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5670 in this circuit?
5670 in this circuit?
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Old 29th December 2017, 11:04 PM   #1
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Default 5670 in this circuit?

Hi all
I have been searching for tube pre designs and came across this in google image search

Click the image to open in full size.Schematic Prints



Guys this looks like the easiest build that I can find as I can get it in kit form and get started on the stereo preamp that I really need. I think I can build this in stock form from instructions in the manual

The manual states voltage gain 22. Does this mean 22db?

I would like to request all your assistance here pls, its important in my setup and means a lot to me and I finally have been able to devote a lil time to it

Is this suitable to stick between a stereo amp and 10 channels of passive summing resistors?

Possibility and changing of component values to up the gain towards 40db?

Can this be somehow turned mono to up the gain?

Can a pot tie the L + R channels together to up the gain or make a dutty bass channel together with an input pot?

If this circuit can do more then stereo hifi then I'll start getting the parts together. I looked a t a 12au7 circuit before but its a lot more diy then my design ability, this one seems easier

Thanks, greatly appreciated!
Attached Files
File Type: pdf 6N3 SRPP Preamplifier Schematic.pdf (10.6 KB, 22 views)

Last edited by Randell Jon Bassinga; 29th December 2017 at 11:08 PM.
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Old 30th December 2017, 07:39 AM   #2
GeorgK is offline GeorgK  Austria
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You criteria was that it looks easy? Don't get fooled.

First, as the schematic suggests, this is called an SRPP circuit. And while it does not need many components it can be a difficult beast in some respects.
For instance, it works best with well-defined output impedances.
The upper and lower triodes should be matched.
The DC potential should be pot above GND to protect the cathode isolations of the upper triodes. Do not see this in the schematic.

22dB equals a voltage gain of about 12. You can go higher by using a bypass cap on the cathode resistors of the lower systems, but you probably won't reach 40dB.

You can connect both channels in series anyway.

Not sure what you need it for, but I do not think it is the best partner to drive a summing stage as its output impedance is not very low (although lower than a common anode follower)

And not sure what you mean with a 12AU7 circuit? You can also build an SRPP stage with a lot of tube types, some resistor values maybe have to be changed then.

I would settle for a simple one- or two- stage amplifier, possibly with a cathode- follower back-end.
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Old 30th December 2017, 09:23 AM   #3
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Thanks George. Yeah criteria is looks easy, this is the kit
6N3 (5670) SRPP Preamplifier Kit (Stereo)_Preamplifier Kit_Tube Amplifier Kit_Analog Metric - DIY Audio Kit Developer

I just occasionally build a kit or something if I cant afford a production piece, I do not yet have any design ability. I just need 3 or so mono pres for a few jobs like mics and bass and a hi fi stereo one

Voltage gain is 22 not 12, I am trying to find out what that means. I think I need about 40db or so gain for mic use. This shop also has a similar buffer board
6N3 (5670) Tube Buffer Kit (Stereo)_Preamplifier Kit_Tube Amplifier Kit_Analog Metric - DIY Audio Kit Developer

Can that be used in conjunction? Its a cheap tube and another forum member linked me to a cheap high volt switching kit so just might be able to fit a number of these pres for the price of one 12au7. That is in my other thread here. help with tubes n tings

Last time when I wanted a boat in a certain style I studied boat design (naval architecture) to the point where I was comfortable designing boats that size without pleading for help but this time I just need a handful of pres
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Old 30th December 2017, 06:16 PM   #4
GeorgK is offline GeorgK  Austria
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Quote:
Originally Posted by Randell Jon Bassinga View Post
The datasheet reads 20dB, that means a factor of 10, too low for a mic pre.
You can put 2 in series, this would result in a voltage gain (factor) of 100 or 40dB. A gain control could be added between the stages maybe.
But you still have no input transformer to properly connect balanced mics, and no phantom power supply (if needed).
And the SRPP amp uses two triodes per stage, a "conventional" design would need only one.
This is a line preamp by design, maybe someone has an idea where to get a "real" mic pre, with audio transformers included? Won't be cheap anyway.
If you are just looking for a cheap and simple solution, you maybe would be better off with a semiconductor-based pre. No HV, no heater supply, cheap PSU, no need for expensive audio transformers. Low output impedance, therefore easy to add a summing stage. Athough I would use an active one. Basically one opamp and a few resistors.
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Old 30th December 2017, 09:29 PM   #5
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Hi George, I have a Peavey Unity with 12 mic pres, it sounds fine for a solid state oldie. a Lexicon Ohmega an a Behringer which got bricked last year (only the pres are working, USB is dead) 12somethingfx (works half the time and the USB and fx features are garbage

I just came across some specs that list 36db +-8 gain per triode for the 6n3p. I am assuming that it can mean around 60 max using both sides of which there might be cleanish 40s? :/

I really only need one tube mic pre and two channels for the bass amp. One stereo channel for summing amp. Thats 5 channels of pres. All the other stuff is active. I just found some 1;10 input transformers on ebay from around $20+ and I am sure I have come across some adapter type ones too, I wonder if that might do the trick.

I would like to explore tubes. 12a series are around $20AU shipped each and Nos Russian 6n3p-e (=5670) are $3.50 each or $12 for a matched pair shipped. I would just like to play with some cheap options. I think I'll just dive in blind, sitting and typing why I feel the urge for a particular project just to beg some help after a 12 hour shift driving my taxi feels a bit ordinary. Might help another noob stay clear of the mistakes I make along the way

I'll order one set of 4pc 6n3p-e, some ceramic sockets, the $5 high voltage psu and build one stereo pre and one stereo buffer point to point and see how it sounds. I think I can figure out how to hook up switches and pots and things nosing around online. But swapping out component values for mods is way out of my league. Hopefully after the festive season there might be more activity on the board
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Old 30th December 2017, 09:51 PM   #6
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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8pcs x 6N3P-E ( 6N3P-EV) / 2C51 / 6385 / ECC42 GOLD GRID TUBES

$26.65 on their way. Lol sounds like a the brag but I have no idea what they are or if they any good!
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Old 30th December 2017, 10:16 PM   #7
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Found a bass pre schematic too

5670 in this circuit?
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Old 30th December 2017, 10:39 PM   #8
GeorgK is offline GeorgK  Austria
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Quote:
Originally Posted by Randell Jon Bassinga View Post
I'll order one set of 4pc 6n3p-e, some ceramic sockets, the $5 high voltage psu and build one stereo pre and one stereo buffer point to point and see how it sounds. I think I can figure out how to hook up switches and pots and things nosing around online. But swapping out component values for mods is way out of my league. Hopefully after the festive season there might be more activity on the board
Are you going to build the SRPP design with these?
With a decent input transformer I think this can sound fine as a mic pre too. If you need a little more gain, put an electrolytic capacitor over the cathode resistor of the "lower" triode, just like in an ordinary gain stage. The value is not critical, 16...25F/25V is fine. No need to be afraid of sensible changes to the circuit.
The reason why this was not done in the original design is probably because more gain is not necessary in a line amplifier.

For bass, I would stick to some standard pre, just like the one you posted. But I do not really get the idea of its parallel channels?

Last edited by GeorgK; 30th December 2017 at 10:43 PM.
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Old 30th December 2017, 11:24 PM   #9
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Quote:
Originally Posted by GeorgK View Post
Are you going to build the SRPP design with these?
With the 8 on order
1 stereo SRPP pre: for the summing mixer. This is going to be the nexus of my living room. Multiple sources, pc, iphone, bass amp, synth, jfet mic pres x 3 on drumset, jfet mic pre 9 x vocal, guitar pedal. Am saving up for a Roland Mx-1 with will remove the need for the passive summing as everything will plug into that through to the SRRP pre

1 mic pre: with the same SRRP schematic

Bass amp: with the bass pre schematic above

1 stereo buffer from the same folks with the SRRP schematic

Maybe a couple of tubes left for a nice tube tone control or something

Quote:
Originally Posted by GeorgK View Post
With a decent input transformer I think this can sound fine anyway
Would you or anyone else reading know if something like this can be used to test it?

10k to 600 ohm audio transformer microphone step-up step-down impedance hi-z | eBay

My very old but very nice yamaha receiver is dying. My living room has always been music focused so time for a nice TPA3255 class d amp with tube pre. Hence the priority shift to the stereo tube pre project as the hub of my living room.... I can be fancy and call it the Bassinga Homestage
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Old 30th December 2017, 11:31 PM   #10
Randell Jon Bassinga is offline Randell Jon Bassinga  Australia
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Quote:
Originally Posted by GeorgK View Post

For bass, I would stick to some standard pre, just like the one you posted. But I do not really get the idea of its parallel channels?
Some of the old Dub basslines from the 70s and 80s by Robbie Shakespeare sounds like parallel clean hard dwanged upright style notes with a shadow of something that sounds like tubes beeping in bass ( dont know how to describe that) I think that might be a way of nailing that sound. Thats why I am keen to experiment with parallel channels

btw, mate lol I have no idea what I am talking about half the time!
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