Perhaps off topic here but in the absence of nfb valves are imo trickier to use with ordinary speakers than transistors. Why? Because it is impossible to get an acceptably low output impedance. Unless you go for a follower or a massively parallel stage.
You are right. But You should try to listen to a no nfb tube amplifier and explain yourself how could you renounce the clarity and truthfulness of its sound. I tried to raise the gain of the driver stage and compensate it to a normal level by the nfb, in order to increase the df. The open-loop bandwidth went down to 8KHz (from 40KHz) and I didn't like the final result. Better: I liked it but I preferred much better the no nfb version.
For this reason, I searched for something affordable (price and work) with no feedback from the output and I only could find the 108 clone.
I had the luck to listen to an OTL no nfb with a lot of 6C33C for a decent df, made by SiAudio and it is still the best of the best I have ever listened.
For this reason, I searched for something affordable (price and work) with no feedback from the output and I only could find the 108 clone.
I had the luck to listen to an OTL no nfb with a lot of 6C33C for a decent df, made by SiAudio and it is still the best of the best I have ever listened.
Would that be the A60+ designation? I cannot very well see the circuit, as it probably is not meant to be seen in its full Ali glory, but from what i do see it appears to be severely compromised compared to any of the Accuphase amps. No idea why, perhaps Accuphase paid for that
Do not hesitate, just push the "Buy Now" button. It simply pays-off. I have purchased two A60+ and three smaller A60. I also have tested A60+ and it sounds splendid indeed. Someone else on internet said its sound is "golden" and has gone that far to state that it has "euphoric tone". He is right it really sounds extraordinary. Just read this review.
I have also done extensive measurements: it measures even better than NHB-108. It is done right across the whole audio spectrum and beyond. I will repeat the measurements and make them soon public.
In addition to this the board incorporates a solid power supply and effective speaker protection. You only have to add your heat sinks large enough, transformers, transistors and capacitors.
Just take care: only capacitors with diameter 35mm and 10mm lead spacing will fit into this board. Initially I was afraid that just 4X10.000uF per channel wouldn't be enough, but it works indeed very well.
And: carefully with biasing - this is a wild beast and can quickly go incredibly hot.
In the few ongoing weeks I will try the smaller board with "just" three output pairs. But the rest is identical.
In addition to this you may chose large enough radiators and set higher bias.
I never wanted to purchase a Maos' Rollex and these days are long gone anyways. What I have observed over the past decade is that China is an emerging giant capable producing any high quality products, or even better if the customer is ready to pay the price.
They only have to learn the art of selling snake oil. The only obstacle is colonial mentality of potential customers.
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Well, yes, if anyone has ever asked that question, but the question itself is pointless anyways.
First, it involves personal perception and the answer to such question itself depends on preferences.
Second, the Chinese A60+ has almost unbeatable set of undeniable parameters. So, how should one prove superiority of the "original", except by using personal perception.
Finally, no one ever has claimed that A60+ is a clone of Accuphase A60. That was just a clumsy Chinese marketing wording "reference to" which means nothing.
Let me conclude with a wise German proverb:
Schönheit liegt im Auge des Betrachters.
or in plain English: Beauty is in the eye of the beholder.
And, honestly A60+ has beautiful sound and is quite adequate for a DIY project and that's exactly why we are here. So why shouldn't we simply start yet another thread:
A60(+) amp. Build this?
No offense meant and no attempt to start an of-topic conversation.
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I am a practical person I also keep my promises:
Here we are:
A60(+) amp. Build this?
Welcome aboard dear friends.
Here we are:
A60(+) amp. Build this?
Welcome aboard dear friends.
Yes, you're quite right though better way of learning the truth is without the need for (bitter) dispute, through polite dialog and without having to deal with fake "facts".No one should be offended, the discussion has moved on to another channel and this is good. And there is nothing terrible, the truth is born in the dispute.
Hi Erlend!
Have you soldered your amplifier or you've just purchased the "finished" board. There is a difference. I have meassured inferior bandwidth of "finished" board.
There were different "opinions" regarding the servo but it doesn't affect the sound quality at all, just eliminates the unwanted DC-drift, very efficiently. Also, speaker protection doesn't affect the sound too. Abandonment of speaker protection in the original was just a commercial trick.
But what does matter indeed is the quality of power supply. To eliminate hum it is necessary to build this amplifier as two separate channels, starting with transformers - two separate transformers, followed by separate channels.
I have found that danny_66 has provided an excellent guidelines how to build this amplifier properly. Unfortunately, his wise suggestions were literally suffocated in a flood of "wise" opinions and grumbling based on wrong interpretation of fake models.
To correct this, below I am re-posting an important post by danny_66. It is advisable to go back to the beginning of this thread to find reliable information. Look what he said at the opening: "a simulation is not the complete story but a nice guideline". I have seen some who wrongly consider simulation as the Holly Scripture. Based on fake data, oh my dear Lord.
Also, note that danny praises verions with 2 and 3 output pairs, while some have arrived the opposite conclusion just by looking at the schematics. Fake geniuses. Danny is most probably right about that. Fortunately, these days I have ordered 20 pairs of output transistors because there is a serious shortage of semiconductors worldwide.
Besides danny_66 I miss several wise and capable people who have abandoned this thread. I understand them.
Yep, a simulation is not the complete story but a nice guideline
Without a DC servo the DC bias is done by injecting DC at the signal input, before the first transistors.
So the input caps are needed to not offset the DC bias when there is DC on the input signal from the preamp or source.
Most commercial products have input/output caps, just to make them more foolproof.
But as DIYer I know very good what the previous component feeds to my amps, I hope
I use the following PCBs for 3 pairs or 2 pairs
but with the operating points of the transistors optimized for 4 ohm speakers by changing some resistor values.
The multiple pairs output have additional source resistors for better stability and matching of the output pairs.
I've also added speaker protection, added a 20watt 6ohm resistor to the open circuit for when the relays are not connected to the speakers, so the output stage has always a load.
Definitely use two transformers so you can build completely separated channels, with one transformer I had hum.
Regards,
Danny
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Hello everyone, I would like to raise again the issue of protecting speakers from DC at the output of the amplifier. My friend and I have collected several links. Please comment on these models and is there a strong advantage over relay protection, since the price difference is almost 4-5 times. Guardian-86: High-End Speaker Protection Circuit for use in DIY Amps – Neurochrome RTR SSR Speaker Protection Gen2 | Etsy Audio Solid State Relay (HPA-SS/Relay One) – Holton Precision Audio
Yet another different opinion without measurements and/or facts. Here is something else I would rely on with full confidence:
DC Servos
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