Low power High quality amp for driving a tweeter:ideas?

[marcelooms]

I'm currently driving my actively DSP-filtered 3 way DIY speakers with an old Yamaha 7.1 amp. Sounds fine, but I want to upgrade the amp to modules, optimising each for ita task: low, mid, high.

Now I'm looking for a simple amp to drive the tweeters (Scan Speak 9500 tweeters). These can be low power. I'm unable to spend a lot of money, so I'm thinking about a kit, or a second-hand stereo amp with nice highs. From what I understand is building an amp that sounds good on low power is difficult, as the cross-over distortion becomes relatively large with low outpu (there usually is little energy in the higher frequencies in music).

I'm more of a PC-DSP-DAC guy, don't know much about amps. I've been reading up, but there's not much to be found on optimising driving tweeters. Does anyone here have a golden tip for driving tweeters on a budget? Soldering no problem 🙂

Any input would be highly appreciated!

 

[Jonathan Bright]

You could do worse than look at the JLH 10 watt class-A amp. No cross over distortion. V simple. V big thread here at diyaudio and an extremely comprehensive site dedicated to this amp' by Geoff Moss. Just Google "Class A amp" and it should turn up. It was originally UK based but now hosted by ESP Audio (Sydney, Australia) Omit the big electro' output cap and replace it with a quality plastic cap of suitable value for the upper cross over point.
The Nelson Pass amps would also be appropriate. See passdiy and threads here at diyaudio.
Good luck. Jonathan

 

[indianajo]

For some simple 6 or 7 transistor lower power amps see post 45 of www.diyaudio.com/forums/solid-state/250380-biguns-tgm8-single-supply-5.html
or with opposite polarity see later posts of http://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-20.html
I've built the AX6 the retro amp. I listen to it daily. The transistors indicated are fast enough for tweeters. As Andrew says in TGM8 is is better to do your filtering of frequency in the preamp, not the power amp. So see analog line level forum threads about how to build mixers and high or low filters.
Both of these amps have single supplies with an output capacitor to provide a 1 part protector against burning your speakers with DC voltage out. Great for newbies that make soldering errors that can cause that DC. Parts cost for either should be about $10-15, excluding board and power supply. Shipping is $8 typically.
For a tweeter, you don't need 50 watts, so you can use a lower power supply like a salvage 30 v wall transformer from a printer/copier/fax machine. Or you can by a 24 vac doorbell transformer at a home store for really low power. A $2 bridge rectifier, a 3300 uf cap, a 0.1 uf ceramic cap across the 3300, a 2 amp fuse and holder, DC power out.
put in a metal box like a salvage index card file, or PCAT power supply housing.
For best centering of the voltage of the input of the output capacitor, one fiddles with the values of the pull up and pull down resistors of the first input transistor (after the input capacitor). Pots are okay temporary but they tend to oxidize over the years, so I tend to put in higher value resistors, and parallel them with smaller ones tacked on top, for a permanent solution. The resistor values shown on the deisgn work for the gain transistor the designer bought, but the the transistors you buy may have higher or lower gain (usually higher these days).
I don't even bother buying a PCB. I build on Nema CE laminate with soldered kynex insul. wire as you can see on the last post of retro 50w amp. bilbo of sydney builds on perf board see http://www.diyaudio.com/forums/solid-state/276300-2n3055-amplifier.html
You should be able to debug these with a DVM, and maybe for tough problems, an analog VOM with a blocking input capacitor (.047 uf to .47 uf) in the negative lead on the AC scale. I'm not committed enough to afford a working scope, hfe sorter, or any of the other instruments of the more professional builders and designers here. I'd rather spend my spare cash on records or CD's. And speakers - my setup is good enough to make MP3 files sound gritty. $1000 for the speakers, $100 for the amp & preamp is my hobby plan.
Have fun.

 

[vzaichenko]

Hi Marcelooms,

I recommend a rather simple cool amp - VHex+, excellent at low volumes.
You can find a number of very good reviews here on the forum.

More info >here[/U]<.
Available as PCBs, kits, tested modules or fully built amplifiers - depending on the desired level of involvement 😉

Cheers,
Valery

 

[marcelooms]

You could do worse than look at the JLH 10 watt class-A amp. No cross over distortion. V simple. V big thread here at diyaudio and an extremely comprehensive site dedicated to this amp' by Geoff Moss. Just Google "Class A amp" and it should turn up. It was originally UK based but now hosted by ESP Audio (Sydney, Australia) Omit the big electro' output cap and replace it with a quality plastic cap of suitable value for the upper cross over point.
The Nelson Pass amps would also be appropriate. See passdiy and threads here at diyaudio.
Good luck. Jonathan

Hi Jonathan,
Thank you so much for your answer. Class A would be nice indeed!
Afraid to ask, but could not find a kit or PCBs for the JLH10? Maybe I overlooked, the ESP site is somewhat convoluted. Or is there no kit?
The Pass amps seem to be peculiar as they have a relatively high ouput resistance. But I guess that would hurt driving tweeters?

 

[marcelooms]

For some simple 6 or 7 transistor lower power amps see post 45 of www.diyaudio.com/forums/solid-state/250380-biguns-tgm8-single-supply-5.html
or with opposite polarity see later posts of http://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-20.html
I've built the AX6 the retro amp. I listen to it daily. The transistors indicated are fast enough for tweeters. As Andrew says in TGM8 is is better to do your filtering of frequency in the preamp, not the power amp. So see analog line level forum threads about how to build mixers and high or low filters.
Both of these amps have single supplies with an output capacitor to provide a 1 part protector against burning your speakers with DC voltage out. Great for newbies that make soldering errors that can cause that DC. Parts cost for either should be about $10-15, excluding board and power supply. Shipping is $8 typically.
For a tweeter, you don't need 50 watts, so you can use a lower power supply like a salvage 30 v wall transformer from a printer/copier/fax machine. Or you can by a 24 vac doorbell transformer at a home store for really low power. A $2 bridge rectifier, a 3300 uf cap, a 0.1 uf ceramic cap across the 3300, a 2 amp fuse and holder, DC power out.
put in a metal box like a salvage index card file, or PCAT power supply housing.
For best centering of the voltage of the input of the output capacitor, one fiddles with the values of the pull up and pull down resistors of the first input transistor (after the input capacitor). Pots are okay temporary but they tend to oxidize over the years, so I tend to put in higher value resistors, and parallel them with smaller ones tacked on top, for a permanent solution. The resistor values shown on the deisgn work for the gain transistor the designer bought, but the the transistors you buy may have higher or lower gain (usually higher these days).
I don't even bother buying a PCB. I build on Nema CE laminate with soldered kynex insul. wire as you can see on the last post of retro 50w amp. bilbo of sydney builds on perf board see http://www.diyaudio.com/forums/solid-state/276300-2n3055-amplifier.html
You should be able to debug these with a DVM, and maybe for tough problems, an analog VOM with a blocking input capacitor (.047 uf to .47 uf) in the negative lead on the AC scale. I'm not committed enough to afford a working scope, hfe sorter, or any of the other instruments of the more professional builders and designers here. I'd rather spend my spare cash on records or CD's. And speakers - my setup is good enough to make MP3 files sound gritty. $1000 for the speakers, $100 for the amp & preamp is my hobby plan.
Have fun.

Hi Indianajo,
Thank you for your answer. I'm afraid I would be in a bit over my head with the Bigguns-amps and such. I'm too neurotic to be able to work without a single clear and tested design, and a ready-made PCB. The amp-to-be would be oscillating in my nightmares 🙂 .
I agree on the speakers: that's where the money should go. And it has indeed gone there, so now I'm on a budget, No worries, my setup is already sounding great, but always I'm looking for ways to improve even further. And that is where the story about the problem of the first Watt being the most important comes in. It lets me lean towards class A. An experienced amp builder could probably do it your way, but I somewhat out of my comfort zone here.

 

[AndrewT]

The peak current of a fast transient can be surprisingly high for a tweeter.
You need to ensure the amp is capable of meeting that transient current demand.
It's high sensitivity of the tweeter that reduces the need for high voltage drive.
Work back from sensitivity to determine your maximum voltage requirement. Then base your current requirement by assuming the worst case transient current equals what a half impedance resistor would demand.

eg.
If you need 100dB SPL @ 1m from a 92dB/W @ 1m tweeter, then you need 8dBW of power i.e. ~ 6.3W into 8ohms
max Voltage = sqrt(6.3W*8ohms) = 7.1Vac (this will need >22V rail to rail for the supplies)
max Current = sqrt(6.3W/8ohms) = 0.89Aac
And double this for a halved impedance gives 1.78Aac = 2.5Apk
A ClassA push pull amplifier biased to 1.3A will stay in ClassA upto 100dB SPL for all fast transient audio/music.
This is very close to a standard F5 build, but with supply rails reduced to ~±15Vdc.

If either 100dB @ 1m, or 92dB/W @ 1m, are not what you want/need, then redo the numbers.

Finally, build two mono-blocks and locate each at the speaker's input terminals.