Dahlquist DQ LP1

[CaliforniaBob]

Glenn

more stuff:
Audio Basics (Frank van Alstine's past newsletters) had a whole description of the DQ-LP1
and I recall the schematic (in case you don't have one) with tips like replace the
resistors with metal films, etc.

with the replacement of the PS, I would recommend you decouple the opamps
(caps between + and - and ground and between + and -) in case you roll
super high speed opamps in.

CaliforniaBob

 

[Boomzilla]

Hi again, @CaliforniaBob -

The more I read about it, the less enthused I'm becoming about replacing the original ICs with any higher-current models. Does ANYONE make pin-compatible replacement chips that draw no more current than the originals? That option (if available) would allow me to avoid messing with the original power supply.

Thanks - Boom

 

[CaliforniaBob]

nope, when I looked at replacing the OEM opamps, I found that they all drew
more current and overtaxed the power supply. to increase the current capacity,
you will need a bigger transformer. finding one that fits the solder pin config
is easy but the size will not fit inside the DQ-LP1 case.

but even if you could, say using an external supply, you'd have to be very
careful about the replacement opamp's functionality. some are/are-not
unity gain stable (I forget if the DQ-LP1 has unity gain stages), then there's
compensation, bandwidth limitations, etc.

I left mine at upgraded caps and to fix the silent bass channel (I used
all new replacement opamps ).

back to normal and usable for another few decades

Bob

 

[CaliforniaBob]

one more last item:

van Alstine had mistakenly bought lots of silver mica caps
and created the van Alstine mods for the DQ-LP1. in turn
HP of the Absolute Sound used this unit+mods to create
the QRS/1D - the Infinity and Magneplanar combo.

you, too, can do this for that final touch.

Bob

 

[Will Meyer]

Regnar changes out the op amps to Burr-Brown units - so they must make a Low Power op amp.

 

[sonoflawrence]

Just bought an upgraded DQ-LP1

I recently bought an upgraded DQ-LP1 from gmsgms on eBay. It came with some nice mods such as a separate power supply that connects to an added XLR socket. I am driving a Cambridge Audio CXA-60 amplifier, whose input impedance is 47K ohms, so I needed a pair capacitors to augment the .027 uf signal pass caps. I thought a schematic would be nice, so I found one.

I also have a scanned instruction manual if anyone needs it.

sonoflawrence

 

[evsentry3]

What I keep wondering is why everyone thinks they have to replace five op-amps?

I'd bet a wooden nickel that very few are using that center channel output. If you don't populate the Z3 position that feeds that center out, then you only have to account for power draw of four chips instead of five.

As far as chips go, I'd go wild then and go with Doritos!! The hot ones! A smash hit choice even if slightly unusual pick!

EV3

PS...and...for bonus points, if you don't plan on using the center outputs as intended, then you can instead jumper the high sides additional cap insert location (Cx) over to that position. This allows you to build external RCA plug based alternate frequencies for the high pass. Just remember that the load of the highs amp will change the turnover frequency. Uh-oh...now we're going from chips to turnovers...