I recently gave my granddaughter my Sony STR5600 and Kenwood KL5050 speakers which she has been begging me to give her for years. I had been using it in the bedroom as a stereo/TV sound system as I have some hearing loss and the speakers in most TVs are lacking for me.
So, I moved my spare 6P41S SE amp and FF125WK speakers to the bedroom, but found the amp does not have enough gain (TV output is very low and I had to crank the STR5600 past 3 O-Clock to hear it).
So I now need a pre-amp. Rather than design one, I decided to see what I could pick up from the Bay of E's for not so much.
I came across one advertised as "HiFi 12AX7 +12AT7 Tube Stereo Preamplifier Board Base On MATISSE Preamp".
Un-assembled kit for $40 plus $4 shipping. I messaged the seller for a schematic and received one several days later.
After entering it into LTSpice, I was pleasantly surprised to see that the distortion at 0.5Vrms out into 100K (6P41S input pot) was quite reasonable at 0.0004%. I was originally planning on redesigning it to use a different output tube, maybe a 12BH7 for better drive and load tolerance. After simulating it I decided to go with it as is for now to see how it sounds.
As it stands, I am waiting for some connectors to arrive to finish the build and start testing.
I was not able to find any reference to this board in searching the site.
Full construction time was less than 2 hours. They just don't supply input and output connectors, although the spacing supports them.
Has anyone else built one?
The design is basically parallel 12AX7s common cathode circuits cap coupled to parallel 12AT7 in common cathode with feedback from the output back to the cathode resistor of the 12AX7 stage.
So, I moved my spare 6P41S SE amp and FF125WK speakers to the bedroom, but found the amp does not have enough gain (TV output is very low and I had to crank the STR5600 past 3 O-Clock to hear it).
So I now need a pre-amp. Rather than design one, I decided to see what I could pick up from the Bay of E's for not so much.
I came across one advertised as "HiFi 12AX7 +12AT7 Tube Stereo Preamplifier Board Base On MATISSE Preamp".
Un-assembled kit for $40 plus $4 shipping. I messaged the seller for a schematic and received one several days later.
After entering it into LTSpice, I was pleasantly surprised to see that the distortion at 0.5Vrms out into 100K (6P41S input pot) was quite reasonable at 0.0004%. I was originally planning on redesigning it to use a different output tube, maybe a 12BH7 for better drive and load tolerance. After simulating it I decided to go with it as is for now to see how it sounds.
As it stands, I am waiting for some connectors to arrive to finish the build and start testing.
I was not able to find any reference to this board in searching the site.
Full construction time was less than 2 hours. They just don't supply input and output connectors, although the spacing supports them.
Has anyone else built one?
The design is basically parallel 12AX7s common cathode circuits cap coupled to parallel 12AT7 in common cathode with feedback from the output back to the cathode resistor of the 12AX7 stage.
Attachments
Last edited:
The heat sinks in the back are 2x filament regulators which I think are not necessary since this is not a phono-preamp, and a cap-multiplier filter for the B+ set at 400V (a nice addition).
The circuit looks sufficiently overkill to squash any possible objections. But, could I, of your generation, propose a heretical option? Everybody's hearing is different, but if yours is like mine, much decreased ability to follow dialog in various accents, loss of top two octaves, maybe a better solution for TV, where available, is to extract a center channel, where dialog is conventionally placed, so it can be adjusted in volume.
Yes, this means some semi-con electronics, three channels. I've gotten over it. Whatever works is my motto. Life is short.
All good fortune,
Chris
Yes, this means some semi-con electronics, three channels. I've gotten over it. Whatever works is my motto. Life is short.
All good fortune,
Chris
<< But, could I, of your generation, propose a heretical option? Everybody's hearing is different, but if yours is like mine, much decreased ability to follow dialog in various accents, loss of top two octaves, maybe a better solution for TV, where available, is to extract a center channel
My solution to clarity is a DHT stage, currently 26, into a EL12n triode output stage (mu=18). Just that and nothing else, fed by my Dac. No 9 pin tubes, no unwanted gain, no volume control since it's in software on my Mac. I hear everything clearly even at very low volumes. My TV and Internet all go through the same Dac/output stage so all dialogue is easy to follow.
My solution to clarity is a DHT stage, currently 26, into a EL12n triode output stage (mu=18). Just that and nothing else, fed by my Dac. No 9 pin tubes, no unwanted gain, no volume control since it's in software on my Mac. I hear everything clearly even at very low volumes. My TV and Internet all go through the same Dac/output stage so all dialogue is easy to follow.
Thanks Chris.
If I were designing something to build from scratch that would be an excellent idea. My plan here was simply to find something on ebay that (1) was inexpensive (LT $100 delivered), (2) would produce moderate gain at low distortion, and (3) could be assembled rather quickly (It only took 2 hrs). I am not even going to put this into a chassis for now, just mount it and the transformer, etc, on a piece of plywood and put it inside the console the TV sets on. (No kids around, so no safety issues).
This board is designed for tubes which are readily available, and as such might make a good project for others out there who are looking for a Preamp board to build to add to their system.
(I was going to modify it for tubes which are not readily available, but I have on hand should it not have performed as well as it seems it will.)
That said, a SS combiner with band pass filter from 200-4KHz followed by a chipamp and center speaker might be a good plan for the future. Thanks for the idea.
If I were designing something to build from scratch that would be an excellent idea. My plan here was simply to find something on ebay that (1) was inexpensive (LT $100 delivered), (2) would produce moderate gain at low distortion, and (3) could be assembled rather quickly (It only took 2 hrs). I am not even going to put this into a chassis for now, just mount it and the transformer, etc, on a piece of plywood and put it inside the console the TV sets on. (No kids around, so no safety issues).
This board is designed for tubes which are readily available, and as such might make a good project for others out there who are looking for a Preamp board to build to add to their system.
(I was going to modify it for tubes which are not readily available, but I have on hand should it not have performed as well as it seems it will.)
That said, a SS combiner with band pass filter from 200-4KHz followed by a chipamp and center speaker might be a good plan for the future. Thanks for the idea.