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Old 1st August 2003, 06:36 PM   #1
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Default Looking for a Preamp

Just completed my "Back into tubes" project, a Dyna 70 clone with goodies. Sounds wonderful, so good to hear the detail again. Next project, a line stage/ phono preamp any suggestions?I will wind up with a SET amp so the quality of the preamp will be critical. Your thoughts please.
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Old 1st August 2003, 09:48 PM   #2
dhaen is offline dhaen  Europe
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Default My thoughts:

Hi Peter,

Unless you actually need gain, or there is a long interconnect between the sources and the power amp, there's nothing to beat passive.

Sorry if you wanted a valve project, just my opinion.

I'm sure there will be others.......

Cheers,
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Old 1st August 2003, 10:27 PM   #3
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Hi,

Quote:
I'm sure there will be others.......
How about passive + valved buffer?

Passive could be resistive attenuator, buffer could be any decent CF.
And than there's also the CVTs to consider...rather pricey though.

If a linestage with gain is required, we had a bunch of those here already to pick from....

Cheers,
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Old 2nd August 2003, 12:06 AM   #4
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Since I wish to include a phono preamp stage as well as an attenuator I believe that the unit will have to be active. My last experience in this area was a Dyna Pas-3 but I do not need switchable inputs, just a phono- in and one "aux" input for the CD player. Since cable length may be an issue I thought of a cathode follower output, so I am picturing two stages for the unit.
Pete
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Old 2nd August 2003, 12:17 AM   #5
EC8010 is offline EC8010  United Kingdom
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Is there room to put the controls in the power amplifier, and simply have a remote RIAA stage?
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Old 2nd August 2003, 12:20 AM   #6
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Hi,

Pete...what if I suggested something I concocted myself?

You can cater for MM, MC cartridges...the volctl anyway you like it, and the aux is a follower that would drive anything bar a dead short?

Heck, there's even a choice between a passive or active RIAA and if you absolutely dislike the 12AX7As you can use 6SL7s instead..?

The thing is ...it does not come cheap, though.

MY MODEST ATTEMPT

Sorry about the self promotion...just seems like the ticket for you...

Cheers,
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Old 2nd August 2003, 01:08 AM   #7
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Don't think I could squeeze anything else into the Dynaclone what is more it will not be the amplifier of choice for the system. Frank, that is a bunch of info to digest and at my age, comprehension is a major challenge. Looks great but I'll have to think on it.
Thanks
Pete
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Old 3rd August 2003, 12:02 AM   #8
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Hi,

Quote:
Frank, that is a bunch of info to digest and at my age, comprehension is a major challenge. Looks great but I'll have to think on it.
Take al the time you need...I ain't all that young either...especially at 6.00 AM.

...Heatwave is being announced for next week here, so expect my response time to be rather slooooow...

Tell us more what you have in mind conceptually and we'll get you started.

Cheers,
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Old 3rd August 2003, 04:35 AM   #9
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Does the ST70 have enough gain for you with your line level sources, eg CDP, DVDP VCR etc?

If it does, then I'd combine the other suggestions, thus;

- make a small enclosure with a selector switch then a volume control and place it beside/under the ST70. Have the selector switch and pots at the rear of the enclosure close to the sockets. Use extension shafts and couplers (try Welborne). This keeps the capacitance after the volume control to a minimum and gets rid of most of the adverse effects of a passive pre.

- build a good phono stage and place it next to the TT. Make sure it can drive the length of cable you require and has about enough gain to match the levels of the line sources. The easy way to calc this is to take the nominal cartridge output level and divide it into 325mV, which is approx the average level of a CDP.

eg: .325/300uV = 1083
20*log(1083) = 60.65dB

This is how I've set up my system with my TT's about 6m to the side of the system.

If you do need gain or have impedance problems (not likely), then build something active.

If you're an experienced builder, I'd suggest building this.
You'll be very hard pressed to better it. Replace the volume control with 50k resistors if you use the passive preamp option outlined above. It's not really that hard or expensive to build and whilst the superreg is great, it's not neccessary. A good passive supply will work fine.

I will wind up with a SET amp so the quality of the preamp will be critical. Your thoughts please.

Don't automatically assume an amp is better because it's a SET. There are a number of PP designs that walk all over every set I've ever heard, top, bottom and the mids. Try it first.
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Old 3rd August 2003, 03:57 PM   #10
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Brett; thank you for the reply! The St-70 does indeed have the gain to drive directly from a CD player even though it is Triode wired, it uses a hand wired version of Triode Electric's upgrade circuit and has no trouble driving my inefficient Satellite units. I will certainly try your suggestion. Thanks also for the Wright Schematic, as I said to Frank, it takes time for me to digest so response will take awhile. I understand your comment re- SET Amps and am certain you are right. Lynn OLson certainly agreed when he designed his Amity amps with PP 2A3's. As i stated in an earlier thread, Jack Eliano's DRD amp interested me, but that project is aways upstream so there is time to research.
Will keep you posted as to progress.

Pete
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