Welcome, Guest. Please Login or Register
Decware Audio Forums
08/21/14 at 11:20:17


Pages: 1 2 
Send Topic Print
High Pitched Squeal from MT (Read 4025 times)
Ron
Senior Member
***




Posts: 87
High Pitched Squeal from MT
04/22/13 at 02:32:41
 
I have been using my MT since I opened it up and I love it. I went through a small phase of cold feet but have finally realized the true potential of this beautiful amp.

That said, my MT has developed sort of a high pitched squeal... my guess is somewhere around 16-18 kHz. As you could imagine it is quite distracting.

Any ideas?

The only tubes that are not stock in my MT are the EZ81 rectifiers because my JJ's didn't work. I am using RFT's I got off of eBay.

I have tried rolling in new signal tubes, new power tubes, new 0A3 and 0D3 regulators... sometimes I hear a  difference in frequency, yes, but it is never gone Sad
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #1 - 04/22/13 at 02:58:30
 
I'm not sure if this is related to the RFT EZ-81, but I've experienced some sibilance with this tube and replaced it with the RFT EZ-80, and problem solved. I even prefer the EZ-80 sound contribution overall.

Having said that, I've never experienced any 'squeals' with the RFT EZ-81, just a loss of control on high pitch passages, which I presume may turn into a squeal if the particular tube involved is in worse shape than in my experience, or if your system tends to be on the bright side.

If you already replaced that tube with the same EZ-81 spec, I would urge you to try the EZ-80 (the tube sounds better anyway, IMO)
Back to top
 
« Last Edit: 04/22/13 at 03:01:46 by Fireblade »  

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #2 - 04/22/13 at 04:14:39
 
Thanks! I will give the EZ80 a shot for sure, would you stick with an RFT? Where would you get the tube from? Maybe eBay is not the best place?
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #3 - 04/22/13 at 05:13:42
 
As far as I know, German made RFT's are great tubes. I got them from Tubemonger, at a good price.

The EZ-81 has shown to be a little sibilant depending on the amp and tube complement.  It may work well with smoother drivers, but with my Brimar 12AT7's, it tends to misbehave in some high frequency passages.

The RFT EZ-80, on the other hand, is quite neutral and does not overdo it at those frequencies. These seem to create better synergies with my tube setup.

Alternatively, try to determine if you have a tube with high microphony (ringing sound due to some elements within that tube which resonate with vibration), in which case any spec tube in your setup could be causing this effect.

I'd try the EZ-80 first. If not, then replace each of the other tubes involved, one at a time. You need to discard a likely microphonic tube in that case.

Good luck!

Back to top
 
 

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #4 - 04/22/13 at 11:29:20
 
Thanks for the help...

Would I still hear anything if I have no music being played through the MT? Right now even if it is on it will squeal.

The frequency changes sometimes if I move the feedback/tone knob.

I have tried multiple 12AU7's, (RCA Triple Mica Black Plates & Stock)
I have stock 6v6's and Tung Sol 5881 Reissues
I have tried a 2nd set of OC2 (Raytheon), 0A3, and 0D3 regulators.

The only thing that is not stock and I cannot test is the rectifiers... so that is my start point and seems to align with your thoughts.

Steve is now shipping with the EZ90, are they backwards compatible as well? If so I will get some EZ80 tubes and EZ90 tubes as well to test.

Thoughts?
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #5 - 04/22/13 at 12:48:44
 
I have not yet experienced microphonic issues myself, so I don't know how these issues present themselves exactly, although a very microphonic tube (i.e., one that squeals), would probably still do it to a lesser degree, even at iddle, from vibrations coming from the trannies.

I understand the most common microphony scenario is the faulty tube's resonance with vibrations stemming from the sound waves created by the speakers, though. Also, the more the amp is under load, the more microphonic that tube should become.

Can you try to apply some dampers to both rectifiers and drivers, and see if the squeal issue improves?

I believe the official description on the Mini Torii keeps the old EZ-90 (6x4) rectifiers listed by mistake, since these have been replaced for quite a while now with the EZ-81's. Do not try those 6x4 (EZ-90's) in your recently revised model.

In case there is a more organic cause for this issue, I suggest you call Steve and ask him directly about it. I'm sure he will help you solve this in no time. In the meantime, get those EZ-80's, as one or both of your current EZ-81's seem at this point the most suspicious candidates for either spec sibilance (systematic) or microphony (non-systematic).

Keep us posted.
Back to top
 
 

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #6 - 04/22/13 at 13:03:32
 
I can't find a RFT right now. What about a NOB Tunsgram?

I will be sure to keep everyone posted.
Thanks again!
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #7 - 04/22/13 at 13:48:24
 
No problem, Tungsram rectifiers are reported as very good also.
Back to top
 
 

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #8 - 04/22/13 at 14:03:28
 
Thanks, I have ordered the Tungsram EZ80 tubes, should be here on Friday! I am also looking at some RCA Grayglass 6v6's or Tung-Sol 6v6-gt power tubes incase I need to swap those out as well.
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
grinnell
Senior Member
***




Posts: 64
Re: High Pitched Squeal from MT
Reply #9 - 04/22/13 at 15:03:27
 
I have a similar sound from the right side.  Its not the power tubes been swapping those around.  It will stop when i turn off that side and turn it on again.  And i have tube dampers on 2 tubes.

I suspect is a microphonic tube.  just havent had time to track it down.
Back to top
 
 

MT w/ 1940's RCA 6v6g st
Ref 3A de Capos
VPI HW-19 mk iv
Mac Tuna MR-67
MH 25.2 CDP
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #10 - 04/22/13 at 18:57:46
 
I was listening during my lunch break today.

Current tube setup:

  • JJ 6V6S
  • RCA Triple Mica Black Plate
  • Raytheon 0A3/Raytheon 0C2
  • RFT EZ81


So I noticed no sibilance at first then as the tubes warmed up it did get more pronounced. I am hoping that it really is the rectifiers, this makes sense here as the EZ81 rectifiers to get quite hot during use.

The Tungsram EZ80's shipped. Haven't ordered anything else yet, going to try this first. Might spring for NOS RCA 6V6GT grayglass or just go with Tong Sol 6v6GT reissue.

Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #11 - 04/22/13 at 20:38:29
 
Nice tube complement. I would go for the current production Tung-Sol 6V6GT's, unless you already have an overly bright system. These are better sounding output tubes than the JJ's, by far (pace, transparency.)

You did not specify if the RCA's are 12AU7 or 12AT7's. If the latter, these could tend to make the EZ-81's even more sibilant on high pitch passages.  I personally prefer 12AT7's in general, coupled with EZ-80's.

Discarding any more organic issues, the weakest link in Mini Torii's tube complement remains the rectifiers. These work hard, which explains some sibilance on EZ-81's when pushed too far (high frequency pitches), or when these tubes are not in top shape. Never use JJ EZ-81's in that position (don't last long).

I would stick to 6V6 output tubes for now. These sound the best in general (with some reported good exceptions out there), and won't press the rectifiers too much.

Back to top
 
« Last Edit: 04/22/13 at 20:50:46 by Fireblade »  

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #12 - 04/22/13 at 21:52:33
 
Well I reached out to Steve just in case we were wrong... He wants me to ship it back to the mothership.

At least I have a nice pair of EZ80 rectifiers.

(The RCA Blackplates I have are 12AU7's)

Don't the 12AT7's give you too much gain?
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Fireblade
Seasoned Member
****


Knowledge comes, but
wisdom lingers.
A.L.Tennyson

Posts: 702
Re: High Pitched Squeal from MT
Reply #13 - 04/23/13 at 01:01:29
 
I'm sorry it looks like there is something organically wrong with your unit, after all. I'm glad you called Steve, who will fix it in no time.

12AT7's do increase the gain, but not dramatically. The end result is less range used on the volume pots to reach your sweet spot listening volume, but not by much.

I can't generalize given my limited exposure to the vast variety of 12au7/12at7's out there, but the benefits I perceive from 12AT7's in my system, in general, is the improved openness and pace.

Some forum members enjoy the 7062 (slightly less gain than a 12at7), a driver that I will be trying myself eventually.

I'm sure you will like the EZ-80 rectifiers.
Back to top
 
 

Laptop-Foobar2K-ASIO Direct//WD 2.0Tb HDD//Audio Gd USB cable//Audio Gd NFB 3 (2014) DAC//Decware Silver Ref IC's//Decware Mini Torii SE//Kimber Kable spkr cbls//Decware DM945's//Velodyne DLS 3500//BJC SUB Cbls//Tripp Lite 500 Isolation Trnsf.//Jellyfish Pwr Cord
  IP Logged
Ron
Senior Member
***




Posts: 87
Re: High Pitched Squeal from MT
Reply #14 - 04/25/13 at 01:22:34
 
So good news, I waited till I received my EZ80 rectifier tubes. Set the MT back up with the stock tube complement and swapped in my EZ80 tubes. Everything works perfect and it runs SILENT.

Clearly I got a bad batch of RFT tubes, maybe they were not as NOS as the seller said they were. Oh well. Lesson learned.

I have emailed Steve, want to ensure he is ok with me if I don't send it in unless I hear some squealing in the future. Smiley

Thanks all for the help!
Back to top
 
 

Mini Torii; Custom Mark Audio A12P SuperPensils; Kenwood KD-2055 TT; Audio-Research PH3 Phono Pre
  IP Logged
Pages: 1 2 
Send Topic Print