My head amp

Anything to do with the things that make the music we listen to.
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Paul Barker
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Post by Paul Barker » Mon Mar 19, 2012 8:00 am

You have no idea how hard it is to hold myself back from reverting to audio amp mode.

But in my defence the Black Gates facilitate the timbre and if Buddy Guy was buying an amp from me his instrument would have an even more beautiful sound than he has already.

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IslandPink
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Post by IslandPink » Mon Mar 19, 2012 6:05 pm

The Stratmangler wrote:Ferget all them fancy caps.
They'll screw the sound up.
What was availible back in the late 1950s - them's the ones to go fer 8)
Paul would probably have to go out of his way to order some ordinary caps. He's practically tripping over those damn Black Gates around the house, he's got so many !
White flags of winter chimneys waving truce against the moon ( Mitchell )

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Paul Barker
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Post by Paul Barker » Mon Mar 19, 2012 6:13 pm

I think I only have 5 wkz's and 3 VK's a couple of red bipolars N something or others..

But I paid full price at the time they were available at great cost to the family budget.

And I have found that a shunt regulated valve is better sounding.

But you can't do an overkill power supply for everything.

In this design the sag in the power supply is important. Later when they used solid state diodes they added series resistance to emulate the diode sag. I am sure a weak valve diode does it much more musically though.

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The Stratmangler
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Post by The Stratmangler » Mon Mar 19, 2012 10:45 pm

Paul Barker wrote:if Buddy Guy was buying an amp from me his instrument would have an even more beautiful sound than he has already.
That's a big claim to make.
What speaker/s are you going to hang off the end of it?
Chris :happy3:

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Mike H
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Post by Mike H » Tue Mar 20, 2012 12:27 pm

The Stratmangler wrote:Ferget all them fancy caps.
They'll screw the sound up.
What was availible back in the late 1950s - them's the ones to go fer 8)
They used whatever was available at the time that would do the job but it couldn't cost a fortune obviously, as there was a budget. :D

You might have a point though if you want a more authentic (?) "50's/60's" kind of sound.

Also, every original Vox or whoever's innards I've seen so far has a noticeably distinct lack of "boutique" like components, quite the opposite. :D
 
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Paul Barker
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Post by Paul Barker » Tue Mar 20, 2012 12:37 pm

The Stratmangler wrote:
That's a big claim to make.
They didn't use Black Gates.
The Stratmangler wrote: What speaker/s are you going to hang off the end of it?
I can't claim to make a better combo, just a head amp.

Can't afford the proper genuin speakers used those days. just a fun project for myself.

other aspects of life raise their head for attention higher than this. Next money in pocket will go in fuel tank for instance which is presently 38 miles into the warning light, further than I am comfortable with.

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Post by Mike H » Tue Mar 20, 2012 12:54 pm

Not to be confrontational or anything :D but there's lots & lots of guitarists & musicians topics & pages on the net about modifying gear. It's quite different to what you might normally consider to make a "good amp", seems it's more about "tweaking" the instrument at the input end.

Hence tone stacks, I once read a while ago "one has a tone stack because basically an electric guitar has no tone, it's a flat piece of wood" (that's a quote not my opinion :D )

I've not yet successfully produced an original working guitar amp design cos I have what I think is a good idea (especially as if it doesn't seem to have been done before) then someone else who knows more about it then says "ooh no no no no no" :D
 
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Post by Dave the bass » Tue Mar 20, 2012 1:26 pm

Mike H wrote: Hence tone stacks, I once read a while ago "one has a tone stack because basically an electric guitar has no tone, it's a flat piece of wood" (that's a quote not my opinion :D )
No no no no no!

Tone stacks are fitted to give guitarists summat to play with in-between songs whilst the singer jibber jabbers with the audience. When the guitarist has finished playing with the controls he'll nod to the singer and the gig can carry on.

It's the 1970's 4th law of Rock.

innits!

S'true.

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Post by Paul Barker » Tue Mar 20, 2012 5:28 pm

Back to the circuit,

I have put a 6em7 (pin1,2,3) cathode follower in between the two valves. As discussed the purpose was to provide an infinite load to the 110k output impedance of the 6sj7 rather than the 250k pot which would have lost me considerable gain. Direct coupled to the 6sj7, on the output I have just shifted the cap and 250k pot along one. Only extra part is a cathode load resistor. To keep the current down as the 70mA power supply is stretched I used 16k8 (10k +6k8, remember these things are made with what I can find scratching around in parts boxes).

the drive is hugely improved. The volume in a small room is ear destroying from a 6v6 probably 4.5 watts.

But the sound is not so sweet. It is OK though.

Last night it was going through my mind when I should have been asleep. What I have decided is that the interloaper has no partner to cancel it's ill effects. the two stage pentode design has two pentodes in antiphase each sharing the same dirt in the power supply and each facing the pentode distortion with no feedback to correct it. But as they are in antiphase there is considerable mutual cancellation. This is borne out by a wonderful sound to the ear.

But the 6em7 CF, even though it enjoys the benefit of complete local feedback, it is highlighting what I think must be grunge in the power supply. We have a single stage here with no partner to cancel it's problems.

in my hifi world I would have a tight ovekill shunt reg power supply, but here we have a deliberately weak power supply which sags on overdrive with the purpose of feathering in the distortion smoothly.

The whole two pentode concept was such a huge success for timbre and for cancellation of power supply noise that I am seriously considering as a model for my next hifi design. But that I would shunt regulate and apply local feedback for damping factor.

But anyway if I have time to do nothing else I have a guitar amp to bring to Owsten if someone who can strum a guitar could be there.

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Post by Paul Barker » Tue Mar 20, 2012 6:31 pm

Image

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Post by Mike H » Wed Mar 21, 2012 3:15 pm

Where de vol pot now then? :D
 
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Post by Paul Barker » Wed Mar 21, 2012 4:18 pm

I didn't draw it right. It is where the 250I resistor is.

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Post by Paul Barker » Wed Mar 21, 2012 4:18 pm

I didn't draw it right. It is where the 250I resistor is.

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Post by Mike H » Fri Mar 23, 2012 1:28 pm

Oh right over there! OK :D
 
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Post by Nick » Fri Apr 06, 2012 3:31 pm

I am afraid I just made the mistake of having a hour to kill in town and needed to get some more plectrums. I came out of the shop with one of these.

http://www.blackstaramps.co.uk/products/ht-1r/

One whole watt, who could ask for more. Don't know the details of the circuit, but I think from reading its a two stage ecc83 into a ecc82 push pull output stage. Reverb I think is digital. I will know if it was a good purchase or not later after I have a chance to play in the comfort of my own sofa :-)

I guess I could have built something for a bit less (£199 - a set of strings and a lead), but not much I would think.
Resistance isn't futile it's V / I.

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