[jdkJake]

 
 

 
Quote:

Hey Jake, you gotta lay off the steroids.

 How did the amp sound with the LCD2's?
 
Again, nice case work.

Hellofatime for a 'roid rage, huh? 

 
Thanks for the kind words regarding the case. Amazing how a bit of paint can perk something right up and turn it into something completely different and IMHO, quite elegant and modern.
 
As for the LCD2's, let me get a bit more time on them before I comment on the overall sound. I will say this however, one of the strengths of this amp, at least for me, is the gain structure. The overall gain is quite low, even on the Hi-Z setting. As such, if you like it VERY loud or have a weaker source, you may find it more difficult to get all the volume and attendant power some phones tend to crave. I do not listen too loud, so, it is not much of an issue to me. I find I am maximizing the signal into the amp, which is always a good thing. It is also nice to get a wide range of travel out of the potentiometer. That said, one man's strength is another man's weakness. The amp might not have enough 'umph' for some phones and some listeners. The LCD2 may fall into that category, but, it is a bit early to tell. 
 
With Grados however, this amp really, really shines. An open, dynamic and detailed sound that is never harsh or biting. Lot's and lot's of presence, soundstage and clarity that you can listen too all day long if it were not for the comfort issues with those damn Grado ear pads. 

 A really wonderful combination. For the price point, I suspect it would be difficult to find this level of refinement for Grados. 
 
Good stuff. 

 

[jdkJake]

Quote:

I have an spud amp that is similiar to this one.  It can be worthwhile to ground the heatsinks for the heaters,  they tend to pick up the EMI from the transformers ( I saw 60hz @ -90 reduced to -100db) and this was a separate chassis.  Another thing to try would be adding  decoupling capacitors right at each heater pin (~200pf). 
 
These are just suggestion,  the emi from the torroid is generally vertical,  so it sounds like when you put the lid on it gets bounced around and picked up but the OPT.  
 
A plastic lid would be something to look for,   even plexiglass top with the sides from the stock case may be worth trying.   It is worthwhile to get rid of audible hum with Grados,  that seemingly benign low level hum adds significantly to the IMD. It is even worthwhile to get rid of non-audible 60hz hum because of its influence on IMD.  Has anyone done RMAA with/without the top on ?
 

Are you referring to the heatsink for the heater power supply? This design is using a DC heater supply. Certainly easy enough to try.
 
BTW, this uses an E-I core, but, I get your point. The effect is the same in that RF starts bouncing around with the lid on. I agree a different material for the top would be one way to skin the cat. It would just be nice to get the current case to work if at all possible as it makes the build more approachable for a wider audience of builders.
 
I will try a couple things later today once I get it back online. Are you thinking of a small ceramic to decouple the heaters?
 

 

[jdkJake]

Quote:

The Torpedo website is up and running!
 

Wow! Great work on the Torpedo site TomB. Very impressive and most informative.
 
Well worth the wait.
 

 

[tomb]

Quote:

Are you referring to the heatsink for the heater power supply? This design is using a DC heater supply. Certainly easy enough to try.
 
BTW, this uses an E-I core, but, I get your point. The effect is the same in that RF starts bouncing around with the lid on. I agree a different material for the top would be one way to skin the cat. It would just be nice to get the current case to work if at all possible as it makes the build more approachable for a wider audience of builders.
 
I will try a couple things later today once I get it back online. Are you thinking of a small ceramic to decouple the heaters?
 

Thanks for the kind comments on the Torpedo website!
 
Just an FYI about the discussion in the quote above - Dsavitsk and I have found that the bottom of the case contributes, too.
 
Crappyjones123 - many thanks on your kind comments about the Beezar packing!  I've never had a damaged shipment, yet (knocks on wood!) and hope to keep it that way. 

 
 

 

[glenda]

Quote:

Are you referring to the heatsink for the heater power supply? This design is using a DC heater supply. Certainly easy enough to try.
 
BTW, this uses an E-I core, but, I get your point. The effect is the same in that RF starts bouncing around with the lid on. I agree a different material for the top would be one way to skin the cat. It would just be nice to get the current case to work if at all possible as it makes the build more approachable for a wider audience of builders.
 
I will try a couple things later today once I get it back online. Are you thinking of a small ceramic to decouple the heaters?
 

Yes a small ceramic right at the heater pin really helped mine,  this type of tube are notorious for oscilating by picking up HF off their pins.
 
 
edit:  also yes I never would have thought about until I felt the dc heater supply hetsink vibrating,  grounding it quickly cured that. 

 

[UKToecutter]

Glenda,
 
Have you tried grounding all of the heatsinks?

 

[funch]

 
Quote:

Wow! Great work on the Torpedo site TomB. Very impressive and most informative.
 
Well worth the wait.
 

 x2.
 
BTW, I see that C7/8 are optional, but can't seem to find any info on them.
 
Jake - could the choke maybe have anything to do with the hum?
 

 

[UKToecutter]

Quote:

 


 x2.
 
BTW, I see that C7/8 are optional, but can't seem to find any info on them.
 
Jake - could the choke maybe have anything to do with the hum?
 

x3
 

 

[tomb]

Quote:

 


 x2.
 
BTW, I see that C7/8 are optional, but can't seem to find any info on them.
They are spec'd on the BOM as 470uf 10V.  I haven't found them to make any difference, but it might be that they could improve the performance of some tubes that I haven't tried.
 
Jake - could the choke maybe have anything to do with the hum?
I've tried both and things are slightly better with the choke, IMHO.  The improvement seemed to be more on the right channel, but that may just be because the choke becomes a steel frame in the line of sight of the right tube.

 

 

 

[funch]

Thanks, tomb. I saw them on the BOM and schematic, but couldn't find why they were optional.

 

[jdkJake]

Quote:

 


 x2.
 
BTW, I see that C7/8 are optional, but can't seem to find any info on them.
 
Jake - could the choke maybe have anything to do with the hum?
 

C7/8 are bypass/decoupling caps for the transistor bias LED. I threw them. Figured why not?
 
I did not try the resistor, but, as TomB has posted, he seems to have better results with the choke. I do get a slight mechanical buzz from my choke, but, it does not telegraph into the audio circuit. You have to get your ear dangerously close to even hear it. Not recommended. 

 

 

[jdkJake]

Quote:

Yes a small ceramic right at the heater pin really helped mine,  this type of tube are notorious for oscilating by picking up HF off their pins.
 
 
edit:  also yes I never would have thought about until I felt the dc heater supply hetsink vibrating,  grounding it quickly cured that. 

Okay. I will have to see if I have a ceramic around that rating. I think I have a 100pf ceramic, but, not much beyond that. I know I have a film cap around that rating I could experiment with. Let me trudge through the parts bin and see what I can dig up.
 

 

[dsavitsk]

Let this serve as a caution. The fuse drawer is apparently somewhat fragile. That or I am far more powerful than I ever knew. :eek:

So, be gentle on installation of that fuse! 

Wow, I can't say I've seen that before. I use a lot of these fuse drawers and have yet to have a similar issue.

I have an spud amp that is similiar to this one.  It can be worthwhile to ground the heatsinks for the heaters,  they tend to pick up the EMI from the transformers ( I saw 60hz @ -90 reduced to -100db) and this was a separate chassis.  Another thing to try would be adding  decoupling capacitors right at each heater pin (~200pf). 

These are just suggestion,  the emi from the torroid is generally vertical,  so it sounds like when you put the lid on it gets bounced around and picked up but the OPT.  

The hum actually seems to be being picked up by the tubes which have no internal shielding -- they were originally meant for differential duty, so probably didn't need it. But, we have tried the transformers in the same cases with other tubes and not had an issue.

The heaters are grounded. There is a DC supply to pin 4 and a pin 3 is grounded. I am doubtful that the heaters are the issue, but you never know. C6 decouples the post regulator, so you could try increasing that. You could also decouple pin 4 right at the tube which would just entail putting a cap across pin 4 and 3.

How did the amp sound with the LCD2's?

Probably not an ideal combination as the LCD's turn out to have a lot of back EMF which makes driving them with a SET amp problematic.

 

[dsavitsk]

BTW, I see that C7/8 are optional, but can't seem to find any info on them.

The impedance of the bias supply is a function of the the source impedance to the transistor's base, and the Hfe (~Rs/Hfe). With the LEDs, the Source Z is ~11 Ohms. Since Hfe is ~300, that means that the bias Z is less than an Ohm. This impedance is multiplied by the mu of the tube and added to the Zout of the plate which is why keeping it low is important here -- especially as the rp of the 6J6 is not particularly low.

But, bypassing the LEDs may lower this even more. We thought it was incidental, and neither of us could hear a difference. On the expensive version of this amp, I don't bypass.

 

[jdkJake]

 
Quote:

Wow, I can't say I've seen that before.

I use a lot of these fuse drawers and have yet to have a similar issue.
 

 
Wild, huh?
 
So, my grandfather (on my mother's side) was the ultimate DIY man. Built his own house, made knives/tools, grew/raised his own food. You name it, he did it. 
 
My other grandfather (on my father's side) could not change a light bulb without risk of breaking it. Hell of a baker though.
 
While both had most excellent qualities, I like to think I turned out more like my DIY grandfather. 
 
That said, sometimes the recessive gene comes to the forefront just to remind you of where you come from.