[siddharta42]

Hi all, first of all, great community here. Very impressed with the quality and depth of what I've read here so far and surprisingly friendly all around.

I wanted to ask for recommendations on DIY tube pre-amp kits. I've assembled a TPA3116 amp bought as a kit from Yuan Jing, attached to a pair of JM Renaud floorstanders, which so far no complaints (all the contrary). Many have commented on the merits of adding a tube pre-amp to the chain and I'd like to give that a try as a next project. I'm looking at something that would have

- 3 or more inputs (3 would suffice though)
- remotes not required
- not too expensive, considering I spent less than 150 EUR on the TPA3116 amp
- with a PCB

Ideally I'd like to find a kit like the Juan Ying TPA3116 one, with enclosure and transformers would be great, to minimize possible errors in matching.

I've seen some kits that come close on eBay, such as this one from Douk http://www.ebay.es/itm/Douk-Audio-6N1-2-6Z5P-Tube-Pre-AMP-HIFI-Stereo-Preamplifier-DIY-KIT-Amplifier-/251525821504?hash=item3a901b7440:g:PYsAAOSw34FVB03b, that doesn't have a PCB and I'm not comfortable with putting something like this together. I'm also not sold on the retro aesthetics to be honest.

There's various inexpensive tube pre-amps on Juan Ying as well as on eBay as assembled PCBs, less than 50 EUR/USD, that look like they can be mounted with transformer in an aluminium enclosure, but those typically don't come with an input selector and I'm not sure which one would be a good match for the TPA3116.

I did search the forums as well as in other places, but what I've found is either outdated/not available or way above what I'm thinking to spend on this project. Thanks for any feedback/recommendations.

[FullRangeMan]

Welcome Sid hope you enjoy the forum
I dont like preamps-except for phono stage,
but since you need various source inputs...

[DaveC113]

IMO... if you're not going to use good parts and more advanced circuit designs tube pramps and driver sections will not be so great. IMO simple one-triode preamps are mostly effects boxes. No problem with that if that's what you like, or want it to warm up poor recordings, etc, but consider that most source/amp combinations have no problems at all with passive pres and if you want to not spend so much it's worth putting the cash into a good volume control rather than a mediocre preamp.

It'll cost more than you want but I don't think it's possible to beat Broski's Aikido kits unless you spend many thousands. Built with good parts it'll smoke most commercial designs.

http://glass-ware.stores.yahoo.net/

I'd go with an Octal Aikido using 6/12SN7s if you want gain or an ACF-2 Octal if you want a buffer.

For passive pres lots of options out there....

[borism]

My recommendation is to go with a Bottlehead kit:

http://bottlehead.com/product/smash-dht-preamplifier-kit/

They start at $500 but are in my experience great DIY kits. There is also an upgrade path for most kits. I have built 2 Bottlehead components - the Stereomour integrated SET amplifier and the Crack OTL headphone amplifier. The instructions are great and the website provides support for any issues during the build.

Good luck!

[undertowogt1]

I built and am using a Bootlehead Reduction Phono Preamp. There product and customer service are great. The Instructions are very good and if you have issues with the built they have a great forum where the Bottlehead owner and product designers, and fellow builders chime in to help

[dB Cooper]

http://www.tubes4hifi.com/pre11.htm

[timind]

Another Bottlehead recommendation. My experience is with the Crack and the elcheapo, Quickie pre. I really liked the Quickie.

[ebag4]

+3 Bottlehead.  I built the foreplay 2 long ago.  More recently the Stereomour and Kaiju.  While only the foreplay is a pre, all of the kits are well documented and sound great.

Best,
Ed

[glynnw]

+4 Bottlehead.  While not a PCB, they provide a disc with detailed instructions and photos of each step.  I cannot read a schematic and I have built at least 5 of their kits successfully.  And if you do screw it up, they have a program to fix kits as long as you have made an honest attempt to complete them.

[JLM]

http://www.transcendentsound.com/Transcendent_Sound_Grounded_Grid_Preamp.html

[Phil A]

Welcome to AC - lots of choices like those above or - https://www.tubedepot.com/products/elekit-tu-8500-stereo-tube-preamplifier-kit

[mick wolfe]

http://www.tubes4hifi.com/pre11.htm

These are gaining a very good reputation. A friend has a "factory-built"  SP-14 line pre-amp. Excellent refined product that can compete with much pricier company.....at least to my ear.

[richidoo]

How well the tube preamp will work with your amp depends on the input impedance of the amp. The old rule of thumb is the preamp output impedance should be <1/10 of the amp input impedance. This is to assure that the preamp can provide enough current to drive the amp and cable to avoid FR rolloff and distortion.

The datasheet for the amp chip says the input impedance is dependent on the amplifier gain, as set by external resistors. It can range from 9kOhm to 60kOhm. When driven by a tube preamp, you want the highest amp input impedance possible.

Since it's hard to check the values of the surface mount resistors on the amp, or to even see them hidden under the big caps, you might call Parts Express tech support to find out the input impedance of the amplifier, or if they don't know that, ask what's the gain, then you can look up the impedance on the datasheet chart.

Typical audio amplifier gain is 26dB (20x voltage amplification) so that would give you 30kOhm input impedance, so you'd be looking for <3kOhm (3,000 Ohms) output impedance for your preamp. Most tube preamp designs should be able to handle that load.

After you decide on the preamp, something else to consider while building it, especially since you are driving a solid state amplifier with lower input impedance than typical tube amplifiers: Coupling Cap Calculator

[siddharta42]

Wow! Thanks guys. I almost missed your replies as I didn't get any mail notifications for some reason

Those are really nice suggestions. The Bottleheads looks amazingly nice, and I'm very tempted to look at one of those. Bit more than I was thinking of spending, but that's hardly new ...

edit: the amp is indeed set to 26 dB gain setting which corresponds to an input impedance of 30k Ohms. So that shouldn't pose an issue for the preamps I've been looking at so far.

[DaveC113]

Wow! Thanks guys. I almost missed your replies as I didn't get any mail notifications for some reason

Those are really nice suggestions. The Bottleheads looks amazingly nice, and I'm very tempted to look at one of those. Bit more than I was thinking of spending, but that's hardly new ...

edit: the amp is indeed set to 26 dB gain setting which corresponds to an input impedance of 30k Ohms. So that shouldn't pose an issue for the preamps I've been looking at so far.

That should be no problem but keep in mind a tube pre without a follower output will have an output impedance about equal to Rp (plate resistance) of the tube. For DHTs that might be around 3k, which is an order of magnitude or so higher than many follower outputs and won't work well with every amp out there. Say you also want to feed a subwoofer amp that might have a 10k input impedance, this wouldn't work out so well...

It also depends on what you want, single triode preamps are high distortion units by design. A circuit like the Aikido minimizes distortion and noise but still has the positive attributes of tubes.