Bipolar input ones don't all manage good offset in this preamp's servo. Those that do manage, also bring some tube like tone IMHO. In a rather sloppy way though. But try that super LME also when already in hand and if its easy enough to apply, it may do differently.
@Salas a quick question regarding the volume pot on my upcoming DCG3 build as I am going to pair it up with my newly built Sony VFET2 power amp. Should I go with 20k DACT type pots that are available on eBay stores?
Here is my build of the Sony VFET 🙂
My Sony VFET2
Here is my build of the Sony VFET 🙂
My Sony VFET2
Your amp build looks great with the blue VU meters. Yes the 20K log "DACT type" budget switch pots are compatible for the job. Not the last word in mechanical construction, but for the money they are honest.
Thanks Salas, that DACT type 20k pot I found from my bin got from eBay. Any other pointers for pots in a reasonable budget like around $50 or so which goes well with DCG3 and VFET amp.
Not really worth to invest in medium priced switchers in my view. They will be clunky and you will end up aspiring to a Khozmo or a Goldpoint again. Listen also with an Alpha 20k log dirt cheap but tonally decent carbon VS your Ebay compact switcher so to get the idea of switcher VS track pots and then project that in your mind VS TKD and the like. Those better resistance track pots occupy a middle ground for budget too.
Salas I used this RFT switch which I populated with Takman. Seems very well built. Are you familiar with it? Any opinion?
RFT Rotary Switch 24 Positions 4 Poles Attenuator Volume Control Germany | eBay
nash
RFT Rotary Switch 24 Positions 4 Poles Attenuator Volume Control Germany | eBay
nash
I think I have seen that in some old scopes. They made them to last back then. If its NOS materials and contacts still hold mechanically and you find it usable without intruding switch action noise then it can be a decent solution. That's DIY making a pot so you plan your value you choose your resistors and you save $. Is it the metal film Takman you used?
Yes they are NOS. Yes I used Takman metal film wired as a shunt and used a Shinkoh as the series.
nash
Does it feel like switching an analog scope's horizontal sweep dial? So you configured for a shunt type pot i.e. a steady input resistor and switching only parallel to GND ones? If yes what is the value of the steady one?
You may recall that I built a balanced unit. For each channel a 13k series to + and another 13k series to the - on the board direct from the XLR. The appropriate shunt resistor is switched singly by the attenuator which is placed between the + and - so at any attenuation level there are only three resistors in the signal path for each channel.
Happy with the preamp used only as a line preamp for a year but itching to experiment. Thinking about the 327 in the mirror but want to complete my OBL15 build before I do anything else.
nash
Happy with the preamp used only as a line preamp for a year but itching to experiment. Thinking about the 327 in the mirror but want to complete my OBL15 build before I do anything else.
nash
Can even install header pin sockets for Q1 Q2 to easier compare types back and forth before making them permanent. Like in this old video from Tea back when he was trying general works, parts matching, and offset trim. YouTube
Salas,
You may have replied earlier but I will still ask again here.
The transformer specified for DCSTB is 18-0-18 50VA. The actual voltage output will be 25V after converting to DC. Does this reduce to around 18V after capacitance multiplier? I just wanted to be sure before I proceed.
You may have replied earlier but I will still ask again here.
The transformer specified for DCSTB is 18-0-18 50VA. The actual voltage output will be 25V after converting to DC. Does this reduce to around 18V after capacitance multiplier? I just wanted to be sure before I proceed.
Yes, its an always reduced and fixed voltage at DCSTB's output. Just over 17V usually. Dictated by the bargraph LEDS group voltage drop which is a steady thing put under local JFET CCS control.
@Salas, that means that as we discussed earlier in the thread for my build I will be reusing the Salas BiB PSU boards (+/-IRF) with a 23-0-23v 1A (dual secondaries) RCORE transformer. So I got a 150R 5W load resistor for the BiB psu boards to set the voltage to +/-17V DC for the DCG3. Am I correct in assuming that the DC output voltage for DCG3 should be fixed at +/-17V?
Thanks
Thanks
I have just tried without the opamp in the Preamp
not so much difference ,,maybe a bit more clear ,than the ad823
the opa2134 give a little more clear top .compared to no opamp
i will think the ad823 come close to the sound without opamp
question,,, how much DC from preamp will be ok.....30mV or what ?? what will amp and speaker accept
not so much difference ,,maybe a bit more clear ,than the ad823
the opa2134 give a little more clear top .compared to no opamp
i will think the ad823 come close to the sound without opamp
question,,, how much DC from preamp will be ok.....30mV or what ?? what will amp and speaker accept
Measure dc at the speaker output of the power amp.
In general a few mv is optimal but usually speakers can tolerate about 50mv, even 100mv.
Beware that DC offset from DCG3 is not constant and varies.
In general a few mv is optimal but usually speakers can tolerate about 50mv, even 100mv.
Beware that DC offset from DCG3 is not constant and varies.
i will try to measure the DC on amp ouput,,
my amp have a DC protection ..works fine with to high DC
and i kan se that the Salas pre without opamp is max 15mV
i am just trying all small things to change in the Salas pre ..just to se what it gives in sound
will also try some Cree diode in the Salas supply..so i can try some big 10000uf Kemit rifa cap at the first cap
my amp have a DC protection ..works fine with to high DC
and i kan se that the Salas pre without opamp is max 15mV
i am just trying all small things to change in the Salas pre ..just to se what it gives in sound
will also try some Cree diode in the Salas supply..so i can try some big 10000uf Kemit rifa cap at the first cap
Remember that any DC from your pre will be multiplied by the voltage gain of your poweramp and outputted. For example a 26db gin typical poweramp is a voltage ratio gain of 20, so even 2mv scales up to 40mv.
No matter DCSTB or BiB or other PSU its output has to be set at +/- 17V as noted in the DCG3 schematic.
@ Beardman
If you need more top attack in your system try with a 10k log volume potentiometer.
No servo chip DCG3 use is precarious. Not recommended. Relying on DC detection/protection systems further in the chain is your responsibility.
Make sure you never on/off the preamp when the amp is on. Give the power amp time to discharge its PSU capacitors before considered truly off.
If you need more top attack in your system try with a 10k log volume potentiometer.
No servo chip DCG3 use is precarious. Not recommended. Relying on DC detection/protection systems further in the chain is your responsibility.
Make sure you never on/off the preamp when the amp is on. Give the power amp time to discharge its PSU capacitors before considered truly off.