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A Noob Valve Preamp Build?
A Noob Valve Preamp Build?
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Old 23rd October 2018, 12:32 PM   #1
Wot is offline Wot  Australia
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Default A Noob Valve Preamp Build?

I finished an Aleph-J amp which had a pretty comprehensive build guide and didn't expect too much from the assembler in terms of in-depth calculations or even too many choices which allowed me and I suspect lots of others to build this amazing amp and many other amps.

I run it using a cheap Monoprice integrated amp which happens to have a line out from the valve preamp and I am pretty happy with the sound. However I would really like to make a good quality valve preamp[line stage] and even a phono one as well as mine is a tiny solid state Rega.

OK here's the thing. I have spent day after day reading through various preamp threads but I have not found one that documents the build completely in a way that makes it possible to just buy the parts and build it. Even the Aikido has so many choices that I was left confused and would need advice to choose the various components and still more advice to choose the specific transformers.

Every single thread goes into interminable arguments about all kinds of variants many of which are only measurable with pro equipment and the knowledge required exceeds my very newly acquired interest in this field. I could probably build from a schematic but then I get crossed wires about how many transformers are needed and all the talk of valve substitution and it goes on and on and on and the more I read in a thread the less inclined I am to get halfway into one of these projects only to find I can't get through it or fix too much hum or something.

So I'm actually begging for someone to do a full build guide for a 12B4 or something sweet and simple, including the whole process, power supply, BOM and layout whether or not there are circuit boards available, but using components that are easily purchased.

I believe something like this may be in the pipeline in the DIY shop which will then no doubt have an excellent build thread by 6L6 and we'll be able to join the ranks of the experts at least in being able to have this stuff to listen to.

But I'm putting this thread up here in the hope that some alternatives are already about that apply to this beginner level.

Cheers.
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Old 23rd October 2018, 01:02 PM   #2
AllenB is offline AllenB  Australia
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A Noob Valve Preamp Build?
You might start with your own gain and output impedance needs. Sometimes you need gain and sometimes you don't. You might want to run more than one amp from this, put in a volume control and other things that might need a certain amount of drive or buffering.

Other things you can work toward are a clean ground point to start, along with input RCAs into a chassis. Source switching, balance control, amp level matching and whatever else.
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Old 23rd October 2018, 01:25 PM   #3
Wot is offline Wot  Australia
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I wouldn't mind some gain but it isn't really needed with the AlephJ for room listening. It would be nice to run different amps later no doubt but that's unknown. It would need a volume, tone and possibly balance. Aikido attenuation units look to be good there except I wasn't convinced by the tone solution that equally increases bass as it decreases treble and vice versa.

I am more inclined towards them being independent. I have an external source switch but I don't understand what is meant by amp level matching. So I see the predicament you are illustrating, that it probably can't be a one size fits all scenario. That's why Aikido seems the best option with a wide choice but it gets complicated by high voltage versus low voltage, old and new variants etc. It's also unclear which transformer is need for what etc. I get confused there. Maybe I should write them a letter explaining my requirements and they can advise. Unless there's a simpler option.?
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Old 23rd October 2018, 03:07 PM   #4
Eli Duttman is offline Eli Duttman  United States
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Really good tone controls are complex. The provided Max Robinson design requires (sic) 2X 12AX7/ECC83s per channel. Also, few recordings benefit from the use of tone controls. Most of the time, tone controls should be completely out of the signal path. The provided setup is "unity" gain, which greatly assists the defeat feature.

FWIW, I suggest you forget tone controls, this time around. You said a small amount of gain would be good. There are quite a few 12B4 based designs in the archives, which should meet the need. Don't worry about a PCB, as these are simple circuits. "Monkey see, monkey do", will get you to a satisfactory end point.
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Old 23rd October 2018, 03:17 PM   #5
Bigun is offline Bigun  Canada
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A Noob Valve Preamp Build?
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Old 23rd October 2018, 06:13 PM   #6
rongon is offline rongon  United States
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A Noob Valve Preamp Build?
I was looking at the manual for the Aleph J. It says the input impedance is 242k ohms (very high) and the input capacitance is "vanishing" low. It requires 1.5V signal input to reach full power (25W). That's about 14V rms into 8 ohms, so if that 1.5V input signal is rms, then the gain is a bit less than 10X, or almost 20dB. So I don't know what good an active preamp would do going into this amp.

I think the best way to go about this is to define the benefits you want from this project.

- How much gain, if any?
- What input impedance, and what output impedance?
- Do you want to add some 'tube sound'? Or do you want this to be as low distortion as possible?
- Tone controls? Or no tone controls?
- Do you want to isolate the amp's inputs using signal transformers?
- What input switching capabilities do you need?
- What kind of attenuator do you want to use?

If all you need is input switching and a volume control, you might want to try an inductive attenuator like those from Intact Audio or similar. They do sound really good. Put one of those in a nice chassis with a good input selector switch and good RCA jacks, and that might be the solution.

It all depends on what you want this thingie to do for you.
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Old 23rd October 2018, 06:24 PM   #7
kerux is offline kerux  United States
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Tube Buffer Preamp Design

If you don't need any gain. This is a good thread for options.

I am a noob so I built the Muchedumbre buffer preamp since I have a Tubelab SSE and did not need any gain,

Muchedumbre Buffer Preamp – wauwatosa tube factory has a BOM, plenty of details and pictures to build the amp for noobs. The only thing I needed to look up was the tube details on wiring it up which the documentation mentions.
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Old 23rd October 2018, 06:26 PM   #8
kerux is offline kerux  United States
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Tube Buffer Preamp Design

If you don't need any gain. This is a good thread for options.

I am a noob so I built the Muchedumbre buffer preamp since I have a Tubelab SSE and did not need any gain,

Muchedumbre Buffer Preamp – wauwatosa tube factory has a BOM, plenty of details and pictures to build the amp for noobs. The only thing I needed to look up was the tube details on wiring it up which the documentation mentions.
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Old 23rd October 2018, 11:26 PM   #9
Wot is offline Wot  Australia
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Thanks guys, That's a very good start and has given me something to go on with. Kerux, I like the look of this Muchedumbre unit, it's only one channel right so I'd need a pair, maybe fitted in the same box. I only ask because I am muchedumbre. I'd probably add a volume attenuator instead of the pot but otherwise yes I think it can suit me for a start. Eli Duttman, thanks for your comments, you've convinced me about tone controls. Is your schematic there somewhere else with a build thread ? You say the power supply is so simple, but for me there are too many unknowns about transformer types, and the various voltages required. Or are you saying there could be a universal valve power supply? I thought some valves take 6.3volt heaters and others are 12v. And the main power seems to vary from 250 volts to 500vDC. That's where I get confused and worried.
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Old 24th October 2018, 12:57 AM   #10
Eli Duttman is offline Eli Duttman  United States
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The signal circuitry is simple, in my version of a 12B4 preamp. The PSU in the schematic I'm providing is somewhat involved, but using it is not essential. I worked up that design to accommodate what "Buzz" had on his parts "pile". Well filtered "150" VDC and 10M45S plate loads will be fine into the "friendly" I/P impedance of the "Aleph".

BTW, you don't need pricey Mundorf O/P coupling caps. too. "Buzz" likes "boutique" parts. Given the high I/P impedance of your "Aleph", 0.22 μF. Soviet surplus K40 paper in oil (PIO) parts will be FINE.
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