L0rdGwyn's DIY Audio
Feb 4, 2021 at 6:08 PM Post #2,086 of 2,524

Galapac

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Feb 4, 2021 at 6:14 PM Post #2,087 of 2,524

JazzVinyl

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I had a slow night at work, which is very rare, brought along my laptop and went into a LTSpice deep dive on the 801A amp. I think I have found a more elegant and simplified solution to the pentode gain stage that I am very excited about. I believe it will be much more forgiving to the feedback loop as well, very excited to prototype it in the real world.

Very nice! Can't wait to see what you come up with LG.

How about your 4 volt tube amps? What was your final thoughts on those, SQ-wise? Do you still have them?
 
Feb 4, 2021 at 10:15 PM Post #2,088 of 2,524

Tjj226 Angel

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Gyrator PCBs arrived today, going to try to do this DarkVoice modifications this upcoming weekend, probably Sunday into Monday. I will pray to the oscillation gods Saturday night in preparation.

IMAG3003-2.jpg

Also received all of the replacement resistors and capacitors for the Zenith radio restoration. Replacing all of the original circuit components will be laborious, looking forward to having the circuit functional so I can focus on the fun part, which is polishing/restoring the bakelite chassis. I will likely be using my buffing wheel to shine it up.

Let's see what else...once the DarkVoice stuff is mostly done and the radio is done, I really only have the 801A amplifier left on the big "to do" list (obviously there is an endless list of little tweaks to be done on my completed gear, but nothing super major that I have planned).

I am not rushing it as it has been a long time coming and I have huge expectations for the sound based on previous prototypes. Right now I am playing with some simulations, ideas I have to alter the pentode input stage, more to come on that.

More fun is thinking about the final aesthetics of the amplifier. What I think I want is to make it look more like a "vintage" SET amplifier. Might not be for everyone, but I like the look of these Asano SET designs, sort of a high-gloss burnt reddish brown with vintage bakelite knobs and toggle power switch.

unnamed.jpg

We will see if tastes change, but that is what I am liking at the moment.

I do really like those new age vintage amps. They look pretty freaking cool. The problem I have always ran into is that when you try to stick a bunch of film caps in an amp like this, you quickly run into problems.

Look up the old synthesis amps. They are gorgeous and can come in some unique colors.
 
Feb 4, 2021 at 10:34 PM Post #2,089 of 2,524

L0rdGwyn

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Very nice! Can't wait to see what you come up with LG.

How about your 4 volt tube amps? What was your final thoughts on those, SQ-wise? Do you still have them?

Oh yes! The 4V tubes are alive and well, they are the drivers in my main two-channel amplifier, my 3.5WPC 6A5G SET. I have been using the Philips E424N as input tubes for quite some time in it, they sound great, here is a photo from around Christmas time

DSCF6245-2.jpg
 
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Feb 4, 2021 at 10:36 PM Post #2,090 of 2,524

L0rdGwyn

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I do really like those new age vintage amps. They look pretty freaking cool. The problem I have always ran into is that when you try to stick a bunch of film caps in an amp like this, you quickly run into problems.

Look up the old synthesis amps. They are gorgeous and can come in some unique colors.

Awesome I will check them out! Does look like it could get pretty cramped in there, but as usual this will be my spin on it via Landfall chassis, so should be able to make some space.
 
Feb 5, 2021 at 1:15 PM Post #2,093 of 2,524

bcowen

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I have a lot of meters here - about one thousand per kilometer. How many do you need?

LOL! Obviously he needs about 20 feet of them. :smile:
 
Feb 5, 2021 at 1:20 PM Post #2,094 of 2,524

L0rdGwyn

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Keenan did you ever get those meters that were supposed to come your way?

No sir. Think it probably slipped Glenn's mind with all of his job and life changes going on. No big deal though as I didn't have an immediate plan for them, but I do appreciate you offering them to me, they are beautiful. I'll ask Glenn about it when he makes his way back to Head-Fi.

For the 801A amplifier, which will be fixed bias, I plan to use panel mount test jacks rather than a panel meter to measure voltage drop across a current sense resistor on the 801A cathode for bias adjustment, like these. Keeps the footprint small in what will be a crowded amplifier. In the current iteration, it is going to have seven tubes :joy:

Test Jack.png

I have been working on this amplifier a lot this past week, making design changes via simulator and planning for real-world components. This is the most confident I have felt about the direction, it is very nearly complete, will just need a breadboard to confirm once I have the mains transformer. Definitely the most ambitious design I have worked on, ever since @Xcalibur255 planted the 801A seed in my brain, I hitched my horse to that cart but didn't realize the odyssey I was committing to LOL it has been extremely educational working on this amplifier. It will put out 6-7WPC, move over 300B :)
 
Feb 5, 2021 at 1:50 PM Post #2,098 of 2,524

L0rdGwyn

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I have a question for the group: is it possible for an amp's input sensitivity to be too high and if so what would that sound like in terms of a negative effect on the sound?

High input sensitivity as in the amp requires, for example, 3Vrms instead of 2Vrms input signal to reach full output?
 

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