Two simple Current Amplifiers for low impedance loads

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #20 on: 1 Apr 2009, 09:03 pm »
+1

Paul Hynes

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #21 on: 3 Apr 2009, 01:34 pm »
Hi Folks,

For those interested in building the current amplifiers SE1 or CIRC1.

I have checked with one of the UK distributors of IXYS Semiconductors and they will supply me with a smaller quantity than Mike was quoted from USA distributors. Unfortunately the price is not comparable to ordering 60, but who wants to order 60 when you only need 4.

After covering my costs and the time element of order processing I can offer the IXTH 20N50D at £12 each plus insured carriage and packing at cost. I will be ordering some for myself, during the next week, so if anyone is interested, let me know and I will include them in the order. I have been told I can have a small order shipped within 14 days at present as they can access some stock fairly quickly. I will work out the carriage/packing cost tomorrow and post the details.

Regards
Paul

jkeny

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #22 on: 19 Apr 2009, 01:16 pm »
Hi Paul,
I have picked up on this from your post on DIYA. Thank you for introducing us to an innovative & simplistic & more importantly good sounding circuit. It's these moments that keep me coming back to to the DIY forums - you never know when or where these unique ideas might spring up!

Not wanting to drag the thread off in another direction but you mentioned that lateral mosfets may be used. I have some of these lateral mosfets (12A 200V 125W RMS) http://www.classd.ltd.uk/product.php?productid=16174&cat=0&bestseller=Y which come at a very keen price of £3.30 & I thought of using these. There are also double die versions (24A 200V 250W RMS) available for £7.48.

Could you post a suitable bias circuit, please. Any other considerations need to be taken into account in using these?

I'm also wondering if the added cost & complexity of the extra bias circuitry needed for these parts is worth the few bob in savings?

I'll no doubt have some Qs about the PS when I study some more - if that's OK?

« Last Edit: 19 Apr 2009, 02:23 pm by jkeny »

jkeny

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #23 on: 19 Apr 2009, 02:48 pm »
I would be interested in a group buy - only need 15 people at 4 devices each for the minimum order qty of 60!

I don't have high efficiency speakers. My two current sets are both mini-monitors - Jordan JX92S & Rogers LS3/5A - not efficient by any means so I need a voltage gain stage. I'm building one based on a beam deflection tube circuit by John Swenson which gives a balanced out signal. This, I imagine, would be perfect for use with the Circ1.



Paul Hynes

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #24 on: 19 Apr 2009, 06:14 pm »
Hi JK,

The CIRC1 circuit with Lateral Mosfets works very well. I would use the double die version but in a metal can if you can get these. This will give plenty of reserve to drive difficult loads. The bias circuit (positive for the lateral mosfets) is quite simple and can be driven from the HT in the voltage gain stage. I will prepare some documentation for you when I have finished posting the "Lightspeed" remote control documentation on my website. This is nearly ready now as it just needs tidying up and including in the updated website which I should have posted over the next day or two.

With low efficiency 8 ohm speakers you will need higher supply rails than the amplifiers I use to drive the line arrays so you would have to use a bias circuit on the IXYS devices (in this case a negative bias just like a valve) to drop the quiescent current to limit the dissipation to sane levels.

How much voltage gain will the Swenson circuit give you?

Regards
Paul


jkeny

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #25 on: 19 Apr 2009, 06:59 pm »
Hi Paul,
I'm looking forward to your VCCS - I'm on the prepaid list for these.

John Swenson has had this circuit up to 90V PP without any increase in distortion. Schematic here:

Without giving away your commercial secrets, any pointers to a good regulated high current PS schematic?

jkeny

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #26 on: 19 Apr 2009, 07:46 pm »
BTW, this BDT preamp is like the lightspeed in that the signal doesn't go through a potentiometer. The volume is controlled by adjusting the voltage on the screen & as such is also open to remote control

Edit: The Jordans are 8 Ohm, I think but the Rogers LS3/5As are nominal 15 ohm speakers - are there other considerations for a 15 ohmer like this?

Paul Hynes

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #27 on: 22 Apr 2009, 01:16 pm »
Hi JK,

Sorry I can't release any power supply schematics as they are either in use commercially and/or the subject of non-disclosure agreements.

I can recommend a regulator module for the HT supply for you, but I had better not do that on this thread, as I would break the commerce rules. It will be tomorrow before I can get back to you as I will be busy for the rest of the afternoon preparing for a director's meeting this evening. I will also deal with your post about loudspeaker impedance tomorrow.

Regards
Paul




jkeny

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #28 on: 22 Apr 2009, 07:36 pm »
No problem, Paul

Paul Hynes

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #29 on: 23 Apr 2009, 01:06 pm »
Hi JK,

The Rogers LS3/5a is very insensitive at 83 dB for 1 w at 1 mtr and with limited power handling (only 25 w continuous with the earlier models). I used these speakers extensively in the 1980's so I am aware of their quirks. I would aim for around 50 watts into 15 ohms nominal for these speakers and forget high level listening. This will get you to around 100 dB before clipping.

The CIRC1 configuration on 45 volt supply rails using lateral mosfets biased just high enough to remove crossover artifacts would work well with the LS3/5a and would allow 100 w delivery into the 8 ohms Jordans. The sensitivity of the Jordans is higher at 88 dB for 1w at 1 mtr and the power handling is 50 w continuous. 100 w should take you to around 106 dB before clipping.

If you are worried about exceeding the power handling of the speakers you would be more likely to damage them by repetitive clipping of a smaller amplifier  (this can generate a surprising amount of energy that can overheat the driver voice coils) than occasional clipping of a larger amplifier.

The amplifier power supply should be rated to delivery at least 5 amps for 100w into 8 ohms and more if you intend to use it with lower impedance loads in the future. Because this application will use 45 volt approx supply rails It would not be sensible to use it on very low impedance loads like my line arrays. 4 ohms would be ok.

I posted about a regulator option on the "Paul Hynes Power Supplies" thread in the "Industry Talk and Events" circle.

Regards
Paul

gstew

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #30 on: 15 Nov 2010, 01:21 am »
Paul,

I saw the recent posts by you and Sondale on your SE1 and was very intrigued. I have very inefficient planar speakers, but Sondale's speakers seem to be about as in-efficient and the SE1 works well for him... so now I'm very interested.

In your first post in this thread, you said:

"These output stages are adaptable to any loudspeaker load, not just low impedance loads, and I have made versions up to 100 watts into 8 ohms by adding voltage gain stages constructed with valves and resizing the power supply voltage/current capability. I will present designs for voltage gain stages if any interest is shown on the forum."

Could you please?

THANKS!

Greg in Mississippi

Paul Hynes

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #31 on: 16 Nov 2010, 06:32 pm »
Hi Greg,

How are you keeping?

Use of the SE1 with inefficient speakers will depend on how loud you tend to play your music. The CIRC1 may be the better option as it can be engineered for much greater output without too much thermal management penalty.

I have had a number of enquiries about applying these output stages, and providing voltage gain stages for them, so they are more user-friendly with normal systems. So I am going to re-open the case on these projects and also the open baffle line source array I use in my system as people have been asking about this too. It will have to be done in sections, as time allows, as I am very busy at present and have little free time. I will set up threads in the Paul Hynes Design Circle so all the discussions can be centralised and easier to find.

Regards
Paul

gstew

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Re: Two simple Current Amplifiers for low impedance loads
« Reply #32 on: 17 Nov 2010, 02:56 am »
Paul,

Doing pretty well here, working too much to do much audio work right now tho!

I'm not a head-banger & am very intrigued by the Circlotron version too, but I'm slowly getting my turntable setup running again too and all of my current & potential phono stages are SE, so the SE-1 looks like a better compromise option.

I'll watch for your future posts in your circle. Keep up the great work!

Later!

Greg