[CButterworth]

I am looking for a good tube preamp to drive my AKSA 55N ss amplifier.  While, I enjoy the amp, I do find that the music lacks the warmth characteristic of tube amplified music.  There are a couple of preamps designed for the AKSA available from Aspen Amplifiers - the TLP, a unity gain preamp which uses two sides of a single tube, and the GK preamp which clearly separates the channels.  I am unsure of the gain of the GK, but my guess is that it is pretty low, as the AKSA's are easy to drive.

Anyway, I would like to find plans for a low-gain tube driven preamp for my AKSA that has separate tubes for each channel, as I am sure that this will ensure maximum channel separation.  As far as I remember, Hugh Dean (the AKSA designer) reckons that a little gain fed into the ASKA 55 will improve its lower frequency response.


I have looked for such designs, but have not found any that indicate the amount of gain.

Can anyone recommend any sources for such plans?  Or maybe even a relavant book that might allow me the necessary insight to cook my own.

Also, bare in mind, that while I have successfully built my own AKSA, I have not had experience with tube-level voltages, although I guess that as long as simple safety procedures are followed, things should be fine.

Regards,
Charlie

[JoshK]

I would suggest having a look at diyparadise.com under the projects link there is a very simple 12B4 preamp (maybe its called etude).  It has a gain of 4 (which is low, but not unity).  Most tube preamps use their tube in a "grounded cathode" configuration which yields a gain a bit lower than their mu (typically 8-40 times). 

There are ways of using the same tube and providing no additional gain (i.e. gain = 1, unity gain), most common of which is a cathode follower.  Tube purists typically frown on the CF stage saying it just sounds wrong.  There are variations of the CF that apparently improve the sonics but they aren't newbie projects. 

Basically the 12B4 linestage can be used in standard (good sounding) GC configuration while provide only a fair amount of gain (4).  This is likely your best compromise.   This is an inexpensive and easy to build project as well.

[CButterworth]

Josh

I like the idea of the Etude.  However, as I am new to tube electronics, I would love to see a schematic, so that I can be sure to get the correct parts, and get them connected in the correct manner.  Of course, I would also have to make changes to the power supply given that the original PSU utilizes 240V and I have 110 volts, although this is likely not too difficult.

Charlie

[JoshK]

The schematic is the same as it is for the simple 5687 preamp (which even has a step by step powerpoint pres on how to build it).  There are a few resistor changes around the tube.  This is explained in the discussion about the Etude.  I can help you figure out which resistors to change and if I ever get a schematic drawing software I can redraw it for you with the correct values.  But Yeo says x ohm cathode resistor (I can tell you which is the cathode resistor, which is the grid bias resistor, which is the anode load resistor).  He uses the exact same powersupply as the 5687.  The tube pinout will be different but I can talk you through that too....tsdl.duncanamps.com has a bounty of tube data and pinout diagrams.

[mgalusha]

... if I ever get a schematic drawing software I can redraw it for you with the correct values.

Josh,

If you haven't tried it, TinyCad works fairly well for a freeware schematic drawing program. There is a fairly active community and the author makes semi regular updates.

http://tinycad.sourceforge.net/

Mike

[CButterworth]

Josh and Mgalusha,

I have the "Simple" schematics and will redraw them for the Etude.  I have Adobe Illustrator, which will work for this, although I may download TinyCad and see what it can do.  I am still a little unsure of how to implement the PSU transformer, as I don't know enough about them - such as whether DIYParadise is designed for 220V AC from mains, while in the US we use 110V AC, and if that changes which power transformer to use.

Once, I get a drawing, I'll get it checked.

Regards,
Charlie

[JoshK]

Changing to 115V mains is no big deal. I'll look up the model # for the Hammond I used (I built the simple 5687 preamp as my second ever diy project). 

[JoshK]

I used the Hammond 274BX which is spec'd for 110 mains and appropriate secondaries.  I got most all my parts from www.hndme.com but it looks like they don't have the 274bx in, partsexpress does but they are a bit more expensive.  There are a number of other places on the web to get it...try a google. 

[Frihed91]

I know you want to DIY, but Mapletreeaudio is planning to offer their preamp 2ASE with seperate power supply as a kit soon.  Also McAlister Audio will build you his PL-10 preamp for about the same price.  It is among the lowest gain active preamps i have ever heard and works as a killer headamp also.

I know NOT DIY.

[andyr]

I am looking for a good tube preamp to drive my AKSA 55N ss amplifier.  While, I enjoy the amp, I do find that the music lacks the warmth characteristic of tube amplified music.  There are a couple of preamps designed for the AKSA available from Aspen Amplifiers - the TLP, a unity gain preamp which uses two sides of a single tube, and the GK preamp which clearly separates the channels.  I am unsure of the gain of the GK, but my guess is that it is pretty low, as the AKSA's are easy to drive.

Anyway, I would like to find plans for a low-gain tube driven preamp for my AKSA that has separate tubes for each channel, as I am sure that this will ensure maximum channel separation. 

Hi Charlie,

Sorry but as you're an AKSA 55 owner, I'm having a difficult time trying to figure out what your problem is?  Is it that you prefer the intellectual exercise of designing something, rather than just building it? 

Why not simply buy the GK-1 kit ... it certainly will make your AKSA amp sound a whole lot more "tubey"!!  Of course, if the GK-1 kit is out of your price bracket then that would explain why you're searching for plans for a tube preamp.  But then you'll have to take the chance that the parts you source yourself will be good-sounding ... whereas Hugh has already done all that work for you!! 

Regards,

Andy

[CButterworth]

Andy,

You're right!  I have looked at the AKSA offerings.  The GK-1 would be my choice, although I do not have sufficient funds to jusity the price-tag.  I have read opinions on the GK-1 and folk love it, when paired with their AKSA amps.  I have also considered the TLP, but I know that it is unity gain, and I remember that Hugh said that the AKSA 55 could use a little gain to improve the bottom end.  I would also like to maximize channel separation, so would like to have very separate tubes for each channel (maybe even power supply also).

I think that I could source parts for the Etude for around $200 US, which is considerably cheaper than the GK-1.

Another reason for going cheaper on the preamp is that I need to replace my CD-source. Over the weekend, I managed home demos of the Music Hall CD25.2 and the Rega Apollo.  The CD25.2 was the first to be tried, on Friday evening. My previous source was a Toshiba 3950 with an outboard Art DAC - both with very minimal mods.  Anyway, the Music Hall blew my previous source - the detail was amazing, and the soundstage much more open.  Even, my wife (who exercises caution about new gear) was wowed with the extra things she was hearing in Alan Parson's Time Machine.

We also had an Antique Sound Lab 1003DT, and it brought out much more bass than the AKSA, although we returned that after hearing very little difference between the ASL and the AKSA with a Gregorian Chant CD by Chanticleer.

Anyway, I got the Rega Apollo on Saturday.  Although it is twice the price of the CD25.2, I doubted that there would be much difference due to manufacturing cost difference between China (Music Hall) and Britain (Rega).  Well, we had a second WOW.  Where the Music Hall was good, the Rega was way better, although I do have to admit that aspects of the Rega chassis seem lightweight compared with the Music Hall  - the rubber feet on the Rega are even riveted to the chassis.  I guess that I'll have to change these out somehow.

So, the Rega will stay, and I will have to go with a cheaper option for preamp.  I was even amazed that my Polk rt600i speakers could reveal such differences in source.

Once, I get my version of the Etude preamp drawn, I'll likely ask for someone to check it for accuracy - maybe against Josh's schematic?

Thanks,
Charlie