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Old 29th April 2014, 11:50 PM   #1
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Default Recommendation for 5-10W amp.

Hi,

Been looking around to build a nice sounding 5W amp, I have the ACA which I truly enjoy so this leads to for wanting more of Mr Pass design.

I bought some components to built the F5 but this will be later, a fall project. I have a whole bunch of NOS TO3 lateral mosfet that I'd like to use soon.

Looking for some recommendation, I heard that sound wise the Aleph 3 sounds like the ACA, makes sense ? I'd like to avoid building an amp that sounds extremely similar to the ACA which I already own, I'd like to taste a 'different wine' while building a Pass design.

I'm now looking into the Zen but a low power version (+24V-Gnd) to get about 5W. Any other recommendation are welcome.

My speakers are MLTL with FE206E and my music taste is mainly Blues, Jazz and Classic.

I own a few low power tube amps, all SE except for one.

LATEST INFO : Juma came up with a design, please see post no. 217.

Thanks for your time.
Eric

Last edited by e_fortier; 25th July 2014 at 04:05 PM.
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Old 29th April 2014, 11:55 PM   #2
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Old 30th April 2014, 01:37 AM   #3
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Laterals make good versions of the F5, I have several laying around.

Here is a simple one. You will note that it looks very much like a stripped
down version of the Selectronics product.

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File Type: gif lat f5.gif (22.0 KB, 2010 views)
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Old 1st May 2014, 01:42 AM   #4
fab is offline fab  Canada
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Hi Eric

F5 meets Buzquito

You have already heard it a few years ago...

Fab
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Old 1st May 2014, 02:54 AM   #5
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Hi,

Thank you all for the suggestion.

I'm looking for a compact 5W Class A amp., is it possible to use an existing Pass design and reduce the rail voltage while maintaining the overall great sound ?

Thanks,
Eric
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Old 1st May 2014, 03:00 AM   #6
fab is offline fab  Canada
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Quote:
Originally Posted by e_fortier View Post
Hi,

Thank you all for the suggestion.

I'm looking for a compact 5W Class A amp., is it possible to use an existing Pass design and reduce the rail voltage while maintaining the overall great sound ?

Thanks,
Eric
For the one I have pointed out, You can use a regular F5 type pcb , cut the pcb traces for the on-board MOSFET drains to the output and run wires to your to-3 lateral mosfets and that about it. You can use +/- 12 vdc for about 6 wrms/8 ohms.

Fab
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Old 1st May 2014, 05:30 AM   #7
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Hi Fab,

Sounds great, so basically a reduced power F5 with lateral mosfet

Thanks again for your help,
Eric
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Old 1st May 2014, 10:46 AM   #8
juma is offline juma  Germany
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So, it's a single rail 24V power supply, clean 5W cl. A amp that you want - Laterals at the output, different sounding than ACA, right ?

This is what I like (sch. in attachment) - one more F5 modification. Input stage is rearranged to avoid unobtainum small Toshibas (all who tried it reported that it doesn't sound worse than k170/j74, some even like it better). Of course, k170/j74 can be used but in this case I'd recommend GR variant (Idss 3-5mA) since LatFETs need less current drive and have lower Vgs. In that case all additional biasing shebang is not needed (R4/R6, C1/C2).

When I made it, I had reasonably matched transistors and it worked lovely as it's drawn - 12v at the node where drains meet, Id was about 0.7A which is quite all right since with no source resistors we can enjoy the extended class A regime (thanks to FETs' square law transfer curve). If you want to experiment with Id value, use 1k or 2k trimpots instead of R3/R5.

Current through BJTs is set at about 2.5mA (it depends on R4/R6 value) which I chose as a compromise between the need to have enough drive for decent bandwith (>=100kHz) and Ib low enough to provide for decent Zin (50k is fine, good 2u2 coupling caps are plentiful and inexpensive).

Edit: I used k1058/j162 at the output but they are just k135/k50 in flat package.
And yes, C2 polarity should be reversed (drawing error).
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File Type: gif F5-BJT+LAT-SR24.gif (9.4 KB, 1819 views)

Last edited by juma; 1st May 2014 at 10:57 AM.
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Old 1st May 2014, 11:57 AM   #9
flg is offline flg  United States
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Old 1st May 2014, 01:29 PM   #10
fab is offline fab  Canada
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Quote:
Originally Posted by e_fortier View Post
Hi Fab,

Sounds great, so basically a reduced power F5 with lateral mosfet

Thanks again for your help,
Eric
This description fits more the one Nelson shown in post 3.

The last one from Juma should also be a good alternative although I would use double polarity supply to get rid of the big output cap...

Fab
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