2A3 "Pink SET" Amp Rebuild.

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ed
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#121 Re: 2A3 "Pink SET" Amp Rebuild.

Post by ed »

I'm kind of understanding/following whats going on here...

I was going to try and bring a 3 stage lateral fet to owston(based on a Rod Elliot project) as well as the SE choke loaded source follower but I've been diverted by a pp lateral fet with a jfet opamp input stage. This is allowing good visibility of decoupling the output from the input stage. I'm currently testing two power supplies versus 1 power supply with zener decoupling for the input stage. Spice shows quite a bit of difference.

On paper 2 supplies deffo shows a difference, but building all these power supplies takes time. I will report findings in the fullness of time.

I still may bring the 3 stage if it gets built....in which case 3 amps and 1 pair of new speakers at Owston...making up for missing the last couple of years.
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#122 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Looking forward to this lot then Ed. :D
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#123 Re: 2A3 "Pink SET" Amp Rebuild.

Post by RhythMick »

I had a similar moment, but for me the switch was from cap dominated to choke dominated with minimal uF. I tend to go LCLC, the first LC with 200uF, the 2nd with either 100uF or down to 30uF. I make that decision based on the mA, low mA means I can use higher henries and thus need lower uF to achieve the smoothing I want.

In my experience choke dominated power supplies make for much better music.
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#124 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Aye, choke input supply for SE DHTs is the preferred method.

I messed about for quite a while yesterday trying to provoke LF instability. I even (horrors) got the scope and sig gen out.

Nothing untoward.
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#125 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Rummaging through boxes for something else, I found an old Hammond 150H 8mA choke and thought "I know where that could be put to good use.
Got another one from our Ant and stuck them in the feeds to the front end, to give an LCLC supply and isolate the front end.

Image

Bit more conventional.
Also upped the HT to give 6WPC out of the 2A3-40s once more.

Sounds really nice.
It is better than the non-decoupled; not night and day, but a subtle increase in the musical quality of fingerbells, shakers and brushed cymbals. No increase in "hi-fi" ness, thank goodness. The chokes would have been straight out if any of that crap had started.

The non-decoupled supply was better than the LCRCRC first version.

So from this we can deduce that LCRCRC can be worse than nothing, depending on capacity in the supply.

LCLC is the best of the lot.

But then some of us knew that anyway.

Personally, I've never used LCLC (only used Pi filters before in my SE amps) so it is quite interesting, the degree of musical enjoyment you get.
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#126 Re: 2A3 "Pink SET" Amp Rebuild.

Post by pre65 »

Could you not use the 150mH choke instead of the anode resistor on the input valve ?
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#127 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Been there, done that before. That is why I got them years ago. I didn't like the result, but I do like the sound they give when used as power supply components.
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#128 Re: 2A3 "Pink SET" Amp Rebuild.

Post by pre65 »

Cressy Snr wrote: Mon Apr 16, 2018 10:57 pm Been there, done that before. That is why I got them years ago. I didn't like the result, but I do like the sound they give when used as power supply components.

Fair enough Steve. :)
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#129 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Aye,
What is surprising to me, from all this experimentation, is the degree of sonic degradation and musical damage, resistors seem to cause, when placed in SET amp power supply rails.
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#130 Re: 2A3 "Pink SET" Amp Rebuild.

Post by pre65 »

Must admit I try not to use resistors in power supplies.
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#131 Re: 2A3 "Pink SET" Amp Rebuild.

Post by simon »

Cressy Snr wrote: Mon Apr 16, 2018 11:18 pm Aye,
What is surprising to me, from all this experimentation, is the degree of sonic degradation and musical damage, resistors seem to cause, when placed in SET amp power supply rails.
Dr Low Mu alert! ;-)
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#132 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Well I wouldn't go that far. :lol:

Anyway I got out the DIY NVA this afternoon, and it's time to stop fooling. Yes, the pink SET now sounds better than it ever has, but the SS amp is just as good, just as beautifully musical, uses far less electric, does not weigh as much as a small safe and has more power.

So I guess that's that.
I don't feel bad having made the decision to move away from the hollow state stuff. Being on a pretty modest pension, I don't have the money to run two hobbies, and low the budget valve stuff I can afford to make, isn't going to cut it against good solid state.

It's either valves or speakers, it can't be both.
I've a lot of catching up to do with my speaker devs and lots of walks to go on now the weather is improving.
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