As I wrote in earlier post:
Recently I purchased an amazing low cost SET integrated amplifier: MP-401 EL156 Integrated Amplifier [MP-401] - $599.99 : Musical Paradise - Audio Art . It's the first SET I owned or listened to and I'm highly impressed by it's sound quality, which, as I understand, is to be expected from good SET amps. This amp comes with Chinese EL156 and it can accept various tubes. I tried it with current production 6550 and KT88, but I like best the sound of the EL156.
Alas, this amp with it's declared 15Watt doesn't have enough power to drive my speakers to their full ability. Also, in high listening volume it distorts.
Being retired I cannot afford buying a commercial good SET with enough power (>20W). Such amps are way beyond my means.
Consulting a guy I know with over 20 years of experience building tube amps, he told me that the problems I encountered with this amp are probably due to poor design and low quality OPT. He said that EL156 SET, deigned properly and with good OPT, should give me enough power to drive my speakers which have sensitivity of 91dB and only 2 elements and it should sound great.
So, I decided to build an amp based on EL156 and pay the cost of good quality OPT's and chokes. That much I can afford.
As for the topology, he suggested 2 stages only. Also he said that the best approach is anode choke loaded driver, since anode CCS adds high order harmonic distortion.
The schematic of my initial idea is posted below.
From the triode mode anode curves, what I got is over 30W output.
PSU schematic will follow.
All comments and suggestions are welcomed.
Recently I purchased an amazing low cost SET integrated amplifier: MP-401 EL156 Integrated Amplifier [MP-401] - $599.99 : Musical Paradise - Audio Art . It's the first SET I owned or listened to and I'm highly impressed by it's sound quality, which, as I understand, is to be expected from good SET amps. This amp comes with Chinese EL156 and it can accept various tubes. I tried it with current production 6550 and KT88, but I like best the sound of the EL156.
Alas, this amp with it's declared 15Watt doesn't have enough power to drive my speakers to their full ability. Also, in high listening volume it distorts.
Being retired I cannot afford buying a commercial good SET with enough power (>20W). Such amps are way beyond my means.
Consulting a guy I know with over 20 years of experience building tube amps, he told me that the problems I encountered with this amp are probably due to poor design and low quality OPT. He said that EL156 SET, deigned properly and with good OPT, should give me enough power to drive my speakers which have sensitivity of 91dB and only 2 elements and it should sound great.
So, I decided to build an amp based on EL156 and pay the cost of good quality OPT's and chokes. That much I can afford.
As for the topology, he suggested 2 stages only. Also he said that the best approach is anode choke loaded driver, since anode CCS adds high order harmonic distortion.
The schematic of my initial idea is posted below.
From the triode mode anode curves, what I got is over 30W output.
PSU schematic will follow.
All comments and suggestions are welcomed.
Attachments
You've got 50W quiescent dissipation. 30W output sounds very optimistic figure for triode mode. Can you post the loadline plot (which I assume you have handy since you calculated the relevant values for your schematic) ?
Preamplifier cathode resistor, something isn't quite right there (U = R * I, but not in your case of 1.4V, 50R and 22 mA).
By the way, don't worry about calculating things out to two digits past decimal point, your real life tube is likely to deviate from your calculation by 10% or so anyway 🙂
Preamplifier cathode resistor, something isn't quite right there (U = R * I, but not in your case of 1.4V, 50R and 22 mA).
By the way, don't worry about calculating things out to two digits past decimal point, your real life tube is likely to deviate from your calculation by 10% or so anyway 🙂
In the driver, Ia is 22mA and Ig2 is 6mA, so Ik is 28mA which drops 1.4V over 50R.
A copy of anode curves for triode mode with 3K dynamic load is attached.
On the 3K load line I plotted the delta voltage and delta current between Vg=0V and VG=-48V, multiplied the 2 which gave me peak power and divided that by 2 which gave me approximate RMS power.
A copy of anode curves for triode mode with 3K dynamic load is attached.
On the 3K load line I plotted the delta voltage and delta current between Vg=0V and VG=-48V, multiplied the 2 which gave me peak power and divided that by 2 which gave me approximate RMS power.
Attachments
You've got 450V peak to peak and 140 mA peak to peak. In order to do the "divide by 2 to get RMS value" thingy you need to use peak values (wrt quiescent point) only, not peak to peak.
450 p-t-p = 225V peak = 160V RMS
140 mA p-t-p = 70 mA peak = 50 mA RMS
Pout(RMS) = V(RMS) * I(RMS) = 8W in your case
The "divide by 2" shortcut works because there is a 2^(1/2) factor in each term (U and I) when calculating RMS value from peak, and 2^(1/2) * 2^(1/2) = 2. When using p-t-p values you should be dividing by 8 to get RMS power value.
Sorry Joshua, but you must have some kind of error in your calculations. You will not get over 10W out. Even in pentode mode you will not be near 30W.
You get a p-t-p swing of ca 460V. 460/2=230V peak, rms is 163V. 163*163/3000=9W
To lighten the burden of the tube, don´t go over 40-45W Pd.
If you want as much power as possible with low distortion a Schade D3a/EL156 could be an option.
EDIT: Ooops Arnulf, our posts crossed😀
You get a p-t-p swing of ca 460V. 460/2=230V peak, rms is 163V. 163*163/3000=9W
To lighten the burden of the tube, don´t go over 40-45W Pd.
If you want as much power as possible with low distortion a Schade D3a/EL156 could be an option.
EDIT: Ooops Arnulf, our posts crossed😀
On the 3K load line, at Vg=0 Va is about 162.5V and Ia is about 170mA while at Vg=-48 Va is about 620V and Ia is about 20mA. So, dV is 457.5V and dI is about 150mA. Multiplying dV by dI gives 68.62Watt. These numbers are for p2pV and p2pI, thus it is peak instantaneous power. Thus, dividing peak power by 2 gives approximate RMS power for sine wave, which in this case is 34.31Watt. Look here: How to Design an SE Power Amplifier .
I don't know right now what is the idle anode power consumption since I don't know yet the DC resistance of the OPT which is to be ordered from Sowter. Once I'll know the DC resistance of the OPT, the idle working point will be finalized and I intend not to go over 40Watt at idle. While listening to actual music, peak output power is very seldom reached, so safety power margin is usually given at idle.
I don't know right now what is the idle anode power consumption since I don't know yet the DC resistance of the OPT which is to be ordered from Sowter. Once I'll know the DC resistance of the OPT, the idle working point will be finalized and I intend not to go over 40Watt at idle. While listening to actual music, peak output power is very seldom reached, so safety power margin is usually given at idle.
What do you mean by Schade? Do you mean omitting the coupling capacitor? I don't think it's possible with driver's anode choke loaded. Right now I don't want to use anode CCS.
Optimistic isn't the word, to be blunt, dreaming is closer.
There is NO WAY you will have over 50% efficiency from a single SE triode in Class A.
I don't care what your curves may say, I predict from experience that with 50 watts anode + screen dissapation, you's be lucky to actually get 25% efficiency, after OPT losses etc, which equals 12 1/2 watts, unless you are happy with 10% distortion.
If you force the EL156 into Class A2 you might get more power, but a pentode drive can't do that without the addition of something like a CF driver.
So the 15 watts claimed for your Chinese amp is also doubtful, but as you have it there, run a power test on it. Find the max output before clipping, then back down until the distortion is acceptable. I expect you will be in for a disapointment.
The other point is if you do have 15 watts now and it's not loud enough, then 20 watts will not make any difference at all. To double your volume you need 10X the power - TEN TIMES - so a big beefy P-P amp with 4 KT88s per ch (or 4 x EL156) is more like it.
Sorry to be so down on your plans, but as money is short, you can't afford to take too many blind alleys.
Regards, Allen
Thanks Allen.
I don't lack loudness with the present amp, it only distorts and seem to be choked on loud listening levels. I have a power amp with PP 6550 and I don't like its sound at all. It seems to me that no PP amp can give the details and micro-dynamics that a SET amp gives.
I don't lack loudness with the present amp, it only distorts and seem to be choked on loud listening levels. I have a power amp with PP 6550 and I don't like its sound at all. It seems to me that no PP amp can give the details and micro-dynamics that a SET amp gives.
Then you have been listening to inferior P-P amps.
If you send me (aw@vacuumstate.com) your email addess, I'll send you the schematic of a KT88/EL156 P-P amp that will match and most likely better the sound of any SE amp you are likelyto hear. Maybe you can rebuild your P-P amp to this new circuit.
Regards, Allen
Ditto.
The theoretical maximum efficiency for a SE class A amp is 50%. A2 operation is required to get that much. Most tubes run far less than this. My Simple SE with a KT88 in triode runs about 400 volts of DC across the tube and I often run the current up near 100 mA to tighten up the bass. The amp prodces about 7 or 8 watts in triode. This puts the efficiency in the 18 to 20% range.
On the other hand I have an 845SE amp that runs in A2 and I get 40 watts out of it when I push the Chinese tubes to 100 watts of dissipation. I don't crank the NOS RCA's nearly that hard. It is the most efficient SE amp that I have ever built (except for the one that used a DSP modulated power supply).
At either rate you are going to fall somewhere within these extremes depending on the driver circuitry, the OPT losses and how hot you bias the tube. Expect 8 to 15 watts in A1 and maybe 20 watts if you do A2 exactly right. This requires a stout driver like a mosfet, and an output tube that saturates at a very low voltage.
That said if most of your distortion is on the bass notes the problem is likely cheap OPT's that are saturating. So when you get yout Sowter transformers, wire them into your existing amp and see what happens. You might be pleasantly surprised.
Distortion is mostly in the mid-high frequencies, though low frequencies also distort a bit.
I'll try to loan for a short while a good SET of about 15Watt to se if it doesn't distort with my speakers on high listening levels.
I'd like to remain in A1 for sound quality and EL156 will probably burn out in A2. Furthermore, I'd like to choose a tube for how it sounds, rather than for how hard I can drive it.
Maybe a parallel SE with EL156's. That could get you close to 20W on a stiff power supply.
But if you have already ordered OPT's then that option is probably out, as the primary impedance will be too high for PSE.
But if you have already ordered OPT's then that option is probably out, as the primary impedance will be too high for PSE.
These are not peak values (peak = with regards to center point, that is quiescent point), they are peak to peak values, hence the 2^(3/2) factor in each term for combined factor of 8.
Check out the URL you mentioned above once again and refer to picture with the loadline (the bottommost one of the article). You'll notice that the author is referring to peak values and that peak values are not full delta U and delta I, rather they are half of those values (third paragraph down from the picture with loadline; read the values off the chart and you'll surely notice where you went wrong).
Don't worry about DC resistance, it is usually negligible compared to full impedance (shouldn't be more than 500R in your case, and it's probably less than half that value). There is more variation to tube parameters from datasheet charts (10+%) than the effect of DC resistance.
In single-ended amplifiers anode dissipation is usually maximum in quiescent point (= no output). With loud music (= full output swing) anode dissipation goes down. This is the reason why any safety margin should be set at idle.
Hey Joshou,
Once again after that 4-5 of us have explained that power will not be over 10W, so here we go again😉:
If we assume that your line is right we get the following theoretical figures:
458V peak to peak gives us 229V peak. 229*0,707 gives us 162V RMS. As P=V^2/R we get 162^2/3k=9W.
You can also doublecheck by using the two examples in Telefunken datasheets and count backwards.
About Schade you will find lots of info here if use "Search" in the upper right corner. In short it gives you pentode effiency with close to triode performance. The output tube must be driven by a current-source though. This means you use the D3a pentode-connected.
Good luck with your amp whatever you choose to build.
Once again after that 4-5 of us have explained that power will not be over 10W, so here we go again😉:
If we assume that your line is right we get the following theoretical figures:
458V peak to peak gives us 229V peak. 229*0,707 gives us 162V RMS. As P=V^2/R we get 162^2/3k=9W.
You can also doublecheck by using the two examples in Telefunken datasheets and count backwards.
About Schade you will find lots of info here if use "Search" in the upper right corner. In short it gives you pentode effiency with close to triode performance. The output tube must be driven by a current-source though. This means you use the D3a pentode-connected.
Good luck with your amp whatever you choose to build.
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I'm not sure why your SE amp you bought has so many driver tubes in it, but you could check with a scope where the clipping is occurring, it may be at the driver stage - you never know.
Strangely my Sweet Peach FU50 throws out more power than I need for my 87dB/Watt X-718 speakers and that's a cheap amp, running off a 435V B+ idling at 55mA, so I'm puzzled why yours does not. It also only needs two driver tubes in total (one of the three is for show) for an integrated amp.
BTW a Sweet Peach + the mods (see the thread) are probably cheaper than you buying the bits separately, and it sounds awesome 😉
Strangely my Sweet Peach FU50 throws out more power than I need for my 87dB/Watt X-718 speakers and that's a cheap amp, running off a 435V B+ idling at 55mA, so I'm puzzled why yours does not. It also only needs two driver tubes in total (one of the three is for show) for an integrated amp.
BTW a Sweet Peach + the mods (see the thread) are probably cheaper than you buying the bits separately, and it sounds awesome 😉
Thank you all for your comments.
Few points:
1. Indeed, I was wrong about the RMS power calculation. Right now it looks that I can get from EL156 in triode mode less than 9W RMS while maintaining safe limits.
2. I'm neither into armchair design nor into DIY fun. My present stereo set, less the power amp, is high-end and excellent sounding. What I'm looking for is a SOTA power amp that will match the quality of the rest of my setup and that I can afford with the little money I have.
3. My preference is to stick with all triode tubes, no pentode(s). That is, pentodes in triode mode are fine, but not in pentode mode.
4. Also, at this stage, my preference is not to use any CCS.
5. My preference is to stay in Class A1.
6. At this stage I prefer not to experiment with experimental topologies which I don't know their final sound quality.
7. I'm not into a race after maximum power, I only what to get enough clean power to drive my speakers, which aren't very difficult to drive.
8. At this stage my preference is to stick with SET, should I be able to have a DIY SET with enough clean power to drive my speakers.
9. I have no intention to replace my speakers, not now and not ever.
10. The Sowter OPT aren't ordered yet, they are to be ordered. They will be ordered once I’ll have the final circuit.
11. As for output tubes, my present preference is EL156, since I like their sound.
12. As for the Musical Paradise MP-401 amp I have:
a. I assume that the 15Watt RMS OP power published is incorrect, unless they drive the tubes beyond their safe limits. 1 OP tube burned out after about 1 month of use, so they may drive the tubes too much.
b. I don't have yet its' schematic and I don't know what they did there, how and why they did it.
c. By the weigh of its' OPT I assume they aren't of good enough quality. Therefore I assume there is no point in trying to modify it.
As for the Sweet Peach amp, I cannot refer to it since I didn't hear it.
Also, I cannot follow blindly others comments about the good sound of this or that amp. In my experience, the way an amp will sound depends much on the rest of the setup. Also, it is given to personal preferences: what sounds excellent to one person may sound horrible to another person.
Few points:
1. Indeed, I was wrong about the RMS power calculation. Right now it looks that I can get from EL156 in triode mode less than 9W RMS while maintaining safe limits.
2. I'm neither into armchair design nor into DIY fun. My present stereo set, less the power amp, is high-end and excellent sounding. What I'm looking for is a SOTA power amp that will match the quality of the rest of my setup and that I can afford with the little money I have.
3. My preference is to stick with all triode tubes, no pentode(s). That is, pentodes in triode mode are fine, but not in pentode mode.
4. Also, at this stage, my preference is not to use any CCS.
5. My preference is to stay in Class A1.
6. At this stage I prefer not to experiment with experimental topologies which I don't know their final sound quality.
7. I'm not into a race after maximum power, I only what to get enough clean power to drive my speakers, which aren't very difficult to drive.
8. At this stage my preference is to stick with SET, should I be able to have a DIY SET with enough clean power to drive my speakers.
9. I have no intention to replace my speakers, not now and not ever.
10. The Sowter OPT aren't ordered yet, they are to be ordered. They will be ordered once I’ll have the final circuit.
11. As for output tubes, my present preference is EL156, since I like their sound.
12. As for the Musical Paradise MP-401 amp I have:
a. I assume that the 15Watt RMS OP power published is incorrect, unless they drive the tubes beyond their safe limits. 1 OP tube burned out after about 1 month of use, so they may drive the tubes too much.
b. I don't have yet its' schematic and I don't know what they did there, how and why they did it.
c. By the weigh of its' OPT I assume they aren't of good enough quality. Therefore I assume there is no point in trying to modify it.
As for the Sweet Peach amp, I cannot refer to it since I didn't hear it.
Also, I cannot follow blindly others comments about the good sound of this or that amp. In my experience, the way an amp will sound depends much on the rest of the setup. Also, it is given to personal preferences: what sounds excellent to one person may sound horrible to another person.
Hi !
How about EL156 SE Ultralinear? You will have more power,with good performance! I want to make a similar amp,but not decided yet the configuration to apply! But i will use a ECC88 to drive the EL156.
When you finish the amp,let us know about the sound with the Sowter transfos!
Regards
How about EL156 SE Ultralinear? You will have more power,with good performance! I want to make a similar amp,but not decided yet the configuration to apply! But i will use a ECC88 to drive the EL156.
When you finish the amp,let us know about the sound with the Sowter transfos!
Regards
I'm not sure you will - the max anode voltage is too low!
You need an ECC82 or a 6SN7 I think...
Save the ECC88s for a phono stage 🙂
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