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SE84C-EX Hum (Read 11978 times)
144cubits
Ex Member



SE84C-EX Hum
01/14/05 at 16:55:38
 
My EX was finally hooked up yesterday after a series of mishaps for which Steve Deckert was most accomodating. As I excitedly popped in the rectifier tube and flipped the switch. My excitement turned to dismay as a very audible hum was heard both from the speakers ( at a distance of 7 feet) and the amp itself?!  :'(

Now I am not technical whatsoever so I do need some very rudimentary (talk to me like I'm a 10 year old) instructions to try to eliminate this very distracting buzz.

I've left a message for Steve but was hoping you guys could help a new member of the family out!

I covet your suggestions.

Fred
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nodiak
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Re: SE84C-EX Hum
Reply #1 - 01/14/05 at 17:24:06
 
oh man, say it isn't so! This problem seems to be hit and miss from those that have the ex mod. I'm expecting my C back from decware soon, after having the ex mod. A loud hum would be very disappointing. I know zip about this but there has to be a solution...right? Don
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Gary_H.
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Re: SE84C-EX Hum
Reply #2 - 01/14/05 at 18:33:48
 
Try the link below of Stev's paper on hum problems.

http://www.decware.com/newsite/mainmenu.htm

If the link dosn't work go to the Articles section of the main menu and see the Hum Problems article.

I hope you find an answer there.

Gary
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selmerdave
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Re: SE84C-EX Hum
Reply #3 - 01/14/05 at 18:34:32
 
What do you mean by mishaps?  Obviously something is wrong.

Dave
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dc007
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Re: SE84C-EX Hum
Reply #4 - 01/14/05 at 19:01:49
 
welcome Fred...
I too have noticed a more noticeable hum from my EX C, however it is not distracting and does not interfere with the music at all but still in a dead quiet room you do notice it at about 2 feet.
Are you sure your interconnects are good? Unplug all but the speaker cables and see what gives. Do not power the amp up with no speakers hooked up. Also do you have a new set of tubes....possibly a bad tube and lastly is the power source a reliable one?

Good luck
Mike
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144cubits
Ex Member



Re: SE84C-EX Hum
Reply #5 - 01/14/05 at 19:16:18
 

[quote author=selmerdave  link=1105725338&amp/0#3 date=1105727672]
What do you mean by mishaps?  Obviously something is wrong.

Dave
[/quote]

Well I'm going to try to make a very long story short.

When I called Steve to determine delivery time he informed me that the unit was delayed due to a small blem on the case. He gave me 2 options I elected the second.

Upon delivery the unit wouldn't power up, after trying everything I called Steve. He thought it was a bad rectifier that had blown the fuse. He told me to remove the bad fuse and replace it. I got home promptly popped out the IEC and voila! No Fuses.  

Called Steve again explained the unit was shipped without fuses, he apologized and told me the type and amperage so  I promptly picked them up at RS and gleefully popped one in.
Voila! All tubes glowing except the rectifier. Upon closer examination I noticed bits of metal sloshing around inside.

Back to Steve, he overnighted a rectifier (UPS delivered 2 days later, but that's another story) It arrived yesterday and ...well you're up to date.

Couple of points I'd like to make:
1) I bought a SE84C with the EX mod I was not a previous owner.
2) Steve was very accomodating and I sensed he felt badly that being a new customer I had this type of experience.

From all of the posts I've read on this forum Decware seems to build a quality product. I believe my experience is unique and hope that this latest glitch is just that and that I can start experiencing some of the thrills I've read about.

All of your comments, input, feedback is appreciated.
Fred


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144cubits
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Re: SE84C-EX Hum
Reply #6 - 01/14/05 at 19:31:50
 

[quote author=dc007  link=1105725338&amp/0#4 date=1105729309]
welcome Fred...
I too have noticed a more noticeable hum from my EX C, however it is not distracting and does not interfere with the music at all but still in a dead quiet room you do notice it at about 2 feet.
Are you sure your interconnects are good? Unplug all but the speaker cables and see what gives. Do not power the amp up with no speakers hooked up. Also do you have a new set of tubes....possibly a bad tube and lastly is the power source a reliable one?

Good luck
Mike
[/quote]
Thanx Mike for your feedback. I have pretty good interconnects but will try your suggestion, As for tubes I am new to "tube rolling" I'm open to suggestions. My tastes tend more toward a smooth, holographic type of sound. Lastly I must confess I have not invested in any type of power conditioner because this is my "budget sytem" its hooked into a power strip...again I'm open to suggestions ( keep in mind I'm just a po' southern boy).

Thanx again Mike
Fred  
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dc007
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Re: SE84C-EX Hum
Reply #7 - 01/15/05 at 16:03:00
 
Fred...do not necessarily need a power conditioner...just be sure the outlet would not be 'noisy' with any equipment. In other words are you confident the outlet and/or power strip would not be contributing to the noise. Heck I use a power strip for components and just plug the amp into the wall myself. Also wasn't suggesting to start rolling tubes but it is always good to have spares just in case one of them may be not quite up to par.
take care
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nodiak
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Re: SE84C-EX Hum
Reply #8 - 01/15/05 at 17:08:25
 
   Fred, I have a weird situation in the old building i live in. If the plug (for amp, ext. cord or powerstrip) isn't setting just right in the outlet I get a loud hum. If it is just right no hum. I will eventually replace one outlet to dedicate to system. Maybe similar problem for you ? Good luck, I hope it isn't the ex mod. Don
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Steve_Collins
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Re: SE84C-EX Hum
Reply #9 - 01/15/05 at 19:44:17
 
Hi Fed
Sorry to hear of your troubles. I too had an 84C, which i upgraded to a CS and then fitted the EX transformers which revealed a hum in the system. Eddie Vaughan has kindly made some suggestions and as soon as I have the parts I'll wield the soldering iron.
It sounds like you don't do any diy, and with the noise coming from the transformer too I think you should box the amp up and send it back to Steve for a check-up. I feel sure that's what he would want you to do. You need to send it back to establish if it's a problem with the amp or your setup at home. I know you probably don't want to send it back but you'll keep the amp for many years and a few weeks more won't matter in the long run.
Best of luck.
Steve
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144cubits
Ex Member



Re: SE84C-EX Hum
Reply #10 - 01/18/05 at 17:46:45
 
Thanx everyone for the suggestions. I printed out Steve's article on hum and have tried removing the interconnects...hum. Removed the input tube...hum. tried different outlets...hum. Popped out the rectifier...hum. The only thing I've not done is change the output tubes which I really need some suggestions from you guys.

I am loathe to send back the amp just yet I want to try the tubes, and go from there.

Tube rollers I need you! Sad

Fred
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144cubits
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Re: SE84C-EX Hum
Reply #11 - 02/02/05 at 19:31:02
 
I gave in and sent the unit back. Awaiting Steve's response.
Fred
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dc007
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Re: SE84C-EX Hum
Reply #12 - 02/02/05 at 20:56:42
 
Be sure an post what Steve says on this issue

Regards
Mike
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StingRay
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Re: SE84C-EX Hum
Reply #13 - 02/02/05 at 21:06:19
 
I'm also interested since my measured hum level is 2 to 3 times the level specified for this amp.
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144cubits
Ex Member



Re: SE84C-EX Hum
Reply #14 - 02/07/05 at 19:33:39
 
I just got off phone with Steve. Turns out my unit had a bad bypass cap on the output stage. This was generating 4.5mv of hum! Whew! Glad it wasn't my equipment.

I should get it back in a week or so at which point I will hopefully let you guys know that all is well.

Stay tuned.... Roll Eyes
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StingRay
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Re: SE84C-EX Hum
Reply #15 - 02/07/05 at 19:47:26
 
4.5 mv of hum is the measurement I made with my DMM.  I don't have the extra digit of resolution and it was floating between .004 and .005 so I called it 4.5mv.

Looking forward to your comments.

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144cubits
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Re: SE84C-EX Hum
Reply #16 - 02/09/05 at 18:59:25
 
Got the unit back today and the hum is significantly better. I 'm told that some hum is virtually unavoidable with tubes particularly with sensitive speakers. As long as it doesn't interfere with the music I'm OK.

I will allow the unit to break in some more and roll some tubes to give you gents a proper posting of my thoughts in the near future. For now it appears my crisis is solved.

Thanx for all of your help guys!
Fred 8)
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StingRay
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Re: SE84C-EX Hum
Reply #17 - 02/10/05 at 02:49:33
 
I made a series of measurements of hum on my Select EX.  Following Steve's recommendations in his paper on hum, I measured between 3.5 mv and 4.6 mv of hum depending on my tube combination.  The lowest hum (at 3.5 mv) was measured without the input tube in place.  

I emailed Steve for advice, and he recommended that I remove the 1000 uf bypass cap on the cathode resistor for the output tubes.  I performed the very minor operation, and put the amp back in service.  With all tubes installed, the hum had dropped to 2.3 mv and is now essentially a non-issue.

The interesting part is that in addition to cutting the hum in half, the operation has changed the sound of the amp for the better (in my system YMMV).  I didn't like the results so much with the stock SV-83's in my system.  They sounded a little thinner and almost too detailed.  The JJ EL-84's were a completely different story.  The weight and presence was back, but the detail in the mids and highs were much improved.

One nice thing about this mod is that anybody can do it.  There is only 1 cap to clip out, and it is piggybacked on top of the cathode resistor.  It is very easy to reach, and takes only about 5 minutes to remove it from the circuit.  It would be almost as easy to add it back in if you didn't like the change.  

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« Last Edit: 02/20/05 at 22:31:01 by StingRay »  
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dc007
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Re: SE84C-EX Hum
Reply #18 - 02/10/05 at 13:06:09
 
Stingray
What about the SE84C EX.....would that be the same fix as with the Select EX?

Regards...Mike
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StingRay
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Re: SE84C-EX Hum
Reply #19 - 02/10/05 at 13:35:25
 
Mike,

I believe the fix would apply to the SE84C EX as well, although I didn't specifically ask Steve that question.  Steve also mentioned that I may be interested in changing the 100 ohm 25 W Dale resistor to 150 ohm.  At this point, I'm not planning on doing that, but additional listening and a description of what the increased resistance will do to the circuit may change my mind.

Jerry
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144cubits
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Re: SE84C-EX Hum
Reply #20 - 02/10/05 at 14:39:28
 


[quote author=StingRay  link=1105725338&amp/15#17 date=1108003773]

The interesting part is that in addition to cutting the hum in half, the operation has changed the sound of the amp for the better (in my system YMMV).  I didn't like the results so much with the stock SV-83's in my system.  They sounded a little thinner and almost too detailed.  The JJ EL-84's were a completely different story.  The weight and presence was back, but the detail in the mids and highs were much improved.
[/quote]
Stingray, I rolled some tubes last night and noticed an immediately change also. I replaced the stock rectifier with a JAN Cetron and the input tube with a Mullard 6dj8. Big difference. With the stock tubes the detail was there in spades but the instruments tended to drown out voices. When I replaced them the voices came back and the overall sound softened albeit with less detail.

I'll keep rolling until I find the right mix. I'm trying to get some Mullard EL84's but man are they expensive. I think I'll go the JJ route and see what happens.

I'm open to any suggestions as I'm looking for a smooth, holographic sound. C'mon tube rollers I know you're out there!

Fred 8)
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StingRay
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Re: SE84C-EX Hum
Reply #21 - 02/10/05 at 16:40:41
 
My two favorite combinations to date are:

NOS RCA 5U4G Rectifier
JJ EL-84's
Phillips JAN 6922 input

or

Stock Ruby Rectifier
JJ EL-84's
Phillips JAN 6922 input

I find these combinations to be exactly what you describe.  Smooth, detailed and holographic.  As a matter of fact, I would use this configuration as a benchmark for comparing other amplifiers.
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144cubits
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Re: SE84C-EX Hum
Reply #22 - 02/10/05 at 17:06:04
 
Stingray, Thanx again for your suggestions. One question, since I have the C with the EX mod I can't use the 5u4 family of rectifiers that's why I bought the JAN Cetron. Any suggestions? I'm going to try your combo of JJ's and Jan Philips and see what happens.

As far as DIY is concerned, I've only done one project in my life and it turned out well, but one project does not make a successful DIY'er. That's why I didn't attempt it.

I agree with you that Steve has been a gentleman in this whole process and through it I've met a number of very helpful individuals such as yourself that has made this bumpy road a lot smoother.
 
Thanx again for all of your continued help. I'll keep you all posted.
Fred 8)
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dc007
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Re: SE84C-EX Hum
Reply #23 - 02/10/05 at 19:36:01
 
144

Try a RCA 5y3gt....inexpensive and very good in the EX modded C

IMHO
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144cubits
Ex Member



Re: SE84C-EX Hum
Reply #24 - 02/11/05 at 12:46:36
 
Thanx DC. I'm busy collecting tubes but will allow the amp to break in some more before doing any serious rolling.

Fred 8)
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StingRay
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Re: SE84C-EX Hum
Reply #25 - 02/20/05 at 22:46:34
 
Update.  I may have jumped the gun by reporting too soon on my impressions of my EX after the hum reducing cap-ectomy.

On the material I was listening to at the time, I noticed what I perceived to be an increase in detail.  On other material, I noticed a thinning in the bottom end.  This thinning is especially evident on the SV-83's, but not as apparent on the JJ's.  Today, I attached some aligator clips to the ends of the cap that I snipped out so I could do some A/B comparisons with and without the cap.

So far, with the cap, the hum goes up, but the amp sounds fuller.  Without the cap, the hum goes down, but the amp sounds thinner.  I am going to do this with some other brands and values of caps to see what happens.  The stock cathode resistor bypass cap is a Xicon electolytic and looks a little out of place in a circuit that uses higher quality parts throughout.  I'll update this thread as I learn more.
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Steve_Collins
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Re: SE84C-EX Hum
Reply #26 - 02/21/05 at 12:41:33
 
Hi Stingray
I too tried removing the 1000uf cap, actually in my case it was a 470uf cap following Eddie's hum reducing suggestion, but I found the same as you. No hum, well 1.2mv, but the sound became super clean, recessed, and just lacking in body, presence, call it what you will the involvement factor had gone. I put the cap back and added the extra power supply capacitance to keep the hum down and the system is back to normal i.e. slight hum but sounding great. BTW, mine is a CSex diy upgrade from the C. I picked up on the suggested 5V4G rectifier and managed to find a NOS RCA version. Coupled with ex factory Mullard EL84's and Tele E188cc this rectifier sounds better than the Mullard GZ32, Sylvania 5U4G, RCA 5R4 that I've tried so far, so like others before me I can recommend it. BTW speakers are HDT drive units in non hdt cabs.
All the best
Steve
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144cubits
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Re: SE84C-EX Hum
Reply #27 - 02/22/05 at 14:32:38
 
Stingray
 [quote author=StingRay  link=1105725338&amp/15#25 date=1108939594]
On other material, I noticed a thinning in the bottom end. [/quote] 

As I am new to the Decware "sound" I am not quite sure what I should or should not be hearing. I did notice that bass was not as full as I remember but I attributed it to the amp still breaking in. The amp now has about 70 hours and sounds good but yes recessed with voices not as palpable as I've heard in other amps.

Keep us posted Stingray as I would like to hear what these amps are truly capable of.
8)
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StingRay
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Re: SE84C-EX Hum
Reply #28 - 02/23/05 at 02:39:38
 
If you're bypass cap was removed and not replaced, I don't think you're getting the full Select experience.

It seems that removing the cap attenuates the lower frequencies making the hum less of a problem, but trimming off the bottom end response in the process.  I decided the tradeoff is not worth it, and I'm working to get a replacement cap that will be an overall improvement.  I ordered two very high quality caps per the recommendation of our resident guru.  If there is an improvement after I install mine, you're welcome to the spare.

If it turns out that my amp has to have double or triple the specified hum to sound full, I guess I'll live with it.  I'll post the results after I install the new cap.
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Yoda
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Re: SE84C-EX Hum
Reply #29 - 02/23/05 at 05:24:37
 

[quote author=Steve_Collins  link=1105725338&amp/15#26 date=1108989693]
Hi Stingray
I too tried removing the 1000uf cap, actually in my case it was a 470uf cap following Eddie's hum reducing suggestion, but I found the same as you. Steve
[/quote]

Where is this post from Eddie...he has so many!

Matt
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Steve_Collins
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Re: SE84C-EX Hum
Reply #30 - 02/23/05 at 12:28:32
 
Hi Yoda
You'll find Eddie's reply here.
http://www.decware.com/cgi-bin/yabb/YaBB.cgi?board=zen&action=display&num=110536...

In my opionion upgrading the 1000uf cap to a high quality/expensive one doesn't make hardly any difference to the final sound quality.
Eddie suggested either a 470uf or a 330uf to see if it reduced the hum. I did have a 1000uf blackgate fitted, but after trying the no cap cure ( i.e. removing the 470uf ) I've put in a basic rubycon 330uf that I had and the sound has not suffered when compared to the 1000uf Blackgate or the 470uf Evox/rifa.
IMO the biggest bangs for your buck happen when changing the 84C to CSex by fitting
Audionote .1uf copper foil coupling caps
Vishay dale 1k and 150ohm power resistors + RCA5V4G
EX transformers
1k Audionote tantalum resistors on input tube
1k Allen Bradley on power tubes ( not 330ohm as SE84CS )
Mullard EL84's
Input tube of your choice

I've found that as the internals of the amp were improved the SV83's and 6N1p sounded better too, and I could quite happily live with them if EL84's etc never existed. When you couple the 84CSex to HDT drive units you really get the magic going. BTW, HDT's need every hour of the 220 hour break in period. But beware, the combo demand 1st class sources.

All the best
Steve

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144cubits
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Re: SE84C-EX Hum
Reply #31 - 02/24/05 at 14:28:11
 

 [quote author=StingRay  link=1105725338&amp/15#28 date=1109126378]I ordered two very high quality caps per the recommendation of our resident guru.  If there is an improvement after I install mine, you're welcome to the spare. [/quote]

Stingray you are the man! I would be happy to remunerate you for any caps, resistors you find that will bring the magic back...just one request is there any place I can find pix of the procedure. I know everyone says how easy it is and how you should dive in, but I've only done one DIY in the past  but I had pix that showed what was what.

Any help would be appreciated.
8)
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StingRay
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Re: SE84C-EX Hum
Reply #32 - 02/24/05 at 16:05:06
 
I took a pic when I snipped the Xicon out, and I'll take pics when I put the Elna Cerafine in.
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144cubits
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Re: SE84C-EX Hum
Reply #33 - 02/24/05 at 17:42:16
 
Thanx! Looking forward to hearing your impressions.
Fred 8)
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StingRay
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Re: SE84C-EX Hum
Reply #34 - 02/26/05 at 19:27:15
 
I've installed the new cap, and I'm pretty much back to where I started.  There is a slight improvement in the hum, and possibly a slight improvement in the sound.

From my experience there are things I think and things I know regarding the Select EX hum and cap upgrade:

Here's what I know:

1.  The hum values on my amp are not within spec.  They are 2 to 3 times higher than the specification.
2.  Removing the cathode resistor bypass cap improved the hum, but attenuated the low end response of the amp.
3.  Replacing / upgrading the stock Xicon 1000uf cap does little to improve the hum problem or improve the fidelity of the amp.  There are slight differences (hum is now at about 3.9 mv, and the amp may sound slightly better).

Here's what I think:

1.  Leave the amp alone.  Trying to fix the hum issue by fooling with the cathode resistor bypass cap causes more harm than good.  It apparently masks the 120 hz hum by attenuating the low end response of the amp.
2.  Even with the slight improvement I noted, it was a lot of trouble for very little improvement.
3.  The hum specification for the Select EX amp may need to be re-written.  With two amps confirmed at 4.5 mv, the specification of less than 1.5 mv may not be accurate.


FWIW, the hum is not a problem at normal listening levels.  It is only apparent between tracks.

I have pictures and a description of my findings at:

http://www.geraldcurtis.com/selectex_mod.htm

Jerry



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Steve Deckert
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If the 1st watt
sucks why continue?

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Re: SE84C-EX Hum
Reply #35 - 02/26/05 at 20:20:59
 
We have been modifying the SE84C and SE84CS amplifiers with "EX" transformers for over a year and have even built several that way as brand new amps.  Hum on these amps has always been within spec.  Spec on an EX modded amplifier is 2mv or less.

It has only been recently that a few people have reported hum issues.  

If you have an EX modded amp that has excessive hum you should consider sending it in to be checked out so we can find out what happened.  If you do, please include the tubes that you use with the amp.  

By design this amp will have a higher hum figure then a non-ex modded amp.  Example, a stock Select can be 0.7 mv and most are.  An ex mod usually bumps it up to 1.7mv which is very acceptable.

For those of you who are trying different things on your amps to reduce hum, first find out where the hum is coming from.  Pull the input tube out of the amp completely and then measure the outputs with no speakers connected, volume control all the way down.  Wait for it to warm up for several minutes.  If the hum you measure is below or at 2mv, then the power supply and output stage is not the cause of your hum problem.

If this is the case, you should roll input tubes and see if all of them behave the same.  If so, raising the bias resistors total value by 1K on each half of the tube will drop the hum by at least 1 mv or more.

Removing or lowering the value of the bypass cap on the output stage cathode circuit can also drop the hum by 1 mv or more as can adding another 40 uf to the second section of the power supply filter. I consider both of these options last resorts.
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StingRay
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Re: SE84C-EX Hum
Reply #36 - 02/26/05 at 20:42:35
 
Steve,

Thanks for your input on this thread.  

Quote:
An ex mod usually bumps it up to 1.7mv which is very acceptable.


I agree.  I got hum down to 2.3 mv by removing the bypass cap, and it was very acceptable.  1.7 mv would be just about perfect on my 94 db/w/m speakers.  Unfortunately, with extended listening, the amp sounded too thin.

Quote:
Removing or lowering the value of the bypass cap on the output stage cathode circuit can also drop the hum by 1 mv or more as can adding another 40 uf to the second section of the power supply filter. I consider both of these options last resorts.


I am now familiar with the impact removing or lowering the value of the bypass cap has on the amp.  In addition to lowering the hum, what impact would another 40 uf on the second section of the power supply filter have on the amp?  Would it impact the sound, rectifier choices, etc?  Also, what would your choice of cap be if you decided to add it?


Thanks,

Jerry
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« Last Edit: 02/26/05 at 20:47:11 by StingRay »  
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144cubits
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Re: SE84C-EX Hum
Reply #37 - 02/28/05 at 14:02:52
 
Hey Jerry thanx for your determination on this EX Hum issue. Your help has been invaluable. I sent you a message on your forum.

Fred 8)
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StingRay
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Re: SE84C-EX Hum
Reply #38 - 03/01/05 at 00:49:27
 
Happy to help.  This forum has been a tremendous asset for me, and I'm glad to hear you're enjoying it.  Posted a reply.
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StingRay
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Re: SE84C-EX Hum
Reply #39 - 03/12/05 at 16:37:47
 
Latest update.  I am thinking about reworking the PS filtering in my Select EX, but I wanted to try a few inexpensive / easier fixes first.

Today, I added a 30uf cap in parallel with the second stage of the PS filter.  This was easy to do, and the hum is now down to about 2.8 mv.  I'm going to do some listening to see if it slowed anything down.  

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decwarite
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Re: SE84C-EX Hum
Reply #40 - 03/13/05 at 04:02:03
 
I have just come to some similar conclusions regarding grid stoppers.  Definitely, tantalum on the input tubes and allen bradley on the output tubes.  I thought the dale aluminum body power resistors  sounded thinner than the regular dale ww black body power resistors.  They sport a lower power rating but sound better to my ear.  I've taken the bypass cap off my amp and it sounds great.  Believe it or not the xicon cement resistor that came with my "c" sounds the best on the cathodes over the mills and dale aluminum body.  It has a richer and my lively sound.
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Re: SE84C-EX Hum
Reply #41 - 05/07/05 at 02:42:47
 
[quote author=StingRay  link=1105725338/15#28 date=1109126378]If there is an improvement after I install mine, you're welcome to the spare.

[/quote]

Jerry, I now have about 300 hours on my EX and have changed all of the tubes. It seems that you are absolutely right. The tradeoff of the lower hum is not worth the lack of presence and thin sound.  :'(              

I would like to get to where you are. If your offer is still good I'd be happy to accept it...let me know.  
Fred
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proud_indian
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Re: SE84C-EX Hum
Reply #42 - 05/07/05 at 20:34:51
 
[quote author=144cubits  link=1105725338/30#41 date=1115430167]

Jerry, I now have about 300 hours on my EX and have changed all of the tubes.  
Fred [/quote]

While I have no hum problems ( you cant even hear it with your ear to the speaker) 300 hrs is too little. Iam 600 hrs up, and feel that the Ex Mod really cleans up its act around 500 hrs. I still find the highs a bit sharp, but I think I will ride it out. To get over this burn in, I looked at it as a PC burn in, after Eddie mentioned to me about the length of wire used. But then, I had changed all three transformers. Another advice from him was that I was using 96 db Lowthers. Less load . So I pulled out a pair of 88 db speakers, put a blanket over it, and turned up the volume every day I was at work. Dont know what helped, but I am glad I got over the burn in. What a pain.
shreekant
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proud_indian
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Re: SE84C-EX Hum
Reply #43 - 05/07/05 at 20:36:02
 
I forgot. A good time to burn in all your new tubes, while you wait out the burn in.
shreekant
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proud_indian
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Re: SE84C-EX Hum
Reply #44 - 05/18/05 at 09:00:33
 
I am now around 800 hrs on the Ex Mod. It does take a very long time to break in. Even now, at higher volumes, it shouts a wee bit. But otherwise,it is quite amazing.
At very low volumes, the detail is something to hear and belive. Absolutely stunning. It drives the lowthers with such ease now, that it can get really loud. I find that I listen at a much lower vol than I used to.
With the LF kicking in, the mid's that used to be highlighted, have mellowed quite a bit. Iam happy that I took the decision to go in for the Ex. For those who have 8 ohms, don't even think twice. Its better than any other tweek that you can do. No cable or tube costing 100 bucks can even THINK of compairing itself to the EX. Sonic's wise, its miles ahead.
A modified shreekant Smiley
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Joel
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Re: SE84C-EX Hum
Reply #45 - 05/19/05 at 01:53:20
 
I posted some thoughts on the Hornfest and amp comparisons on Ed's site. One of the things I mentiioned was that my CEX has absolutely no hum. Now there are several other members that can verify that. It is one great sounding amp. It just keeps improving.
Joel
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needlz
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Re: SE84C-EX Hum
Reply #46 - 05/19/05 at 04:23:23
 
I have a C-EX too and it is pretty much hum free. I recently added front jacks and wired them directly to the input tube. Since I did that I am getting the weird hum problems that others have described... The amp hums even when it's off. It will continue to hum until I disconnect the rca's  from the front jacks AND remove the power cord. If either of these remain connected, the hum continues.
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proud_indian
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Re: SE84C-EX Hum
Reply #47 - 05/19/05 at 05:04:45
 
[quote author=Joel  link=1105725338/45#45 date=1116464000]. It is one great sounding amp. It just keeps improving.
Joel [/quote]

How long have you had it since it was EX'ed, and how many hours have you put in for burn in and post burn in. Just my curiosity.
Thanks
shreekant
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Joel
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Re: SE84C-EX Hum
Reply #48 - 05/19/05 at 13:07:37
 
I purchased the amp new with the EX option, at the same time I purchased the CSP for gain with rock; both end of year after Decfest. Really only needed the CSP with bias in low position and high volume. I switch between the CEX and an F1, using the CSP as the Pre for both. I usually play either for about 1- 2 weeks, they stay on continuously during that time, that makes a big difference. The CSP stays on all the time. In other words, the amp has lots of time, but there was no hum from the beginning.
Joel
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proud_indian
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Re: SE84C-EX Hum
Reply #49 - 05/19/05 at 15:41:20
 
Yes. Keeping them on all the time make a difference. I do that during the weekends, starting Friday morning. Otherwise I find that it takes about 90 to 120 mts to really start doing its thing.
Thanks,
shreekant
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Jason_S
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Re: SE84C-EX Hum
Reply #50 - 02/16/06 at 19:10:06
 
Bump

what seems to be the average hum levels of everyones EX modded amps?  I think mine's running about 4.5mv with the input tube in and 3.4mv with it out.    

That seems to be a bit excessive given the decriptions here.

Jason
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Sam in USA
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Re: SE84C-EX Hum
Reply #51 - 02/16/06 at 19:33:16
 
Well, the stock C/CS should have a hum <=2.0mV I think
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