Hello,
I have always been on a tight budget, but finally I got me some real triode output tubes. The famous 2A3.
If I don't remember wrong they are from EH.
So yesterday I started thinking of a new amp with these tube just to check that I'm on the right track. The attach'd schematic is what
I came up with. I like your comments so that if there is any errors, I can get rid of them before building the amp. Not that I am saying that I expect every thing to work perfect from day one.
Something to say: Power supply for the anode on 2a3 will be around 250v and a little lower for 6sn7. Ac heating on both tubes. The amp will be conected to a center in the beginning, until I have money to make a preamp and input selector with tubes so I really have pretty much drive to the input of the amp.
Best regards,
Magnus Kofoed
I have always been on a tight budget, but finally I got me some real triode output tubes. The famous 2A3.
If I don't remember wrong they are from EH.
So yesterday I started thinking of a new amp with these tube just to check that I'm on the right track. The attach'd schematic is what
I came up with. I like your comments so that if there is any errors, I can get rid of them before building the amp. Not that I am saying that I expect every thing to work perfect from day one.
Something to say: Power supply for the anode on 2a3 will be around 250v and a little lower for 6sn7. Ac heating on both tubes. The amp will be conected to a center in the beginning, until I have money to make a preamp and input selector with tubes so I really have pretty much drive to the input of the amp.
Best regards,
Magnus Kofoed
Attachments
The design looks good except for the volume control error - the wiper should go the grid of your 6SN7 and the top of the element to your source.
I would also add a 1K grid stopper resistor right at the grid of the 6SN7 and another on the grid of the 2A3. These should be at the socket in series with the grid.
IMHO you should operate the 6SN7 SRPP at =>300V for good headroom and low distorsion.
The 2A3 bias voltage is going to be about 45V so for an effective plate voltage of 250V and a few volts dropped across the output transformer it seems that a supply of 300V here is just about right.
Some of my older amplifiers are quite similar in design, and this topology sounds very good. You should be happy with it.
Hope this helps. 😀
Kevin
I would also add a 1K grid stopper resistor right at the grid of the 6SN7 and another on the grid of the 2A3. These should be at the socket in series with the grid.
IMHO you should operate the 6SN7 SRPP at =>300V for good headroom and low distorsion.
The 2A3 bias voltage is going to be about 45V so for an effective plate voltage of 250V and a few volts dropped across the output transformer it seems that a supply of 300V here is just about right.
Some of my older amplifiers are quite similar in design, and this topology sounds very good. You should be happy with it.
Hope this helps. 😀
Kevin
Hello,
Thanks for the tips kevinkr!
I have attached the new schematic.
I will use around 300v for both stages, forgot the voltage drop in the cathode resistor and transformer. I also didn't realise that a srpp stage need that high voltage to get the distortion down.
Thats is way I like diyAudio, so many great tips to snap up on the way.
Giamie:
Center is a preamplifier, inputswitch, eq and volume control. It has hell-o-many inputs and often also a video switch. The propose of the center is to use it with powerstage that has noting else than input and output. The reason I call'd it center is that what we call it in norway. Never heard any one call it anything else, sorry for the confusion.
Best regards,
Magnus Kofoed
Edit: I see that I forgot the value of the grid resistors, but after Kevinkr adivce they are all 1k.
Thanks for the tips kevinkr!
I have attached the new schematic.
I will use around 300v for both stages, forgot the voltage drop in the cathode resistor and transformer. I also didn't realise that a srpp stage need that high voltage to get the distortion down.
Thats is way I like diyAudio, so many great tips to snap up on the way.
Giamie:
Center is a preamplifier, inputswitch, eq and volume control. It has hell-o-many inputs and often also a video switch. The propose of the center is to use it with powerstage that has noting else than input and output. The reason I call'd it center is that what we call it in norway. Never heard any one call it anything else, sorry for the confusion.
Best regards,
Magnus Kofoed
Edit: I see that I forgot the value of the grid resistors, but after Kevinkr adivce they are all 1k.
Attachments
Hi Magnus,
Just occured to me that you might want to reduce the value of R5 to say 220K or less, and increase C2 slightly to 0.15uF or so to compensate..
In English what you describe as a center would normally be referred to as a pre-amplifier if it has the functionality you describe. There are also music centers which are the cheap all in one music systems usually with a pair of included speakers - I assume this is not what you meant. 😉
Just occured to me that you might want to reduce the value of R5 to say 220K or less, and increase C2 slightly to 0.15uF or so to compensate..
In English what you describe as a center would normally be referred to as a pre-amplifier if it has the functionality you describe. There are also music centers which are the cheap all in one music systems usually with a pair of included speakers - I assume this is not what you meant. 😉
Hello,
I am planning to use Hammond T1627SE.
Its 2k5 primary and 4, 8 and 16ohms primary.
25watt output. Yeah I know, its a little bit overdimensoned.
Best regards,
Magnus Kofoed
I am planning to use Hammond T1627SE.
Its 2k5 primary and 4, 8 and 16ohms primary.
25watt output. Yeah I know, its a little bit overdimensoned.
Best regards,
Magnus Kofoed
It might be good to also add a grid leak resistor (between volume-pot wiper & ground) of say 470K on the input. This will help to avoid noise when changing the volume.
The reason for this is that if the volume-pot wiper ever make intermittent contact, the stage loses the grid to ground reference. With a good quality pot, this shouldn't really be an issue, but it's good practice just in case.
The reason for this is that if the volume-pot wiper ever make intermittent contact, the stage loses the grid to ground reference. With a good quality pot, this shouldn't really be an issue, but it's good practice just in case.
You ought to take a look at the Lundahl line, I assume they would be a lot less expensive in Norway than they are here, and are generally better transformers than the Hammond. Maybe the price difference is not so great.
Kevin
Kevin
What is your estimated voltage swing for driving the 2A3 in this setup (B+=300V) -- about 80-90Vp-p for full drive? And how much gain will the 6SN7 stage give you, ca 10x?
In that case you will need 9Vp-p or 3.2Vrms from your preamp. Is that what you are aiming for?
In that case you will need 9Vp-p or 3.2Vrms from your preamp. Is that what you are aiming for?
Hi Jane,
Your estimate of gain is a little low, typically it should be around 12X - I use a very similar topology to drive 300B. Somewhere around 2Vrms should be sufficient to drive this amplifier to full power.
Kevin
Your estimate of gain is a little low, typically it should be around 12X - I use a very similar topology to drive 300B. Somewhere around 2Vrms should be sufficient to drive this amplifier to full power.
Kevin
There is an "Aussie" tweak for improving both the gain and linearity of SRPPs. Replace R9 with a loading choke/resistor combo whose DCR = 1 KOhm.
Increased gain will resolve any lingering doubts about the ability of a CDP to drive the amp to full power. Obviously, increased linearity is a good thing.
The value of the loading choke should be large enough for Xl @ 20 Hz. to be 3X Rp.
Increased gain will resolve any lingering doubts about the ability of a CDP to drive the amp to full power. Obviously, increased linearity is a good thing.
The value of the loading choke should be large enough for Xl @ 20 Hz. to be 3X Rp.
Hello,
Thanks for all the tips!
Kevinkr,
12x gain in the 6sn7 gainstage is my estimate too.
Seem's that we agreed there. 🙂
Jane,
What I am aiming for is a powerstage to be connected to a pre amplifier. It's not designed to be used directly with a cd player, alltrought, I'll think it will takle it just fine with a watt or two out.
I have tested how much power I use when I play loud and that i 700mw so this amp will do a good job even with a cd player.
Btw, how much voltage swing gives a cd player out?
Eli Duttman,
I really see your point with putting in a choke, but I don't think my budget will be too happy. Last time I check'd choke prices, they were pretty expensive. But thanks for the tip, I will put on memory. Or for the amp my friend ask'd me to build for him...
I have attached what I think is the "final" schematic, but keep the tips coming if you spot something.
best regards,
Magnus Kofoed
Thanks for all the tips!
Kevinkr,
12x gain in the 6sn7 gainstage is my estimate too.
Seem's that we agreed there. 🙂
Jane,
What I am aiming for is a powerstage to be connected to a pre amplifier. It's not designed to be used directly with a cd player, alltrought, I'll think it will takle it just fine with a watt or two out.
I have tested how much power I use when I play loud and that i 700mw so this amp will do a good job even with a cd player.
Btw, how much voltage swing gives a cd player out?
Eli Duttman,
I really see your point with putting in a choke, but I don't think my budget will be too happy. Last time I check'd choke prices, they were pretty expensive. But thanks for the tip, I will put on memory. Or for the amp my friend ask'd me to build for him...
I have attached what I think is the "final" schematic, but keep the tips coming if you spot something.
best regards,
Magnus Kofoed
Attachments
kevinkr said:
My estimates are always a little bit conservative, more like worst case. 🙂
So, if the preamp match the power amp, I cant see any problems with the design.
- Status
- Not open for further replies.