Wondering if anyone has changed the input and the feedback cap to modify an AB amplifier to be a second order high pass.
It would look very easy to change to a 70 Hz. Any down sides? Phase problems? Stability problems?
Then with the built in crossover of a sub plate, you are all set.
It would look very easy to change to a 70 Hz. Any down sides? Phase problems? Stability problems?
Then with the built in crossover of a sub plate, you are all set.
In my mind both are just filters. Have considered this in the past but not tried it.
At 70 hz stability shouldn't be affected.
Square waves may be affected and have a steeper downward slope.
At 70 hz stability shouldn't be affected.
Square waves may be affected and have a steeper downward slope.
You only need to adjust the feedback to account for the gain of the amplifier. A simulator like
LT Spice or MicroCap is a good tool for playing with that. Properly chosen values for a voltage
divider from output to the filter node between the two filter caps would do it.
LT Spice or MicroCap is a good tool for playing with that. Properly chosen values for a voltage
divider from output to the filter node between the two filter caps would do it.
ACA. I put a socket in the place of the input cap to allow swapping it to essentially have a built-in first order PLLXO.
dave
dave
I too have thought about it. But just slightly differently. You mentioned AB amps. In my case I am not a "head banger" and have the raw materials for several low power but good quality Linsley-Hood Class-A units (circa 10 watts). In the original iteration (1969) they ran from a single rail power supply. For sometime I've thought that using them for the mid and higher frequencies and replacing the large value electrolytic at the output with an appropriate smaller value of plastic film cap' had a lot of merit. This would give a First order slope (which for some, would be all they require).
Then of course you have the other options that you mentioned. The virtue of reducing the value of the INPUT cap probably has the advantage of reducing the IMD in the PA whcih is worthwhile....
Cheers Jonathan
Then of course you have the other options that you mentioned. The virtue of reducing the value of the INPUT cap probably has the advantage of reducing the IMD in the PA whcih is worthwhile....
Cheers Jonathan
This A Good Passive Feed Back to Use With Active Tone Controller Circuit For Decent Bass And Treble Here Is A Diagram
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I use it with JBL compression drivers connected directly to the Hood. It is based on the JBL 4430 studio monitor active crossover configuration, which in reality is two first order HP filters and a CD correction (high shelf) in the 4430 passive crossover. This can all be done in the Hood, with a 3.3nf input cap, 20uF output cap, and a RC circuit in parallel with the feedback resistor. Works great, and the amp is dead quiet with ear directly in from of horn - remarkable for such an old construction! Another nice thing about the Hood is the absence of thump when being switched on/of - that could be hard on compression drivers...
Yes, I changed the input cap and feedback cap on a Hafler 120 to be a second order 70 Hz HP. It combines with the tuning of the speaker ( sealed) to give a 4th order HP. I did not change the output filter. Sub has a 4th order low pass.
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search up Romy The Cat, he has a multi-channel horn set up and each channel has a dedicated amplifier designed with the appropriate band-pass frequency response built-in. He uses Class A amplifiers.
For typical Class AB amplifiers incorporating feedback I'd want to be careful about the stability and I'd want the OLG of the amplifier not to be frequency limited other than to ensure stability so that the feedback loop can correct output stage distortion to it's maximum extent.
For typical Class AB amplifiers incorporating feedback I'd want to be careful about the stability and I'd want the OLG of the amplifier not to be frequency limited other than to ensure stability so that the feedback loop can correct output stage distortion to it's maximum extent.
I always do that, since forever, in my Guitar and Bass power amps, with no problems at all.
Lowest frequency in a Guitar is about 80Hz and in a Bass Guitar about 40 Hz, anything below that is waste of power, useless cone flapping, and since both are regularly used overdiven, farting sound.
Lowest frequency in a Guitar is about 80Hz and in a Bass Guitar about 40 Hz, anything below that is waste of power, useless cone flapping, and since both are regularly used overdiven, farting sound.
I was about to post a similar thread then saw this one🙂
I need cap advice, please.
I want to limit the input to my 10 watt per channel tube amp to 70hz and above. From the things I have been looking at all day is I need to insert, in series, a .022uF film cap which of course they range from $1 to $600 so I will be looking more in the $10 to $100 range and likely to stay much closer to the lower scale since all things are exponential in cost for minor or imagined improvements. I am fine with just a first order slope so a single element is what I prefer to use but if I need to add anything else let me know.
The amp is a fully upgraded Baby Sophia driving fully upgraded pair of Edgarhorn Slimline speakers coming from an E30 Topping bought for testing but looking at R2R DACs. The speakers roll off fairly steeply at 70hz so I just want to reduce the load on them and the amps from trying to do what they can't do which should make everything just a bit sweeter.
I would far rather DIY this than buy more gear, more cables, of course and far easier than the headache it was becoming upgrading the crossover in the sub amp. I will run full range to the sub amp and use the variable crossover freq, phase, EQ with Q filter, etc....that works quite well.
Now, what caps to get,,,recommendations will be greatly appreciated even if you tell me I am way up the wrong tree🙂
Thanks,
Rick
I need cap advice, please.
I want to limit the input to my 10 watt per channel tube amp to 70hz and above. From the things I have been looking at all day is I need to insert, in series, a .022uF film cap which of course they range from $1 to $600 so I will be looking more in the $10 to $100 range and likely to stay much closer to the lower scale since all things are exponential in cost for minor or imagined improvements. I am fine with just a first order slope so a single element is what I prefer to use but if I need to add anything else let me know.
The amp is a fully upgraded Baby Sophia driving fully upgraded pair of Edgarhorn Slimline speakers coming from an E30 Topping bought for testing but looking at R2R DACs. The speakers roll off fairly steeply at 70hz so I just want to reduce the load on them and the amps from trying to do what they can't do which should make everything just a bit sweeter.
I would far rather DIY this than buy more gear, more cables, of course and far easier than the headache it was becoming upgrading the crossover in the sub amp. I will run full range to the sub amp and use the variable crossover freq, phase, EQ with Q filter, etc....that works quite well.
Now, what caps to get,,,recommendations will be greatly appreciated even if you tell me I am way up the wrong tree🙂
Thanks,
Rick
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If you have compression driver correction in your passive crossover, you could check my post above, would give you additional headroom with your 10watts. Do not worry about which cap, any audio grade film capacitor will do. It is only one of many your source material has passed through. 22nf polystyrene are still to be found.
Thanks! I forgot to check back and came up with the same value and also type of cap to use, should of come here sooner and saved a lot of time🙂
I am reconsidering everything about this system as being full time RV and the complexity of dealing with noisy power, unstable power, etc...I have two really big AGM batteries I bought for cheap used and might be able to get a third one. I would setup a separate system from the coach batteries just for the audio. I might give up my beloved tube amp and go with car audio amps and even consider building new speakers, bi amp plus stereo subs or tri amp and stereo subs or possibly passive from mid to tweeters. Looking at ribbon, etc mids for a very wide bandwidth though not found one that would work both for mid and tweeter duty.
(I would give the tube amp a try, since only 10 watts it might draw less current than a much higher wattage car amp that would be needed if I built new speakers) I will look for some old school very high end amps, like some I used to run on ID horns, etc.
I have batteries, tons of cable, nearly everything for power, just switch completely to 12 volt and maybe 5 volt(current DAC though looking at other DACs) I have a new Arc audio 1100.1 sub amp but would have to sell it as want to go stereo on the subs, dang. I used to be a dealer, maybe I can work something out, if not I have a buddy that has access to many lines of car audio gear.
Not sure how many have heard a well done high end car audio system but I have, many, built some as well, not in the least bit concerned with achieving exceptional results without spending a fortune, no need🙂
Thanks again, still exploring this idea.
Rick
I am reconsidering everything about this system as being full time RV and the complexity of dealing with noisy power, unstable power, etc...I have two really big AGM batteries I bought for cheap used and might be able to get a third one. I would setup a separate system from the coach batteries just for the audio. I might give up my beloved tube amp and go with car audio amps and even consider building new speakers, bi amp plus stereo subs or tri amp and stereo subs or possibly passive from mid to tweeters. Looking at ribbon, etc mids for a very wide bandwidth though not found one that would work both for mid and tweeter duty.
(I would give the tube amp a try, since only 10 watts it might draw less current than a much higher wattage car amp that would be needed if I built new speakers) I will look for some old school very high end amps, like some I used to run on ID horns, etc.
I have batteries, tons of cable, nearly everything for power, just switch completely to 12 volt and maybe 5 volt(current DAC though looking at other DACs) I have a new Arc audio 1100.1 sub amp but would have to sell it as want to go stereo on the subs, dang. I used to be a dealer, maybe I can work something out, if not I have a buddy that has access to many lines of car audio gear.
Not sure how many have heard a well done high end car audio system but I have, many, built some as well, not in the least bit concerned with achieving exceptional results without spending a fortune, no need🙂
Thanks again, still exploring this idea.
Rick
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