Tube Preamps- Hard to decide, Input Welcomed

[hilldweller]

I have been trying to decide which preamp to go with. It is very difficult to decide on which one to go with. I listen to Classic Rock, Classic Progressive Rock, Classic Jazz, Jazz Standards, And even Blugrass! I know that some of you have been around the block a few times and are quite knowledgable on the subject. The one I am currently considering is a grounded grid preamp that can be viewed at the following link:
http://www.transcendentsound.com/preampkit.htm
Has anyone here have any experience with this type of design "Grounded Grid"??? Yellow_Light_Colorz_PDT_14

[SteveH]

While I am currently running a highly modified PAS2 (lots of trial and error....mouser loves me !), I have always been curious about different preamp topologies. This design seems to offer just about everything:

http://hollowstate.netfirms.com/magic5.htm

"Three complete preamp circuits are incorporated: a classic common cathode-cathode follower cascade (CF), a shunt-regulated push-pull (SRPP) circuit, and a passive path."

And it is quite reasonably priced. Might be worth doing until Shannon comes out with his PAS4 board Yellow_Light_Colorz_PDT_08

[dhuebert]

This stuff looks really nice, but until I see the schematic, I'm not buying. It has been said many times, people hype their product like it's God's gift to audiology and then you see the schematic and it's straight out of the RCA tube manual. The Conrad Johnson PV10 is a good example:

http://www.drtube.com/schematics/cj/pv10a.gif

Not a single original idea, a hundred dollars in parts, yet thousands of dollars to buy. Here at Diytube the manuals are all online so you can see what you're getting.

I think we should start pestering Shannon until he comes up with a preamp just to shut us up.

Don

[TomMcNally]

I agree with Don ... until I build my own tube preamp with
logic controls and relay switching, I'm going to stick with
solid state. You can get a nice used high-end Adcom,
with remote control, some with turntable preamps, for
really good prices on eBay.

[TerrySmith]

There are three preamps I currently like:

1: A Dyna PAS with all tone, filter, loudness, balance and blend switch REMOVED. I currently use one with modded as above and 6GU7 tubes in the linestage. The filament supply is a FWB to suit the 6GU7's. Works very well with my get*set*go!

2: A simple linestage that I copied from Sorenj, two 6SN7's, sounds nice and cheap to build. This one's covered in this forum somewhere.

3: Broskies Aikido preamp. Still have yet to build it.

[SteveH]

The PAS isn't too bad; especially for the price. On mine pretty much everything is removed; and the RIAA was taken off of the selector switch. Made some cap subs, modified the heater supply, etc - so far so good.

[WA4SWJ]

Hi Guys,

If you haven't seen this you might want to look at it. I don't have any preamps (well, I do have an Aikido board that I have not constructed yet) since I use CD's only, but if I had a Dynaco PAS this is what I would do to it.

http://www.normankoren.com/Audio/Spice_preamp.html

Hope this helps some. Sorry if you've already seen it.

Regards,

[Slartibartfast]

The PAS isn't too bad; especially for the price. On mine pretty much everything is removed; and the RIAA was taken off of the selector switch. Made some cap subs, modified the heater supply, etc - so far so good.

What mods have you done to the heater supply?


I have replaced my selector switch with a more modern and less clunky, changed a couple of the low level inputs to line inputs. The PC5 & 6 boards were replaced with modern copies. No tone, balance or blend is in the circuit.

[CpuZapper]

I have played with the pas as well.

Stock the pas to me was a big disappointment but after removing all the controls, replacing the volume pot with a Step volume pot, replace the connectors, beef up the power supply, made changes to the phono section, replace the caps on the boards and use Tungsram 12ax7's. It now sounds very good. Note this will have trouble driving a low impedance amp, that's what Korens changes try to eliminate. For me I would not try to fix up a pas again but make something from scratch as the pas power supply is weak and the case is a bit small once you start changing things.

It sounds good enough now that I have not made a preamp out of Curcio boards that I have laying around or tried a line stage based on Norman Korens changes.

I would like to make a Killer preamp at some point as well but as I read more and ask questions as I go a few knowledgeable people have said they don't really think Norman Korens changes are all that great. I was under the impression it was maybe the use of the 12ax7 that they had issues with.

What would make a great Preamp, where to start?
What tubes are clear winners to use for a Phono stage and a Line Stage?
What circuits are best for each stage?
Making a solid power supply for a preamp, voltage regulated and noise free or controlled as much as possible?
Keeping the design adaptable so different cost points could be targeted, a basic version, mid price version and a bar none all out sound means everything version.

Is there some good guidelines to follow or would it be a good idea to try to make some sort of list?

[Slartibartfast]

I have played with the pas as well.

Stock the pas to me was a big disappointment but after removing all the controls, replacing the volume pot with a Step volume pot, replace the connectors, beef up the power supply, made changes to the phono section, replace the caps on the boards and use Tungsram 12ax7's.

Yes all of the pots on my PAS were in bad shape. The first to go were the tone controls. i still had one channel louder than the other, so next went the OEM selector switch. The problem still remained and out of frustration, I removed the balance, blend, loudness sw, and replace the volume with a new Alps pot. The problem was solved and there was a lot less wiring in the chassis. I think the next thing to do, is to replace the wiring with some 22/2 shielded cable. My preamp is quiet when a line input is selected, even at max volume, but with the volume much past the 12 o' clock position, I get some hum, when the phono input is selected.

It now sounds very good. Note this will have trouble driving a low impedance amp, that's what Korens changes try to eliminate. For me I would not try to fix up a pas again but make something from scratch as the pas power supply is weak and the case is a bit small once you start changing things.

I am driving an ST-70 amp, so that is not a problem. After seeing this site today, I would like to add this power supply to my PAS.

http://www.tech-diy.com/DIY_PWR_LastPass.htm

[CpuZapper]

I remember reading good things about this power supply from people who were using it, I have not tried it myself.

Maybe a power supply expert could comment.

[EWBrown]

If you don't need the extra gain of a phono or tape head stage, a good basic linestage is the VA / CF circuit similar to these two rom Gary Kaufman's Tube Page located at http://www.the-planet.org/



The 407A is a 40V filament version of the WE396A, 5670 or 2C51.
B+ voltage is around 215VDC.



Using a 6SN7 (or 12SN7)

The Bottlehead Foreplay III uses very similar circuit topology, and 12AU7s as originally specified, but 6SN7s, 6CG7s, 6FQ7s and other similar dual triodes can be used with no circuit changes.
There is also a more elegant tube- regulated version.

/ed B in NH

[lth1]

From a cost and sound stand point I still would recommend the Aikido 6SN7 version. Mine is really sounding wonderful with the GSG.

A GSG side note, try the 5691 in place of the 6SL7, let me know your opinions. It sound really good to me.

[EWBrown]

I got one of the octal Aikido stereo kits, when it was on sale a while ago, but never got around to completing it. Also one of the rather unique step attenuators.

Just have to get it all together in a chassis / box and power supply.

/ed B in NH

[jduffy]

From a member here I found out about Rozenblit's line preamp in Glass Audio. So simple to build and sounds wonderful. You can probably build it for less than $100. I'm guessing it's the precursor to the Transcendent Grounded Grid preamp.

For a phono preamp I built the Cornet2. Very simple using a PCB. People build them for about $400 - $600 but being frugal I made mine for about $250.

Good luck with all your choices.