Author Topic: Tube phono preamps  (Read 8727 times)

Online Mars

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Tube phono preamps
« on: October 21, 2015, 10:40:53 AM »
Hi
I have been developing some phono DIY kits using tubes, and would like to share the development with those interested. Is this the right place to discuss this, or should I head off to the vinyl section? :thinking:
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Offline mahleu

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Re: Tube phono preamps
« Reply #1 on: October 21, 2015, 10:54:09 AM »
Either or.

I've always liked the idea, and always worried about getting it to work with a low noise floor.
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Online Mars

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Re: Tube phono preamps
« Reply #2 on: October 22, 2015, 12:24:46 PM »
I am not going to go into the pro's and con's of tube phono's, but rather focus on the different practical aspects of building a tube phono stage, point to point. Aspects to be considered are:
  • integrated and  stand alone power supplies
  • solid state and tube rectifier power supplies
  • electrolytic and polypropylene capacitors
  • volume control or none
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Offline Qualityten

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Re: Tube phono preamps
« Reply #3 on: October 23, 2015, 12:22:35 AM »
IMHO, a tube phono preamp is a tube matter.  I would be interested in following your discussion.  :popcorn:

Online handsome

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Re: Tube phono preamps
« Reply #4 on: October 23, 2015, 09:51:18 AM »
My 2C:

1. Standalone PSU if an integrated PSU causes hum
2. Your choice
3. Polypropylene if you have the chassis space
4. Your choice but will probably require buffering (extra circuitry)

Offline vinyljan

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Re: Tube phono preamps
« Reply #5 on: October 23, 2015, 10:14:10 AM »
I think solid state rectification and no volume control makes it a lot easier to design :2c:
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Offline vinyljan

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Re: Tube phono preamps
« Reply #6 on: October 23, 2015, 02:36:29 PM »
On my Boozhound I have an input and output for MC on the back panel, then 2 more MM inputs. One rotary switch on the front to choose which MM input. The MC out can be connected to another phono amp, or to one of the MM inputs?
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Online Crankshaft

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Re: Tube phono preamps
« Reply #7 on: October 31, 2015, 10:26:26 AM »
A compact unit for desktop use would be great.
All in one unit with volume control and 3-way selector offering 2 line-level pass-though inputs.
MC capability would be a bonus.


Offline Qualityten

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Re: Tube phono preamps
« Reply #8 on: October 31, 2015, 12:42:26 PM »
I understand that it's difficult to build a quiet all-valve MC phono preamp. 

A simple valve MM preamp would have wider use, even for people who have SS amps without a phono stage.  Facility to switch between two turntables would be useful for those of us who have two (or many more) turntables.   

Offline Atom8

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Re: Tube phono preamps
« Reply #9 on: October 31, 2015, 01:08:23 PM »

+1
Volume control on the 2 line levels, making an all in one pre-amp.


All in one unit with volume control and 3-way selector offering 2 line-level pass-though inputs.
MC capability would be a bonus.
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Offline Hi-Phibian

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Tube phono preamps
« Reply #10 on: October 31, 2015, 01:21:18 PM »
I would put some costs to this. 

Like R5000 for MM, adding 2 inputs add X, volume adds Y etc. 

Without considerations for costs everyone will over spec.
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Offline GECO

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Re: Tube phono preamps
« Reply #11 on: October 31, 2015, 02:47:49 PM »
On the Dulcet i use SS for the power supply. Shunt regulated with a "capacitance multiplier" followed by a buffer.....super quiet and extremely low output impedance

The phono uses 1% vishay and wima caps for the RIAA and choice of coupling caps is up to you.
« Last Edit: October 31, 2015, 02:49:51 PM by GECO »

Offline Ampdog

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Re: Tube phono preamps
« Reply #12 on: October 31, 2015, 09:31:27 PM »
Few points,

I understand that it's difficult to build a quiet all-valve MC phono preamp. 

Correct, unless used with a suitable input transformer.  Low noise requirements for valves are all wrong for feeding from a low impedance source.  Novelty value only to my mind.

In addition:

Not often seen are phono input stages using a high-gm valve. John Fuller illustrated the advantage of that in his well-known phono amp of some decades ago. (In valves noise is inversely related to gm, with some relation also to input source impedance.)

One of the lowest noise input stages available is a well-designed triode cascode topology.

I prefer to design a phono stage using a feedback RIAA topology plus inherent sharp low cut-off filter. It follows easily from already present components, and provides useful (sometimes mandatory) filtering of sub-audio articfacts.

As Geco suggested low noise factor requires a low-noise power supply, particularly the input stage. Good dynamic range comes from using a high h.t.; I am not shy to start with 400V which leaves some room for good supply rail filtering.

And don't forget some mains filtering! It is easy and every bit helps.
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Offline GECO

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Re: Tube phono preamps
« Reply #13 on: November 01, 2015, 04:01:09 PM »


......

One of the lowest noise input stages available is a well-designed triode cascode topology.



Interestingly...i use a cascode input on the Dulcet but with a FET for the first stage


Offline fredeb

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Re: Tube phono preamps
« Reply #14 on: November 01, 2015, 05:22:49 PM »
Here's a list with Gm ratings : http://www.pmillett.com/pentodes.htm
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