Problem with Cinemag and AA 2006 phono. - Page 3 - diyAudio
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Old 8th April 2007, 10:32 AM   #21
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Yeah, so I doubt that's the case as well...
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Old 8th April 2007, 04:56 PM   #22
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hey Peng Boon,
would it be possible for you to post some close-up pictures of the setup?
thanks
Byron
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Old 9th April 2007, 12:45 AM   #23
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Sure. I would have to put it together again, as I have to remove it since I am using my Denon SUTs. I'll see what I can do tonight, but it wouldn't be as neat as the first time.
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Old 9th April 2007, 02:07 PM   #24
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Here's a poor picture of it.

Basically this is one half of it, the other channel is identical.
On the left is the input jack from TT, right is output jack to preamp.
Before the cinemags, the input jack signal and ground go into the phono signal and ground, top set of connections on the board. To install the cinemags, I inserted it in between the input jack and phono input. Yellow and brown is connected to input signal, red and green to input ground. Violet to phono input singal, white, black and grey to phono input ground. Blue and orange are floating.

I've tried loading the input of the phono (output of the SUT with 30k, that together with the 50k input of the phono reflects to a 14R loading on the cart, and without. Both without success.
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Old 10th April 2007, 02:20 AM   #25
kevinkr is offline kevinkr  United States
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Not sure about your math but I think the way it is connected is 37:1 voltage gain and with 1kHz reference sensitivity of 0.3mV@5cm/sec is 11mV, not 5mV if everything is working correctly. At a maximum of 25cm/sec this would be 55mV, but it is not likely that you would encounter this very often. Note that at 20kHz it is about 20dB higher.
Worst case this is 5.5Vrms out with 55mVrms in which might clip the phono stage, but I find it hard to believe that the cartridge is producing anywhere near these levels.

Try the 150 ohm tap with a 15 ohm resistor across the cartridge and loaded into 51K if this doesn't work try the next thing below..

I'd borrow a tube phono stage that is known to be able to handle very high levels, and after that I would send them back to Cinemag with a request for a full refund.
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Old 10th April 2007, 02:48 AM   #26
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Hi Kevin,

But I have loaded the cart with 14R, which is the R of the cart, so the 0.3mV will be 0.15mV because of voltage divider?
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Old 11th April 2007, 04:27 PM   #27
kevinkr is offline kevinkr  United States
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The load resistor should appear in parallel with the cartridge, and without knowing the particulars of the cartridge generator it is hard to know how much the output amplitude would drop when loaded. It might be as much as 6dB, then again it might be something else, and probably far less.

Presumably the specified output voltage is when the cartridge is driving the specified load.

What I was suggesting was that you change to the 150 ohm input tap which has 6dB less voltage gain and load the cartridge directly with about 15 ohms, and restore the pre-amp input impedance to 47K - 51K, this should result in a reasonable load on the cartridge and on the secondary of the transformer as well. It's not clear to me how much margin you have before the onset of core overload, and forcing the transformer to deliver more power into the terminating resistance exacerbates the problem.

I suspect that something is wrong with these transformers, and am trying to think of ways for you to make this determination. I would definitely contact Cinemag at this point.

I assume unfortunately that you have neither a signal generator nor scope. This issue could be quickly and easily put to rest if you had some test equipment.
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Old 12th April 2007, 12:16 AM   #28
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Hi Kevin,

You are right, unfortunately I do not have a scope.

Anyway, I did try the 150 ohm without success. What I did was to do exactly what some folks at audioasylum has done, and have feedback good results. Anyway, I have contacted cinemag, and they are very kind to take back the transformers. If their diagnosis prove that the transformers are faulty, I may try them again.

My other option, is to built the JFET headamp on the AA Phono, do you think that's a better idea? It does involve more work.
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Old 12th April 2007, 01:05 AM   #29
phn is offline phn  Sweden
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I like step-up trafos. But there's really no need for them if you use solid-state.

I would look into this: The Phonoclone and VSPS PCB Help Desk
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Old 12th April 2007, 01:18 AM   #30
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Quote:
Originally posted by phn
I like step-up trafos. But there's really no need for them if you use solid-state.

I would look into this: The Phonoclone and VSPS PCB Help Desk
I have already built the AA 2006 phono without the JFET MC headamp stage. Building the headamp stage is the cheaper option, but I was just wondering if step ups would sound better. Currently, I only have my Denon 300LC 1:10 step up. Am keen to build my own though.
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