hi!! its my first post here!!!!!
does anyone knows where i can found plans for DPA-300B constraction.....
thanks a lot...
does anyone knows where i can found plans for DPA-300B constraction.....
thanks a lot...
Sorry to revive an old thread.
I purchased a used pair of Vacuum State DPA-330b amps.
I would like to upgrade the coupling caps. Presently they have 0.47uF installed.
I may be able to purchase a quad of 0.33uF CuTF at a nice price.
What are the cons with lowering the intended value.
I purchased a used pair of Vacuum State DPA-330b amps.
I would like to upgrade the coupling caps. Presently they have 0.47uF installed.
I may be able to purchase a quad of 0.33uF CuTF at a nice price.
What are the cons with lowering the intended value.
Hey jazbo8
They don't NEED upgrading. It's more WANT.
I put CuTF in my Atma-Sphere MA-1 amps, and I'm in love with the smoothness of this cap.
They don't NEED upgrading. It's more WANT.
I put CuTF in my Atma-Sphere MA-1 amps, and I'm in love with the smoothness of this cap.
Not having the schematic, it is hard to tell... but I guess it would change the LF characteristic a tad. You can always try it and find out.
If it was built to stock I cannot imagine that any change to components would represent an improvement to the circuit. Allen was anal about component selection so I cannot imagine you can better his hard won choices.
Shoog
Shoog
Hello Shoog
I'm glad you responded. I will leave cap values alone.
I have a more pressing problem. One of my SuperRegs is down.
1) Would you recommend changing both (one in each amp), or just the one that's broken.
2)I'm trying to figure out my current draw on the 300b's. Do you happen to know some of the hidden resistor values?
Bill
I'm glad you responded. I will leave cap values alone.
I have a more pressing problem. One of my SuperRegs is down.
1) Would you recommend changing both (one in each amp), or just the one that's broken.
2)I'm trying to figure out my current draw on the 300b's. Do you happen to know some of the hidden resistor values?
Bill
No benefit in replacing both. I have never seen a super-reg schematic in the public domain.
€150 seems excessive for what you get so I would attempt to fault find what has gone pop. Most likely one of the transistors. Its difficult to test transistors in circuit so it might require desoldering each one in turn and testing out of circuit. Start be testing the caps though.
Shoog
€150 seems excessive for what you get so I would attempt to fault find what has gone pop. Most likely one of the transistors. Its difficult to test transistors in circuit so it might require desoldering each one in turn and testing out of circuit. Start be testing the caps though.
Shoog
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Depends on the failure mode. Often transistors fail short. That's pretty easy to measure.
I'm with Shoog, though. Usually the silicon blows first, so start there.
Tom
I'm with Shoog, though. Usually the silicon blows first, so start there.
Tom
Thank you
Once powered on, it makes a 'tick' sound, like a relay switching going off. Any ideas?
Once powered on, it makes a 'tick' sound, like a relay switching going off. Any ideas?
It makes the relay clicking sound because there is an relay in the amp (controlled by the timer circuit). So I would first look into the timer circuit. It shouldn't be that complicated.
Regards,
Regards,
The design is in Allen's Cookbook, I have made a couple for the FVP5a Preamp I am building at present. I have had the circuit running for several hours so it appears to works !
Ref the dpa300b, I am having trouble locating a circuit diagram, I would like to see what makes it tick! Does anyone have a copy they can let me see?
Regards,
From talking with Allen — he came for a visit after his visit to the VSAC were he introduced the DPA300 — it is essentially a PP1c with 300Bs and a CCS on the cathodes to ensure perfect Class A PP operation (check out the baby huey for practical CCS). It was also distinguished by no electrolytics anywhere.
My partner heard the amp at VSAC and thot it amoungst the very best amps he has ever heard.
dave
My partner heard the amp at VSAC and thot it amoungst the very best amps he has ever heard.
dave
A major difference with the PP1c, apart from tube choice and CCS on output tube cathodes, is that the DPA300 features cathode followers between input and output stage.
PP1c would also benefit with these buffers as the cascode input stage is not very well able to drive the output stage because of it's very high output impedance; the PP1c I built suffered from HF loss because of this.
There are NO cathode followers
Sorry but there are no cathode followers on the DPA-300. The differential cascode stage consists of two 6H30pi valves as seen by the two pictures attached. There are no other valves apart from the two 300b outputs. Allen made the point that cathode followers were bad news and were not needed by using low Rp, high current valves such as the 6H30pi. While the output impedance is not low, it is the high current through the stage that matters.
Sorry but there are no cathode followers on the DPA-300. The differential cascode stage consists of two 6H30pi valves as seen by the two pictures attached. There are no other valves apart from the two 300b outputs. Allen made the point that cathode followers were bad news and were not needed by using low Rp, high current valves such as the 6H30pi. While the output impedance is not low, it is the high current through the stage that matters.
Attachments
I was under the impression the 300B amp used just the 6H30 cascodes as input/drivers? The PP2C "upgrade" of the PP1C features a change in input tubes from 6922 to 6H30 which would significantly lower the output impedance. I remember during discussion of the PP2C Allen noting that this arrangement would drive parallel 300Bs very well as is.
I could be wrong, though, and would be interested to know what is actually under the hood of a DPA300.
You are right, my bad 😱 The idea of CF's in the DPA-300 had somehow settled in my memory.
I built PP1C with 6922 input cascode and that was not very good in driving the pair of EL34 output tubes, but with 6H30 it should work much better.
Allen was not "against" cathode followers as such; his "super linear cathode follower" is a good example (high cathode load impedance).
Hello,
I don´t want anyone to misunderstand what i am going to say here now, but I have to say it.
The amplifier DPA-300B, It's described as a “differential” tube amplifier, the new is that Allen has also involved the Power output stage to bee “differential” (feeding the 300B:s), maybe for the first time I am not sure…, I think someone have done it before even with tubes, but can´t remember who did it
But it is of course a push-pull, despite claims on the Vacuum State website that it might be something else, the company can of course call it whatever they want, but the topology of the work method is obviously a push-pull amplifier.
I've listened to the amplifier and it's great, but I do not think the explanation lies only in the differential part ofthe amplifier, but I think it's the whole of the design that gives its fingerprints in sound quality positivity.
Seeing that Allen has been using the good output transformers from Swedish Lundahl, who are extremely good at handling winding technology in, especially push-pull output transformers, as the technique used makes the symmetry of both legs of the cores so well balanced, no other transformer manufacurer has this balance when they are completely "bobin" free.
I'm not the right guy to say what the"Differential" part of the amplifier has advantages over a more traditional connection of the output stage, but it would have been fun if comparisons had been made between these, but with blind tests of course, otherwise you do not know.
If the changes are placebo or real differences.
Regards
Goran
I don´t want anyone to misunderstand what i am going to say here now, but I have to say it.
The amplifier DPA-300B, It's described as a “differential” tube amplifier, the new is that Allen has also involved the Power output stage to bee “differential” (feeding the 300B:s), maybe for the first time I am not sure…, I think someone have done it before even with tubes, but can´t remember who did it
But it is of course a push-pull, despite claims on the Vacuum State website that it might be something else, the company can of course call it whatever they want, but the topology of the work method is obviously a push-pull amplifier.
I've listened to the amplifier and it's great, but I do not think the explanation lies only in the differential part ofthe amplifier, but I think it's the whole of the design that gives its fingerprints in sound quality positivity.
Seeing that Allen has been using the good output transformers from Swedish Lundahl, who are extremely good at handling winding technology in, especially push-pull output transformers, as the technique used makes the symmetry of both legs of the cores so well balanced, no other transformer manufacurer has this balance when they are completely "bobin" free.
I'm not the right guy to say what the"Differential" part of the amplifier has advantages over a more traditional connection of the output stage, but it would have been fun if comparisons had been made between these, but with blind tests of course, otherwise you do not know.
If the changes are placebo or real differences.
Regards
Goran
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