• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Valve pre-amp maintenance and purchase

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#144
choky, thank you for elaborating your view on the Foreplay circuit, and most cathode follower (Foreplay-like 😀)

i guess most of you, might disagree with the operating points of the Foreplay, and precisely the reason for modding it with CCS, etc, etc. Could have been it was tuned by ear? :clown:

but going back to mark, who is building his first-ever-preamp-as-suggested-in-the-forum (i dont think Sy would agree to how i hyphen-ized this :devilr: ) it will give him basic understanding of a simple cathode follower. and being an engineering student, it would be interesting for him to find out afterwards the "flaws" of the circuit and then apply his own learning in improving it. then maybe, he will go ahead and make a better one.

all the best for mark 😀
 
#146
Just one point.

The new design reaches an even higher level of sonic pleasure and quiet operation. The original Foreplay's 12AU7 operating points were somewhat limited by the small power transformer used. The new Foreplay III uses 12AU7s running at optimized operating points for lower distortion and beefier output drive - 10V rms before clipping!
Click to expand...
This is taken from the Bottlehead site.


Couldn't believe it when i read it! Would you trust this man! I won't.

Sophists are best avoided.
 
#147
Funny thing is i am probably going to build a Foreplay (1st version).
I don't like the tonality of my PC soundcard and i am planning to use the Foreplay to take out some of the harshness. I don't want a transparent sound here. Not serious hi-fi but probably more pleasurable listenings while i read the emails😉
I'm thinking the success of the Foreplay is because that lowish current colors the sound, great for nasty sources like my soundcard.
Really cheap to make also.

I have the aikido as my "pro" line stage.
 
#148
wire strippers

choose your weapon! 😀

CIMG1311.jpg
 
#151
Well I've just sold the last of my solid state stuff!
Arcam 7SE, Arcam 8R, B&W 602's, Sony MDS-JE330 Minidisk deck all gone for $1075, and picked up a set of temporary Mission 763s for $60!
There's no turning back now!!

choky said:

building one baby preamp (what Foreplay is,without any intention to be rude) and building one serious preamp is almost same thing ,meaning on complexity and amount of work;difference is in choice of parts and actuall schematic,or project-in different words.

most of work is in chassis,most of money is in pure hardware-switches(relays),connectors,pot,xformer etc

tubes are mostly less influent parts in overall sum of money;

thinking about all that,why not making some serious preamp,for change? 😉

just looking in this forum in last several months-12B4 preamp is most promising; I didn't tried it by my self,but I already have enough experience with similar approach;

I personally recommend WOT approach.......
Click to expand...
Any schematics for a good 12B4 pre-amp?
In a way I'd rather jump in and build a fantastic pre-amp, but I'm also afraid of screwing up - mostly the power supply...

arnoldc said:

but going back to mark, who is building his first-ever-preamp-as-suggested-in-the-forum (i dont think Sy would agree to how i hyphen-ized this :devilr: ) it will give him basic understanding of a simple cathode follower. and being an engineering student, it would be interesting for him to find out afterwards the "flaws" of the circuit and then apply his own learning in improving it. then maybe, he will go ahead and make a better one.

all the best for mark 😀
Click to expand...
I would be interested in finding the flaws, but like most things, I'd like to have a base design that isnt fundamentally flawed in the first place!!

Now I am unsure about where to go...

Can I buy the power supplies pre-made? It's the bit I know I'm going to mess up!!
 
#152
Relax...

The power supply is probably the easiest thing to do...

It should be the first thing you design... partially... very roughly. And then it should be the Last thing you design... in a very detailed way.

Hope I'm making sense.

:xeye:
 
#153
Commited said:
Well I've just sold the last of my solid state stuff!
Arcam 7SE, Arcam 8R, B&W 602's, Sony MDS-JE330 Minidisk deck all gone for $1075, and picked up a set of temporary Mission 763s for $60!
There's no turning back now!!


Any schematics for a good 12B4 pre-amp?
In a way I'd rather jump in and build a fantastic pre-amp, but I'm also afraid of screwing up - mostly the power supply...


I would be interested in finding the flaws, but like most things, I'd like to have a base design that isnt fundamentally flawed in the first place!!

Now I am unsure about where to go...

Can I buy the power supplies pre-made? It's the bit I know I'm going to mess up!!
Click to expand...


look in 12B4 threads for Mark G. version ;
just for instance 😉

after that-look what you have in drawer ,or available,and I'm sure that we can make one good PS together...


are you in the mood for few gas stabs in your supply?

:clown:
 
#155
arnoldc said:
mark, the 12B4 linestage adaptation of mark g. is a very easy build, half simpler than foreplay. i am actually building one, the prototype will have a simple power supply, while the ultimate version will use fdegrove's 300V regulated psu.
Click to expand...


sorry-I didn't follow that thread(s) 100%- where I can see that psu schm?
I have just a hunch that series reg is in question....:whazzat:
 
#157
I don't wanna to step on anybodys toes here,especially on fdegrove's ,but series reg is long time ago not my cup of tea;
what I like,and use ,is any sort of shunt reg.

gass tube only,gass tube with resistor in parallel,gass tube as voltage ref with additionall shunt element,whatever...

in strictly line amp psu purpose,usually is plain one gass tube /per channel or even for both channels -hard to beat overkill,especially when combined with at least one choke in preceding stage(s)
 
#159
Since choky mentioned it I suppose I can come out of the closet and tell you that I also use VR tubes. I used a VR150 and VR90 per channel on my line stage also to get a B+ of 250 volts. VR tubes do vary slightly depending on the load. This is what I am using on my version of Frank's 6SN7/5692 line stage.
 
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