xrk971 Pocket Class A Headamp GB

[pvs]

Those Chinese parts can work but the pot and headphone connector are critical to sound quality as bad pots are not linear and can actually add noise and distortion. The genuine ALPs was $3 I think so you are saving if you make more than two.

I also buy and use inexpensive Chinese parts - mostly on prototype P2P serial number 0 jobs. Then I use higher quality stuff for next builds to get best performance.

Ideally, I'll build be building a bunch more after the pilot. The pots and jacks doubled the Digikey bill.

You need about 200mA to work with DC step up. Get ones that don’t whine. That’s not acceptable.

You recommended them, not me.

 

[xrk971]

Which ones did I recommend that whine/whistle. Edit - saw your link from earlie roost - that converter should be good. I have used many of them and the FFT is clean like a battery. It’s powering my Aksa Lender HPA at present. That same white aluminum PCB sits under the main board:

Here’s the FFT using that DC step up (no sign of a whine or anything):

The MT3608 has a 1.2MHz switch speed so that can’t be it:
MT3608 MAX 2A Output 28V DC DC Step Up Converter Booster Power Apply Module Booster Power Module For Arduino-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

These are the ones I have had a problem with whine noise are the XL6009:
DC-DC Adjustable Step Up Converter Power Supply Module 3.2-32V In XL6009 Boost | eBay

Whereas these are very quiet:
DC DC boost converter Constant Current Mobile Power supply 250W 10A LED Driver | eBay

This is quiet too:
8-32V Step-up to 9-46V DC-DC Boost Converter 150W 8A Power Supply Module | eBay

But you need to pass them through a cap multiplier and a CRCRC.

 

[xrk971]

Hi Folks,
I just realized I never posted the correct schematic for the production version of the Desktop Amp. Here is the correct one that corresponds to the numbering on the virtual silkscreen on the stuffing guides. BOM in txt file below.
X

The portrait mode version of the schematic below will print out better on paper.

BOM:

xrk971 Desktop Class A HPA v2 May 9, 2018
BOM

Part Value Device Package Description
C101 10µ0 CPOL-EUE3.5-8 E3,5-8 POLARIZED CAPACITOR, European symbol
C101A C22/10 C22.5B10 CAPACITOR
C101B C27/17 C27.5B17 CAPACITOR
C101C 0µ1 MKC1860-0U1 MKC1860-0U1
C101D 10µ0 MCAP250V10U MCAP250V10U Fidelity Component MCap
C102 10µ0 CPOL-EUE3.5-8 E3,5-8 POLARIZED CAPACITOR, European symbol
C102A C22/10 C22.5B10 CAPACITOR
C102B C27/17 C27.5B17 CAPACITOR
C102C 0µ1 MKC1860-0U1 MKC1860-0U1
C102D 10µ0 MCAP250V10U MCAP250V10U Fidelity Component MCap
C111 1µ0 C5/5 C5B5 CAPACITOR
C111A C10/6 C10B6 CAPACITOR
C111B C15/8 C15B8 CAPACITOR
C112 1µ0 C5/5 C5B5 CAPACITOR
C112A C10/6 C10B6 CAPACITOR
C112B C15/8 C15B8 CAPACITOR
C113 2200uF CPOL-EUE7.5-18 E7,5-18 POLARIZED CAPACITOR, European symbol
C113A CPOL-EUE5-10.5 E5-10,5 POLARIZED CAPACITOR, European symbol
C114 2200uF CPOL-EUE7.5-18 E7,5-18 POLARIZED CAPACITOR, European symbol
C114A CPOL-EUE5-10.5 E5-10,5 POLARIZED CAPACITOR, European symbol
C131 220µ CPOL-EUE5-13 E5-13 POLARIZED CAPACITOR, European symbol
C133 1µ0 C5/5 C5B5 CAPACITOR
C134 2200µ CPOL-EUE5-13 E5-13 POLARIZED CAPACITOR, European symbol
C135 2200µ CPOL-EUE5-13 E5-13 POLARIZED CAPACITOR, European symbol
C141 2200µ CPOL-EUE5-13 E5-13 POLARIZED CAPACITOR, European symbol
C142 2200µ CPOL-EUE5-13 E5-13 POLARIZED CAPACITOR, European symbol
C143 1µ0 C5/5 C5B5 CAPACITOR
C144 1µ0 C5/5 C5B5 CAPACITOR
R101 RK09L12B RK09L12B
R102 100k CMF-55 CMF-55
R103 100k CMF-55 CMF-55
R104 22k0 CMF-55 CMF-55
R105 22k0 CMF-55 CMF-55
R106 1k1 CMF-55 CMF-55
R107 68R0 CMF-55 CMF-55
R108 250R CMF-55 CMF-55
R109 1k1 CMF-55 CMF-55
R111 68R0 CMF-55 CMF-55
R112 250R CMF-55 CMF-55
R113 47R0 CMF-55 CMF-55
R114 47R0 CMF-55 CMF-55
R115 270R CMF60 CMF60
R116 270R CMF60 CMF60
R117 270R CMF60 CMF60
R118 270R CMF60 CMF60
R119 270R CMF60 CMF60
R121 270R CMF60 CMF60
R122 270R CMF60 CMF60
R123 270R CMF60 CMF60
R124 270R CMF-55 CMF-55 (can be up to 1k if using 600ohm cans)
R125 270R CMF-55 CMF-55 (can be up to 1k if using 600ohm cans)
R131 10k0 R-EU_0207/10 0207/10 RESISTOR, European symbol
R132 220R R-EU_0207/10 0207/10 RESISTOR, European symbol
R133 1R5 R-EU_0207/10 0207/10 RESISTOR, European symbol
R134 0R47 R-EU_0309/12 0309/12 RESISTOR, European symbol
R135 0R47 R-EU_0309/12 0309/12 RESISTOR, European symbol
V101 BF862 SST201 SOT23 TEMIC / Siliconix N-Channel JFET
V102 BF862 SST201 SOT23 TEMIC / Siliconix N-Channel JFET
V103 JFET 2SK170 TO92-DGS Field Effect Transistor Silicon N Channel Junction Type 2SK170 Audio Grade
V104 JFET 2SK170 TO92-DGS Field Effect Transistor Silicon N Channel Junction Type 2SK170 Audio Grade
V111 IRF610 IRF512 TO220BV N-CHANNEL MOS FET
V112 IRF610 IRF512 TO220BV N-CHANNEL MOS FET
V131 1N4004 1N4004 DO41-10 DIODE
V132 IRF610 IRF512 TO220BV N-CHANNEL MOS FET
X101 22-27-2021-02 22-27-2021-02 6410-02 CONNECTOR unknown unknown
X102 22-27-2021-02 22-27-2021-02 6410-02 CONNECTOR unknown unknown
X111 22-27-2021-02 22-27-2021-02 6410-02 CONNECTOR unknown unknown
X112 22-27-2021-02 22-27-2021-02 6410-02 CONNECTOR unknown unknown
X131 22-27-2021-02 22-27-2021-02 6410-02 CONNECTOR unknown unknown
X132 AK500/2 AK500/2 CONNECTOR unknown unknown
X1011 SK104 SK104 SK104 HEATSINK manufacturer Fischer/distributor Buerklin
X1012 SK104 SK104 SK104 HEATSINK manufacturer Fischer/distributor Buerklin
X1031 SK104 SK104 SK104 HEATSINK manufacturer Fischer/distributor Buerklin

 

[yourownbuzz]

All good now thanks - I just ordered 3 of them

 

[xrk971]

All good now thanks - I just ordered 3 of them

@YOB: Thanks for the order. I just got the BOM and Schematic posted above.

@dummyaccount: what was the issue because those white aluminum PCB DC-DC converters are quite good - capable of at least 6amps at 29v I know that as was tested.

 

[yourownbuzz]

woah that's quite the parts list !
looking closer - are the input/ouputs some sort of jst-style connector (and not 3.5mm jacks)?

Just noticed the post about the aska lender headphone amp - how does that stack up to the PCA/PCA desktop?

 

[twocents]

Just noticed the post about the aska lender headphone amp - how does that stack up to the PCA/PCA desktop?

Yup, would be interesting to know. Or do we have to wait for the next Blind Virtual Audition?

 

[yourownbuzz]

haha the answer better be pca is better - otherwise id be kicking myself for not adding a set of the lender PCBs to cart before ordering! (postage for the first board is steep and more manageable after that )

 

[twocents]

Yes, otherwise we can try to bribe the author of the poll. Whatever the outcome - we will never run out of amp builds soon.

 

[xrk971]

haha the answer better be pca is better - otherwise id be kicking myself for not adding a set of the lender PCBs to cart before ordering! (postage for the first board is steep and more manageable after that )

I can slip in a few for you before the postman comes. consider it done.

 

[xrk971]

woah that's quite the parts list !
looking closer - are the input/ouputs some sort of jst-style connector (and not 3.5mm jacks)?

Just noticed the post about the aska lender headphone amp - how does that stack up to the PCA/PCA desktop?

The small connectors are all 2.5mm pitch JST or even standard PCB headers broken off to just 2pins work (or, gasp, flying leads soldered to board). The larger one in the middle for power entry is 5mm and usual 2-pin screw terminal block can be used. BOM looks long because of all the optional cap positions for input and output.

Regarding sound quality of Aksa Lender HPA vs this one? I have to build it and then can tell you.

 

[DontHertzMe]

The genuine ALPs was $3 I think so you are saving if you make more than two. The 3.5mm jacks by Switchcraft are actually machined brass that is nickel plated. They engage well and don’t have scratchy noise. They are $5/pair. Pricey but not in the scheme of things.

Good points here . Decent quality pots and jacks are absolutely worth the money.

 

[tonza75]

Good points here . Decent quality pots and jacks are absolutely worth the money.

Alps rk501 is a good pot

 

[pcgab]

Maybe I missed it on the schematic/bom, but what value is the pot?

 

[tonza75]

Maybe I missed it on the schematic/bom, but what value is the pot?

Don't know good pot go for 100 upto.....

 

[xrk971]

I have always used 10k ALPS RK09 series pots on the PCA and that does a nice job. At max volume it’s equivalent to 9k with 100k resistor to ground. Most sources drives 9k loads well. Probably a 47k or even 100k works but maybe noise pickup might be more of a concern.

 

[pcgab]

I have always used 10k ALPS RK09 series pots on the PCA and that does a nice job. At max volume it’s equivalent to 9k with 100k resistor to ground. Most sources drives 9k loads well. Probably a 47k or even 100k works but maybe noise pickup might be more of a concern.

I'll likely build a stepped attenuator ultimately, might run an ALPS blue for the time being, have to see what's in the parts box.

A quick point of clarification:

The desktop can use _either_ BF862 or 2sK170's? or needs both. I would think either, but can't remember exactly.

Cheers,
Gable

 

[xrk971]

Either JFET for the input. Personally, I think the BF862 is higher performance relative to lower noise and higher speed.

 

[pcgab]

Either JFET for the input. Personally, I think the BF862 is higher performance relative to lower noise and higher speed.

Awesome, I was planning on using BF862s. I have ~300-400 of them to match from, should be plenty to get a good match, haha.

Thanks X~
Gable

 

[xrk971]

I have ~300-400 of them to match from

Wow, you have me beat as I have 250 and I thought that was lot

Probably can do it in 25 from same batch to within 1%

Now you need to match IRF610's. You probably know but 3-pin 5mm pitch screw terminal blocks hold TO220 3-legged creatures very well for such testing.