A fun build preamp - UK Vintage Radio Repair and Restoration Discussion Forum

Tubeglow · 29th Mar 2014, 6:47 pm

Here is a preamp that I built for fun.
I wondered what I could do if I just bought low voltage DC into a preamp.
This is what happened..

And yes the main question was how can I build SRRP and get isolation for the heater supply?

What did I learn? Don't use low volt DC use low volt AC and transform it..

But it was good fun.

However I achieved what I wanted with an inverter etc.
And its only got a DC supply. Thinking back it was a moment of madness but that's the fun.

Tubeglow.

Tubeglow · 29th Mar 2014, 7:10 pm

The back of the preamp,

And the Vero board circuits.
The B+ is 400V.
Maida regulator and decade input selector with debounce.
The prism on the top changes colour with input select.
You know when you just want to build something different..LOL
Glass tile with a sparkle on the front drilled for separate volume controls.

Tubeglow.

ValvoStef · 30th Mar 2014, 10:19 am

Very nice build, Tubeglow. What tubes did you use?

Tubeglow · 30th Mar 2014, 10:21 am

I used ECC88.

EM80 indicators.

Tubeglow

mark pirate · 30th Mar 2014, 10:24 am

I love the use of the EM80's as VU meters, very smart!

Mark

Tubeglow · 30th Mar 2014, 6:22 pm

I guess most know how to do this,

however for those that don't here is decade counter input selector with debounce.

You must fit 0.1uF ceramic caps direct across the chips supply rails.
To decouple the supply.(direct on the chip base).
It drives the relay input card.
Just a simple push button to select. The circuit always defaults to input 1 which can be mute or what ever you think.
Somebody might find it interesting. This is the circuit used in the preamp.

Just for interest the type of cable used to couple components together is less critical if the cable is driven.
If its not that's a different situation.
Now here is a thought, could you make just a selector with a passive pre, well yes you can!
The reset is not connected to pin 13.
Its just good fun!

Tubeglow.

30th Mar 2014, 6:47 pm

Quote:

Just for interest the type of cable used to couple components together is less critical if the cable is driven

Doesn't make a ha'peth of difference, I use the stuff to hand.

Tubeglow · 30th Mar 2014, 6:49 pm

Ok no problem.

..You are correct!
I'm not talking audiophool cable.
However you are still correct!

Tubeglow.

glowinganode · 30th Mar 2014, 9:59 pm

Thanks TG, that's a handy little circuit, I may well use it on my next build.
I'd be inclined to use separate series resistors on the LED's to prevent the "off" LED's being reverse biased.

Cheers,
Rob.

29th Mar 2014, 6:47 pm	#1
Tubeglow Retired Dormant Member Join Date: Mar 2014 Location: Wolverhampton, West Midlands, UK. Posts: 153	A fun build preamp Here is a preamp that I built for fun. I wondered what I could do if I just bought low voltage DC into a preamp. This is what happened.. And yes the main question was how can I build SRRP and get isolation for the heater supply? What did I learn? Don't use low volt DC use low volt AC and transform it.. But it was good fun. However I achieved what I wanted with an inverter etc. And its only got a DC supply. Thinking back it was a moment of madness but that's the fun. Tubeglow. Attached Thumbnails Last edited by Tubeglow; 29th Mar 2014 at 6:55 pm.

29th Mar 2014, 7:10 pm	#2
Tubeglow Retired Dormant Member Join Date: Mar 2014 Location: Wolverhampton, West Midlands, UK. Posts: 153	Re: A fun build preamp The back of the preamp, And the Vero board circuits. The B+ is 400V. Maida regulator and decade input selector with debounce. The prism on the top changes colour with input select. You know when you just want to build something different..LOL Glass tile with a sparkle on the front drilled for separate volume controls. Tubeglow. Attached Thumbnails

30th Mar 2014, 10:19 am	#3
ValvoStef Hexode Join Date: Mar 2014 Location: Fareham, Hampshire, UK. Posts: 482	Re: A fun build preamp Very nice build, Tubeglow. What tubes did you use? __________________ Failing to prepare is preparing to fail ...

30th Mar 2014, 10:21 am	#4
Tubeglow Retired Dormant Member Join Date: Mar 2014 Location: Wolverhampton, West Midlands, UK. Posts: 153	Re: A fun build preamp I used ECC88. EM80 indicators. Tubeglow

30th Mar 2014, 10:24 am	#5
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: A fun build preamp I love the use of the EM80's as VU meters, very smart! Mark

30th Mar 2014, 6:22 pm	#6
Tubeglow Retired Dormant Member Join Date: Mar 2014 Location: Wolverhampton, West Midlands, UK. Posts: 153	Re: A fun build preamp I guess most know how to do this, however for those that don't here is decade counter input selector with debounce. You must fit 0.1uF ceramic caps direct across the chips supply rails. To decouple the supply.(direct on the chip base). It drives the relay input card. Just a simple push button to select. The circuit always defaults to input 1 which can be mute or what ever you think. Somebody might find it interesting. This is the circuit used in the preamp. Just for interest the type of cable used to couple components together is less critical if the cable is driven. If its not that's a different situation. Now here is a thought, could you make just a selector with a passive pre, well yes you can! The reset is not connected to pin 13. Its just good fun! Tubeglow. Attached Thumbnails Last edited by Tubeglow; 30th Mar 2014 at 6:35 pm.

30th Mar 2014, 6:49 pm	#8
Tubeglow Retired Dormant Member Join Date: Mar 2014 Location: Wolverhampton, West Midlands, UK. Posts: 153	Re: A fun build preamp Ok no problem...You are correct! I'm not talking audiophool cable. However you are still correct! Tubeglow. Last edited by Tubeglow; 30th Mar 2014 at 7:00 pm.

30th Mar 2014, 9:59 pm	#9
glowinganode Octode Join Date: Apr 2009 Location: Aylesbury, Buckinghamshire, UK. Posts: 1,522	Re: A fun build preamp Thanks TG, that's a handy little circuit, I may well use it on my next build. I'd be inclined to use separate series resistors on the LED's to prevent the "off" LED's being reverse biased. Cheers, Rob. __________________ We have done so much, for so long, with so little, we are now qualified to do anything with nothing.