• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SainSmart 6N3 pre for Pass ACA

Hesitate to ask for fear of being flamed, but…

I’m building Pass ACA mono blocks to mate w/ some of the single full range driver speakers I have built, so I need a pre. I use a passive pre w/ the Dynakitparts ST-35 I built a few tears ago, but the input impedance of the ACA seems too low for this approach.

I’m not a hard-core electronics guy like most of you, nor do I have lots of cash for this project. So I want to do something quick dirty to get up & running. There are some folks on another site who seem to like the SainSmart 6N3, so I ordered one. (see: http://www.amazon.com/SainSmart-Ass...qid=1463360213&sr=8-1&keywords=sain+smart+6n3 ) I also picked up some NOS GE JAN 5670w tubes to use in place of the stock Chinese tubes.

My concern is that the transformer is labeled as 110 v. input. My wall sockets measure 124 v. (most of the time). Output from the transformer measures correspondingly more than the 6.3 v. for the heaters and 170 v. for the plates.

What to do?
1) Use it ‘as is’ & burn through tubes?
2) buy a new transformer? buy a step down transformer? (but I have no clue what to buy)

Any advice would be appreciated!

Thanks, Jim
 

kacernator

Member
2008-01-09 10:38 pm
ACA with 2.2k resistor mod can output max power of 6W. It has gain of 5x. If your source can put out 2V then you do need just buffer preamp - no voltage gain. For this I recommend B1 buffer.

If you really need preamp with voltage gain and want tubes, look at aikido preamp. You can vary its gain by changing input tube type.
 
My question lies around the change of pot to 10 K, why?

2 Reasons:

1. The pot that comes fitted is in the output circuit; it is better to have it on the input.

2. The standard pot has been reported two have an imbalance between L & R; The Alps pot is of a higher quality, and does not have this imbalance.

The beauty of this device is that it works well out of the box, but each subsequent modification has a noticeable, if not quantifiable, improvement.

Lots of information here: "Say Hello! to my new little friend" | Audiokarma Home Audio Stereo Discussion Forums
 

irribeo

Member
2013-04-01 2:46 pm
"works well out of the box" and Audiophile Bargain

Just the bargain part:
-Many report mainstransformer getting really hot, some report transformer failing after powering up just a couple of times.
-Some (freaky) measure the voltage over the 200V electrolytics and find voltages above 200V
-Some actually tell you the heater +voltage is connected to audioground

Audiophiles couldn't care less and start replacing coupling capacitors to improve the amp :D
 
Hi everyone ! I will get one quite soon
on the basis of some very good reviews i am now quite curious ... and the 30USD price has made the rest
anyone who has performed any of the suggested modifications above ?
In particular is not the pot at the output a very strange solution ? i think that the common choice is a pot at the input
and open. I understand some of the resistors are smd ... that complicates things a lot.
I intend to use just the 1st tube as a buffer not needing any voltage gain. :rolleyes:
 
Hi i will get one in the next weeks. I wil take pics and measure voltages with protective gloves. I do not like what other people already disliked ... like the pot at the output. Just tell me how many preamps are done like that ... almost no one. There must be a reason. I intend to take the signal out of the cathode of the 1st tube and use the unit only as a buffer. I just need some tube flavour to my solid state chain. Just that.
Nobody who has it ?
Anyway ... when i saw those smd resistors ... i wanted to cry Why smd i do not understand It is not a dac ... just make the board twice as big and use conventional sized parts
Weird decision indeed
 
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Hi just to ask a question.
If i will take the signal out directly from the cathode pins on the 1st tube will it act as a buffer ?
i intend to insert and use only the 1st tube and take out everything else I will leave it even without volume control. Just a plain buffer as i not need voltage gain at all.
I guess i will have to add just two output 4uF caps soldered on the cathode pins of the 1st tube to block DC on one side and going to the output RCAs on the other side. I do I just need a buffer able to drive 10k Zin power amps.
In this way i would avoid some issues found with the original design.
I also intend to use long pins tube sockets to make things easier
Thanks a lot
 

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Hi just to ask a question.
If i will take the signal out directly from the cathode pins on the 1st tube will it act as a buffer ?
i intend to insert and use only the 1st tube and take out everything else I will leave it even without volume control. Just a plain buffer as i not need voltage gain at all.
I guess i will have to add just two output 4uF caps soldered on the cathode pins of the 1st tube to block DC on one side and going to the output RCAs on the other side. I do I just need a buffer able to drive 10k Zin power amps.
In this way i would avoid some issues found with the original design.
I also intend to use long pins tube sockets to make things easier
Thanks a lot
Don't make the cap too big, this will increase leakage and most important
it might create nasty on / off transients.
Depending on your speakers 0.68 to 1 uF might be more appropiate.
 
Don't make the cap too big, this will increase leakage and most important it might create nasty on / off transients.
Depending on your speakers 0.68 to 1 uF might be more appropiate

Hi ! thanks a lot for the very kind and valuable advice. So any tube in a decent design could work as a buffere if i take the signal out of its cathode ? i am not an expert and this i need to be sure of.
Then i would like to find some tube sockets with longer pins ... that could help with in-air wiring ... to solder parts to the pin i mean. I am quite excited by this project.
I like what one tubes can provide in a all solid state chain. I was thinking also to a dac with tubes at the output as an alternative. Different approach. But just one tube on the signal path can do wonder to the sound.
I am sure of this.
Thanks again and kind regards, gino
 
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