Have you ever generated any impedance plots for your speakers? It's fairly common for them to have significant peaks, especially around port resonances and crossover frequencies. I do not recall seeing any feedback in your amplifier design, so high impedance peaks in the load would likely result in measurable changes in the power delivery.
http://i69.photobucket.com/albums/i43/Ty_Bower/Chorus II/SpeakerTest/ChorusIIleftPR.gif
Impedance minima would also result in measurable changes in power delivery, and my suspicion is that the tweeter impedance is quite low at high frequencies - could well be related to XO design or the driver itself.
Here is a review of the S2 series (mine is the S3) with an impedance graph.
http://www.audioxpress.com/reviews/media/AX201DA.pdf
I expect the graph to be very similar to mine since there were no major updates (S2 already used Nautilus style tweeters, etc).
If I remember correctly the XO has a 2nd filter for the woofer and a 3rd order filter for the tweeter.
Thank you for your help!
http://www.audioxpress.com/reviews/media/AX201DA.pdf
I expect the graph to be very similar to mine since there were no major updates (S2 already used Nautilus style tweeters, etc).
If I remember correctly the XO has a 2nd filter for the woofer and a 3rd order filter for the tweeter.
Thank you for your help!
Bingo!
Here is a review of the DM602 S2 by Joseph D'Appolito, shows very clearly what the problem is. Have a look at figure 1 here:
http://www.audioxpress.com/reviews/media/AX201DA.pdf
IMO this speaker is not a very good match to any tube SE amplifier, or indeed any amp that does not use global negative feedback. The average impedance is about 5 ohms so IMHO the 4 ohm tap should be used. The implication here is that the efficiency is lower than stated based on 2.83V into 8 ohms - I think based on the average impedance (excluding peaks) of 5 ohms or so that the efficiency is probably close to 88dB.
This is a good speaker for use with higher powered PP tube amplifiers with feedback or the typical solid state amplifier for which it was clearly designed.
The effects of leakage inductance at high frequencies in your inexpensive OPTs will be worsened by a load that exhibits below expected impedances at HF so it could well be that a better transformer will help a little if these are really poor in this regard. Again I hope you have a 4 ohm tap! A zobel network tuned to the 24 ohm impedance maxima to level out the load impedance might not be such a bad idea either.. (or not..)
Edit: Looks like we both found the review link at about the same time.
Here is a review of the DM602 S2 by Joseph D'Appolito, shows very clearly what the problem is. Have a look at figure 1 here:
http://www.audioxpress.com/reviews/media/AX201DA.pdf
IMO this speaker is not a very good match to any tube SE amplifier, or indeed any amp that does not use global negative feedback. The average impedance is about 5 ohms so IMHO the 4 ohm tap should be used. The implication here is that the efficiency is lower than stated based on 2.83V into 8 ohms - I think based on the average impedance (excluding peaks) of 5 ohms or so that the efficiency is probably close to 88dB.
This is a good speaker for use with higher powered PP tube amplifiers with feedback or the typical solid state amplifier for which it was clearly designed.
The effects of leakage inductance at high frequencies in your inexpensive OPTs will be worsened by a load that exhibits below expected impedances at HF so it could well be that a better transformer will help a little if these are really poor in this regard. Again I hope you have a 4 ohm tap! A zobel network tuned to the 24 ohm impedance maxima to level out the load impedance might not be such a bad idea either.. (or not..)
Edit: Looks like we both found the review link at about the same time.
I don't have a 4 ohm tap. These OPTs were custom made, and for the sake of simplicity I asked them to be tailored on my (nominal) 8 ohm speakers.
Last edited:
How does one determine the correct C and R values for a zobel, and is the zobel best placed at the amp output or the speaker input?
Guys, what do you say about converting this SE amp into Parallel Feed one? I did it with my ECC82+6C4C SE. Used the same OPT, just added a choke and a cap. The results were satisfactory with my amp.
Is it possible that connecting the OPT windings the "wrong" way (primary with B+ connection to the plate or wrong end of secondary grounded) could result in different parasitic reactances? Maybe try switching connections around.
Sorry for resurrect this post. As I am kind of interested in building a 2A3 headphone amp. Yeah, I knew there will be all sort of questions about why use 2A3 as a headphone amp, but let's assume I am a strange person that want to have about 1~2 W output for a headphone amp. Since I am such a newbie, I have several humble questions and hoping can get some help from people with much deeper understanding about how tube work.
1) How much is the gain for this circuit and how to calculate it?
2) How much is the idle current of the 2A3 and plate resistance? Can I use LL2765 as output transformer? It seems by default, LL2765's max idle current is 30ma. The LL2765's primary is about 5K, although it can change when hooking up with different can.
3) This is a bit tricky. If I want to use dc filament supply for 2A3, what kind of change need to be made?
These questions are not easy get solution for me. Really hoping to gain some knowledge about how these question work out. Tks!
1) How much is the gain for this circuit and how to calculate it?
2) How much is the idle current of the 2A3 and plate resistance? Can I use LL2765 as output transformer? It seems by default, LL2765's max idle current is 30ma. The LL2765's primary is about 5K, although it can change when hooking up with different can.
3) This is a bit tricky. If I want to use dc filament supply for 2A3, what kind of change need to be made?
These questions are not easy get solution for me. Really hoping to gain some knowledge about how these question work out. Tks!
Tube maker/seller suggestions are in the datasheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/021/2/2A3.pdf
You don't need 3.5 Watts. You can run a lower current and a higher impedance. The peak grid drive for max output is similar to the "Grid Voltage". For headphones you may not need that much, but it is common sense to have nearly that much (or else you could have picked a less-unsuitable tube).
http://www.mif.pg.gda.pl/homepages/frank/sheets/021/2/2A3.pdf
You don't need 3.5 Watts. You can run a lower current and a higher impedance. The peak grid drive for max output is similar to the "Grid Voltage". For headphones you may not need that much, but it is common sense to have nearly that much (or else you could have picked a less-unsuitable tube).
2A3 headphone amplifier can be done, but the mechanical design must be considered as well, or the microphony will ruin the pleasure. Starting point is a lightweight sub-chassis to hold the UX4 tube socket, and isolation mounting from there to the amp's enclosure.
Example here: 01A question
Tks for this notice. I have never think about this issue, but yes this definitely raise some concerns and need to be careful.
Hello,
Apologies for resurrecting this old thread, didn't want to create a duplicate one.
Can you please give your feedback/criticism of the following schematic of 6SN7-2A3 SET, is there anything obviously wrong with it?
It was inspired by Kismet 2A3 amp but with a 6SN7 driver tube and interstage transformer coupling.
Thanks in advance,
Igor.
Apologies for resurrecting this old thread, didn't want to create a duplicate one.
Can you please give your feedback/criticism of the following schematic of 6SN7-2A3 SET, is there anything obviously wrong with it?
It was inspired by Kismet 2A3 amp but with a 6SN7 driver tube and interstage transformer coupling.
Thanks in advance,
Igor.
Attachments
Hi Igor
You are using an IT but doing cathode bias, and you are using 6SN7 as input/driver.
Then you are doing cap input power supply (instead of choke input).
I know exactly how this amp will sound. 🙁
Ian
You are using an IT but doing cathode bias, and you are using 6SN7 as input/driver.
Then you are doing cap input power supply (instead of choke input).
I know exactly how this amp will sound. 🙁
Ian
Thanks a lot for your input, Ian, Francois.
Are you referring to potential resonance between inductance of IST and capacitance of cathode bypass cap? Is there a way to calculate/experiment with capacitor value to avoid the issue?
I thought 6SN7 is considered a classical driver tube? It has a reasonable rp of 7kΩ and decent current capabilities. Is this still too high for an IST coupling?
Yes, it's biased a bit colder than classical 250V/60mA operating point, want to be gentle on the tubes.
Would you say that the best sounding 2A3 preamps are usually the ones where the 2A3 tube is driven by a 6SN7 tube?
Actually, I know very little about tube amp design. And the only tube hardware I have is the Don Sachs DS2 preamp I bought early this year. http://www.dsachsconsulting.com/custom line stage.html
Can't audition it until my 93db speakers are finished. I'll be using that preamp to drive my First Watt F4 amp. https://www.firstwatt.com/product/f4/ At 25 wpc into 8 ohms the F4 will easily drive my speakers. And my understanding is that the DC coupled zero feedback F4 was intended to be act as a "chameleon"; sounding very much like whatever's driving it.
But as an alternative to using the DS2 preamp to drive the F4 amp, are you familiar with any 2A3 preamps? I thought of the 2A3 after reading that its sound has a lot in common with that of the 300B. If yes, please suggest 3 or more excellent preamps for ~ $2.5 to 3K.
Actually, I know very little about tube amp design. And the only tube hardware I have is the Don Sachs DS2 preamp I bought early this year. http://www.dsachsconsulting.com/custom line stage.html
Can't audition it until my 93db speakers are finished. I'll be using that preamp to drive my First Watt F4 amp. https://www.firstwatt.com/product/f4/ At 25 wpc into 8 ohms the F4 will easily drive my speakers. And my understanding is that the DC coupled zero feedback F4 was intended to be act as a "chameleon"; sounding very much like whatever's driving it.
But as an alternative to using the DS2 preamp to drive the F4 amp, are you familiar with any 2A3 preamps? I thought of the 2A3 after reading that its sound has a lot in common with that of the 300B. If yes, please suggest 3 or more excellent preamps for ~ $2.5 to 3K.
This probably should have been started as a new thread.
Generally, a 6SN7 driving a 2A3 is called a Low Power Amplifier, not a preamp.
It sounds like you are trying to get a 2A3 "preamp" to drive a much more powerful amplifier, and get a particular sound.
The F4 states that it does not have any (Voltage) gain.
Start with a 2A3 amplifier that delivers 3 Watts into an 8 Ohm speaker.
Then output the 2A3 amplifier (call it a preamplifier if you want) into an F4 input.
The F4, with no voltage gain will put out exactly the same voltage, and so the 8 Ohm speaker will still only get 3 watts.
Now the F4 claims it has large Current Gain. Great!
Just parallel 8 each 8 Ohm loudspeakers, and you will get 24 Watts into the 8 paralleled loudspeakers.
Probably not what you were thinking, and probably not what you want, Right?
Question: do all the components in a stereo have Positive Synergy, or Negative Synergy?
It is a System, not just a random assembly of possibly non-compatible products.
Taking your chances with a random grouping of products, you are better off going to Las Vegas and play the Craps tables, you will have better luck.
A quote from "Sound Practices" magazine:
"I never met a 2A3 amplifier that I did not like".
(all good 2A3 designs that are properly built with quality parts).
How you properly group that 2A3 amplifier with other products is paramount . . . it ends in success or failure.
Generally, a 6SN7 driving a 2A3 is called a Low Power Amplifier, not a preamp.
It sounds like you are trying to get a 2A3 "preamp" to drive a much more powerful amplifier, and get a particular sound.
The F4 states that it does not have any (Voltage) gain.
Start with a 2A3 amplifier that delivers 3 Watts into an 8 Ohm speaker.
Then output the 2A3 amplifier (call it a preamplifier if you want) into an F4 input.
The F4, with no voltage gain will put out exactly the same voltage, and so the 8 Ohm speaker will still only get 3 watts.
Now the F4 claims it has large Current Gain. Great!
Just parallel 8 each 8 Ohm loudspeakers, and you will get 24 Watts into the 8 paralleled loudspeakers.
Probably not what you were thinking, and probably not what you want, Right?
Question: do all the components in a stereo have Positive Synergy, or Negative Synergy?
It is a System, not just a random assembly of possibly non-compatible products.
Taking your chances with a random grouping of products, you are better off going to Las Vegas and play the Craps tables, you will have better luck.
A quote from "Sound Practices" magazine:
"I never met a 2A3 amplifier that I did not like".
(all good 2A3 designs that are properly built with quality parts).
How you properly group that 2A3 amplifier with other products is paramount . . . it ends in success or failure.
Last edited:
That’s exactly what I was trying to achieve, if the 2A3 and 300B do indeed sound similar and produce about the same big 3D soundstage. At 8 wpc a 300B SET should easily run my 93db speakers, but a really good integrated, let alone mono blocks, are more than I want to spend, this year at least, and the needed DIY skills are not there. .
Search [ 2a3 tube preamp ] and see several 2A3 preamps, such as
https://www.wbamp.com/product/blazebird-dual-mono-class-a-tube-preamplifier/
Said Don Sachs about my DS2 preamp, “As for specs,….. flat from probably 15 Hz to well beyond 30 KHz, and gain was roughly 18-19 dB depending on how it was set up. The low end frequency response with an amp was dependent on coupling cap size. Generally a 1.5 uF cap would get you down below 20Hz into a 30K load. Moving to a 2.2 uF cap would get you down to 10K.”
Thus, with gain of 18db and input voltage from my DAC of at least 2v, output will be 14.2v.
https://sengpielaudio.com/calculatorVoltagePower.htm So, ~ 14 wpc; loads of power.
But presumably with a 6SN7/2A3 preamp, the 2A3 output tube will vastly reduce that voltage, converting it to current, thereby producing power but only ~3 watts; too little for driving my 93db speakers.
Okay, so I struck out with finding a suitable a 300B soundalike tube.
Thanks for ending my wild goose chase. I'll just have to save up to buy the real McCoy next year, though via that preamp idea I was also hoping to avoid having to audition multiple 300B amps.
Too bad Tripathi gave away his TA2020 chip amp.
Last edited: