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#41 | |
diyAudio Member
Join Date: Sep 2002
Location: Sacramento, CA
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#42 |
diyAudio Member
Join Date: May 2011
Location: Virginia
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OK, I simmed it. I don't have the types of transistors so I just guessed. It's a good circuit, but kind of strange. As I understand it, the first two transistors in each half (J1, Q1 and J2, Q2)are both set up as gain stages with 100% feedback. The output stage (Q3, Q4) has constant current to each emitter resistor via Q6 and Q7. The output stage transistors seem to be operating as phase splitters though, since a voltage will be developed across the collector resistors R8, R9. I suppose Q3, Q7 and Q4, Q6 operate together to keep constant current in the emitter resistors. Pot P1 provides a feedback path to the input stage.
I measured -3dB of gain with the transistors I used. Distortion was obviously extremely low. Bandwidth had a bump in the 10MHz region, but that's a function of the particular transistors. |
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#43 | |
Account disabled at member's request
Join Date: May 2006
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#44 |
diyAudio Member
Join Date: May 2011
Location: Virginia
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OK, so how much gain is it supposed to have, as shown in the schematic posted earlier in this thread?
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#45 | |
diyAudio Member
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The 2 resistor values in the chart are the source resistors on the JFET's. Dick indicated that he used 51.1 ohms. The devices were NOT matched for that particular run. Note that in the article the designators R3 and R4 were accidentally used twice. I set up the other side substituting matched 2SB649AC/2SD669AC for the MJE (On Semi) devices. Hfe is ~155, Ft is 140MHz for these. The THD is lower, but the noise level is higher. |
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#46 |
Account disabled at member's request
Join Date: May 2006
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I doubt that is the complete schematic, -3db gain means it has no voltage amplification. That would make the circuit virtually useless. Have a look at D Self series about CFP with gain, then Id say your on the right path to discover how the circuit works.
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#47 | |
diyAudio Member
Join Date: May 2011
Location: Virginia
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Look, a zero dB circuit is just fine since the standard output for CD players is 2Vrms, which will make you deaf while wearing headphones. |
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#48 | |
Account disabled at member's request
Join Date: May 2006
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#49 |
On Hiatus
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Dirk, the article on the headphone amp is well worth reading. The schematic posted here is the unity gain buffer section. The overall design has 12dB of gain.
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"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is." |
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#50 | |
Account disabled at member's request
Join Date: May 2006
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Please be polite, I dont want to say too much otherwise Ill have the designer and linear audio on my back, theres an obvious money trail going about. ![]() It will have to be upto them to disclose the circuit if they want, for others that dont understand it I can at max give a hint or two. You dont need his book, this stuff is available on the internet. |
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