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Old 13th September 2012, 10:29 PM   #2811
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Quote:
Originally Posted by PelPix View Post
I have, but my phone's radio is super powerful. I've heard it pick up noise before I get a text when my phone is on the counter on the other side of the room.
The cellphone adjusts its output depending on exactly what it is doing, but more importantly, depending on the location of the basestation mast. If the mast is far away or is out of line-of-sight the cellphone will need to use more power to be heard, but if you're standing in the open close to the mast the phone will reduce its output (as will the mast when talking to your phone). This is a feedback (reporting) operation of increasing sophistication in modern systems dependent on the level of received signal at both ends. Modern basestations point the signal at the phone.

Quote:
Originally Posted by Jaketastic View Post
My cellphone transmits on frequencies of 900 and 1800mhz which gives a wavelength of 0.33 and 0.16 of a meter or 33 and 16cm. I don't believe a cell phone would be shielded against transmissions outside it's frequency bands. I'm unsure of the specifics but I do believe that the receiving aerial needs to be a multiple of the wavelength of the transmitted frequency.
A receiving antenna works best (as a generalisation) when a fraction or multiple of the wavelength, but it is not absolutely necessary for it to be a fraction or multiple of the wavelength to receive (or transmit).

A cellphone by its nature is designed not to respond to (is shielded or otherwise protected against) frequencies other than the tuned frequency, otherwise there would be problems with receiving unwanted signals, since in most modern environments there is a plethora of potentially interfering signals.
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Old 14th September 2012, 07:37 AM   #2812
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Default Very loud switch on transient

Just thought I'd post to help anyone else with a similar problem - I had a very loud switch on transient. All tests were ok, voltages, resistances ok. It sounded fine but there was a very very loud switch on transient. I narrowed it down to Q1. Replacing that solved the problem.
Hope this helps...
Cheers,
Andy
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Old 14th September 2012, 11:32 PM   #2813
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Hello,
I received my O2 from JDS Labs a few days ago, and I would now like to change the gain settings. 2.5x is plenty for my LCD-2.2's from all my sources, and I'd like to have a 1x setting for IEM's. So I would like to change the 6.5x setting to 1x gain. Earlier in this thread somebody explained which resistors to clip to change the 2.5x to unity gain, but I want to keep the 2.5x and change the 6.5x to unity. Could anyone help?
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Old 15th September 2012, 12:06 AM   #2814
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Found the answer on head-fi, looks like I'll need to clip the R19 and R23 resistors.
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Old 18th September 2012, 02:43 PM   #2815
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Hello,

I have a major problem with a massive DC offset. I have about -5.8V on the pot, U1 ( pin1 -5.81V, pin8 -6.6V), Also on the gain switch and gain resistors, but the resitors near the input (r3,7,14,20) are fine. Output is fine and U3+U4 also fine.

I've already double checked the TS section and all measurments are fine except D3 and D4 are 0.4V apart (d4 is lower) when powered on but within spec (0.1V) when off. I do have a working unit (o2) and i've compared the regulators and mosfets volatges and they're almost identical when power on.

*I don't detect any solder bridges or any of the sort.

This issue manifests as the volume control not working, only when i turn it all they way i hear the faintest audio signal.

Please advice, and If it's been discussed already please let me know roughly when i should start searching.
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Old 18th September 2012, 03:38 PM   #2816
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Location: Athens
Hello,
has anyone driven the O2 with an aikido preamp line stage, especially with 6sn7, or the O2 inputs will be overloaded?
The idea is that I would like to add a robust and capable to drive low impedance headphones amp module in my existing tube preamp, without getting involved in a "real" and time consuming diy project . My other choice will be the class A JLH amplifier, but it definitely needs some more work...
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Old 18th September 2012, 05:31 PM   #2817
Zigis is offline Zigis  Latvia
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Location: Riga, Latvia
Aikido with 6SN7 at output stage can drive 300 ohm phones direct, I use with HD580.
If you have lower impedance phones, best way is to build output buffer on IRF510 or similar, or on two LM317 (see 24V Aikido).
Next option - build unity gain buffer on opamp (maybe similar like O2 output)
If you already have O2, you can try to remove gain stage opamp and send input signal direct to pot. In this case you use buffer only and not overdrive it.
Building O2 only for driving with Aikido is waste of time and money, better build one of simple buffers on protoboard, it is easy and direct what you need.
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Old 18th September 2012, 05:57 PM   #2818
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Thank you Zigis,
I want to drive ergo 2 headphones, with nominal impedance of 100 ohms, so I will go for a buffer with two lm317, in other words just copying Broskie's approach on 24v Aikido...
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Old 18th September 2012, 06:47 PM   #2819
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In fact I will use a buffer with a power MOSFET and an IXCY 10M45S regulator as the active load. I hope it will be OK. Thank you again and sorry for hijacking the thread
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Old 18th September 2012, 10:16 PM   #2820
Zigis is offline Zigis  Latvia
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100 ohms? Maybe tray plain Aikido first, if you convert output stage to White CF, probably it will drive your phones.
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