diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Pass Labs (http://www.diyaudio.com/forums/pass-labs/)
-   -   Aleph 2s And The Grounded Grid (http://www.diyaudio.com/forums/pass-labs/48091-aleph-2s-grounded-grid.html)

Mark A. Gulbrandsen 20th December 2004 01:12 AM

Aleph 2s And The Grounded Grid
 
I haven't had nor built any tube stuff for a long time but recently decided to build a Rosenblit Grounded Grid line stage. This was the easiest audio related thing I've built in along time and cost under a hundred bucks even with three new 6189W JAN tubes. The results are absolutely mind blowing and the best my system has ever sounded. Several changes I made after some listening tests were to change the feedback resistor to 150K and the output coupling caps to 5 mfd(Multicaps).

The preamp did go through a break in time of several days with a very overbearing bottom end and reduced high end and poor resolution. After about 48 hours things started to change and kept getting better and better. I've tried other 12AU7's but so far the Sylvania 6189W's sound the best and are free from microphonics so they get to stay.

Anyone else here paired up any of the Alephs and the GG?

Mark
(Highbias)

eLarson 20th December 2004 12:14 PM

I'm not the most tube-savvy guy out there, but isn't the Wyetech Lab series of preamps based around a grounded grid stage? (Or rather--I think I have this right, terminology-wise--cathode follower, grounded grid, cathode follower?)

It seemed to me there were at least a couple of reviewers out there who used Wyetech Labs stuff as their personal references.

eL

grimberg 26th December 2004 05:54 PM

Mark,

I had considered building Bruce Rozenblit's Grounded Grid Preamp to use with my Aleph 2. However, I don't have experience building tube gear and ended up putting the project aside.
Would you mind posting pictures of your unit so I can use it as a reference for my layout?
Also, if I understood correctly, you used 5F for C2 and C3, and 150K for R9 and R13. Is there any other improvement you could suggest?

Mark A. Gulbrandsen 27th December 2004 01:01 AM

2 Attachment(s)
I will post it all here because this really is a "Use the GG with the Aleph 2" thread other wise I suppose it should really be in the tubes section of the forum. Hopefully the moderators will allow us to cross post a bit.

Sure, here are a few shots of the GG line stage. I've been wondering if there could be a grounded gate mosfet version put together to be its solid state equivelent???

Mine was hastily built on a flat 6061 alumnium plate 3/16" thick that is finished with Hammerite Black Hammertone paint. Yes the caps are 5uf PPMFX bypassed by .1's and 150K feedback resistors. The larger caps seems to give the bottom end more solidity. The transformers for the plus and minus 200 volt supplies are Stancor P6406 and the filament is a Triad F344X. All of the parts were I bought surplus locally including the 6189W Sylvania made JAN tubes which I highly reccomend you track down and purchase because they have little to no microphonics which are normally very bad in the every day 12AU7 tube.

The attenuator is a very old Daven 10K T type that I convereted to a ladder style 50K. As soon as I have some time the plans are to build a coco bolo or some other exotic wood base for the plate and the attenuator will be mounted on the front of the base. This will eliminate the unsightly fry sauce box that it now resides on.... the label says best if used within 30 days..... hummmm....

Those that need the GG schematic can find it in Bruces book "Audio Reality". I had to buy it to get the schematic too and you will also need to since the design is Bruces property!

I hope all this helps somewhat.....

Mark

Mark A. Gulbrandsen 27th December 2004 01:04 AM

2 Attachment(s)
The audio end of the bottom of the plate....... Although there are a number of high quality 1% resistors there are also an equal number of aweful carbon 2 watt jobs in there.... nothing really too exotic seems to be required to get top notch performance and supposedly little to no gain in performance would be had by using higher quality parts. I do intend to experiment with a 12AU7 based CSS in the near future and possibly to eliminate the zeners in favor of gas regulator tubes. Zeners although cheap are somewhat inherently noisy.....

Mark A. Gulbrandsen 27th December 2004 01:06 AM

2 Attachment(s)
The power supply end of things. The filament regulator is mounted to the small finned heat sink. That will be eliminated and mounted directly to the chassis as soon as I get some insulated mounting hardware.
The feedback resistors are in the lower center of the photo. I located them in an easy to experiment with location!! For my system the 150K value seems best but anywhere form the original value to 175K will give you minor changes in the bottom end. Also let this preamp break in for at least a week before making any major judgements on overall sound quality. The break in is somewhat dramatic and the unit will under go a number of shifts and changes in its sound before it finally settles down. Sound staging and clarity are incredible.

Grimberg.... The negative 200 volt supply does hold a charge so be sure to be careful or install a 25K bleeder resistor on both 200 volt supplies if you are nervous about the high voltages present.

grimberg 27th December 2004 01:59 AM

Mark,

The pictures are very helpful. Thank you very much!
The Tube Store has the GE brand JAN 6189W. Do you have any experience with those?

http://www.tubestore.com/phil6112au7.html

Mark A. Gulbrandsen 27th December 2004 03:52 AM

The GE's should be good and their price is not unreasonable either. Regular GE 12AU7's also sound really nice. There is no problem subbing in the 6189W as all specs are identical... they are just built better. I paid ten dollars each for six 6189W's and six 12AU7 Tung Sols. The Tung Sols sound excellent but have the usual microphonic problem. I would assume that most of the new Chinese and Russian 12AU7 stuff available today also suffers from microphonics.......

One thing I forgot to point out was the Star Grounding point which is right between the two feedback resistors in the power supply photo. My GG has zero audible hum or noise even with my ear right at the drivers of my speakers. Use 105 deg c. caps in the power supply!

Good luck building yours... let me know if you run into any problems.

Mark


All times are GMT. The time now is 01:30 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2