How high would I need to go?
I was thinking 22 volt rails would do. I also understand that the rails are limited to 17 volts due to the relay. Could I bypass the relay without cap coupling the preamp out?
Rush
You got to always mind the power up/down sequence for transient cycles then. Make C1 15pF also to cut on bandwidth because its going to go even faster internally on higher rails. An OPA2604 can take +/-24V max for U1. R6=3.3k will allow it gain for near 44V pk-pk on 2V input.
But try a 12V 1W Zener instead of the three Leds first when on 22V rails. Cathode opposite to leds orientation cathode. See if that idea works for keeping the relay.
Oh, great idea.
The OPA2604 have been discontinued it seems. Is there another substitute?
Rush
But there must also be a 18V same relay type version to use with 22V and the leds (?) Look if available.
I don't know, search for 48V max JFET input op-amps. They usually refer to their PSU max with the sum rails voltage.
I'm going to try this first, I already soldered the relay in place. 🙁
I'll order the OPA2604 from eBay and see. Several USA sellers have them. That IC is in a socket, so easy to change.
Rush
Dcg3 powered up and playing for a couple hours. Lid on the chassis. Inner heatsinks on the psu are 49 degrees. Is this ok? They feel pretty hot now.
49C won't pose any danger to the sinked transistors. The electrolytics around there are all 105C also. Does the lid have ventilation holes over the sinks? You would surely prefer 40-45C though. Feels better. Ok the transformers are over nominal voltage but is it on the high bias setting too?
Thanks once again for your help
I placed a closed lid on for an experiment so I can cool things down with holes in the lid.
I set bias as low as possible.
I think with a vented lid I shall be ok. It gained 10C from being enclosed.
I placed a closed lid on for an experiment so I can cool things down with holes in the lid.
I set bias as low as possible.
I think with a vented lid I shall be ok. It gained 10C from being enclosed.
On Q1 Q2 mirror BJTs yes, we did that often here. For J1 J2 uPA we didn't try sockets though. Its not a phono stage on the other hand, shouldn't be sensitive to socketing.
It could be handy if planning to listen with alternative LTP JFETs (J1 J2).
In any case and for any parts see to achieve oxide free and firm contact to female socket pins though. Shorter legs help the parts stay firmer.
For quality contact use a lens under good light and clean the parts pins. Because there will be no soldering for its flux to automatically clean them somehow. Almost all the candidate JFETS are NOS. Their pins should be oxidized enough already.
It could be handy if planning to listen with alternative LTP JFETs (J1 J2).
In any case and for any parts see to achieve oxide free and firm contact to female socket pins though. Shorter legs help the parts stay firmer.
For quality contact use a lens under good light and clean the parts pins. Because there will be no soldering for its flux to automatically clean them somehow. Almost all the candidate JFETS are NOS. Their pins should be oxidized enough already.
Salas, I have 2 18v xformers for the the dcstb and a 12v xformer for the I Select board. If I don’t use the 12 v xformer I can make the preamp much smaller. Is there any penalty to use a tap off one 18 v to power the I Select? Or since I got the xformer just use it?
VA you mean not mA?
The extra Tx for the selector can save on chances of ground loop low level spikes when you don't monitor the result with FFT analysis so to tweak the cabling etc.
Due to better power source separation. You could achieve a fine result with a tap from DCSTB's raw DC to I-select DC in though. Especially useful when short on box space.
The extra Tx for the selector can save on chances of ground loop low level spikes when you don't monitor the result with FFT analysis so to tweak the cabling etc.
Due to better power source separation. You could achieve a fine result with a tap from DCSTB's raw DC to I-select DC in though. Especially useful when short on box space.