HELP! Struggling to find the right amp!

spamjam · 12th November 2010, 03:05 PM

Hi,

I am new to the forum so please forgive me if I have posted in the wrong place or something!

I have a slightly unusual problem in that I am trying to find an amplifier that can generate a voltage of up to about 70V as part of a scientific project I am working on. Previously I have seen the Rolls RA2100b and the Crown DC300A used for this but I cannot obtain either of these and don't know what I should use as an alternative. I am new to this field and so am not familiar (yet) with all the terms and details of the amplifiers, although I am learning!

The signal I need to amplify is a square pulse and so to avoid distorting the signal it is my understanding that the THD and the frequency response need to be as good as possible?

My query is whether a 'standard' audio amp (such as those available from hi-fi stores) can generate this kind of voltage as these seem to offer the best in terms of distortion and frequency response? I have been trawling through the manufacturers details but am not seeing anything that relates to voltage output, just the power ratings. Is there a way of working out the voltage from this?

As the budget is is quite tight I cannot afford to spend thousands of pounds on this, so far I have had a range of PA type power amps suggested but I am unsure if this would do the job?

In the long-term I would like to build something for the job but at the moment I need to get hold of one asap. Any help/explanations/advice would be very much welcome!

Thanks!

bobodioulasso · 12th November 2010, 03:45 PM

You speak about voltage only. Though, we need to know more about the load you intend to use. Do you need power or voltage only?
Is it resistive, reactive? How much current do you need into that load.

An audio power amp is intended to produce power, not voltage only.

spamjam · 12th November 2010, 03:56 PM

Hi,

Thanks for your reply, I will try to include more detail but as I am new to this field there are many things I do not know!

The voltage signal produced will be amplified by the amp and then passed on to wire electrodes and then through artificial tissue that would probably be high resistance. My understanding is that it is the voltage that we are after and that the power is less of an issue. the main thing is to produce a stimulation voltage of something in the range of 20-70V with minimum distortion of the square pulse.

I hope that this helps in some way, it is quite hard to explain what I am trying to set up - please forgive my ignorance on this topic at the moment, trying to learn!

richie00boy · 12th November 2010, 05:10 PM

If it is a square wave then an audio amplifier - which has a necessarily limited bandwidth - would not be the best choice.

It sounds like you don't need much current, probably milliamps. This makes things easier.

spamjam · 12th November 2010, 05:18 PM

OK thanks, if an audio amplifier would maybe not be the best choice then can you suggest any other options that I could look into? I have mainly been looking at audio/PA places and RDL too but haven't really got a clue where to look for alternatives.

I would love to be able to build one but as I am so inexperienced and just trying to get my head around using LabView software at the moment too to build this system it would be easier to buy one at this stage and build one if necessary later when I know a bit more about it!

Nico Ras · 12th November 2010, 05:27 PM

What is the pulse width and period. It sounds like a TEMS device.

spamjam · 12th November 2010, 05:31 PM

Thanks Nico Ras - I think the pulse width will vary depending on the experiment - ranging from 0.2-2 ms for example. The pulses will either be a single pulse, or a train of pulses at varying frequencies in the range of 20-100Hz.

What is a TEMS device?

bobodioulasso · 12th November 2010, 06:56 PM

At this frequency, an audio amp will do the job.
Though it would be a waste as you do not need power.
You need a voltage amplifier. Or an audio amp without his output stage. And without the need of a big powerfull transformer.
If it was me, i would use an LME49830 powered at +/- 75 volts with a small (20Va) transformer, and without output stage.
You can google for lme49830, download the pdf, and look at p 6.
This circuit diagram shoud meet your requirements if you do not need more than 50mA.
Just an idea. Any comment?

djk · 12th November 2010, 08:22 PM

Crest Audio CKV100 Power Amp - eBay (item 250725072787 end time Nov-17-10 16:16:35 PST)

Two channels at 70V/50W, will probably go cheap.

Xoc1 · 12th November 2010, 10:26 PM

Is the 70V in relation to ground, or could both terminals be floating? There are many amps that could generate 70V potential in bridge mode.

12th November 2010, 03:05 PM	#1
spamjam diyAudio Member Join Date: Nov 2010	HELP! Struggling to find the right amp! Hi, I am new to the forum so please forgive me if I have posted in the wrong place or something! I have a slightly unusual problem in that I am trying to find an amplifier that can generate a voltage of up to about 70V as part of a scientific project I am working on. Previously I have seen the Rolls RA2100b and the Crown DC300A used for this but I cannot obtain either of these and don't know what I should use as an alternative. I am new to this field and so am not familiar (yet) with all the terms and details of the amplifiers, although I am learning! The signal I need to amplify is a square pulse and so to avoid distorting the signal it is my understanding that the THD and the frequency response need to be as good as possible? My query is whether a 'standard' audio amp (such as those available from hi-fi stores) can generate this kind of voltage as these seem to offer the best in terms of distortion and frequency response? I have been trawling through the manufacturers details but am not seeing anything that relates to voltage output, just the power ratings. Is there a way of working out the voltage from this? As the budget is is quite tight I cannot afford to spend thousands of pounds on this, so far I have had a range of PA type power amps suggested but I am unsure if this would do the job? In the long-term I would like to build something for the job but at the moment I need to get hold of one asap. Any help/explanations/advice would be very much welcome! Thanks!

12th November 2010, 05:10 PM	#4
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	If it is a square wave then an audio amplifier - which has a necessarily limited bandwidth - would not be the best choice. It sounds like you don't need much current, probably milliamps. This makes things easier. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

12th November 2010, 08:22 PM	#9
djk diyAudio Member Join Date: Feb 2001 Location: USA	Crest Audio CKV100 Power Amp - eBay (item 250725072787 end time Nov-17-10 16:16:35 PST) Two channels at 70V/50W, will probably go cheap. __________________ Candidates for the Darwin Award should not read this author.

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12th November 2010, 03:45 PM	#2
bobodioulasso diyAudio Member Join Date: May 2008	You speak about voltage only. Though, we need to know more about the load you intend to use. Do you need power or voltage only? Is it resistive, reactive? How much current do you need into that load. An audio power amp is intended to produce power, not voltage only.

12th November 2010, 03:56 PM	#3
spamjam diyAudio Member Join Date: Nov 2010	Hi, Thanks for your reply, I will try to include more detail but as I am new to this field there are many things I do not know! The voltage signal produced will be amplified by the amp and then passed on to wire electrodes and then through artificial tissue that would probably be high resistance. My understanding is that it is the voltage that we are after and that the power is less of an issue. the main thing is to produce a stimulation voltage of something in the range of 20-70V with minimum distortion of the square pulse. I hope that this helps in some way, it is quite hard to explain what I am trying to set up - please forgive my ignorance on this topic at the moment, trying to learn!

12th November 2010, 05:18 PM	#5
spamjam diyAudio Member Join Date: Nov 2010	OK thanks, if an audio amplifier would maybe not be the best choice then can you suggest any other options that I could look into? I have mainly been looking at audio/PA places and RDL too but haven't really got a clue where to look for alternatives. I would love to be able to build one but as I am so inexperienced and just trying to get my head around using LabView software at the moment too to build this system it would be easier to buy one at this stage and build one if necessary later when I know a bit more about it!

12th November 2010, 05:27 PM	#6
Nico Ras diyAudio Member Join Date: Nov 2005 Location: Amanzimtoti - East Coast of South Africa	What is the pulse width and period. It sounds like a TEMS device.

12th November 2010, 05:31 PM	#7
spamjam diyAudio Member Join Date: Nov 2010	Thanks Nico Ras - I think the pulse width will vary depending on the experiment - ranging from 0.2-2 ms for example. The pulses will either be a single pulse, or a train of pulses at varying frequencies in the range of 20-100Hz. What is a TEMS device?

12th November 2010, 06:56 PM	#8
bobodioulasso diyAudio Member Join Date: May 2008	At this frequency, an audio amp will do the job. Though it would be a waste as you do not need power. You need a voltage amplifier. Or an audio amp without his output stage. And without the need of a big powerfull transformer. If it was me, i would use an LME49830 powered at +/- 75 volts with a small (20Va) transformer, and without output stage. You can google for lme49830, download the pdf, and look at p 6. This circuit diagram shoud meet your requirements if you do not need more than 50mA. Just an idea. Any comment?

12th November 2010, 10:26 PM	#10
Xoc1 diyAudio Member Join Date: Nov 2008 Location: Devon UK	Is the 70V in relation to ground, or could both terminals be floating? There are many amps that could generate 70V potential in bridge mode.

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