Hi - does anyone have a source for A10/A12 OUTPUT transformers - the so-called "uprated" ones? They are encapsulated so not as plentiful on the usual places. The original amp suppliers want an absolute fortune for them no not going there. I want to use an existing A10 chassis (bare) which is pre-drilled. I no longer have my A10 as sold it a few years ago to go for a Yaqin MC100B.
Encapsulated is my preference for better aesthetics, rather than trying to mount a non-encapsulated with wires showing.
Many thanks in advance
Encapsulated is my preference for better aesthetics, rather than trying to mount a non-encapsulated with wires showing.
Many thanks in advance
Well, I am learning in fast pace. Modding an amp is easier than I thought. Especially with all the great tutors and tutorials.
While working on the BRZHIFI A20, I have learned the Reisong A10 was initially designed for 6v6 tubes. Link to forum
The EL34 Cathode resistors were already lowered to 300Ohm/3w to accomodate a better voltage in the BRZHIFI A20.
I also learned the cathode resistors in the pre-amp stage for the 6n2 tubes are 4k in the BRZHIFI instead of the 2k on the Reisong . While modding the amp I discovered why. I must say the engineer at BRZHIFI did a pretty decent job getting most out of the amp within the given pricepoint and task at hand. He also cleverly masked some weaker points of the amp that unveiled themselves while upgrading the amp.
The BRZHIFI A20 is already in triode mode out of the factory. I can only conclude the BRZHIFI A20 is the better version of the A10, purely looking at the schematics and the design choices made by the manufacturer already. It even came with a Russian rectifier tube over the Chinese one in the A10.
Modifications I have done in the chonological order
1) Replace coupling caps
I have replaced the stock Vishay 220nf with Auricap XO 220nf versions.
The sound cleared up dramatically and the frequency response and sustain below 100Hz got completely resored, as also the higher frequencies became better audible. It sounds super smooth, but something also went missing!
It became clear the amp had some more flaws to adress.
While the dynamics had been restored now, the amp now sounded lifeless. As it the soul was drained by some dementors. Also I noticed a lot of unpleasant distortion going on in the upper ranges (above 10khz). It also became clear the engineer at BRZHIFI matched all the parts in such a way to get the most out of the amp voice wise. The stock coupling caps provided the "soul" to the voices which was now gone. Also the stock caps were more rolled of the in the lower and higher frequency band, masking some flaws in the amp.
I'd say this was about a 40% improvement over the stock caps despite the amp losing it's "soul".
2) Bypassing EL34 cathode resistor
I read that bypassing the cathode resistor increases gain and can deliver better sound. I installed some 2000uf Cambridge Audio (probably rebranded Nichicon) caps. Immediately the soundstage came more to life due to 2nd harmonic distortion. It was about a 15% improvement.
2) Experimenting with different cathode resistor values on the chinese 6n2 's
I read that the Reisong A10 is using a probably too high value in it's pre-amp stage running the 6n2's quite cold. The Reisong A10 uses 2k resistors, the BRZHIFI uses 4k resistors which are bypassed.
I experimented with different values: 840 Ohm, 1k and 2k.
Based on this article I installed the 840 Ohm resistor. While I noticed an improvement in the 2nd harmonic, it became VERY clear the 6n2's are the limiting factor in further upgrading the sound. While the 2nd harmonic had increase, also have all the other distortions resulting in an even more muddy sound and more distortion in the higher end of the spectrum.
I reverted back to the original value of 4k.
3) Replacing the Chinese 6n2 with Voskhod 6n2-ev
While working on this amp, I ordered some NOS Voskhod 6n2-ev 's. I read that they should improve the soundstage and give better treble. Both things that the stock ones are missing.
When I finally received them, I noticed the immense difference in the build quality. The Voskhod is built way better overal. This looks promising!
In installed them, using the stock 4k cathode resistor. Wow! What a difference that made! Not only did the holographic image improve, also did indeed the higher end of the frequency spectrum. Also the unpleasant distortions are gone as far as I can hear!
This made a 60% improvement in the system.
4) Lowering cathode resistor value on the Voskhod 6n2-ev
Now with better tubes installed, I decided to lower the cathode resistor values once again.
I decided to go for 1k as skunkie uses this in her A10 / A12 modification.
And wow did this improve the sound enormously! The voices are really singing like they are in my room.
The holographic image improved a little also. And best of all: No added unpleasant distortion. The sound is very clear.
Overall I would say this is another 60% improvement over simply replacing the tubes.
Overall impressions in retrospect:
I'd say this is a nice amp to learn the basics of tube amp design. It was at least for me. As you can see in the pictures I also own a Thule Spirit IA60. Great solid-state amp which I use as a reference. With the mods done I am very impressed of that the BRZHIFI A20 can deliver. When I first got the amp, I could not decide which one to keep. I decided to keep the BRZHFI A20 to see if it would grow on me. But something still was missing. After the mods that might actually change! I will give it some more days and that will switch back to the Thule to see which I like better. Ofcourse the Thule is "better" in every single way on paper. It has wayyy more power, wayyyy better highs. But it does not have a "soul" like the BRZHIFI A20 does now. I guess that simply comes down to 2nd harmonic distortion.
Some pictures:
While working on the BRZHIFI A20, I have learned the Reisong A10 was initially designed for 6v6 tubes. Link to forum
The EL34 Cathode resistors were already lowered to 300Ohm/3w to accomodate a better voltage in the BRZHIFI A20.
I also learned the cathode resistors in the pre-amp stage for the 6n2 tubes are 4k in the BRZHIFI instead of the 2k on the Reisong . While modding the amp I discovered why. I must say the engineer at BRZHIFI did a pretty decent job getting most out of the amp within the given pricepoint and task at hand. He also cleverly masked some weaker points of the amp that unveiled themselves while upgrading the amp.
The BRZHIFI A20 is already in triode mode out of the factory. I can only conclude the BRZHIFI A20 is the better version of the A10, purely looking at the schematics and the design choices made by the manufacturer already. It even came with a Russian rectifier tube over the Chinese one in the A10.
Modifications I have done in the chonological order
1) Replace coupling caps
I have replaced the stock Vishay 220nf with Auricap XO 220nf versions.
The sound cleared up dramatically and the frequency response and sustain below 100Hz got completely resored, as also the higher frequencies became better audible. It sounds super smooth, but something also went missing!
It became clear the amp had some more flaws to adress.
While the dynamics had been restored now, the amp now sounded lifeless. As it the soul was drained by some dementors. Also I noticed a lot of unpleasant distortion going on in the upper ranges (above 10khz). It also became clear the engineer at BRZHIFI matched all the parts in such a way to get the most out of the amp voice wise. The stock coupling caps provided the "soul" to the voices which was now gone. Also the stock caps were more rolled of the in the lower and higher frequency band, masking some flaws in the amp.
I'd say this was about a 40% improvement over the stock caps despite the amp losing it's "soul".
2) Bypassing EL34 cathode resistor
I read that bypassing the cathode resistor increases gain and can deliver better sound. I installed some 2000uf Cambridge Audio (probably rebranded Nichicon) caps. Immediately the soundstage came more to life due to 2nd harmonic distortion. It was about a 15% improvement.
2) Experimenting with different cathode resistor values on the chinese 6n2 's
I read that the Reisong A10 is using a probably too high value in it's pre-amp stage running the 6n2's quite cold. The Reisong A10 uses 2k resistors, the BRZHIFI uses 4k resistors which are bypassed.
I experimented with different values: 840 Ohm, 1k and 2k.
Based on this article I installed the 840 Ohm resistor. While I noticed an improvement in the 2nd harmonic, it became VERY clear the 6n2's are the limiting factor in further upgrading the sound. While the 2nd harmonic had increase, also have all the other distortions resulting in an even more muddy sound and more distortion in the higher end of the spectrum.
I reverted back to the original value of 4k.
3) Replacing the Chinese 6n2 with Voskhod 6n2-ev
While working on this amp, I ordered some NOS Voskhod 6n2-ev 's. I read that they should improve the soundstage and give better treble. Both things that the stock ones are missing.
When I finally received them, I noticed the immense difference in the build quality. The Voskhod is built way better overal. This looks promising!
In installed them, using the stock 4k cathode resistor. Wow! What a difference that made! Not only did the holographic image improve, also did indeed the higher end of the frequency spectrum. Also the unpleasant distortions are gone as far as I can hear!
This made a 60% improvement in the system.
4) Lowering cathode resistor value on the Voskhod 6n2-ev
Now with better tubes installed, I decided to lower the cathode resistor values once again.
I decided to go for 1k as skunkie uses this in her A10 / A12 modification.
And wow did this improve the sound enormously! The voices are really singing like they are in my room.
The holographic image improved a little also. And best of all: No added unpleasant distortion. The sound is very clear.
Overall I would say this is another 60% improvement over simply replacing the tubes.
Overall impressions in retrospect:
I'd say this is a nice amp to learn the basics of tube amp design. It was at least for me. As you can see in the pictures I also own a Thule Spirit IA60. Great solid-state amp which I use as a reference. With the mods done I am very impressed of that the BRZHIFI A20 can deliver. When I first got the amp, I could not decide which one to keep. I decided to keep the BRZHFI A20 to see if it would grow on me. But something still was missing. After the mods that might actually change! I will give it some more days and that will switch back to the Thule to see which I like better. Ofcourse the Thule is "better" in every single way on paper. It has wayyy more power, wayyyy better highs. But it does not have a "soul" like the BRZHIFI A20 does now. I guess that simply comes down to 2nd harmonic distortion.
Some pictures:
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