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Missing low freq's (Read 1044 times)
funch
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Missing low freq's
11/03/13 at 04:19:07
 
I recently picked up a V-cap'ed, config. 1 Rachael on Audiogon to use
with my Audeze LCD2's. It's driven with a CSP2+. While the mid's
and highs are to die for, I'm noticing that the very bottom low's are
MIA, at least compared to my Taboo II. The output tubes are PSVANE
6CA7's; inputs are Mullard CV2493's. I've tried the stock tubes, but
no luck.

Any thoughts? Is it just the nature of the beast?
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Lord Soth
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Re: Missing low freq's
Reply #1 - 11/03/13 at 04:52:35
 
Hi,

Have you tried using other tube rectifiers?

I have encountered your problem before but with other tube equipment.

I suggest trying out a Philips 5R4GY from Upscale Audio.
If you are using the stock rectifier, it is likely to improve all freqs and not just the bottom end.
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funch
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Re: Missing low freq's
Reply #2 - 11/03/13 at 04:56:30
 
I'm using a United USAF 596 rectifier. I do have the 5Y3 from Upscale,
as well as a couple of 5U4G's. I give them a try. Thanks.
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funch
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Re: Missing low freq's
Reply #3 - 11/03/13 at 05:18:48
 
No luck with any of the rectifiers. I'm wondering if could be a slight
impedence mismatch with the 'phones?
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« Last Edit: 11/03/13 at 05:29:44 by funch »  
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Lord Soth
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Re: Missing low freq's
Reply #4 - 11/03/13 at 06:32:11
 

Using different types of rectifiers should change the operating point of your tubes.

Did any particular rectifier type make any improvement in the low end, even slightly?
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alper_yilmaz
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Re: Missing low freq's
Reply #5 - 11/03/13 at 08:43:41
 
Hey funch,

I have had the same issue with my SE34I.2+.  I have received some suggestions when I posted the issue here.  I ended up going for a subwoofer, yet I realize I am still not happy with the bass in contrast to the amazing mids and treble.  At first, I thought I solved the issue but after hearing the bass on few friends' (even) mediocre systems at best, I was planning to write to Steve about this.

I am not familiar with your speakers, but mine are 97dB single driver Hoyt-Bedfords.  I do not have the impedance curve, but my guess is they reach a peak at lower frequencies and therefore there is an unevenness in the frequency response.  I have this problem even with my TORII mkII.  

I personally am considering having the EX mod on the SE34 which will make it more suitable with 6-16 ohm speakers.  I am not sure if this will be the ultimate solution, but the other potential solution that comes to my mind is having a two-way speaker with the least complex crossover (which is less likely to soak the power of the amp).

Folks, please chip in with tour two cents and correct me f I am talking gibberish here!  :)

Best,

Alper
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DBC
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Re: Missing low freq's
Reply #6 - 11/03/13 at 14:14:53
 
Alper_yilmaz,

I have the Super Zen and had similar issue. Mid's & High's to die for but light on the low end. With low watts just not enough power for the low end.

Added an HSU sub but did not fully solve the problem. Went with an HSU Mid Bass Module and problem solved. Read the thread "Adding Weight & Body" and I explain my theory as to why the Mid Bass Module works so well.
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Oppo BDP-83SE, SE84CKC amp, Klipsch RF-7 mains, HSU MBM-12 MK2 mid bass module, HSU ULS-15 sub
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funch
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Re: Missing low freq's
Reply #7 - 11/03/13 at 22:40:32
 
Thanks for the replies guys. I don't use speakers. The Audeze LCD2
is a planar headphone, and the bottom end is definitely present with
the Taboo II, so it sounds like the issue might be an impedence
mismatch. The 'phones impedence is around 50 ohms.

What is the EX mod? I'm not familiar with it.

I know. I'll get out the soldering iron, and transplant Rachael's mid's
and highs into the Taboo.
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« Last Edit: 11/03/13 at 22:41:28 by funch »  
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alper_yilmaz
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Re: Missing low freq's
Reply #8 - 11/04/13 at 00:52:09
 
To the best of my knowledge, the EX mod simply changes the output transformers' impedance from 9600 ohms down to 3300 ohms (I might wrong about the exact figures) so that the amp can run speakers with higher impendance.  This causes lower output but with efficient speakers it still should be more than enough volume.

The mod is based on the fact that single-driver speakers with no crossovers tend to have fluctuating impedances across its frequency range.  It is highly likely that such a speaker has a peak in lower frequencies and therefore the lack of bass.

DBC's suggestion makes sense to me but I am looking for a solution without any subs or mid-bass enhancing designs.  

Best,

Alper
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funch
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Re: Missing low freq's
Reply #9 - 11/04/13 at 01:24:01
 
Thanks. It sounds like I need to investigate the mod further.

I was also getting a fair amount of hum (not surprising through
headphones). I discovered the problem was of my own doing.
I use DIY IC's using Cardas cabling. The shield is connected on
one end, which should then be connected to the source end.
I discovered that I had both IC's connected 'backwards'. Flipping them
cleared up the hum by about 80%. It's tough being dumb.
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hifitubes
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Re: Missing low freq's
Reply #10 - 11/24/13 at 10:30:34
 
I don't find the low-end lacking with Rachel, but I have a powered Deep Hemp sub that I can dial in. I'm thinking about running Mini Torii to sub when it get here. Glad you solved your hum problem!
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