I need a Buffer with gain?

wttaylor

Member
2010-02-22 11:54 am
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
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
"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.
 
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wttaylor

Member
2010-02-22 11:54 am
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
 
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.

210601 ZGF20 Line Stage Public.JPG


Probably not as cheap as Nelson's, but no NOS unobtainiums.


Cheers,
Patrick
 

wttaylor

Member
2010-02-22 11:54 am
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!
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?
 

dreamth

Member
2010-11-18 9:12 am
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.
 

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dreamth

Member
2010-11-18 9:12 am
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.
 

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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
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...

:snail:
 
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wttaylor

Member
2010-02-22 11:54 am
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
 

jean-paul

diyAudio Moderator Emeritus
2002-09-20 7:20 am
Germany
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.
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
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.
If you are referring to the circuit I mentioned, it uses J113's, with option of the Toshiba parts.