[Jon L]

It seems I am getting a grounded grid preamp with Goldpoint attenuator, Grayhill switch, and stock Ei 12AU7's.

I'll listen to it before changing things, but I have a couple of questions if you don't mind:

1.  What's the stock value of the coupling cap (uF, V-minimum needed)?  I seem to have read somewhere these coupling caps only have about 70V of DC on them..

2.  Can E80CC tube be substituted for 12AU7 in the GG?  E80CC has double the filament current but some (many?) circuits can provide the extra current, like my old Cary CDP.

3.  Do all 3 12AU7's have to be identical brand/make? Any specific ones that work especially well in the GG?

Thank you for the help.

P.S.  I actually have a pretty low expectation going in, as I am firmly in the no-preamp/passive preamp camp, even after auditioning some famous and some very high $$ preamps.  But I wouldn't mind being pleasantly surprised 

[doorman]

My GG pre is very insensitive to tube-rolling, having tried numerous 12au7/variants, I've yet to detect a difference worth mentioning. Ymmv, of course.
(if yours is the one currently listed on A'gon, the asking price was well below what they usually go for!)
Good Luck, Don

[Jon L]

My GG pre is very insensitive to tube-rolling, having tried numerous 12au7/variants, I've yet to detect a difference worth mentioning. Ymmv, of course.
(if yours is the one currently listed on A'gon, the asking price was well below what they usually go for!)
Good Luck, Don

Thanks for the reply.  I did get a reply from Transcendent that all 3 tubes don't have to be identical, but should I still keep the 2 tubes (on L and R?) identical but maybe OK to use different one for the middle tube?

Anyway, the coupling cap is apparently 1uF, and coincidentally I have a bunch of 1uF teflon caps laying about  aa

[richidoo]

Edit: you already have the answers.  Enjoy!

[Ric Schultz]

Jon,
If you want it to sing....you need to do the following:

bypass all the switching and the volume control.....simply wire a 10K resistor from one of the input jacks to the grid of the first tube....and from the same spot run a wire to the pot which will just be used as a shunt to ground.  Super way better sound.

Change the rectifying diodes to some IXYS soft recovery types. 

Bypass the power supply with serious caps.

Remove the fuse.

Damp the tubes.

Change those output caps.  The one I had here had Axion 1uf caps....film and foil polyprops....not bad...did not try any others.

Use two of them dual mono.  The last tube shares both channels....this is a no no in my book.  I did not listen dual mono.....even one with the above mods was pretty killer.  Certainly, with mods,  the best preamp for the money I have ever heard.....stock it is OK at best......

Ric

[Jon L]

Jon,
If you want it to sing....you need to do the following:

.....even one with the above mods was pretty killer.  Certainly, with mods,  the best preamp for the money I have ever heard.....stock it is OK at best......

Ric

Ric, are you volunteering?  For a fee, of course.  After all, all preamps eventually have to outperform EVS ultimate nude attenuators in my system to stay 

Just looking for a little more body and oomp, esp down below without losing the EVS attenuator transparency..

[andrewbee]

Remove the fuse.

This is a safety device, why would you remove it?
Is it being replaced with something else e.g. circuit breaker?

[richidoo]

The temporary contacts of the fuse and holder are not as good as a permanent connection like wire or solder. The fuse itself is designed to be a resistive element that will deliberately overheat at certain current. So it is by design a lousy conductor. In a tube preamp every change is audible, this is a potentially big one since it limits current to the power transformers.

But you are right, if you remove the fuse then something else has to take the punishment if there is a fault. The GGpre is very well designed, and the PCBs and parts are extremely good quality. The circuit breaker on the mains will maintain safety but not protect internal components.

[andrewbee]

Richidoo,

I don't understand what you are talking about here. Lets look at it.

The fuse itself is designed to be a resistive element that will deliberately overheat at certain current

So far so good and I am with you here. It has a design centre that when exceeded the element will open and therefore cut power to the device for safety.

So it is by design a lousy conductor

How is it a lousy conductor? When measured with a multimeter what is the result?

In a tube preamp every change is audible, this is a potentially big one since it limits current to the power transformers

If you have a circuit with a design current draw of E.G. 2 Amperes and you have installed an E.G. 2.5 Ampere fuse how is that limiting the the current to the power transformers? The circuit demands the current which the power transformer is there to supply (transformers do not draw the current). Once the power transformer is able to supply the current demand the circuit performs as designed. If the fuse cannot handle the current draw then it opens. Having a piece of 10 A.W.G. wire in place of a properly rated fuse will not make any difference to current draw versus a fuse unless the circuit malfunctions, then without the fuse something will do real damage or perhaps ignite.

But you are right, if you remove the fuse then something else has to take the punishment if there is a fault

That is my point, and the punishment may be dealt out to you or whoever removes a fuse and replaces it with a piece of wire.

The GGpre is very well designed, and the PCBs and parts are extremely good quality.

I agree but that has nothing to do with removing a fuse.

The circuit breaker on the mains will maintain safety but not protect internal components.

The circuit breaker in your house mains is probably a 15 or 20 Amp which is what is used for a standard branch. You get a failure in your preamp and have no fuse but depend on the circuit breaker then you pretty much better pray that whatever has failed pulls a lot of current very fast in order to trip that breaker!

IOW NEVER REMOVE A FUSE OR COMPROMISE SAFETY!

[Jon L]

I have been playing with the GG, and while I was happy it already had the Goldpoint stepped attenuator, Grayhill switch, Auricap upgrade, and solid core silver wire in teflon, it still sounded like I inserted a tube preamp into my system and what that implies   



Before GG fans get upset, do understand that my previous system did NOT even use a preamp.  I was able to tweak the gain stages and my audio PC's digital signal output to do fine without a preamp.  When I got the GG, I simply placed it in my system, so the setup now had one more active component and another run of (same) interconnects.  And yes, I could hear them..

What was most bothersome was what I perceived as fuzzy bloom overlaying everything and slightly "puffy" bass and loss of absolute transparency of resolution, especially in the upper-midrange.  I am sure someone replacing a less-well-engineered preamp with GG would be delighted by it, but I'm comparing it to the proverbial "no preamp."

Luckily, a lot of the character I heard, I recognized from my capacitor-rolling experience with Auricaps.  I then replaced the Auricap output caps (which was already an upgrade from stock caps) with VH Audio Teflon capacitors of the same value. 

Color me impressed!  Fuzz turned into resolution, especially in the problematic upper-midrange, and now that bass, so defined with much more PRAT and impact.  Now we are getting somewhere, getting much closer to the no-preamp transparency with just a touch more richness and drive. 

What's next?  If I could just figure out what the heck Ric (EVS) was talking about in the post above and actually carry them out without causing trouble   

[richidoo]

IOW NEVER REMOVE A FUSE OR COMPROMISE SAFETY!

Then you will never understand the benefit of the mod. Risk is to be managed, not feared.

[Jon L]

Photo of GG with VCap Teflons swapped in.  While in there, I also bypassed the main PS electrolytic cap with VCap Teflon as well (underneath the board).  Smashing sound compared to before..

[JimJ]

Looks good

I've seen too many things happen in my 12V installing experience not to always have a fuse somewhere in line...I know we're dealing with a lot less current in AC apps, but I just wouldn't be comfortable with it, especially if I paid a bunch for boutique components.

[andrewbee]

Then you will never understand the benefit of the mod. Risk is to be managed, not feared.

Richidoo,

With all discussed here so far I see no modifications, only part substitutions. There are no operating or topology changes.

I will not rain on your parade anymore.
I criticize constructively trying to explain errors using facts and am only trying to help.
I certainly don't have to sit down and respond to posts such as yours but when I see such glaringly incorrect and dangerous information I feel obligated to correct same.

You are of course free to do what ever you wish, it is unfortunate however that there are so many on the WWW who read posts such as yours and not having the knowledge may follow same blindly, having no idea what they are actually doing and the risks they are taking.

All the Best to you.

Andrew.

 

[richidoo]

All the Best to you.

And to you... 

Jon, which PS electros did you bypass with the small VCaps? Heater, rails, or all of them?
Thanks

[Jon L]

Continuing on with the fun, I finally got around to bypassing the selector switch and wiring just one input directly to the Goldpoint ladder attenuator.  That Grayhill switch must not be too shabby because the improvements were not very large, perhaps a touch more liquidity and coherence was attained.



But what really hit the ball out of the park was getting around to trying my Omega Mikro power cord on the preamp.  Of all the power cords I have laying around, this old favorite upped the ante on transparency, neutrality, and that upper-bass PRAT. 

And after all these mods to increase resolution, tube swaps yield tremendous differences though I have repeatedly read that tubes don't make too much difference in the grounded grid.  No longer true 



I finally have a preamp that I can honestly say I enjoy having in my system vs. having no preamp, and I have tried quite a few.  It does seem to best enhance my low-gain 2A3 SET relative to higher-gain amps, so be it 

[RooX]

Im in the process of tracking one of these pre's down.  I'll join in the fun once i get use to the sound and figure out what i might want to tweak!  Keep up the updates, its interesting to see what you find works well and what doesnt.

[Ric Schultz]

Jon,
I forgot the 10K resistor was already on the board.  So, just run a wire from the input jacks on each channel directly to the input side of the 10K resistor on the board.  On the other side of the resistor (tube side) run a wire to the output of the pot and I believe that is it.  The pot is already grounded and then there would be no wire to the input of the pot.  You are then using the pot (goldpoint attenuator) just to switch resistors to ground.....there you have it.  Shunt attenuator.  No pot in series with the signal....only the pot to ground.  You have added nothing in series with the signal that is not already there.  I hope this is clear. 

Another way to say this is take the input wires now on the pot and directly solder them to the input side of the 10K resistors.  Desolder the output wires from the pot at the board and extend them so they are now soldered to the tube side of the 10K resistor.  Let us know how it sounds with a shunt instead of a ladder atteuator.

[Jon L]

Another way to say this is take the input wires now on the pot and directly solder them to the input side of the 10K resistors.  Desolder the output wires from the pot at the board and extend them so they are now soldered to the tube side of the 10K resistor.  Let us know how it sounds with a shunt instead of a ladder atteuator.

Thanks to Ric, I finally configured the attenuator in shunt mode instead of ladder.



I have gained a little more purity, smoothness, and natural detail, improvements definitely worthwhile given the zero cost involved. 

Still, I would say the largest improvement came when the Auricaps were exchanged for VCap Teflons, which happens to cost the most  aa

At any rate, this modified Grounded Grid with VCap teflons, working in shunt mode, now plays in the big leagues IMO.  Some of my favorite preamps have been the likes of Aesthetix Callisto Signature and VAC, but this GG has just as much transparency and resolution, perhaps even more of "straightwire with gain" sound than those preamps with many, many tubes in them. 

The only area the GG still doesn't quite compete with those $$$ preamps is the sense of effortless macrodynamic wallop and bass "pressurization," but I suspect I will not be able to achieve these rare attributes without a complete overhaul and ground-up rebuild of the power supply into a massive behemoth 

[Jon L]

Now that I am getting VERY close to that "straight wire with gain" thing, with a two-tube-stage preamp no less, I made some further mods to get it even closer.  The tedious process of comparing a new mod vs. no preamp in the chain continued endlessly. 

In the end, I ended up adding FT-1 Russian teflon caps to the large VCap teflon output caps.  It's kind of counter-intuitive, but even a great cap like VCap can benefit from a small teflon bypass as the cap size increases. 

Where small teflon caps seem to really thrive is bypassing power supply electrolytics, and I added some more FT-1 teflon caps to various PS electrolytics. 

These changes ended up giving me that last 3% of extreme treble air, extension, and coherent sweetness.  I'm still surprised when improving the high frequency seems to enhance bass definition, but that happened as well once again