A little less than a year ago, I successfully completed my first tube audio project: an RIAA phono amplifier. It was a fantastic success, and my family and I have been thoroughly enjoying it. Winter is coming again here in the Rockies, so it's time to start thinking about indoor projects. At the moment, the preamp feeds into a set of computer speakers, which is pretty anticlimactic. It's time to start working on the rest of system!
I think what I want to do is an integrated amplifier (I might could be convinced to go another route) with a similar basis. I want the most minimalist circuit possible (100% tube and passives), single-ended class A, all analog (including power supply, because this is part of the fun for me), low power (pushing shelf speakers in a living room, rarely might need to compete with a vacuum cleaner), using modern, current production components (future proofing). My current setup consists exclusively of a record player, but there's an ancient Sonos that my wife uses from time to time, and I'd like to replace it with a better streamer down the road (phase three?). A third, maybe fourth channel would probably make for all the extensibility I'd need for quite a while. Aside from that, I think I don't really want much more to it than a volume control, again, for the minimalism to keep the part count to a minimum.
What thoughts or advice do people have for me? Any designs/schematics out there that fit the bill?
I think what I want to do is an integrated amplifier (I might could be convinced to go another route) with a similar basis. I want the most minimalist circuit possible (100% tube and passives), single-ended class A, all analog (including power supply, because this is part of the fun for me), low power (pushing shelf speakers in a living room, rarely might need to compete with a vacuum cleaner), using modern, current production components (future proofing). My current setup consists exclusively of a record player, but there's an ancient Sonos that my wife uses from time to time, and I'd like to replace it with a better streamer down the road (phase three?). A third, maybe fourth channel would probably make for all the extensibility I'd need for quite a while. Aside from that, I think I don't really want much more to it than a volume control, again, for the minimalism to keep the part count to a minimum.
What thoughts or advice do people have for me? Any designs/schematics out there that fit the bill?
First, decide if you want more than 2 channels. That’s going to be an enormous driver of cost.
As for an amp circuit, I’ve never heard a push-pull EL84 amp I didn’t like. It’s one of the last tubes specifically made for audio. Something like this schematic has all in-production tubes. Adding an input selector and volume pot would be trivial.
As for an amp circuit, I’ve never heard a push-pull EL84 amp I didn’t like. It’s one of the last tubes specifically made for audio. Something like this schematic has all in-production tubes. Adding an input selector and volume pot would be trivial.
How much gain does your phono preamp have?
Start with a stereo amplifier circuit, and add more later if you really want to.
With a lower voltage HV secondary, you can use silicon diodes instead of a rectifier tube.
Start with a stereo amplifier circuit, and add more later if you really want to.
With a lower voltage HV secondary, you can use silicon diodes instead of a rectifier tube.
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The Poddwatt is my favourite simple but sweet sounding EL84 integrated. However, I sense that it suffers from the 'not-invented-here' syndrome in these forums.
Pretty much the same experience here. We have 3 outstanding EL84 designs on the forum: El Cheapo (6AQ5), Baby Huey, and the Red Light District.
Add a 100kΩ pot at the front and a selector switch and you have an integrated amp.
We did a Class A, triode vartiation of El Cheapo, it is one of my 2 best ampifiers, the other a SIT-3.
You can do a lot better than the EL34 circuit shown by 6L6, but the LTP driving the output stage is my personally preferred splitter topology (but should have a CCS on the cathodes). Whether you need the extra gain of the first tube depends on what levels you are feeding the amp. Quite unnecessary in an EL84 amp.
dave
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The Podwatt is a nice design for minimizing parts count by making the output stage a cathode coupled amplifier, doing its own phase splitting.
The problem with that is that you don't get as much power out as you do when using the output tubes with push-pull drive from a dedicated phase splitter before the output stage.
I get 3.2 w our=t of my EL84 triode PP, pushing heavily into AB maxes out at about 17w, somehow with trick OPTs, and high voltages, considerably more can be had.
An ACA is about 8 w and will have longer lifespan, less space, less cost. Get smoked by my little EL84 PP within the power limitations.
And if the ACA is mentioned so should the ACA Mini.
dave
An ACA is about 8 w and will have longer lifespan, less space, less cost. Get smoked by my little EL84 PP within the power limitations.
And if the ACA is mentioned so should the ACA Mini.
dave
SE, Scade feedback, RH84 probably the best example but can be tweaked up a bit. We built a parafeed variation in monoBloks that are very good (and have appreciated significantly given what they were recently listed at on Canuck Audio Mart).
I don’t rate them as good as the PP (very different sound) but has near twice the power. The single biggest thing you can do to the sonics are the big black things. At least the last stage of the power supply should be a poly cap since it is in the signal path. Ours had no
\elcos, was parafeed (a pair of OPTs & PS Trafos from Grundig consoles), one used as the parafeed choke. Separate filimant supply, hybrid rectifier, and a ckoke in the PSU.
This was the 7th iteration of the amplifier that started out as a Decware ZEN clone. They kept getting better. I do have som edifferent deas for version #8.
If you want to do one on a budget, OPTs and PS Trafo from old consoles. Especially if you are lucky enuff to find one parked on the side of the street with a free sign on it. For example i thing the parts cost of the monobloks above was on the order of $150.
dave
I don’t rate them as good as the PP (very different sound) but has near twice the power. The single biggest thing you can do to the sonics are the big black things. At least the last stage of the power supply should be a poly cap since it is in the signal path. Ours had no
\elcos, was parafeed (a pair of OPTs & PS Trafos from Grundig consoles), one used as the parafeed choke. Separate filimant supply, hybrid rectifier, and a ckoke in the PSU.
This was the 7th iteration of the amplifier that started out as a Decware ZEN clone. They kept getting better. I do have som edifferent deas for version #8.
If you want to do one on a budget, OPTs and PS Trafo from old consoles. Especially if you are lucky enuff to find one parked on the side of the street with a free sign on it. For example i thing the parts cost of the monobloks above was on the order of $150.
dave
SE Shade is what I suggested originally, and about as simple as it gets. Nobody seems to have discovered the link I posted earlier, so I try again with the schematic:
6SH7 may sound exotic and certainly not available in new production. Fortunately they are cheap and abundant, so grab yourself an extra set and the amp should last a lifetime.
6SH7 may sound exotic and certainly not available in new production. Fortunately they are cheap and abundant, so grab yourself an extra set and the amp should last a lifetime.
Two channels is perfect. Two bookshelf speakers is the peak of my ambition for this project here. It'll hang out on the shelf in the living room, and if/when I eventually upgrade, it'll go in my office or something.
40dB.
Part of the logic with SE class A goes hand in hand with the minimal part count. I want to keep the signal path as simple as possible. The guy that introduced me to all of this way back when I was in college sold me on the philosophy, and that's what drove my process on the first project.
I want 3-4 stereo inputs, a selector switch, a volume knob, and then as little else as required. Tube rectification is part of the game here. I know diodes are better for this, that, and the other, but 100% tubes and passives is a key part of the goal for me. No one said I was being rational or logical here.
I didn't say this in the OP, but another requirement is the ability to use off the shelf low-mid range (think Hammond) transformers, chokes, etc. I'm not looking for an end all be all solution, I'm still learning. This is only my second adventure here; I'm stepping up the complexity, but don't know what I'm doing enough to feel in any way justified in spending a ton of money on this.
I loved the last project so much. I get warm fuzzies looking back at the previous thread (big thanks again to @rongon ), the encouragement from RJM, the excuse to reach out to my friend from nearly 20 years ago that introduced me to all of this, and the positive feedback I got on the forum here generally. I learned a ton, and I'm really looking forward to this project! Hopefully it doesn't take two whole years this time!
I've got to get 3-almost-4yo down for bed, but I'm looking into the Poddwatt over coffee in the morning.
Can you post the schematic of the 40dB phono stage?
It's necessary to determine what loading the phono stage can accept.
It's necessary to determine what loading the phono stage can accept.
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Keep in mind that an SE amp will have highish output impedance and it is fairly important that the loudspeakers have a fairly flat impedance. Big peaks near the XO point can be problematic. And the bass loading. We avoided XOs completely.
dave
PS: The SE monobloks have more parts than the PP. The circuit may be simplier but the power supply usually needs to have more attention
What's up with 300Bs? They seem to be simultaneously sought and avoided…
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The usual. Some swear by them, others swear at them, and some ignore them.
DHT tubes require special care with heater power supplies, 300B need good drivers, and good ones are expensive.