Upgrading the Dahlquist DQ-LP1

@Freddymac2 no problem - my threads are to pay back AK and all those who provided so much information.

yes, you will have to use a larger transformer to provide more current in order to use any other
opamp than the original . the middle one in the pix in post 9, shows a Hammond 160f34
which is 4.4VA which I calculated to be enough. check the Hammond pdf for secondary
voltages. you can up the VA for more margin but NOTHING (I tried as you can see)
would fit. (original was 3.4VA so I think so one more amp would have provided approx.
200 ma more for each opamp - more than enough).

here's the problem the DC power supply is built around the traces for that transformer,
if you just have an external transformer then you'll have to snake its wires back into the
chassis using hopefully shielded wires for hum control. otherwise you could simply
build an equivalent power supply with more "jazz" (like voltage regulators, etc)
and then cable back the power supply. if you then pull the old transformer there
won't be any of its PS circuitry to worry about. I would be careful of the grounds
both units should not have a third (earth/AC) ground to worry about
(multiple grounds in amps and such are beyond my patience maximums)

next up. socket those puppies - follow the tips and orientation from above.
use a white dot of paint to note pin 1.

now for the exciting part, you can now use any opamps since the 1970s
like the ones you mentioned. I would advise reading the opamp specs
for cautions.specifically their minimum gains (some of the opamp stages
in the DQ are unity (1) gain buffers so any opamps that need to be circuits
where gain is say greater than 5 can't be used. second, you could isolate these
and keep the originals or use different opamps that are stable under all conditions

check here at AK and diyaudio for those threads that talk about opamp upgrades
and follow their discoveries.

I would also advise you to look into putting 1) caps from V+ and V- to ground, 2)
caps across V+ and V-, these are bypasses and will prevent any other problems.
do note these are not absolutely required (many commercial units like the Hafler
DH100 don't have them ) but are recommended. you can do this while you are socketing it.
note: I didn't do this. and you can use the smallest wimas either mylar
(MKP I think) or polypropylene (MKT I think). solder everything at once.

I would have loved to use the 4562s.

PS. PM me, you can have my two extra transformers. free.
 
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Hi
This is my first post. I literally just bought one of these today used on ebay. I have 24 y/o Dahlquist Prelude Series speakers (the LAST models made by Dahlquist)(Ca2/W2) that I want to biamp. I am not technically proficient so I want to take the DQLP-1 in to a local service shop that does most of my hifi repairs here in AZ. Of all the noted modifications you all list above what would be the best for the most immediate impact on improving its performance? I am on a limited budget for now, and this hifi stuff is one of the only things I can do currently to distract from my current unemployment situation., So....if you could only afford 2 or 3?
thanks!
Matt
 
in order of expense, assuming you research/understand/write-down-everything-desired,
and assuming it is a working unit.

1. add the van alstine mods (research van alstine's audio basics, and determine how many
you need, buy them if it saves money, or DIY.)
2. upgrade all caps in two stages.first stage is all the ecaps because they are almost 50 years
old and need refreshing. you can find a schematic and go with the original specs or use the
ones I list which are (partially - do research) the van alstine mods. then stage two is to ugrade
the non ecap caps, the film caps, of which some are polyester (aka mylar) with better films
(such as polypropylene in various forms, polystyrene (careful here), or Teflon or micas.
3. repair the back panel rca females. if needed.

see posts 4,5 and others above for the exact parts, counts, positions, pictures. if you just
send them this URL, then you're paying them $50+/hour to read. study the schematic, build
the parts list from the schematic and this post, and then decide what to do.

if this is not working, then you need to diy or have someone investigate. Mine had a bad output
channel, not directly able to be diagnosed (at least with my patience, fortitude, at that time), until
I unsoldered them, put sockets in, re-inserted them in, then using one new IC replaced them
one-at-a-time until I found the problem. recommend this use of sockets because the next time
troubleshooting is 10 minutes (9 minutes to pull unit, 1 minute to pull ICs, - a major time saver).

as you might be able to ascertain, the more work you put in, and the more you describe
what you need, the faster you get a quote and the unit back. I recall the parts costs were
about $25. so the labor component is going to be much higher.

plan B - use it for a while as is, it should work unless there's some undisclosed or yet-to-happen
problem. this way you get to know the unit as you progress into bi-amping. then you can decide
which way to spend your money and time.

I recommend using small speakers on the treble end, and big floor standers for the bottom. each
is allowed to work at its design best without compromise by trying to do it all. however it will still work
with 4 identical speakers. the sound in all cases is better and the bass continues even with low volumes.

Bob
 
in order of expense, assuming you research/understand/write-down-everything-desired,
and assuming it is a working unit.

1. add the van alstine mods (research van alstine's audio basics, and determine how many
you need, buy them if it saves money, or DIY.)
2. upgrade all caps in two stages.first stage is all the ecaps because they are almost 50 years
old and need refreshing. you can find a schematic and go with the original specs or use the
ones I list which are (partially - do research) the van alstine mods. then stage two is to ugrade
the non ecap caps, the film caps, of which some are polyester (aka mylar) with better films
(such as polypropylene in various forms, polystyrene (careful here), or Teflon or micas.
3. repair the back panel rca females. if needed.

see posts 4,5 and others above for the exact parts, counts, positions, pictures. if you just
send them this URL, then you're paying them $50+/hour to read. study the schematic, build
the parts list from the schematic and this post, and then decide what to do.

if this is not working, then you need to diy or have someone investigate. Mine had a bad output
channel, not directly able to be diagnosed (at least with my patience, fortitude, at that time), until
I unsoldered them, put sockets in, re-inserted them in, then using one new IC replaced them
one-at-a-time until I found the problem. recommend this use of sockets because the next time
troubleshooting is 10 minutes (9 minutes to pull unit, 1 minute to pull ICs, - a major time saver).

as you might be able to ascertain, the more work you put in, and the more you describe
what you need, the faster you get a quote and the unit back. I recall the parts costs were
about $25. so the labor component is going to be much higher.

plan B - use it for a while as is, it should work unless there's some undisclosed or yet-to-happen
problem. this way you get to know the unit as you progress into bi-amping. then you can decide
which way to spend your money and time.

I recommend using small speakers on the treble end, and big floor standers for the bottom. each
is allowed to work at its design best without compromise by trying to do it all. however it will still work
with 4 identical speakers. the sound in all cases is better and the bass continues even with low volumes.

Bob

Bob

Thanks for the detailed plan!
I am going to test it out first and then move from there.
 
Bob

Thanks for the detailed plan!
I am going to test it out first and then move from there.

Bob

As I am not a technical expert on electronics the process hit a wall. I am having an issue determining the exact capacitors to use to match the input impedance for my main amplifier and I don't want to blow it up.
My amp is a PARASOUND A21 Input Impedance 33 kOhms. The formula in the old Dalhquist manual to determine the proper capacitor "uf" rating and resistor (measured in "K') is like Greek to me. I have decided to just get the parts and take to a local shop. They only stock parts to be able to set the input impedance to 25k. Would this suffice in your opinion for the quality sound and match potential? As the original LP-1 is set for 100 kOhms I can only assume going to 25 kOms is at least close for my 33 kOhm Parasound!

thanks

matt

You seem to be well versed on this unit and I hope to really get the benefit of a proper match.
thanks!
in order of expense, assuming you research/understand/write-down-everything-desired,
and assuming it is a working unit.

1. add the van alstine mods (research van alstine's audio basics, and determine how many
you need, buy them if it saves money, or DIY.)
2. upgrade all caps in two stages.first stage is all the ecaps because they are almost 50 years
old and need refreshing. you can find a schematic and go with the original specs or use the
ones I list which are (partially - do research) the van alstine mods. then stage two is to ugrade
the non ecap caps, the film caps, of which some are polyester (aka mylar) with better films
(such as polypropylene in various forms, polystyrene (careful here), or Teflon or micas.
3. repair the back panel rca females. if needed.

see posts 4,5 and others above for the exact parts, counts, positions, pictures. if you just
send them this URL, then you're paying them $50+/hour to read. study the schematic, build
the parts list from the schematic and this post, and then decide what to do.

if this is not working, then you need to diy or have someone investigate. Mine had a bad output
channel, not directly able to be diagnosed (at least with my patience, fortitude, at that time), until
I unsoldered them, put sockets in, re-inserted them in, then using one new IC replaced them
one-at-a-time until I found the problem. recommend this use of sockets because the next time
troubleshooting is 10 minutes (9 minutes to pull unit, 1 minute to pull ICs, - a major time saver).

as you might be able to ascertain, the more work you put in, and the more you describe
what you need, the faster you get a quote and the unit back. I recall the parts costs were
about $25. so the labor component is going to be much higher.

plan B - use it for a while as is, it should work unless there's some undisclosed or yet-to-happen
problem. this way you get to know the unit as you progress into bi-amping. then you can decide
which way to spend your money and time.

I recommend using small speakers on the treble end, and big floor standers for the bottom. each
is allowed to work at its design best without compromise by trying to do it all. however it will still work
with 4 identical speakers. the sound in all cases is better and the bass continues even with low volumes.

Bob
 
good for you. I 'd have to dig out my manual on this and do the calc. may take a while...

meanwhile, do adjust the DQ-LP1 for your speakers (top and bottom) then match the
levels and then enjoy the music.
 
Looks like the value for my two amps (Parasound A21/Rotel 990BX) with 33 kOhm impedances require odd capacitors that shop doesnt stock for the "normal" upgrade service. The shop I use said they can set for 25 kOhms which would at least be below 33 and much better than the existing original numbers(75-100 kOhms) for the old DLP-1 units. I set my crossover low( 40-60) so I should maintain pretty solid signal and range in my main speakers from the HP.
 
what values of (caps, resistors) do you need? I may have something that works - note that caps
follow an equation that makes +/- 50% may mean a minor difference in the shift point,

as I recall, the treble output of the DQ-LP1 is a cap at the signal input and will pass a signal
to the treble amp even if the DQ-LP1 is turned off. this means, most of the time, the cap
quality and the rest of the treble signal chain is ideal - especially for female vocals, and
just about any classical music.

when mine had a bad opamp for one of the bass channels, I simply combined both bass
into a "center" channel mono and didn't miss a beat.
 
Bob and any others,

Do you have a board layout for the LP-1?

I have the schematics, circuit description and instructions for the unit. A board layout of the circuit would be immensely helpful to identify each capacitor, resistor, etc.

Thanks,

Andy
 
I just bought an lp1 after yrs of just running dq1’s through an 80hz xo. All this great info but why isn’t someone offering this upgrade as a service. Realky about all I can do is upgrade the xo on the speaker xo, or recap a protection board from a pioneer sx 950 receiver.
 
DQ-LP1

I'm a big fan of the DQ-LP1. I have mine driving a Carver TFM-24 and feeding two DQ-SW1 subs (left and right channels). My JBL L100t's are positioned on top of the subs. System sounds great. I have the VanAlstine mods on the unit.

I recently had to replace the transformer (age related failure). I've got a buddy (Jeff) who's an electronics genius; He was able to locate a higher output transformer that fits in the LP1 case. Here is a pic. The Mouser part number is 530-LP-24-100.

I'm sharing as there is alot of postings and traffic on the under-powered transformer of the LP1. I think its worthwhile sharing that there is an alternative and it will fit in the stock case and you can get the lid on.

BTW, Jeff and I worked together and redesigned the LP1 circuit to use modern components and a quality regulated power supply. Here's a pic of the board. It's not designed to slot into a DQ-LP1 case (for several reasons). I'll post a seperate thread of that project. We did it as a fun exercise- not as a commercial venture. I ordered 10 boards. Jeff has built up his, I hope to get to mine in a couple of weeks.
 

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A couple of notes on the caps I used

C2, C14 the 2Uf cap: originally the Mullard tropical fish was replaced with the Panasonic ECW-FE2J225J which is black. It is a polypropylene unit that is intended to provide spooky black bass notes that stops your heart with a bass thwack.


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Hi Bob,
are you sure the ECW-FEJ225J is a 2µF C? Mine have 2,2µF. Thanks for the great manual on rebuilding the LP1. I started work a few days ago ;-)

Best - Sascha
 
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