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Old 23rd December 2012, 04:45 PM   #301
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Hi!

Quote:
Originally Posted by merlin el mago View Post
Thanks Andy, I have on hand the Lundahl 1660/18mA for #26 tube preamp and wired as you: Alt Q SE Line Output 4.5 : 1 with that configuration have a gain x10 & and output impedance of 2K?
If you wire the LL1660 4.5:1 You will loose gain by that factor: 4.5 at the same time output impedance will be redued by that factor squared or about 20! Which is a huge benefit

The 1660 performs and sounds far better in 4.5:1

Quote:
Originally Posted by merlin el mago View Post
can be enough gain for vynils?
Well this depends on your system. Nobody can answer this for you without more information. Of course you will need a phono preamp with the proper RIAA eq in additon to such a linestage.

In my opinion the linestage is the wrong place to add gain to the system. ideally the linestage provides a high impedance to the sources. Means to select between sevral sources and a volume control. It should have a low output impedance to drive cables and amps. This is already a demanding task. Asking it to also deliver gain can easily lead to compromises in sound.

The power amp should have an input sensitivity such that it can be easily driven to full output with typical line levels. Phonostages should have the correct gain to bring the signal up to a similar level as the other sources so they can work with the same linestage.

A linestage should just have a little gain maybe 3-6db to have some room left for records with low levels and when you want to crank it up.

Of course you can deviate from this approach if you adapt everything exactly so that the gain structure of the system works for you. In that case you should exactly know what you do.

Best regards

Thomas
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Old 23rd December 2012, 04:48 PM   #302
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My MC phono preamp has aproximately 60dB, MC cart 0,25mV, is enough?
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Old 23rd December 2012, 05:08 PM   #303
regal is offline regal  United States
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Quote:
Originally Posted by Rod Coleman View Post
Hi Dave,

The 4П1Л will drive the 6C4C into clipping easily.

It's very well behaved in pentode mode - there are no sharp rises in screen current, even with the anode down at 50V.
.
Thanks but I'm looking at why it couldn't drive a 6C4C/2A3 fairly well in triode mode.

Say I have 4Vrms input from my SS balanced DAC (using an input transformer on the amp):

4vrsmx1.44x2= 11.5 to the 4p1l grid.

My goal is about 1.5 watts max, 1 watt normal listening

with a ccs anode supply should get a gain of at least 8 so:

11.5x8 = 92V's. Divide by 2 gives 45V which is a typical bias for a 2A3. I guess I would rather have a low overall system gain and have the low Ra driving power in triode mode rather than higher gain I won't use in pentode mode.

Am I missing something looking at things this way ? I guess what trade-off am I missing ?

Last edited by regal; 23rd December 2012 at 05:18 PM.
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Old 23rd December 2012, 05:29 PM   #304
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Well, why not. With -45V on the 2A3, you do only need 45V zero-to-peak (=peak voltage)

Ale measured a mu of about 8 for the 4П1Л, so yes, you can clip the 2A3 for, say 6.5V peak, a little over 4V rms.

I don't think you are missing anything, providing the 4V rms from the DAC does not involve any bad-sounding compromises.
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Old 23rd December 2012, 05:30 PM   #305
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Here's the preamp schematic as requested. Andy
Attached Images
File Type: png 4P1L LL1660_3.png (58.0 KB, 382 views)
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Old 23rd December 2012, 05:36 PM   #306
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Thanks Andy, attached pic with questions.
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File Type: png 4P1L LL1660_3.png (60.5 KB, 398 views)
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Old 23rd December 2012, 06:12 PM   #307
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I have DN2540, I only need to know the value in mA to 4P1L and the schematic?

VR150 are these tubes?

vr150 tube | eBay

Recommended brand?
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Old 23rd December 2012, 06:35 PM   #308
JoshK is offline JoshK  Canada
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Quote:
Originally Posted by merlin el mago View Post
I have DN2540, I only need to know the value in mA to 4P1L and the schematic?

VR150 are these tubes?

vr150 tube | eBay

Recommended brand?
I'm not andy, but yeah, those are the VR150s. I have a bunch of them and they all work regardless of brand, but I have mostly used GE/RCA/american ones. You the CCS needs to provide the 18mA to the 4P1L + whatever current you need to light up the VR150. I don't have the doc in front of me, but close guess is about the same for the shunt as for the circuit. Shunts aren't efficient, but they sound good.
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Old 23rd December 2012, 06:39 PM   #309
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Thank you.
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Old 23rd December 2012, 06:43 PM   #310
regal is offline regal  United States
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Quote:
Originally Posted by Rod Coleman View Post
Well, why not. With -45V on the 2A3, you do only need 45V zero-to-peak (=peak voltage)

Ale measured a mu of about 8 for the 4П1Л, so yes, you can clip the 2A3 for, say 6.5V peak, a little over 4V rms.

I don't think you are missing anything, providing the 4V rms from the DAC does not involve any bad-sounding compromises.
Do you see what I'm doing? with a single stage all DHT amp there's opportunity for better 2H & 3H harmonic cancellation if you make the first tube "work" harder and the output tube work less, if it doesn't work of course I can re-wire for pentode mode.
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