DIY speakers need the right level of internal damping material - about 8g per litre using Acousta-Stuff.
Also it is important to use an acoustic ratio for the box dimensions to reduce the effects of standing waves and to fit hard-wood braces between the sides of the box. If it can be made convenient so the longest dimension of the box is the depth that assists with damping the back wave of the speaker.
It is hard to get all of this right with a small bass-reflex speaker. The most neglected thing is to pay little attention to making the box.
One trick I have used is to flare the back of the inside opening for the bass driver which speeds up the airflow and causes less turbulence which improves bass impact even with a small box. I used a Fibonacci ratio for box dimensions - close enough to 1:1.26:0.79
Also it is important to use an acoustic ratio for the box dimensions to reduce the effects of standing waves and to fit hard-wood braces between the sides of the box. If it can be made convenient so the longest dimension of the box is the depth that assists with damping the back wave of the speaker.
It is hard to get all of this right with a small bass-reflex speaker. The most neglected thing is to pay little attention to making the box.
One trick I have used is to flare the back of the inside opening for the bass driver which speeds up the airflow and causes less turbulence which improves bass impact even with a small box. I used a Fibonacci ratio for box dimensions - close enough to 1:1.26:0.79
Probably not.
My plan is by-amping but I'm waiting for Rod Elliot electronic crossover. Meanwhile I'm ussing a couple of bookshelves speakers with a 5 1/4 driver and a tweeter with a capacitor in series I just built.
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That is a good point. Reproduction of music it might be affected by the room as much or close to recording of it.
The rest is home work for me.
Thanks
The speakers are 12 by 7 . Eigth inches depth. No damping material at all. Two holes 1" as port.
I built one with better dimensions (16 X 7 X 9), lead sheeet glued to side walls and 1/2 cork to the back. Not sure I like it better.
What stuffing material sure be used for vented box?
Thanks
That's pretty obvious Olddiy. What would be the bennefit of clossing ports. By the way, they are 3/4 "
Thanks for your reply.
Manel
If those are the internal dimensions of your box the first mentioned one is the better choice but is not entirely satisfactory and you will not resolve this with damping material alone.
There should be some information on the bass unit you are using - what the recommended volume of your box should be, and whether this is suited for use as a closed box or ported. If for either the volumes for each will differ accordingly.
When you have decided which route to take, establish the cube root of the volume of the box required and use a golden ratio to find the other dimensions. Do this to avoid a prominent low frequency resonance.
There are online calculators you can use for this - see Golden Ratio Calculator.
Hi Jemraid.
I'm working on a new amplifier and making a similar PSU solution.
I think you will need 2 units of the above filter because it has 2 Amperes of max. current.
How do you like this 60s circuitry?
https://www.diyaudio.com/forums/att...s-amp-hohner-electra-piano-schematic-hner-pdf
https://www.diyaudio.com/forums/att...s-amp-hohner-electra-piano-schematic-hner-pdf
I would like to understand how to adjust the bias current and the gain of this amp. How is the gain calculated and what is the useable range of adjustment ?
I am using 19 v laptop power supply and 2n 3055 output resistors.
regards
kp93300
Bias is adjusted by current through R1&R2. The ratio between these will also affect the AC current sharing between the output transistors.
Gain is in R3/R4. I have no idea what gain limits there are, will probably vary between amps. I think you can just adjust Iq and don't worry about gain.
Others please correct me if I'm wrong.
Gain is in R3/R4. I have no idea what gain limits there are, will probably vary between amps. I think you can just adjust Iq and don't worry about gain.
Others please correct me if I'm wrong.
R4 220 ohms sets the gain without upsetting the reference voltage points. To reduce the gain one might use 470 ohms. I wouldn't recommend that without an oscilloscope and knowledge of what you see. To increase the gain is very easy. You could add an additional 220 ohms to the existing one in parallel. This will double the gain. Bass will be reduced a little. Hum and hiss increased a little. Sound might seem more open especially when an amplifier has never been oscilloscope tested. This gain suits. CD and typical mobile phones. LP and radio tuners need a preamp.If building a preamp add enough current gain to drive headphones as it helps everything. In that case build in enough voltage gain to drive the standard JLH. One can even reduce the JLH gain if so. At that point you find out if you will become an electronics engineer. If using a lot of care and listening this can be a big improvement. A well designed preamp can improve the sound. Very often it is worse as the simplicity is lost. LPs can have a treble control that doesn't change complexity. That can be a big difference. 25 to 100 uS perhaps. Jukebox 45s might appreciate that.
Should the increased gain be pleasing the bass can be restored. C3 could have an identical 220uF added in parallel. Douglas Self likes this capacitor to be as large as possible. If looking to try that go in 220 uF steps. The builder who found the bass exaggerated might need to tune this capacitor. More bass might be the answer. It might be a defect in the speaker the amplifier is finding. If a port loaded speaker try loading the port with drinking straws of the same length. This gives a half way compromise towards sealed cabinet . It looks really neat and easy to reverse. Use enough straws to pack the tube.
Should the increased gain be pleasing the bass can be restored. C3 could have an identical 220uF added in parallel. Douglas Self likes this capacitor to be as large as possible. If looking to try that go in 220 uF steps. The builder who found the bass exaggerated might need to tune this capacitor. More bass might be the answer. It might be a defect in the speaker the amplifier is finding. If a port loaded speaker try loading the port with drinking straws of the same length. This gives a half way compromise towards sealed cabinet . It looks really neat and easy to reverse. Use enough straws to pack the tube.
Hello KP,
I adjusted R2 by changing the resistor, less resistance means more Amps and then I worked out what the output would be. The resistor must be able to handle 1 Watt, 2 - 0.5 Watt ones will do be OK. E.g. two 470R in parallel = 235R
If you use odd values say 330R & 470 do this 330x470 divided by 330+470 = 193R this is what Mr Hood did. There are online calculators to do this.
From that you can work out the output wattage, taking Mr Hoods 8 Ohm recommendation 27V x 1.2 Amps = 32.4 Watts this is for a 10 Watt output so 10 divided by 32.4 = 0.31.
If say you've got 18V and 1.2 Amps = 21.6 x 0.31 = 6.7 Watts output. There is no need whatsoever to use the 10 Watt output, if you can get away with say 6 Watts then do so. I first heard FH3's (86 dB) speakers driven by a 6 Watt SET valve amp at detailed concert level at Colin Topps house.
Nigel will attest to using all of 2/3 Watts to drive some 85 dB speakers. Watts all dis den, b***sh*t!
Cheers
I adjusted R2 by changing the resistor, less resistance means more Amps and then I worked out what the output would be. The resistor must be able to handle 1 Watt, 2 - 0.5 Watt ones will do be OK. E.g. two 470R in parallel = 235R
If you use odd values say 330R & 470 do this 330x470 divided by 330+470 = 193R this is what Mr Hood did. There are online calculators to do this.
From that you can work out the output wattage, taking Mr Hoods 8 Ohm recommendation 27V x 1.2 Amps = 32.4 Watts this is for a 10 Watt output so 10 divided by 32.4 = 0.31.
If say you've got 18V and 1.2 Amps = 21.6 x 0.31 = 6.7 Watts output. There is no need whatsoever to use the 10 Watt output, if you can get away with say 6 Watts then do so. I first heard FH3's (86 dB) speakers driven by a 6 Watt SET valve amp at detailed concert level at Colin Topps house.
Nigel will attest to using all of 2/3 Watts to drive some 85 dB speakers. Watts all dis den, b***sh*t!
Cheers
1 watt 10 watts 100 watts. Although not totally reliable these are the real differences. If you can live with 5 watts you very likely will get better sound.
Spendor Prelude was a supurb low cost low distortion design. With 1 watt it could go quite loud. It was more or less from a BBC design made with an Audax rather than Celestion tweeter.
0.7A is worth a try. LS5/8 and Spendor BC3 hybrid. Spencer taught me. Mostly to spot the Elephant in the room when engineering. An exceptionally nice person as is his son.
My friend Janine is a fan. She was a BBC engineer. Shame she doesn't write here. Spendor was the origine of nearly all of these designs. Janine has a 10 watt Leak Stereo 20 that sounds wonderful.
Chartwell LS3/5 Loudspeakers by Graham Audio | Hifi Pig | Hifi Pig
Spendor Prelude was a supurb low cost low distortion design. With 1 watt it could go quite loud. It was more or less from a BBC design made with an Audax rather than Celestion tweeter.
0.7A is worth a try. LS5/8 and Spendor BC3 hybrid. Spencer taught me. Mostly to spot the Elephant in the room when engineering. An exceptionally nice person as is his son.
My friend Janine is a fan. She was a BBC engineer. Shame she doesn't write here. Spendor was the origine of nearly all of these designs. Janine has a 10 watt Leak Stereo 20 that sounds wonderful.
Chartwell LS3/5 Loudspeakers by Graham Audio | Hifi Pig | Hifi Pig
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It seems to me that that kp93300 hasn't seen the original article describing the JLH 1969 design yet; i.e. how it works, what variations will suit his build etc. That should give him and others a comprehensive overview. It's interesting too, the way Jemraid seems to have copied JLH's perfboard layout from photographs of the prototype wayback then. Take a look and compare.
The original magazine articles and many possible variations, updates etc. until around 2000, are maintained together at Geoff Moss's "The Class A amplifier Site" now hosted as an archive at Rod Elliott's ESP site, here: The Class-A Amplifier Site
Good reading - it's well worth the visit
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Hello Ian,
You are quite right, after fiddling about with some stripboard and Chinese 'kit'. I thought the best place to go was the source as you often point out.
I made the original photo a bit clearer and used that in conjunction with the schematic. When I first started adding components I could have kicked myself .... this Matrix Board (from Cricklewood Electronics) is just so easy to use. Components can be just slid in and out or like the amperage adjustment one just soldered in edge to edge to trial a setting.
Completely daft! Brings on a smile! 10/10 for Mr Hood Worra bloke!
Cheers
You are quite right, after fiddling about with some stripboard and Chinese 'kit'. I thought the best place to go was the source as you often point out.
An externally hosted image should be here but it was not working when we last tested it.
I made the original photo a bit clearer and used that in conjunction with the schematic. When I first started adding components I could have kicked myself .... this Matrix Board (from Cricklewood Electronics) is just so easy to use. Components can be just slid in and out or like the amperage adjustment one just soldered in edge to edge to trial a setting.
Completely daft! Brings on a smile! 10/10 for Mr Hood
Worra bloke!Cheers
It appears to be a fairly standard, ultralinear tube design of the times so perhaps the wonderful sound quality was in the transformers? Schematic - Leak Stereo 20 Tube Amplifier @ AmpsLab.com