I purchased a low output (1.0 mv) moving iron cartridge to transcribe my rarer vinyl to digital. I plan on using the single ended tape output of my preamp to a studio type adc/dac (RME). The RME analog input is either +4dBu, +13dBu,+19dBu or +24dBu. The output from my preamp is 100.0 mv for 1 mv in. I need a "line level" amp to make up the difference. I'm thinking +13dBu is the target. My first thought is to build a ACP+ preamp/headphone amp. Is there a better Pass design for this need. Output impedance from the preamp should be about 330 ohms, the input to the RME should be about 9k unbalanced. I wouldn't think impedance in or out would be much of a problem. Temporarily I have proven my concept using a dual channel HP instrumentation amplifier in single ended mode in and out. I need a gain of 10x +/- a skosh. My skills use to be high, so even at my age I think I'm up to it. For reference, in 1977, I built a couple of A20s an so on. What are your thoughts?
Thanks in advance to all.
Bill Taylor
Thanks in advance to all.
Bill Taylor
"Buffer" is often shorthand for "impedance problems". You just need an amplifier.
I doubt the RME really needs over +4dBu (1.23V). Internally it is probably a 5V p-p signal, 1.78Vrms, and the 1.5X difference may be a filter. OK, that is "a gain of 10x +/- a skosh."
Are you sure 1.0 mv ? That seems 5X lower than typical, and a tough sell.
I'd start with a TL072 and two 9V batteries, but you may have other notions.
I doubt the RME really needs over +4dBu (1.23V). Internally it is probably a 5V p-p signal, 1.78Vrms, and the 1.5X difference may be a filter. OK, that is "a gain of 10x +/- a skosh."
Are you sure 1.0 mv ? That seems 5X lower than typical, and a tough sell.
I'd start with a TL072 and two 9V batteries, but you may have other notions.
Thats what threw me. The GRADO Statement3 indeed has an output of 1.0 mv @ 1khz, 0 dB, 5 cm recorded. It comes in two flavors and I chose the low output version because I thought (still do) that it would be more faithfull. The input levels into the RME are standard in the recording industry. I just didn't pay close enough attention to the mismatch. Thats for your reply and sugggestion
Best Regards
Bill
Best Regards
Bill
I have a new jfet (mostly) discrete line stage with gain, designed for high quality at the cheapest price. I can get a kit into the store next month after BAF.
AND I MEAN CHEAP!
😎
AND I MEAN CHEAP!
😎
I also happen to have one, only one SMD Toshiba dual JFET (still active at Mouser / DK).
Else all low-noise Toshiba SMD BJTs.
Zero global feedback, stable with any gain, very low noise and distortion.
Can drive 32 ohm headphone also by adding 2x TO220 devices.
Probably not as cheap as Nelson's, but no NOS unobtainiums.
Cheers,
Patrick
Else all low-noise Toshiba SMD BJTs.
Zero global feedback, stable with any gain, very low noise and distortion.
Can drive 32 ohm headphone also by adding 2x TO220 devices.
Probably not as cheap as Nelson's, but no NOS unobtainiums.
Cheers,
Patrick
oops.
"I just didn't pay close enough attention to the mismatch. Thats for your reply and sugggestion"
last line should have said thanks, not thats.
"I just didn't pay close enough attention to the mismatch. Thats for your reply and sugggestion"
last line should have said thanks, not thats.
Since I cut my teeth on "glow fets" I ham happy to wait for your line stage design until after BAF. I had thought about a JE-990 but was a tad concerned about impedance. Are you saying by inference that the ACP+ would suffer likewise?
Your tape preamp probably has NAB correction...for vinyl you need RIAA eq correction.
It looks like you need a jfet input phono preamp set for high mc input with the loading capacitor and resistor for mc carts removed and the rc loading for mm carts active.The specs of your cart show a loading of 10k..47k and they say it's unsensitive to capacitive loading which I kinda doubt because of the 5mH cart's inductance so better remove that rc loading for mc carts,leave just the standard 100pF...47k in place.
Tons of schematics outhere.Try the first one with C103 and R102 removed.This is the phono input of Nakamichi SR4A. Next two pictures are Technics su v6.Just look for any jfet input mc cart phono preamp schematic and remove the input loading for mc, but use the loading for mm carts instead.
It looks like you need a jfet input phono preamp set for high mc input with the loading capacitor and resistor for mc carts removed and the rc loading for mm carts active.The specs of your cart show a loading of 10k..47k and they say it's unsensitive to capacitive loading which I kinda doubt because of the 5mH cart's inductance so better remove that rc loading for mc carts,leave just the standard 100pF...47k in place.
Tons of schematics outhere.Try the first one with C103 and R102 removed.This is the phono input of Nakamichi SR4A. Next two pictures are Technics su v6.Just look for any jfet input mc cart phono preamp schematic and remove the input loading for mc, but use the loading for mm carts instead.
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Oh...I didn't realize it's NP corner...I promissed once to stay away from this place cause mortals can't deal with immortals. Then I should probably recommend its own designs from Nakamichi CA5E where you change C110 with 220...2200uF and R113 with 100... 220 ohms.I said once that the CA5 must be a genious design...didn't know at the time it was NP's.
There's also the CA7 mm input stage, but I can't see a clear schematic in my download manual...
I'm sorry @ Nelson Pass! It wasn't in my intention to do any harm 🙂 I'd be really greatful though if I'd be able to see a clear schematic of CA7 model.
There's also the CA7 mm input stage, but I can't see a clear schematic in my download manual...
I'm sorry @ Nelson Pass! It wasn't in my intention to do any harm 🙂 I'd be really greatful though if I'd be able to see a clear schematic of CA7 model.
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No problems. Mine is just a simple little minimalist circuit with 4 jfets and a bipolar. The board has pinouts for 2sk170 or J113 input devices, but comes with the J113's It should sell for about $10 in the store. Full info at BAF...
Ca5 looked pretty minimalist to me and we were told it's your design too from Treshold ...At least it's a proper phono preamp that can do this job, not a NAB tape preamp.
Interesting conversation I know nothing about.
Back to my ACP+ question... I need the output voltage of +12dBu with a minimum of say +4 or 5 but could be as high as +24dBu.
My problem is not input matching of cart or really the input voltage alone. I have multiple variables for input on both MM and MC from 100uV to 7.75mV.
Its the output that runs out of steam. This is why I looked at the ACP+.
Best Regards
Bill
Back to my ACP+ question... I need the output voltage of +12dBu with a minimum of say +4 or 5 but could be as high as +24dBu.
My problem is not input matching of cart or really the input voltage alone. I have multiple variables for input on both MM and MC from 100uV to 7.75mV.
Its the output that runs out of steam. This is why I looked at the ACP+.
Best Regards
Bill
Isn't it time to stop designing new designs based on 2SK170/2SJ74? I already see the future threads where to find these. Prices start to become ridiculous too and don't get me started on the types that buy "originals" from Ebay.
These designs attract many people that are exactly those that don't have the JFETS.
These designs attract many people that are exactly those that don't have the JFETS.
First of all I don't see any hint of the fact that the OP understands he needs a RIAA preamp not a NAB one...Once he gets it everything should fall in place.
If you are referring to the circuit I mentioned, it uses J113's, with option of the Toshiba parts.
2sk117 is found in greater quantities in Fostex cassette multitrackers and multitrack reel to reel and they are close enough to 2sk170 performance. A friend gave me in exchange for a job a defective Fostex 8A which has 88 x 2sk117.
So why not also stop any discussion about tubes ?
Ah, but tubes are still being made, right ?
JFETs are also still being made, BTW.
Just that they are called LSK170 / LSJ74.
Not to mention all the active JFETs in SMD.
Cheers,
Patrick