Niobium - Valve pre for SS Power Amp

What people are working on at the moment
Post Reply
little eddy
Old Hand
Posts: 533
Joined: Sun Nov 09, 2008 2:06 pm
Location: Manchester

Niobium - Valve pre for SS Power Amp

Post by little eddy » Sat Apr 07, 2018 11:48 am

Now that my LM3886 SS power amp is nearing completion , it's time to start thinking of a suitable partnering valve pre.

I am considering converting the Foverture5 SS amp to an F4 due to it's reported neutral character, so the aim is to achieve a good tonal balance by using a valve pre with a combination of conventional and SS support circuitry.

Based on the use of my existing 41MP valves, will call this project Niobium. Talking to Nick, he has confirmed these would be a suitable alternative to the 76 he has previously used with the F4.

So initially posting a draft schematic for comments/advice, and when firmed up I can start to acquire the remaining bits.
18-03-29 Niobium Mono PSU Amp Schematic 41MP IT Shunt.jpg
I have a 300-0-300 tx and wishing to employ a choke filter, the total dc current is limited to 78mA for a 100mA choke allowing for the ac current element.

Rectification is proposed using the double damping diode 6BY5G.

Although I have a pair of the MJ zener regulators, will initially try valve regulation to provide a degree of valve coloration, (this power supply is on reflection very similar to that employed in my AN DAC).

The one thing I am interested in would be the optimum grounding scheme, so the attached tries to show how it might be strung together.

The target is to have a prototype constructed for Owston.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

User avatar
pre65
Amstrad Tower of Power
Posts: 17024
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex

Re: Niobium - Valve pre for SS Power Amp

Post by pre65 » Sat Apr 07, 2018 12:28 pm

After what Nick said about active pre amps (maybe on here, not sure) I'd think of a passive switchbox with pot and possibly a valve buffer. Just saying.
People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is a light from within
Dr Elisabeth Kubler-Ross

G-Popz THE easy listening connoisseur. (Philip)

User avatar
Nick
Site Admin
Posts: 11075
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Niobium - Valve pre for SS Power Amp

Post by Nick » Sat Apr 07, 2018 12:36 pm

pre65 wrote:
Sat Apr 07, 2018 12:28 pm
After what Nick said about active pre amps (maybe on here, not sure) I'd think of a passive switchbox with pot and possibly a valve buffer. Just saying.
That is a valve buffer.
Resistance isn't futile it's V / I.

User avatar
pre65
Amstrad Tower of Power
Posts: 17024
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex

Re: Niobium - Valve pre for SS Power Amp

Post by pre65 » Sat Apr 07, 2018 12:48 pm

Nick wrote:
Sat Apr 07, 2018 12:36 pm
pre65 wrote:
Sat Apr 07, 2018 12:28 pm
After what Nick said about active pre amps (maybe on here, not sure) I'd think of a passive switchbox with pot and possibly a valve buffer. Just saying.
That is a valve buffer.
Just goes to show what I know. :oops: :oops:
People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is a light from within
Dr Elisabeth Kubler-Ross

G-Popz THE easy listening connoisseur. (Philip)

little eddy
Old Hand
Posts: 533
Joined: Sun Nov 09, 2008 2:06 pm
Location: Manchester

Re: Niobium - Valve pre for SS Power Amp

Post by little eddy » Sun Apr 15, 2018 2:44 pm

Have most parts now so will start next week when the choke arrives. Using cheap plastic chopping boards for the 2 decks (poor mans Teflon).

The other layout option, perhaps favored, would be to swap the positions of the vr tubes and 41MPs having all of the AC and power towards the front. Signal, output txs and amplification at the back. Just seems a shame having the expensive triodes obscured by the vr valves. Weight would also be more evenly distributed and the output txs would be well away from the power tx and choke.

It's going to be a lot heavier than I though a pre-amp would be. I need to think again about how I will mount the top board off the bottom one. Initially was thinking of using screwed bar but would have little rigidity and lateral strength. Might order some alu angle and perforated sheet and build a frame.
Attachments
Layout top small.jpg
Layout bottom small.jpg
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

User avatar
IslandPink
Thermionic Monk Status
Posts: 5692
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

Re: Niobium - Valve pre for SS Power Amp

Post by IslandPink » Sat Apr 21, 2018 7:00 pm

Nice thinking - good to see things being re-purposed !
White flags of winter chimneys waving truce against the moon ( Mitchell )

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest