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Old 17th March 2013, 01:11 PM   #401
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Rixsta View Post
i think i will need a little more gain.
That's easy - in your F5, change R5, R6, R7, R8 to 220ohm 3W. It will decrease the feedback a bit and increase the gain to better match a 'normal' amplifier.
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Old 17th March 2013, 03:27 PM   #402
Marra is online now Marra  United Kingdom
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I agree with 6L6 having just built an F5 turbo with the 220R feedback resistors there is a noticeable difference in the volume control setting i.e several clicks less req'd.
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Old 19th December 2013, 01:46 PM   #403
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I just did a transformer coupled SE tube preamp with 6SN7 and Sowter 8650. It didn´t turn out very well, so I will not pollute the thread with that one. High amplification, but distorted sound.

... But I took out an Aikido 6SN7 preamp I build some time ago. I sounds very good, and measures incredibly well.

I just bought a Rigol 1022 signalgenerator and own a 100 MHz analog Tektroniks scope. I hooked up the Aikido and did some measurements, and I couldn´t believe how good they were. Sinus: Linear from 1 Hz to 20 KHz, still OK @ 100 KHz. 2 division out of 6 down @ 200 KHz and half output @ 300 Khz.

Obvious that I at the moment am not able to do the dB calculation, isnt it :-)

What about square waves then: Nice @ 5 Hz, very nice @ 10 Hz, very clean @ 30 Hz to 20 KHz, OK @ 50 Khz, ramping @ 100 Khz.

Is everything good then ? No, it doesnt drive longer cables very good. For different reasons I have 5 m signal cables between my preamp and my F5, and only the tweeters did play :-)
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Old 19th December 2013, 01:48 PM   #404
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I am still waiting for PCB´s for a BA-3, so it will be interesting to see how the BA-3 will do.
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Old 19th December 2013, 03:02 PM   #405
AndrewT is offline AndrewT  Scotland
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What's the output impedance of your Source?
That combined with the capacitance of the cable and the RF filter capacitance in the Power amp make an audio Low Pass filter if you are not careful to get the ratios correct.
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Old 19th December 2013, 08:21 PM   #406
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If you're running about 7mA thru the front gain stage and the o/p buffer pair, the gain will be around the 10 - 15dB area (you only need about 6dB with 2V signal) and the o/p impedance should be around the 600 ohm mark - still quite okay for driving long interconnects into the 100kR load of the F5 amp inputs.

Perhaps you might check that there's enough current going thru those 6SN7s? Or that the interconnect is a good one .....

Curiously, the DC B1 has an o/p Z of about 200R and drives long cables quite well.
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Old 20th December 2013, 01:23 PM   #407
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Andrew,
the output impedance of the Akaido preamp should be 500 ohms, according to documentation, which I think is ok low.

The cables were 5 m QED cables, I have no specs on capasitance, but it showed up that the sound is fantastic with a pair of similar 1 m QED cables.

My system is not placed as it will be when I am finished ... if I ever will be :-)
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Old 20th December 2013, 01:28 PM   #408
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jameshillj,
you could be correct about the interconnects, but my my Musical Fidelity´s preamp could easily drive them.

I took the transformercoupled preamp apart yesterday, and today I got PCBs from The Shop for a BA-3. which could be ready for testing tonight. I need to match the FETs and put them in.

I decided to try a couple of 180 ohms source resistors to keep the gain down.
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Old 20th December 2013, 01:32 PM   #409
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When I have decided which of the preamps I will go with, I will put in a switched relay attenuator from a small danish company called Dantimax.

He makes unbalanced and balanced attenuators with remote controls and optional LCD displays, to very reasonable prices.

It is however not that easy to find out what to put together for a working system.
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Old 20th December 2013, 01:41 PM   #410
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I think I posted it earlier, the F5 is quite clinical, it does sound better with the Impasse pre-amp which gives it a more Aleph type "tubey" sound.
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