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Old 3rd March 2012, 03:38 PM   #1
JdAo is offline JdAo  Portugal
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Default Cross talk and better caps / should I sell this ?

Hi, I'm having a bit of a dilemma here. I have this absolutely mint condition vintage amp that has great reviews at the time with brilliant specs confirmed by readings and good sound. However there is one spec that bothers me, and that is the stereo separation, which is only 75db. If I simply replace it's caps with high quality Mundorfs (original rating is 4x caps of 10000uf 71V) will I improve the stereo separation ? I think the caps are in need for a replacement anyway, but I'm considering getting a Pionner M90 which has dual transformers but not the same cool look of the A5 IMO. The amp in question is a Technics SE-A5, you can read on old review at the following link:
http://adrian-kingston.com/images/SE...oundReport.pdf

What should I do ?
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Old 3rd March 2012, 04:50 PM   #2
DF96 is offline DF96  England
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Why does 75dB bother you? LP and FM have separation in the 30-40dB region, yet they can sound OK.
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Old 3rd March 2012, 11:15 PM   #3
JdAo is offline JdAo  Portugal
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Well, maybe you're right, but I want to hear the recordings as they were originally done. So I'm not gonna get that with 75db separation, CD has 96db dynamic range so the separation should be at least 96db. Unless the recording process already takes into account the cross talk in consumer devices (does it ?) in which case high end audio amps with separate transformers are not the ideal reproduction equipment ?!
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Old 3rd March 2012, 11:29 PM   #4
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To put things into perspective, 75 dB of channel separation means no more than 1.4 mOhm of ground return common to both 8 ohm speakers, or half that for 4 ohm ones. (It's very hard to reach even 60 dB on low-impedance headphones like 16 ohm ones, simply due to contact resistance at the single ground connection in the headphone jack.)

The main restriction tends to be capacitive coupling between traces though, giving a characteristic decrease of channel separation at higher frequencies. Even then, 75 dB throughout the audible range is not a bad value at all, though you might be able to do 90+ dB today.

Realistically, I don't think anything more than 40 dB of channel separation is necessary for stereo speaker playback, if that. At some point the louder speaker just entirely masks the quieter speaker's output. Headphones need even less, in fact hard-panned recordings ("ping-pong stereo") requiring extreme channel separation tend to be a pain to listen to on them, so people have invented ways of reducing channel separation like crossfeed.

As mentioned, channel separation on LPs tends to be in the 20..30 dB region. FM stereo typically achieves 30..40 dB, sometimes more (up to ~50 dB) when using larger IF bandwidths and fancier stereo decoders.

The only case in which extreme channel separation would be important is playback of entirely different material in different rooms. Doesn't exactly sound like your average stereo amp's job.

Last edited by sgrossklass; 3rd March 2012 at 11:38 PM.
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Old 4th March 2012, 01:44 AM   #5
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Default Don't sell

I remember selling a couple of those amps way back when. I loved them but never had the money to purchase one myself and have regretted it ever since. I'm sure with time the electrolytics will need replacement, but I would recommend against selling the amp. There are many great amps out there in the world, and for whatever reason, Technics was able to build some pretty great amps in that time.

The only negative that I can remember about the big Technics amps from that time is that they sounded best with a 'warmer' or 'fuller' sounding set of speakers. The amps could be a bit 'technical' in their sound.

Good luck.
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Old 4th March 2012, 12:44 PM   #6
JdAo is offline JdAo  Portugal
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Does capacitive coupling between traces affect the signal quality of the other channel when it mixes with it ? Won't it be like out of phase with the same info from the other channel or something...

BTW, the amp's spec states 75db at 1Khz to be more precise, so judging by what you guys said it's probably less than 75db at higher frequencies.

Thanks for the info, I'm really hesitating here and reaching the point of no return where a decision has to be made
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Old 4th March 2012, 02:14 PM   #7
DF96 is offline DF96  England
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Capacitive coupling will be somewhere between in-phase and 90 degrees out of phase, and it is likely to get worse at higher frequencies. Similarly for inductive coupling. It won't affect signal quality because you won't notice it. You really are worrying over nothing. Some might call it 'specmanship'. The 'channel separation' between your two ears will be somewhere around 0-10dB, depending on frequency (gets better at higher frequencies).
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Old 4th March 2012, 02:45 PM   #8
JdAo is offline JdAo  Portugal
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Then why do we have amps with huge separate transformers, which makes them a lot more expensive ? It's not like the normal Joe will buy their amps to open and stare at them.
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Old 4th March 2012, 02:53 PM   #9
DF96 is offline DF96  England
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Fashion? Better weight distribution? Failure to understand grounding?
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Old 4th March 2012, 04:29 PM   #10
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Quote:
Originally Posted by JdAo View Post
It's not like the normal Joe will buy their amps to open and stare at them.
Perhaps not. But they know.

They know...


Marketing works.
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