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C+ (older Ver) Volume pot (Read 2038 times)
Johnny
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C+ (older Ver) Volume pot
11/13/12 at 01:13:34
 
I've just aquired my first Decware amp.  A nice vintage (4/2011) SE84C+.   I must say I have been missing out,... the Manley Stingray hits the blocks soon.  Ultimately I'll be looking at the Integrated or the Tori for a little more power, but the little Zen has me hooked!  Even plays rather nice with my 89db Meadowlark Ospreys,  which honestly were the reason I hadn't pulled the trigger earlier.  
  Now,  the real reason for the post.  I'm getting less than a quarter of volume knb travel before the onset of clipping.  Im using a 2 volt source which the amp should be setup for.  I've read that with a 2 volt source you should get apprx. 3/4 of a turn before the amp runs out of steam.
  I cracked open the lid and took alook.  Volume pot has a pcb attached to it.  Reads  20K-40K,  and has 2x  150K (I assume one for each channel) resistors soldered to it as well.  Ultimately,  I want more usable range out of my volume knob.  If the pot that is in there is not 'normal' (ie, maybe it was switched for weaker sources (ipod))  what should I replace it with for my 2 volt source?  standard 100K pot?   I have pictures  but since I'm a noob on the forum it wont let  do anything till I have 5 posts under my belt.

Thnks in advance for the help,...
-Johnny
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ZENCDUSER
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Re: C+ (older Ver) Volume pot
Reply #1 - 11/13/12 at 03:46:30
 
Johnny,
It may not be the volume pot but rather the speaker impedance.  There are two types of output transformers for the SE84C's: Type A for 2-6 ohm speakers, and Type B for 6-12 Ohms speakers.  Give Steve a call.  If your amp is has the Type A transformers into 8 ohm speakers (coupled with 89db sensitivity) your power output is going to be significantly reduced.
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« Last Edit: 11/13/12 at 03:53:00 by ZENCDUSER »  
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #2 - 11/13/12 at 14:29:54
 
I have the standard 6 ohm (9800) OPT's  (EM0406).   In correction to the manufacturing date,  it is 4/2009.   Thanks for the respones.  I was hoping maybe Steve or one of the Techs would see this post, but maybe a quick call is in order.
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ski bum
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Re: C+ (older Ver) Volume pot
Reply #3 - 11/13/12 at 20:16:56
 
Hello Johnny.  It is rather amazing how these unassuming little amps have such big-league sonics, isn't it?  Welcome to the club.

You need two things.  First, at Torii for the Ospreys.  (Those speakers look bad ass, by the way.)  Second, a pair of high sensitivity single driver speakers to unleash your SE84C and let it show what it can really do.

With the Ospreys you will get to know your zen's clipping characteristics in a very up front and personal way. There is only so much you can squeeze out of two watts, particularly with passive crossover bits (minimal that they are), and the somewhat low sensitivity t-line woofer loading.  Realistically, you will be limited to rather low spl playback.  It is what it is.

In the meantime, while you enjoy the little se84's sweetness at modest volumes, maybe double check how much mileage on the power tubes.  Tired tubes will result in lower output and earlier onset of distortion.  I get about two years of heavy use out of the output tubes before freshies are notably better sounding.  Yours is about that age, and you did not mention if it had fresh tubes or not.  Another suggestion is to put the input tube bias switch in the more laid back sounding setting, as that will push the onset of clipping slightly higher on the volume control.
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #4 - 11/13/12 at 21:10:35
 
Thanks SB,...  I tried the amp with a fresh pair of el84's,  no difference in knob position and didn't much care for their sound.  Moving the bias switch gave me a little more movement but not much.   I prefer the sound with the bias in aggressive possition. I did switch out the stock 6n1p for an EH 6922 that sounded much better in my system.   Surprisingly,  the Osprey's get good volume for my room and setup.  Much more usable volume than I was expecting with the amp.   For 70% of my listening, the SE84 will work fine.  That of course leaves 30% to want for.   I've got my eyes on some Zu Audio speakers, (have for some time) as a replacement  and the Rachael or Tori.  They may be in my near future, or at least I'm hoping I can work it out.
 For the time being, I would still like more usable travel out of the volume knob (1/5th of travel is barely any),  so I would like to figure out the proper replacement to acomplish that.  I've got a feeling that it's more than a different impedance pot though,  and has to do with some of the circuit design.
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ski bum
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Re: C+ (older Ver) Volume pot
Reply #5 - 11/13/12 at 21:33:21
 
I agree, you should be getting much more useful range from the volume.  Something is definitely wrong.  

You're sure your source is 2V?  If so, then your zen's gain is way out of whack.  Did the previous owner modify it so it would work with an ipod or other weak source?
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ski bum
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Re: C+ (older Ver) Volume pot
Reply #6 - 11/13/12 at 22:27:03
 
If you find Zu interesting, check out Tekton designs for a higher value take on essentially similar designs.

EL84 tubes in a zen are rather 'meh', fresh or not.  SV83 or nothin'!

You may be wise to send your amp in to Steve to sort out the input sensitivity/gain issue, and get the latest mods while you're at it.  If you're an experienced solder jockey, then a discussion with Steve is in order.
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« Last Edit: 11/13/12 at 22:34:23 by ski bum »  
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #7 - 11/13/12 at 23:08:48
 
Per an earlier conversation with the previous owner, he never modified the amp.   It does have the latest 'Hazen' mod and appears to be factory done.  I believe I'll give them a call.   I have no problem operating a solder gun, so hopefully Steve can tell me exactly what to check and adjust.
 I'll give the Tek's a look.  Thanks again!
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #8 - 11/14/12 at 21:58:59
 
Got 5,  now I can email,....
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #9 - 11/14/12 at 22:08:38
 
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #10 - 11/14/12 at 22:44:29
 
After talking to Steve, it appears that I have an odd ball v. pot and replacement with a standard 100K will solve the issue,....  time to breakout the gun!
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clowkoy
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Re: C+ (older Ver) Volume pot
Reply #11 - 11/18/12 at 14:48:25
 
Get an Alps 100K pot, it's much better than the stock.
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Johnny
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Re: C+ (older Ver) Volume pot
Reply #12 - 11/19/12 at 15:48:08
 
Stuck a $2 Radio Shack pot in just to make sure it corrected the problem,...which it did.   Have an Audio Note pot on its way.  Turns out the pot in their was a 20K Bourns pot,..Actually a really good sounding pot compared to the radioshack one.  Unfortunately just not enough usable range.   I believe it must have been for integration with low output sources like ipods, etc....  Gotta feeling the ANote pot will blow both away!
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