xrk971 Desktop Class A (DCA) Headphone Amp

maulana · 2021-12-29 11:15 am

xrk971 said:
Over in the Yarra thread we discuss the new setpoints for PCA/DCA daughterboard (same as DCA in principle) either the 2SK209GR or 2SK170BL(available from GB’s) or LSK170BL. Those 2SK209GR’s are Toshiba JFETs and still available.

The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Use IRF610 or Fairchild FQP4N20 work very well too.

You will wait a long time since I have a lot of the original boards left.

Hi. Can i use MPF102 or 2sk30? Can you help with the resistor adjustment for MPF102 or 2sk30?
Thank you so much

xrk971 · 2021-12-29 3:04 pm

I don’t have models for those actives. You could search for the models yourself and put it into the LTSpice model. If you send me the schematic .ASC file with the models I can help you adjust it and optimize it. But I don’t have time to go find models and get it all to work for you. That’s your DIY part. Or you can use the parts I specified and no tweaking or adjustments necessary.

R Man · 2022-01-02 5:17 pm

I built this up on veroboard with 2sk209gr as in the above schematic with a linear power supply. Sounds fantastic on my Grados! Very smooth and natural. Not quite as musical and nuanced as my much more expensive and complex 4p1l tube amp, but very good indeed. Thanks for sharing the design. Notice the gigantic 4.7uF Obbligato Copper input caps left over from a tube amp build.

xrk971 · 2022-01-02 6:17 pm

Rman,
Fantastic plank amp! That’s how most of my amps look.

Glad that is sounds great. It works superbly as a preamp as well. Those caps are superb looking. Probably cost as much as BOM of one of these amps to build.
Cheers,
X

maulana · 2022-01-04 9:19 am

Hi X. Thank you for the reply.
I want to build this amp as a standalone device. I decided to use 2sk170, based on this schematic and using resistor setting from this post

https://www.diyaudio.com/community/...or-melbourne-db-group-buy.334457/post-5898779
The question is:

1. Is the value correct for 32 ohm headphones?
2. What is the output impedance for this particular setup?
3. On the description it says that R102+R104 = 2K. That means 1K each, right?
BTW, am using cap multiplier on this thread.

Thank you

xrk971 · 2022-01-04 9:49 am

maulana said:
Hi X. Thank you for the reply.
I want to build this amp as a standalone device. I decided to use 2sk170, based on this schematic and using resistor setting from this post

https://www.diyaudio.com/community/...or-melbourne-db-group-buy.334457/post-5898779
The question is:

1. Is the value correct for 32 ohm headphones?
2. What is the output impedance for this particular setup?
3. On the description it says that R102+R104 = 2K. That means 1K each, right?
BTW, am using cap multiplier on this thread.

Thank you

The schematics says R103+R104=930ohms for 2SK170BL. That means the sim equals 930ohms not each. So 900ohms plus 30ohms, etc… in series.

It will work for 32ohm headphones but that is the limit for 125mA bias current. Change output cap to 2200uF for 32ohm load.

Output impedance requires a simulation but from memory I seem to recall it’s in the 3-5 ohms range.

maulana · 2022-02-14 10:42 pm

xrk971 said:
The schematics says R103+R104=930ohms for 2SK170BL. That means the sim equals 930ohms not each. So 900ohms plus 30ohms, etc… in series.

It will work for 32ohm headphones but that is the limit for 125mA bias current. Change output cap to 2200uF for 32ohm load.

Output impedance requires a simulation but from memory I seem to recall it’s in the 3-5 ohms range.

Can i increase the bias to 150mA to lower the output impedance?

What is the effect 150mA bias to the harmonic distortion?

Am planning to use 2 transistor CCS, is that change the harmonic distortion?

Thank you

xrk971 · 2022-02-14 11:49 pm

The increase bias current will decrease harmonic distortion of driving lower impedance loads. Adding a CCS will significantly reduce distortion.

vdupham · 2022-11-17 10:16 am

Hi can I use 2.2uf and 1uf for input capacitor ? I see you use 2 10uf capacitor and 0.1uf.

xrk971 · 2022-11-17 12:28 pm

Yes, input cap is as big as you want. But 2.2uF film cap is about perfect. I sometimes use 10uF Silmic II but that’s just convenience and they are tiny. Output should be at least 2200uF electrolytic and bypass with a 2.2uF film cap.

vdupham · 2022-11-17 8:22 pm

xrk971 said:
Yes, input cap is as big as you want. But 2.2uF film cap is about perfect. I sometimes use 10uF Silmic II but that’s just convenience and they are tiny. Output should be at least 2200uF electrolytic and bypass with a 2.2uF film cap.

Hi, pocket version have better gain than desktop version ? I compare two of them, the pocket version only need volume 2-3, than the desktop version need volume 7-8.

xrk971 · 2022-11-18 1:34 am

If you have the same resistor network the gain should be the same. Gain is (R103+R104)/(R105+R106). The JFETs may have different Idss and that may affect the relative volume between the two amps. But if you match Idss between both amps. They should have same gain.

jrKC · 2023-11-15 8:29 pm

pinkfloyd4ever said:
A few more questions...

1) It looks like BF862 is an obsolete part. Is there a good replacement, and if so, what is it and does it require and resistor values to be changed from what's on the BOM?

2) for V111 and V112, the BOM shows IRF610 in Column 2 and IRF512 in Column 3. Does that mean either will work, with the resistor values on the BOM? It looks like IRF610 is currently available, while IRF512 is obsolete.

3) Also, I saw you mention that the next run of DCA boards might have solder mask over all the vias. If I wanted to wait for that next version of the board with the "tented vias", how long might I be waiting?

Pink,
Did you ever build the DCA? I'm considering it and have been stumped by the BOM . . . if you have a more or less complete/up to date BOM, send along.
Thanks!

xrk971 · 2023-11-15 9:05 pm

Tell me what has you stumped in the BOM? A lot of the parts can be substituted. Just make sure capacitor voltages are observed. Use metal thin film resistors in audio signal path. Carbon film resistors can also work well. Its not a finicky circuit so there is wiggle room.

xrk971 · 2023-11-15 9:20 pm

Here is a more detailed BOM for the DCA with capacitor dimensions etc so you can make informed choices for substitutions. Feel free to substitute the boutique Mundorf caps with something else. Many different lead spacings work as it is axial and you can bend the wires to fit. Use metal thin film resistors if possible, especially for parts in the audio signal path.

Part	Value	Device	Package	Description
C101	10 µ0	CPOL-EUE3.5-8	E3,5-8	POLARIZED	Electrolytic 3.5mm pitch x 8mm dia
C101A	C22/10	C22.5B10	CAPACITOR		Film 22.5mm pitch x 10mm width
C101B	C27/17	C27.5B17	CAPACITOR		Film 27.5mm pitch x 17mm wide
C101C	0 µ1	MKC1860-0U1	MKC1860-0U1		Wima part number
C101D	10 µ0	MCAP250V10U	MCAP250V10U	Fidelity	Mundorf Mcap part number
C102	10 µ0	CPOL-EUE3.5-8	E3,5-8	POLARIZED	Electrolytic 3.5mm pitch x 8mm dia
C102A	C22/10	C22.5B10	CAPACITOR		Film 22.5mm pitch x 10mm wide
C102B	C27/17	C27.5B17	CAPACITOR		Film 27.5mm pitch x 17mm wide
C102C	0 µ1	MKC1860-0U1	MKC1860-0U1		Wima part number
C102D	10 µ0	MCAP250V10U	MCAP250V10U	Fidelity	Mundorf Mcap part number
C111	1 µ0	C5/5	C5B5	CAPACITOR	Film 5mm pitch x 5mm wide
C111A	C10/6	C10B6	CAPACITOR		Film 10mm pitch x 6mm wide
C111B	C15/8	C15B8	CAPACITOR		Film 15mm pitch x 8mm wide
C112	1 µ0	C5/5	C5B5	CAPACITOR	Film 5mm pitch x 5mm wide
C112A	C10/6	C10B6	CAPACITOR		Film 10mm pitch x 6mm wide
C112B	C15/8	C15B8	CAPACITOR		Film 15mm pitch x 8mm wide
C113	2200uF	CPOL-EUE7.5-18	E7,5-18	POLARIZED	Electrolytic 7.5mm pitch x 18mm dia
C113A	CPOL-EUE5-10.5	E5-10,5	POLARIZED	CAPACITOR,	Electrolytic 5mm pitch up to 18mm dia
C114	2200uF	CPOL-EUE7.5-18	E7,5-18	POLARIZED	Electrolytic 7.5mm pitch x 18mm dia
C114A	CPOL-EUE5-10.5	E5-10,5	POLARIZED	CAPACITOR,	Electrolytic 5mm pitch up to 18mm dia
C131	220 µ	CPOL-EUE5-13	E5-13	POLARIZED	Electrolytic 5mm pitch up to 13mm dia
C133	1 µ0	C5/5	C5B5	CAPACITOR	Fil 5mm pitch x 5mm width
C134	2200 µ	CPOL-EUE5-13	E5-13	POLARIZED	Electrolytic 5mm pitch up to 13mm dia
C135	2200 µ	CPOL-EUE5-13	E5-13	POLARIZED	Electrolytic 5mm pitch up to 13mm dia
C141	2200 µ	CPOL-EUE5-13	E5-13	POLARIZED	Electrolytic 5mm pitch up to 13mm dia
C142	2200 µ	CPOL-EUE5-13	E5-13	POLARIZED	Electrolytic 5mm pitch up to 13mm dia
C143	1 µ0	C5/5	C5B5	CAPACITOR	Film 5mm pitch x 5mm wide
C144	1 µ0	C5/5	C5B5	CAPACITOR	Film 5mm pitch x 5mm wide
R101	RK09L12B	RK09L12B
R102	100k	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R103	100k	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R104	22k0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R105	22k0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R106	1k1	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R107	68R0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R108	250R	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R109	1k1	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R111	68R0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R112	250R	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R113	47R0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R114	47R0	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R115	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R116	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R117	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R118	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R119	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R121	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R122	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R123	270R	CMF60	CMF60		Dale 1W metal thin film 1%
R124	270R	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R125	270R	CMF-55	CMF-55		Dale 1/2W metal thin film 1%
R131	10k0	R-EU_0207/10	0207/10	RESISTOR,	2mm dia x 7mm long body, 10mm pitch axial
R132	220R	R-EU_0207/10	0207/10	RESISTOR,	2mm dia x 7mm long body, 10mm pitch axial
R133	1R5	R-EU_0207/10	0207/10	RESISTOR,	2mm dia x 7mm long body, 10mm pitch axial
R134	0R47	R-EU_0309/12	0309/12	RESISTOR,	3mm dia x 9mm long body, 12mm pitch axial
R135	0R47	R-EU_0309/12	0309/12	RESISTOR,	3mm dia x 9mm long body, 12mm pitch axial
V101	BF862	SST201	SOT23	TEMIC	SOT23 SMT package
V102	BF862	SST201	SOT23	TEMIC	SOT23 SMT package
V103	JFET	2SK170	TO92-DGS	Field	TO92 package
V104	JFET	2SK170	TO92-DGS	Field	TO92 package
V111	IRF610	IRF512	TO220BV	N-CHANNEL	TO220 package
V112	IRF610	IRF512	TO220BV	N-CHANNEL	TO220 package
V131	1N4004	1N4004	DO41-10	DIODE	DO41 package axial 1A diode
V132	IRF610	IRF512	TO220BV	N-CHANNEL	TO220 package
X101	22-27-2021-02	22-27-2021-02	6410-02	CONNECTOR	Molex KK 2-pin 2.5mm pitch connector
X102	22-27-2021-02	22-27-2021-02	6410-02	CONNECTOR	Molex KK 2-pin 2.5mm pitch connector
X111	22-27-2021-02	22-27-2021-02	6410-02	CONNECTOR	Molex KK 2-pin 2.5mm pitch connector
X112	22-27-2021-02	22-27-2021-02	6410-02	CONNECTOR	Molex KK 2-pin 2.5mm pitch connector
X131	22-27-2021-02	22-27-2021-02	6410-02	CONNECTOR	Molex KK 2-pin 2.5mm pitch connector
X132	AK500/2	AK500/2	CONNECTOR	unknown	2-pin 10mm pitch screw terminal
X1011	SK104	SK104	SK104	HEATSINK	Fischer Heatsink SK104
X1012	SK104	SK104	SK104	HEATSINK	Fischer Heatsink SK104
X1031	SK104	SK104	SK104	HEATSINK	Fischer Heatsink SK104

pinkfloyd4ever · 2023-11-22 7:03 pm

jrKC said:
Pink,
Did you ever build the DCA? I'm considering it and have been stumped by the BOM . . . if you have a more or less complete/up to date BOM, send along.
Thanks!

I did not, sorry. Hopefully xrk can clear up any other questions you have. As you may have seen I too was confused by some of the nomenclature in the BOM, but I believe xrk answered those questions here in the thread.

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