So im looking to add a small tube amp in between my computers amplified speakers and their speakers, solely to "flavor" the sound. Using vintage tubes.
I was looking at the Daven 3 tube amps, using ux201 tubes. Its simple, the power supply would be easy to fabricate (even for me). Im wondering if it will be suitable for my application.
Ive found two designs online, one for the original (which ive read will work with 2 type 40 tubes (the high mu version of the 01a) with a 01a as the final. As well as a design which is made for them, but its not specific on a few of the values of the parts. I know id need an output transformer, so i was thinking of a bogen 725 to connect it to the speaker so the impedance would be matching.
Im a newby, i basically build single tube regenerative radios, so amps are new to me. Any help is appreciated.
I was looking at the Daven 3 tube amps, using ux201 tubes. Its simple, the power supply would be easy to fabricate (even for me). Im wondering if it will be suitable for my application.
Ive found two designs online, one for the original (which ive read will work with 2 type 40 tubes (the high mu version of the 01a) with a 01a as the final. As well as a design which is made for them, but its not specific on a few of the values of the parts. I know id need an output transformer, so i was thinking of a bogen 725 to connect it to the speaker so the impedance would be matching.
Im a newby, i basically build single tube regenerative radios, so amps are new to me. Any help is appreciated.
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An externally hosted image should be here but it was not working when we last tested it.
The tube amp will put out less power than the powered speaker amp produces.
The amplifier will have way too much gain (Av=2400 67.7dB as is). If you substitute the 40 tube for two 01A tubes, you will have a gain of 5400 or 74.6dB. Even worse as it will almost double the gain of the original.
For tube flavor, you only need one low gain stage biased to give poor linearity.
Place it in between the soundcard output and the amplified speaker input.
The amplifier will have way too much gain (Av=2400 67.7dB as is). If you substitute the 40 tube for two 01A tubes, you will have a gain of 5400 or 74.6dB. Even worse as it will almost double the gain of the original.
For tube flavor, you only need one low gain stage biased to give poor linearity.
Place it in between the soundcard output and the amplified speaker input.
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I once, just for yucks, took an old mono RIAA preamp and made it into a tiny 6DJ8 line amp. I think its B+ was only +200V, making for one heck of a steep loadline. It was biased very cool, to something like 3mA per triode. It had a nice 'tubey' sound to it. Not accurate, but pleasant.
I think you could do the same with a lower gain tube, like a Russian 6N6P. Try a single 6N6P twin-triode with a 200V B+. Self-bias it to about 7mA (what the heck). Plate voltage would be about +70V, cathode voltage about +2V. Plate resistor = 18k 3W. Cathode resistor = 270R 1/2W, or use a red LED in the cathode. Use an 8uF 300V paper-in-oil capacitor on the output (for that vintage paper cap sound). Maybe something like these.
I figure the line amp's output impedance will be about 3k ohms. High, but should be 'just ok' into a 10k load. It won't sound great, but it should 'sound like a tube.'
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Oh yeah, what TheGimp said is correct. You want to connect the PC's line out (usually a green jack) to the input of this tube line stage, and connect the tube line stage outputs to the input on your desktop speakers' amp. There will be too much gain, so be careful with those level controls.
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I think you could do the same with a lower gain tube, like a Russian 6N6P. Try a single 6N6P twin-triode with a 200V B+. Self-bias it to about 7mA (what the heck). Plate voltage would be about +70V, cathode voltage about +2V. Plate resistor = 18k 3W. Cathode resistor = 270R 1/2W, or use a red LED in the cathode. Use an 8uF 300V paper-in-oil capacitor on the output (for that vintage paper cap sound). Maybe something like these.
I figure the line amp's output impedance will be about 3k ohms. High, but should be 'just ok' into a 10k load. It won't sound great, but it should 'sound like a tube.'
--
Oh yeah, what TheGimp said is correct. You want to connect the PC's line out (usually a green jack) to the input of this tube line stage, and connect the tube line stage outputs to the input on your desktop speakers' amp. There will be too much gain, so be careful with those level controls.
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Yes,
The normal output of the line out from a computer sound card might be 1Vrms.
If you try to feed that into an amp with a gain of say 10, you will get 10Vrms out (provided the amp does not clip).
It will overdrive the input of a powered speaker which is expecting a max of around 2-3Vrms.
One stage with a gain of 20 would be too much, but you can put a volume control at the input of the stage and turn it down along with turning down the soundcard volume.
You could use a single 01A stage with a gain of 8 and it wouldn't require turning down the volume of the sound card much, along with reducing the input at the grid of the 01A.
The issue with turning down the gain and then amplifying the signal is you introduce more noise and hum. So, you will actually degrade the sound quality. The lower the gain of the tube stage, the less you will do this.
The normal output of the line out from a computer sound card might be 1Vrms.
If you try to feed that into an amp with a gain of say 10, you will get 10Vrms out (provided the amp does not clip).
It will overdrive the input of a powered speaker which is expecting a max of around 2-3Vrms.
One stage with a gain of 20 would be too much, but you can put a volume control at the input of the stage and turn it down along with turning down the soundcard volume.
You could use a single 01A stage with a gain of 8 and it wouldn't require turning down the volume of the sound card much, along with reducing the input at the grid of the 01A.
The issue with turning down the gain and then amplifying the signal is you introduce more noise and hum. So, you will actually degrade the sound quality. The lower the gain of the tube stage, the less you will do this.
this 1117n7 looks intrigueing, i like how its AC powered.
if i add an isolation transformer, would this be suitable for my application?
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Always start with a data sheet. The 117N7 data sheet is here.
Notice that the heater draws 90 mA. and total cathode current is slightly under 60 mA. A low cost Triad N-68X isolation trafo is good for more than 400 mA. The apparent excess is necessary, as cap. I/P filters need 2X the DC current draw in the AC RMS feed. In addition, 1/2 wave rectifiers, like that shown, put a "standing" DC voltage on the trafo, which greatly increases the stress level.
Distortion is pretty high. Adding NFB would require the addition of a gain stage, as a sound card's O/P level would be too low.
BTW, don't forget that you need 2 of everything to support a stereo pair of speakers.
Have to say that is a very ordinary amplifier using some great tubes. Find something better..
Agree with the idea of single 01A, but load it with a lot more than 11k as depicted in the three stage schematic. Rp is 9k or so, and actually higher for the brass based & tipped and also deeper base versions. Short base is the one you want, ST are fine and they all last nearer to forever.
Type 40 has always interested me but such low plate current and such high Rp makes it a non-starter from many view-points.
01A is a great tube. Build it right and hang on to it.. it'll be at home in almost any system, regardless of cost.
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Well the type 40 is just a high mu version of the 01A, designed for use in resistance coupled amps (from what ive read). Ive seen them in use in the daven style amps in the past, thats why i mentioned their possible use.
I build and listen to single tube 1920s regen radios, so ive a small stock of 01A tubes available, UV and UX based, to replenish them and for experimentation like this. My skills arent that great, though i can follow and build from schematics.
With my skills in mind, i need to decide on a good design. The daven seems interesting to me, since the parts count is low and its simple. I know it would produce too much gain to be a buffer, but what if i got rid of the computers amp/speakers all together? Using it as a low powered amp and supplying small speakers. This is mainly for show, just so i can look up when typing and see their glow and know i built them.
Or, would i be best using an ultra simplistic single stage 01A as a buffer stage in the computer amps/speakers?
Something like this but with an isolation and output transformer added?
I build and listen to single tube 1920s regen radios, so ive a small stock of 01A tubes available, UV and UX based, to replenish them and for experimentation like this. My skills arent that great, though i can follow and build from schematics.
With my skills in mind, i need to decide on a good design. The daven seems interesting to me, since the parts count is low and its simple. I know it would produce too much gain to be a buffer, but what if i got rid of the computers amp/speakers all together? Using it as a low powered amp and supplying small speakers. This is mainly for show, just so i can look up when typing and see their glow and know i built them.
Or, would i be best using an ultra simplistic single stage 01A as a buffer stage in the computer amps/speakers?
Something like this but with an isolation and output transformer added?
I think your best approach is to build a single stage amp with a 01A or the like, to use from the output of the sound card to the powered speakers.
The 01A is a small signal amplifier tube. It is not designed to drive a speaker which requires much more power.
Otherwise you need an output tube.
About the smallest output tube in the old numeric series was the 31 followed by the 71. Both produce power in the sub 1W range.
The 45 gets you in to the 1W plus range.
Stepping out of the DHT (Directly Heated Triode) group, you could go with any of the tetrode or pentode tubes like the 38, 41, 42, 43, 47, 48, or 59. I've skipped the class B tubes as they are push pull only.
These tubes give output power levels from 1 to 3 watts, which is acceptable for driving efficient speakers at moderate volumes.
These tubes were predominantly used in radios of the day as the output tube driving a speaker through an output transformer.
The 01A is a small signal amplifier tube. It is not designed to drive a speaker which requires much more power.
Otherwise you need an output tube.
About the smallest output tube in the old numeric series was the 31 followed by the 71. Both produce power in the sub 1W range.
The 45 gets you in to the 1W plus range.
Stepping out of the DHT (Directly Heated Triode) group, you could go with any of the tetrode or pentode tubes like the 38, 41, 42, 43, 47, 48, or 59. I've skipped the class B tubes as they are push pull only.
These tubes give output power levels from 1 to 3 watts, which is acceptable for driving efficient speakers at moderate volumes.
These tubes were predominantly used in radios of the day as the output tube driving a speaker through an output transformer.
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This is a simple 01A amp i built to connect to my crystal radios, to give them better listening volume with headphones. I could build one off the same basic design for use between the sound card and amplified speakers. Hopefully giving me the slight tube buffer sound that I want, with the tube i love.
An externally hosted image should be here but it was not working when we last tested it.
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well id be using an isolation transformer and a matching output transformer as well.
Okay, im trying to understand what im reading here.
So the B+ will be across the output jacks.
Im hooking this single tube amp between the sound card and the computers amplified speakers. What if i run an audio isolation transformer between the sound card and amp, and between the amps out put and the computers amplified speakers?
Would that solve the issue with the B+ running across the outputs, thus not delivering them into the amplified speaker?
So the B+ will be across the output jacks.
Im hooking this single tube amp between the sound card and the computers amplified speakers. What if i run an audio isolation transformer between the sound card and amp, and between the amps out put and the computers amplified speakers?
Would that solve the issue with the B+ running across the outputs, thus not delivering them into the amplified speaker?
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