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PostPosted: 20 Dec 2019, 17:43 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Just completed another (5th, this time three in a row) Holton inspired amps. What I like about this 150W (200 into 4) amp is it only has two power devices. Once agin the Exicon ECW20N20 and 20P20 high end audio lateral dual die FETs are used. My thought is because there is only two power devices detail and transparency should be improved compared to the eight power devices in my recent 300W Holton amp. Regardless. The amp has its usual bass heft and clarity. Quoted distortion is 0.005%.

A 300W Tranni and 80,000uf of capacitance makes up a simple but rugged PS. I used X2 snubbers this time instead on brown polies.
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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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PostPosted: 29 Dec 2019, 17:51 
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Joined: 23 Feb 2017, 02:02
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I like the fancy output transitors but the gain stage seems to be poor, not many transitors.


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PostPosted: 29 Dec 2019, 18:01 
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I never expect my power amps to have high gain. All my tube and SS preamps provide more than enough.

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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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PostPosted: 29 Dec 2019, 18:31 
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Joined: 23 Feb 2017, 02:02
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More feedback for the low distortion, not more gain.

From photos your thing looks like ones with low distortion minize the distortion then feeedback none or very little.


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PostPosted: 30 Dec 2019, 18:06 
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At first and a week ago looking at this post I only saw like 3-4 transitors and the use of 4 capacitors made me think its like a amp with low distortion then feedback none or very little.

Today I see like 10 transitors excluding the outputts, judging from the way its set on the PCB I'm guessing the amp design is a fully symmetrical OP AMP which is widley used for audio。
The cappacitor green one which is HIFI bipolar seems like the capacitor which grounds the feedback resitor.

With those silicone isolators the heat transfer is very poor (2C/W) compared to mica ones which standard ones about 1C/W with smaller To-247 packages, manually cutting the mica thinn will alllow 0.5C/W of themral resistance.


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PostPosted: 30 Dec 2019, 18:18 
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I wondered about the sticky insulators but others building similar amps have used them and not complained. I may have got better cooling with mica but in the end I’m getting good results now.

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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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PostPosted: 30 Dec 2019, 18:36 
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Mica dosen't cost much from aliexpress......


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PostPosted: 30 Dec 2019, 18:40 
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ILoveHiFi wrote:
Mica dosen't cost much from aliexpress......
i have a full set and can purchase them locally at staff price but thought I’d give the sticky ones a go.

I may build a sixth amp - 300Wer - so May use mica then.

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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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PostPosted: 30 Dec 2019, 18:47 
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Don't forgget to use heatsink grease with mica..... mandatory otherwise very poor results
Allot of products from China littratley just slap on mica without paste.


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PostPosted: 30 Dec 2019, 21:29 
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ILoveHiFi wrote:
Don't forgget to use heatsink grease with mica..... mandatory otherwise very poor results
Allot of products from China littratley just slap on mica without paste.

Been using mica and past since 1970. Silipads now and sticky ones too.

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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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