where do you get 2SK389's???
can't seem to find it in the states. know of a good source? i was going to use a pair of K170's otherwise.
P.S. oh wait, duh... i already bought some from MCM. silly me. i was thikning of another device Borbely uses that i couldn't find, forgot which. so should i use my 389 or 170?
can't seem to find it in the states. know of a good source? i was going to use a pair of K170's otherwise.
P.S. oh wait, duh... i already bought some from MCM. silly me. i was thikning of another device Borbely uses that i couldn't find, forgot which. so should i use my 389 or 170?
Re: where do you get 2SK389's???
I'd use 2SK389 to absolutely minimize DC offset both initially and over temperature. Using matched 2SK170 works well too. Actually, that's what I'm listening to when I go home tonight. (Input source selected by some Maxim analog switches, MAX352 I think - simple {certainly not perfect!} buts sounds pretty good)
I've used GR and BL grade successfully in this application. V would work too. I just don't have (and can't get) any. Ooops, Jocko's probably watching and he's going to get me for whining about V grade JFETS again
right Jocko?
mlloyd1
I'd use 2SK389 to absolutely minimize DC offset both initially and over temperature. Using matched 2SK170 works well too. Actually, that's what I'm listening to when I go home tonight. (Input source selected by some Maxim analog switches, MAX352 I think - simple {certainly not perfect!} buts sounds pretty good)
I've used GR and BL grade successfully in this application. V would work too. I just don't have (and can't get) any. Ooops, Jocko's probably watching and he's going to get me for whining about V grade JFETS again
right Jocko?mlloyd1
dorkus said:
dorkus,
Sorry I didn't respond sooner, but I've been busy with the Pioneer AX10/Sowter mods.
You ask about the latest Rowland version. I had it: the 'IIi". I upgraded my Synergy II to the IIi. I was using this prior to my mods (it basically has a PGA2311--still at 5V, why they did this is not clear--feed by same step-down transformer, but now going to an INA103 and then out to the same output transformer). This latest upgrade was decidedly not as good as the PGA2310 mod that I did using it alone in fullly balanced mode.
Since posting these changes, and re-doing the Pioneer, I've decided to convert the Rowland Syngery into a surround preamp. It is VERY easy. All that is required is to piggyback another PGA2310 onto each existing one. Bend up the legs for the SDI, SDO, inputs and outputs. Connect the SDO of the bottom chip to the SDI of the uppermost chip and to digital ground via a 100K resistor. The two inputs/outputs on one upper chip become LR/RR and the other becomes LF/center. Hard wire RCA terminated cables (male on inputs, females on outputs) to these two upper chips routing the wires through the extra set of output XLR holes. (This latter step requires some work, but is reversible. The reason I'd hardwire the cables is there is no room for 4 pairs of RCA jacks on the rear panel.)
Now when the volume control is used the main L/R balanced signals from the DVD player are tracked with the surround signals. The load on the preamp power supply is actually less than stock because I've removed 3 op amps per channel that are no longer being used.
As for the AD627 issue, if you're using the PGA2310, I really don't see the need for an output buffer. The PGA2310 essentially has a built-in OPA134 (but without the FET input stage) as the output buffer. Adding another op-amp makes no sense, unless you wish to play with DC servos and that sort of thing. However, the PGA2310 only has around 0.5 mV of DC offset, so why bother with added components?
For an input to the PGA2310, I suppose you might wish to buffer it, particularly if you were uncertain as to the possible source load placed upon it (especially in a commercial product). In my situation, I can control the source load and I don't need an extra device. Less is better.
As for using a transformer to convert s.e. to balanced, that's a good idea. I've used the JT11P1 for this. Jensen has white sheet on it. You use the normal outputs as the inputs and the inputs as the outputs (they're better balanced) with the shield grounds tied to the each output with a 4.5K resistor.
good luck, Robert
Sorry I didn't respond sooner, but I've been busy with the Pioneer AX10/Sowter mods.
You ask about the latest Rowland version. I had it: the 'IIi". I upgraded my Synergy II to the IIi. I was using this prior to my mods (it basically has a PGA2311--still at 5V, why they did this is not clear--feed by same step-down transformer, but now going to an INA103 and then out to the same output transformer). This latest upgrade was decidedly not as good as the PGA2310 mod that I did using it alone in fullly balanced mode.
Since posting these changes, and re-doing the Pioneer, I've decided to convert the Rowland Syngery into a surround preamp. It is VERY easy. All that is required is to piggyback another PGA2310 onto each existing one. Bend up the legs for the SDI, SDO, inputs and outputs. Connect the SDO of the bottom chip to the SDI of the uppermost chip and to digital ground via a 100K resistor. The two inputs/outputs on one upper chip become LR/RR and the other becomes LF/center. Hard wire RCA terminated cables (male on inputs, females on outputs) to these two upper chips routing the wires through the extra set of output XLR holes. (This latter step requires some work, but is reversible. The reason I'd hardwire the cables is there is no room for 4 pairs of RCA jacks on the rear panel.)
Now when the volume control is used the main L/R balanced signals from the DVD player are tracked with the surround signals. The load on the preamp power supply is actually less than stock because I've removed 3 op amps per channel that are no longer being used.
As for the AD627 issue, if you're using the PGA2310, I really don't see the need for an output buffer. The PGA2310 essentially has a built-in OPA134 (but without the FET input stage) as the output buffer. Adding another op-amp makes no sense, unless you wish to play with DC servos and that sort of thing. However, the PGA2310 only has around 0.5 mV of DC offset, so why bother with added components?
For an input to the PGA2310, I suppose you might wish to buffer it, particularly if you were uncertain as to the possible source load placed upon it (especially in a commercial product). In my situation, I can control the source load and I don't need an extra device. Less is better.
As for using a transformer to convert s.e. to balanced, that's a good idea. I've used the JT11P1 for this. Jensen has white sheet on it. You use the normal outputs as the inputs and the inputs as the outputs (they're better balanced) with the shield grounds tied to the each output with a 4.5K resistor.
good luck, Robert
thanks for the info Robert, very helpful. i realized after re-reading again that you were indeed comparing the stripped-down PGA2310 to the IIi board, i had originally thought you were comparing it to the old board before your mods. i may still follow the PGA2310 with a JFET buffer, to avoid thermal modulation of the internal opamp under load (which Walt Jung and others say all IC opamps suffer from).
are the Jensen transformers as good as they say they are? they sound almost a little too good to be true, but i imagine they are pretty transparent... probably comparable to, say, a good coupling cap at least. i wonder how much DC they can take before distorting due to saturation... if they can take a few tens of millivolts w/o any ill effects they might be a good alternative to a servo or coupling cap where the offset is small (e.g. an opamp or other non-SE circuit), with the added isolation benefit of course.
are the Jensen transformers as good as they say they are? they sound almost a little too good to be true, but i imagine they are pretty transparent... probably comparable to, say, a good coupling cap at least. i wonder how much DC they can take before distorting due to saturation... if they can take a few tens of millivolts w/o any ill effects they might be a good alternative to a servo or coupling cap where the offset is small (e.g. an opamp or other non-SE circuit), with the added isolation benefit of course.
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