There are Chinese boards available on eBay (no silicon except in the power supply). There's a build thread on Lenco Heaven.
Personally I wouldn't build an EAR clone. A better sounding design, IMHO, is the Broskie Tetra at tubecad.com. He sells the board with manual and if you want all of the parts except the power transformer. A more elegant design than the 834P IMHO.
Steve
Personally I wouldn't build an EAR clone. A better sounding design, IMHO, is the Broskie Tetra at tubecad.com. He sells the board with manual and if you want all of the parts except the power transformer. A more elegant design than the 834P IMHO.
Steve
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Count Duku aside, Thorsten did a mod on this phono that was highly regarded and maybe of interest. I don’t know of a better link than this one but somebody else maybe able to help.
GoodSoundClub - Romy the Cat's Audio Site - About voltage starvation of EAR-834P input stage.
GoodSoundClub - Romy the Cat's Audio Site - About voltage starvation of EAR-834P input stage.
I can add a little to this thread, when I was working for EAR in about 95-97, on one occasion Tim did a special phono box for a pro industry friend with JFET cascode mod bodged in somewhere, and a slightly tweaked EQ, 4.7p iirc, but don't quote me. The Circuit circulating on the web, was originally for the CLEAR kit instruction manual, which was an 834 preamp case with a passive pre and the phono box PCB instead of the line level version, sold through moth marketing. The circuit was drawn by me in PC paintbrush with himself breathing down my neck to make sure I had everything to his liking.
A 12AX7 typically has a plate impedance, rp, of 58k Ohms.
That 58k Ohms in parallel with the plate load, RL is what drives the next circuit.
If that next circuit is part of the RIAA network, it works properly with rp in parallel with RL.
Now, change the input to JFET and 12AX7 Cascode.
The new circuit, JFET + 12AX7, has an increased plate impedance, rp, of perhaps 500k Ohms or more.
That requires the next circuit to work properly with a driving impedance that is essentially RL.
If the next circuit is part of the RIAA network, the values of the RIAA network will have to change, in order to get the proper RIAA frequency response.
Post # 1 schematic does not show the following part of the circuit, but I bet part of the RIAA network is there.
The other two schematics that are posted in the thread, do show part of the RIAA network immediately following the 12AX7 plate circuit.
58k versus 500k makes for a very big change of the RIAA network frequency response.
Change part of the circuit, without properly changing the rest of the circuit . . .
Use at your own risk of having an improper frequency response.
"One small change for man".
One large change required for the rest of the phono preamp circuits, or else it will not fit the RIAA curve.
Just my opinions.
That 58k Ohms in parallel with the plate load, RL is what drives the next circuit.
If that next circuit is part of the RIAA network, it works properly with rp in parallel with RL.
Now, change the input to JFET and 12AX7 Cascode.
The new circuit, JFET + 12AX7, has an increased plate impedance, rp, of perhaps 500k Ohms or more.
That requires the next circuit to work properly with a driving impedance that is essentially RL.
If the next circuit is part of the RIAA network, the values of the RIAA network will have to change, in order to get the proper RIAA frequency response.
Post # 1 schematic does not show the following part of the circuit, but I bet part of the RIAA network is there.
The other two schematics that are posted in the thread, do show part of the RIAA network immediately following the 12AX7 plate circuit.
58k versus 500k makes for a very big change of the RIAA network frequency response.
Change part of the circuit, without properly changing the rest of the circuit . . .
Use at your own risk of having an improper frequency response.
"One small change for man".
One large change required for the rest of the phono preamp circuits, or else it will not fit the RIAA curve.
Just my opinions.
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Agreed fully, but still an opinion, in this instance. I am pretty confident the mods were done on a stock board. The eq tweak was to make the RIAA a little more accurate for the pro user. The purpose of the mod performed (by the bearded one, in an ambiance of hushed conspiratorially) was to improve on the already quite acceptable noise floor.
To the OP, if they are still around, you may have an 834p hand tweaked by himself, he may have signed it (dp).