buzz however.

Wonder if my extra preamp inputs should be shorted?

Sounds like Vett93 gave you some excellent suggestions. One additional experiment I would suggest is that besides shorting the two pins on the XLR connectors, you also short the center pin and ground sleeve of the two RCA connectors for the high passed inputs of the amp. If you don't have shorting plugs, you could again use IC's with something conductive inserted at their other end to provide the short.

I would add to your summary, btw, as you mentioned in the other thread where this was discussed, that the noise is present if the preamp is connected to the regular inputs of the amp and the high passed inputs are selected, but disappears if the preamp is connected to the high passed inputs and the regular inputs are selected (while being present if the preamp is connected to the high passed inputs and the high passed inputs are selected).

And yes, the caution about not grounding the negative output terminals of the amp is not applicable if all that is connected is a passive speaker. It shouldn't be applicable with an electrostatic, either.

Best regards,
-- Al

I just read this in my Aesthetix Atlas's manual. " each channel is a balanced bridge amplifier, thus the negative speaker terminal is not a ground, and cannot be connected to a system ground or loudspeaker system with a common ground. Consult your speaker builder to confirm that your speaker does not have internal circuitry with a common ground."

Well, my speaker is passive - Nola Viper Reference. As for what this means above, I have no clue. I can't imagine a passive speaker would have this sort of grounding issue however?

Correct, passive speaker. I ha!ve been working with Vett93 and he has stepped me through all kinds of tests. Thank you for being so patient with me! Through it all I still have the same buzz out of both speakers. The buzz is not present under three conditions we have tested.

1) the Atlas amp turned on and connected to the speakers with nothing else hooked to the amp

2) the Atlas amp hooked to an ic feeding into an RCA socket with the two leads connected and shorted

3) as above with a 1kohm resistor between the RCA ground and center pin.

The buzz is present with any other condition. Here is a recap of what causes a buzz through the speakers.

-Three different single ended preamps turned on or off hooked to the amp. They each caused the same buzz wether they were on or off with or without a source hooked up .

- hooked direct to two different cd players the buzz was the same - no preamp

- cheater plug on amp, then preamp, all xlr inputs on the amp shorted between pin 1 and 3 with purchased xlr connectors having pin 1 and 3 shorted

Vett93 can better explain all the RCA, iec, pin, chassis etc measurements we made concluding all was wired correctly with the amp's input.

Stumped is an understatement. I wonder if a conditioner of passive or active nature is needed to cure other issues?

Through all of this testing all 4 xlr inputs were shorted between pin 1 and 3.

Atmasphere, my understanding is that Granny is now using a pair of passive speakers. There should not be power supply for it....

It is possible that the power supply ground of the speaker is somehow also connected to the speaker terminals. That could cause some amplifiers to be ground-looped. A continuity test between the ground pin of the AC cord and the speaker terminals would sort that out pretty quick.

Granny, can you explain what you meant by "my CD player is grounded to the chassis by the power cord middle pin"? Did you use the multi-meter to measure the chassis and the power cord middle pin and then concluded that?

On the CD player, can you measure the ground of the RCA connector and the power cord middle pin, if you have not done that already? By the "ground" of the RCA connector, I refer to the outside surface area of the RCA connector.

On the power amp, can you also measure the ground of the RCA connector and the power cord middle pin?

Atmasphere, I think it is a system issue. The whole thing worked well previously with the electrostatic speakers. If the only change is the speaker, the only possible cause is the change of grounding.

This is *starting* to sound like the preamp is off the hook. Did you make sure a jumper is there between pin 1 and 3 of the XLRs? If that is missing it may not matter what the source is.

A balanced amplifier has 2 inputs: inverting and non-inverting. When you are using the RCA input you are usually using the non-inverting input, which is often the same as pin 2 of the XLR. If you don't install the jumper the unused input can pick up noise.

My CD player is grounded to the chassis by the power cord middle pin. I did hook it up directly to the amp and still get a buzz out of both speakers. I will try the amp in another system tonight to see what happens.
Maybe a power conditioner?

Yes- if pin 3 is not tied to pin 1, while the RCA is in use, the amplifier will buzz whether the preamp is on or not, and whether its plugged into the wall or not.

Also, FWIW it is not uncommon for a preamp to buzz if it is not powered up. The reason is that the output impedance is usually much higher and can act like an antenna.

If the Aesthetix is really balanced, you should not have any troubles making this work.

Also, you will need to short pin 1 and 3 for the XLR connectors when you try my suggestion. I think it will work for you...

Granny,

I don't think my explanation is clear to you. My point is that the signal ground has to be grounded at one location for the entire system. Otherwise, the whole thing is floating. It seemed to me that your electrostatic speakers provided a grounding point. You lost the grounding point by switching to a set of passive speakers.

If you still use the same CD player as the one you used when we talked last time (a Marantz, I think), it does not provide a grounding point. If you look at the IEC socket of a Marantz CD player, there is no ground pin there.

To test my method, you will need to find a CD player that uses the AC ground pin, and plug in AC power cord to the wall and use the interconnect too. This is so that the CD player can provide a grounding point for you. I don't think you followed my explanation.

I measured the Atlas amp again. It turns out if I touch the back steel plate I get no ohm reading. However when I touch a screw on the back plate with the center power cord ground pin on the iec I get a 14 ohm reading.

I learned this from calling Aesthetix. They tell me the amp is fine and I have some sort of unique room/house situation. Seems they will not be able to help me anymore and suggested I try a balanced preamp. Well, my amp has RCA inputs for a reason and I need to use them!

I am starting to doubt I will ever get an answer.

Vett93, the speakers buzz with my cd player unplugged and ic's also taken out that go to the cd player. So the source it not at all in play here.

I need to bring the amp to another home and system and see what happens.

Bill, in your earlier post today, you said that the chassis was not wired to anything, which was similar to my experience. Then you said it in your most recent post that the chassis was wired to the middle pin of the IEC. So I am a bit confused. Can you use your ohm meter to measure the chassis and the ground pin of the IEC socket?

Did you send your Dude back for re-work? I got my Dude after reading your review a few years back. Being an engineer, I opened it up to review its design as soon as I received it. I found that the chassis was NOT wired to the AC ground. I sent it back to Paul and specifically asked him to do so later on.

I still think you should try my latest suggestion: find a source equipment that has its signal ground wired to the AC ground pin. Then see if it still hums...

Okay, I read through the whole threads and come up with another theory and idea to try. I simply cannot stand a fellow Dude owner not happy with his setup. ;-)

I still think it is a grounding issue. If I understand it correctly, it did not hum with the previous set of speakers which are electrostatics. My theory is that the set of electrostatics provided proper grounding through their AC plugs.

So, Bill, can you try the following and see if it fixes the hum? The idea is to provide grounding at the source. So find any of your source equipment that has the signal ground wired to the ground pin of the AC plug. I don't know what source equipment you have. But you can measure the source's output RCA ground and the the ground pin of the AC plug. If it reads close to zero ohm (meaning there is a connection), then the signal is grounded to the AC line. You can use that equipment as the source.

Then connect the source to the Dude and select the right input. Connect the Dude to the amp. Turn them on and see (or hear) if you still get a hum.

Please let us know. Thanks.

Mine preamp's chassis is indeed grounded to the middle pin of the iec. Again, the buzz comes when the preamp is off and unplugged even. I have an amp issue. I called Aesthetix today and they gave me some other things to measure on the amp.

I will report back on how this ends up so all can learn. Thanks to all for the help.

Atamasphere, if Grannyring's Dude is like mine when I first got it, the chassis is not grounded to the middle pin of the IEC.

Hi Grannyring, if the the chassis is grounded to the middle pin of the IEC, but there is no resistance (open) between the RCA ground and the chassis, then the chassis can act as a sort of antenna- and thus can can buzz.

A resistor of about 100 ohms (1/2 watt) between the RCA shield and chassis should take care of it if this is the problem. If it were me this would be the next thing I would try, based on the measurements you have reported.

Keep posting...

I meant to say I measured no ohms. I assume getting no ohms means there's no connection from the signal ground as measured at the RCA socket to chassis. Same with the power cable ground to chassis. The chassis has no resistive connection and seems isolated from everything.

This does not seem good to me.

Well the amp seems to be the issue after more testing. I tried using Blue Jean cables that are well shielded, but the buzz continues. Again, with the preamp off and unplugged the buzz continues.

I measured as Ralph stated and could not get any reading on my ohm meter (too low) when testing for ground on the RCA 's and the middle (ground) on the AC inlet of the amp. My meter measured too low to read on the (m)ohm setting.

I tried shorting out all 4 xlr inputs between pin 1 & 3 and still have the buzz. This Buzz was not there when my previous Soundlab speakers were in the system. The buzz came for the first time when I replaced the Soundlabs with a passive speaker.

I am at a loss. I spoke with Aesthetex and they had no answers. I will try them again now, but they also seem stumped.

Atmasphere, I will take the measurements you point out and post the results.