DIY Audio Projects Forum

Super simple single stage tube preamp
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Author:  Les [ 31 Jul 2011, 22:29 ]
Post subject:  Re: Super simple single stage tube preamp

rparsh wrote:
Floyd used to rule!

Whadayamean, "used to"? Far as I'm concerned, they still do!

Author:  cheap-Jack [ 03 Aug 2011, 10:39 ]
Post subject:  Re: Super simple single stage tube preamp

Suncalc wrote:
... the placement of controls can have a significant effect on the circuit operation and sometimes single numbers, be they peak or average, don't always tell the whole story.
Questions or comments?

Indeed the plots do give us insight about pot wiper position vs tube O/P Z & HF roll-off.
Thanks for this invaluable info.

However, we should not over worry about the sonic effect given the above plots.

If we read carefully the plot of the 3dB HF roll-off vs pot wiper position, the 'worst' situation is at around 90% of wiper position.- around 60KHz.

IMO, 60KHZ is ultrasonic to my ears let alone the fact that normal music sources, even DVD-audio, can't deliver any HF remotely close to 60KHz. & most most, if not all, tube power amps roll off substantially at way lower HF. So the plots are academic.

My picky ears tell me the same story on the 500KR (log scale) pot at the plate O/P of my 1-stage MM phonostage, driving direct my Dyna ST-70. It sounds best with its wiper set around 2-3 p..m. position. At full volume (5 p.m. position), LF sounds most forceful along with HF. Even for very low vinyl classical recordings, I still prefer keeping the wiper at 90% (4:00 p.m.) position instead of at full volume setting - good balance of LF & HF to me ears.


Author:  cheap-Jack [ 03 Aug 2011, 12:19 ]
Post subject:  Re: Super simple single stage tube preamp

Way way O.T. !!
mwhouston wrote:
Matt; Off thread-Which brand of Kentucky bourbon do you drink? I wonder if I can get it here??

Suncalc wrote:
my old standby is Maker's Mark, very smooth and easy drinking

Well, I envey you guys booze. I can't stand any spirits let alone the somewhat bitter 'burnt' taste of whiskies. A little congac maybe on occasions as brandy tastes neutral without that 'burnt' taste whatsoever.

Green tea is my daily 'drink' though I don't mind a bottle of Budweiser Light for a hot day's meal. For beer, I go only for Bud Light. Why? I can't stand the strong favour of hops added to brew beers. Only Bud Light gets the least hop bitterness neutralized by its faint sweetness. :wine:

Like music, I like it neutral & pure.


Author:  mwhouston [ 15 Aug 2011, 03:43 ]
Post subject:  Re: Super simple single stage tube preamp

Matt: Woodford Reserve. I'm converted but my wallett will never forgive you.

I intend to make the 4S MkIV "Universe" in a totally different enclosure. But its a bit of a drive from my place to where I purchase them so next weekend before I pick it up. But wait there is more. I'm thinking of including both types of NFB, current and voltage and with voltage (plate to grid) have two switchable levels. The current NFB will by by-passed or unby-passed cathode R.

This will make it very flexable 4S!

Author:  mwhouston [ 19 Aug 2011, 20:01 ]
Post subject:  Re: Super simple single stage tube preamp

Today I start construction of the 4S Universe. Instead of going to my local electronics shop and purchasing everything I need across the counter and am sourcing the parts (new) from my surplus. What do I save by doing this, about $20. How long did this take, about 2 hours. Not sure its economic but it will help reduce my surplus parts.

Author:  Grega [ 04 Sep 2011, 05:49 ]
Post subject:  Re: Super simple single stage tube preamp

nice work here. going to chase you mark and use a couple of 12ax7 tubes.
a quick trip to the local jaycar netted me a 24vac 1a wall wart and an mm2008 - with a 1n4004 full wave rectifier circuit no load i get 321vdc.
note the wall wart with no load i scored (unregulated BTW) puts out ~28vac. finding this a little challenging to rectify and get down to 12vdc - the smallest diodes i can find seem to be all 40v - however this could be sorted with a couple of LM regulators to pull down to 12vdc.
note i am pretty new to this and hope the above makes sense to all :)

Author:  mwhouston [ 04 Sep 2011, 06:23 ]
Post subject:  Re: Super simple single stage tube preamp

If you are hitting the Jaycar stores then you are either in Ozz or NZ. The 24VAC 1A wall wart and the tranni (MM2018) will give you the voltages I have specified in a very compact PS. Also you do not want to over-load the 12V reg.

For God's sake don't try ot 12V reg the 260V. Take the heater voltage direct from the 24VAC wall wart. YOU MUST look at the schematic of the PS. It will make sense. If you are a newbie ONLY follow the schematic.

Author:  Grega [ 04 Sep 2011, 06:56 ]
Post subject:  Re: Super simple single stage tube preamp

am in aus mark (vic)
yes its neat little setup - using the secondaries in reverse :)
no i'm not using the 12v on the mm2008 - am taking the 24vac from the wall wart, then, rectifying that with another full rectifier diode bridge using 40v schottkys (jaycar only had 3A ones) - but 40v is way too high for the LM7812.
accordingly using a 27ohm 10w resistor i can bring this down to something much safer for the LM7812 to then regulate :)

mark how did you rectify your 24vac to <25vdc?

Author:  mwhouston [ 04 Sep 2011, 17:07 ]
Post subject:  Re: Super simple single stage tube preamp

I rectify the 24VAC then filter with a 220uf 25V cap then a dropping resistor of 100ohm 10W then one more cap 4700uf 25V. Then into the reg. This works perfectly. The dropping resistor does get hot. I have two small heat sinks on the reg, back to back. Put about a 10uf cap after the reg then a 0.1uf cap on that. The drawing is a little wrong.

Author:  Grega [ 04 Sep 2011, 20:44 ]
Post subject:  Re: Super simple single stage tube preamp

thanks mark.
that 100ohm resistor is pretty large - what vDC are you getting post the regulator?
rather than a full rectified circuit as i can't find a diode small enough, i was going to use a 40v schottky 1n5822 as a half wave rectified circuit with a 100uf 63v smoothing cap and the 100 ohm resistor and then passing that into the regulator. Post that 10uf/.01uf should suffice. Thoughts?

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