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Old 4th May 2013, 07:59 AM   #931
AndrewT is offline AndrewT  Scotland
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Is there an advantage if the LTP tail resistor gradually turns off the tail current when the supply rails are falling rapidly?
Maybe preventing oscillation on falling rail voltage?
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Old 12th May 2013, 09:36 AM   #932
AndrewT is offline AndrewT  Scotland
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bump my question
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Old 13th May 2013, 10:39 PM   #933
Bonsai is offline Bonsai  Taiwan
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This is only an issue at start up/ switch off and any decent amp will provide speaker muting anyway.

I don't think the resistor is there to prevent damage if the current source fails. It's usually used so you can deploy a TO-92 device and not a TO-126.
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Old 14th May 2013, 08:45 AM   #934
AndrewT is offline AndrewT  Scotland
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Yes particularly during power down.
I have a PCB from one of our very reputable amp designers and it whistles for about half the power down period (~15seconds).

That is quite unacceptable. To me that is an amplifier failure.
I have now incorporated an output relay with delayed start, instant off and DC detect. This hides the problem. It does not cure the instability on falling supply rail voltage.

I have another that sends repeated thumps to the speaker as it powers down. Again a design failure. But this time I modified the the PSU layout by separating the low current stages from the high current stage with a high value RC filter. I suspect that I have a motorboating problem. This time I have incorporated a design failure by using a well recommended modification. Again I could hide the problem with an output relay.
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Old 15th May 2013, 04:43 PM   #935
cod3gen is offline cod3gen  Norway
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If i where to use a Lundahl audio transformer on input, what components should i remove on the amp? Since transformer would block any DC from comming to input..
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Old 15th May 2013, 04:47 PM   #936
AndrewT is offline AndrewT  Scotland
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The input transformer does not block the DC from the source.
The transformer will have it's performance ruined if you allow ANY DC to get in from the Source.
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Old 4th June 2013, 08:43 AM   #937
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Perhaps it could be said that signal coupling transformers are not a solution to DC at the source,
since DC flow in the primary could saturate the core and ruin performance.

I think that an interstage audio coupling transformer designed to handle a few watts even, would have
little trouble from say, the output of a single rail transistor preamp or a balanced rail Opamp design.
Just be sure to talk with your bank's credit manager before buying one that approaches hi-fi quality.

SQ is another issue and frankly, a top quality film/foil cap will beat any transformer on fidelity,
however cool the idea of using a transformer somewhere in your system currently is.
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Old 15th June 2013, 12:14 PM   #938
jimchan is offline jimchan  Norway
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hello gents, has anyone made a mouser shared cart with all/most of the components ?

Thx,
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Old 27th June 2013, 03:18 PM   #939
6L6 is offline 6L6  United States
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A request for help...

The DIYaudio store is updating the webpages of the various PCB and other products.

We would like to have better descriptions of the amps so interested parties can get a good sense of what the product is, does, etc... to better inform his choice.

I've done a few of the Firstwatt clones so far - (None are complete yet, but you will get the general idea.)

F-5 clone boards (2 PCBs, makes 2 channels; Rev 2.0) - First Watt Clones - Power Amplifiers - Circuit Boards

F-4 clone boards (2 PCBs, makes 2 channels; Rev 2.0) - Power Amplifiers - Circuit Boards

Aleph J (2 PCBs. Makes 2 channels. Rev 2.0) - Circuit Boards

In general, the store people don't know enough about this amp to make an informed description/flyer/blurb. Espicially as the PSU requirements are such a wide net. Any info would be greatly appreciated.

Can you help? This would be a great chance to give a few moments than can help support the forums. Just put it into this thread and I will assemble all the pertinent bits. (you can see that there is even a decent amount of copy/paste that will work from the Firstatt-style amps. )


Here is the copy of one of those if you don't want to open the other page -

```````````````


Details

This pair of F-5 Clone circuit boards use the same circuit as the Nelson Pass / Firstwatt F-5 model.
Circuit Description
The F5 is a Push-Pull, Class-A power amplifier. It is unique in that it has no capacitors in the amplifier circuit. The F5 is a voltage source amplifier, requiring nothing out of the ordinary from your preamp or speakers.
The F5 is probably the most popular amplifier being built on DIYaudio these days. It is simple to make, sounds fantastic, and has similar gain to many commercial amps.
Populate these boards with your components, then add your own power supply, chassis and heat sinks to complete the amplifier. The mounting hole spacing is the same as all other diyAudio Version 2 UMS boards.
Output power
25WPC into 8ohm
Power supply requirements
A Bipolar power supply of (+/- 24V) is required. This will require an 18V+18V (or 36V Center Tapped) transformer from 300-500VA, and PSU capacitance of 30,000uF per rail or more. The PSU for the F4, F5, and Aleph J are all essentially identical. See the F5 build guide for details.
Chassis suggestions
The 4U Deluxe Amplifier Chassis makes a great home for this amplifier, and has pre-tapped holes that match the circuit board and transistor mounting positions. The DIYaudio "Universal Mounting Spec" (UMS) is a common mounting pattern between the amplifier PCB and the heatsinks. If you utilize the UMS on your heatsinks or use one of the pre-drilled chassis from DIY audio, you will be able to quickly and easily mount different amplifier boards in the same chassis. For example, a 4U 'Jack of all Chassis' with a 400VA, 18V+18V transformer and PSU board, will give you a power supply and chassis where you could try the F4, F5, F5C, Aleph J, and other Pass/Firstwatt amps in the future merely by swapping the amp PCB. The investment in Chassis and PSU needs only be made once.

Please see the F5 thread in the store support forum for any questions you might have and a definitive list of relevant links and resources.


`````````

Thank you in advance,

-Jim
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Old 27th June 2013, 05:00 PM   #940
redjr is offline redjr  United States
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Those of you who have built the Honey Badger amp... what is the ballpark cost for an entire 2-channel amp? Keyword being ballpark. I don't need the cost itemized, but just wanted to make sure the items shown below are included in the estimate.

(1) AMP PCBs
(2) PSU PCB
(3) Complete component BOM for amp and PSU
(4) Heat sinks
(5) Tranny
(6) Suitable enclosure (I know this one can vary a lot)
(7) Misc. items

Thx,

Rick
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