Euro2, thanks for your answer. Do you know it the PX300B is capable of being driven into A2? I have a new pair of them.
I don't know, it's take a position "in situ".
If driving tube (for example below of half dissipation power of maximum operating point, continuously increasing grid modulation) over positive grid voltage peek "will benefit" to increasing distortion (more than it's expected), less suitable for this operation.
A2 operation -in this case of 300B- does not mean that tube working all time with positive grid voltage.
When the grid voltage peek steps over to positive region, grid current (which is before in uA magnitude) started to flow (mA, even tens mA magnitude), IF driver capable serving it.
"Standard" driver unable to serve next tube's grid over 0V (to small anode current, too high output impedance etc.).
For me the A2 "capable" operation not "need" for more power, but it's a better solution to avoiding hard clipping of driver.
Read Thortsten -last- post here:
* 35 watt * 300B SE = super 300B + Class A2
It's roughly as attached, except that the operating point of the 300b is cooler at the moment, -50v bias. I've been listening to this amp now 24/7 for several days and I'm very pleased with it. The op-amp part needs developing - it's very basic at present, just a simple chi-fi pcb with a NE5532.
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Thanks Andy
I already use a DHT preamp.
Are you going to build the 10y? Have you settled on a schematic for it?
I already use a DHT preamp.
Are you going to build the 10y? Have you settled on a schematic for it?
I have built a version with a 10Y driver, but I'm not fully happy with the operating points. My concern at the moment is getting a really good op-amp stage. I'm having various problems getting my circuit build right but I do have a chi-fi stage working fine. Very cheap and simple, but it's reliable and sounds OK. Just single supply - I'm driving it with 15vDC from my bench supply. There are a few different NE5532 pcbs on eBay.
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Indeed - I have a couple of OPA2134. Would these be a direct substitute for NE5532? Just plug and play?
playing with some different DHT triode driver for my 300B amp , 26 71a , even a pair of rare AD1 with choke loading , i get mixed results the sound is nothing than spectacular but i missed the right tone that gave me the pentode driver .. as nothing is perfect the small signal IDHT pentode have some flaws too , the highs are less extended and clean as with the DHT triode driver.
last chance this week i will try the 2P29L in pentode mode perhaps it will be the gap between DHT and pentode 🙂
last chance this week i will try the 2P29L in pentode mode perhaps it will be the gap between DHT and pentode 🙂
Andy ,
Can you modify the dac to up the gain by x3? Might be as straightforward as a resistor change...
Can you modify the dac to up the gain by x3? Might be as straightforward as a resistor change...
That would be a very nice solution. However, the DAC is all SMDs. No leaded components. I've never worked with SMDs and I don't want to destroy the board! But yes, that would be the logical thing to do.
I have a Soekris DAC I haven't connected up yet. That might allow me to change the gain. I haven't worked out all the connections including the USB board. One thing at a time.
You may find that the output of the DAC has a potential divider, simply to get the output down to an industry standard value, like 0.5v. That'd mean just a jumper would be needed.
Another thing to consider is simply plugging in a Quad405-2 and trying that. If the volume is kept low then you are simply listening to an opamp anyway. The power transistors won't have anything to do and by comparison to these "little" valve amps, you'll never be able to drive it to clipping anyway.
kind regards
Marek
Another thing to consider is simply plugging in a Quad405-2 and trying that. If the volume is kept low then you are simply listening to an opamp anyway. The power transistors won't have anything to do and by comparison to these "little" valve amps, you'll never be able to drive it to clipping anyway.
kind regards
Marek
if you want a mix of solid state and tube better to build a discret Jfet line stage " a la Mr PASS sauce" than an Opamp stage 🙂
Good question. "Better" is maybe a simple way of putting it since there are a few considerations. A third tube stage for me would be very large - I use DHTs in filament bias and this means a filament supply with chokes in it. I don't want my tubes setup to get any bigger than it is now - currently 5 different chassis. I'd like to leave the amp as 4P1L in triode into 300b. I tried using the 4P1L as a pentode and gave up. And anyway, building a whole tube stage for x3 gain doesn't make much sense to me.
So what I would like to have is a 3x gain stage which is as small as possible, coming between the DAC and the 4P1L. You guys have already said "increase the gain of the DAC" and that would be an excellent solution if I could - it's all SMD except a socketed NE5532. Failing that I could use a step-up transformer which would need to be very good and would be expensive. That leaves a solid state stage which is cheap and easy to execute (when I sort out my glitches at present). Or a discreet device stage - as juanitox is suggesting - which I haven't even contemplated until I get optimum results out of an op-amp.
I have a very basic op-amp stage working right now and I like what I'm hearing. I'd like it better if I could optimise it.
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I don't think it works like that. As above, I only need an extra gain of x3. I want to preserve the sound of the 4P1L in triode exactly as it is. I could use a DHT stage with a tube with a mu of 3, but why? And I don't need any more gain than that. And solid state is very good at small signals.
So what would I do with a 12B4A with a mu of 6.5? I've made a preamp before with the 12B4A and it's no DHT, not in the same ballpark as a 4P1L in triode.
I have to agree with you that a few months ago I'd never have thought of putting an op-amp stage into a 300b amp, but I've been pleasantly surprised with the results.
I have a hard time understanding the idea that an NE5532 gain stage will ruin the sound of a tube amp. I mean, any modern recording has had the sound go through a dozen or more NE5532s in the recording process anyway. Those big mixer boards in studios are full of them. What's one more?
I mean, I get that this is a tube forum and we like our tubes (I love mine) but sometimes a chip is okay and gets a simple job done easily.
I mean, I get that this is a tube forum and we like our tubes (I love mine) but sometimes a chip is okay and gets a simple job done easily.
Andy,
If you read the Soekris DAC related topics, not accidentally used some DIYers the R2R DAC ladders as output, without any opamps.
Each additional stage cause more or less tone colouration.
If you have only one (music) source, the gain increasing there (in DAC) is satisfying solution, but you lose the opportunity of using more sources (the output amplifier sensitivity remains relative low).
IMHO the most obvious solution is using a low gain preamplifier, with some input possibility.
I can use my DAM1941 (raw output) or PCM63 (I/V transformer + tube output) DACs, or tube output CD player, or tube phono preamp (Gee! nowhere opamp in output signal path 😛pp ) through 801 (or 26/01a) preamplifier, despite my output amplifier has enough sensitivity.
If you read the Soekris DAC related topics, not accidentally used some DIYers the R2R DAC ladders as output, without any opamps.
Each additional stage cause more or less tone colouration.
If you have only one (music) source, the gain increasing there (in DAC) is satisfying solution, but you lose the opportunity of using more sources (the output amplifier sensitivity remains relative low).
IMHO the most obvious solution is using a low gain preamplifier, with some input possibility.
I can use my DAM1941 (raw output) or PCM63 (I/V transformer + tube output) DACs, or tube output CD player, or tube phono preamp (Gee! nowhere opamp in output signal path 😛pp ) through 801 (or 26/01a) preamplifier, despite my output amplifier has enough sensitivity.