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Dahlquist DQ-10 rebuild

C

cupples

pfm Member
Always on the lookout for interesting refurb projects, I've come across a pair of these 1970s US phased array loudspeakers which need a little bit of TLC, so I thought it would be fun to document the repair process. They've had a relatively easy life, on the end of a Naim 160 power amp, mainly playing opera, but hadn't been touched in a while, so I was interested to see what lay beneath...
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There don't seem to be any other DQ-10s out there with a white fabric cover, so I assume they were recovered for domestic reasons in the past. I got down to stripping the frame off to have a look at what lay beneath...
 
Dear knows how many years of thick dust was coating the crossover and cabinet. The front of the speakers weren't much better...
 
Bass units are usually expected to have a full compliment of foam the whole way round, not just a Terry-Thomas style assortment of gaps. I duly wrested the Advent 10" bass drivers from their sealed boxes to get a better look at them...

 
From the hive mind, this seems to be a common problem with these Advent drivers. On further perusal, getting a refoaming kit from the US would run about £50, which for two bits of foam seemed a bit excessive, but after measuring carefully, a pair of generic 10" refoam kits from China were ordered. Meanwhile, extreme dusting happened...
 
Nice to see that there were some components underneath that thick layer of human and dog skin cells. After a bit of internet digging, I've decided to leave the majority of the caps in place, and just replace the sole 80uF NP electrolytic (the blue one), so I'll be waiting for a cheap Chinese film cap to arrive at some stage - it was the same price for a Mundorf electrolytic replacement, so I thought I'd risk it and see how that went. We'll see. Anyway, meanwhile back at the ranch, refoaming was happening. The kits were a fraction too broad on the inside diameter, so I trimmed them down internally by 2mm with a stanley knife. In order to get at the drive units, I needed to prise the hardboard/masonite surround off the the Advent units carefully. I then stuck down the foam to the cones first of all, left them to dry, then stuck them to the inside of the hardboard, while also sticking this back onto the drive unit frame - slightly nerve wracking that all was going to go back into line without any voicecoil rub, but it was done successfully...
 
So, all good so far. Except... one duff midrange unit. Pants. Open circuit Philips DA5060/W8 unit on the right speaker, with no obvious easy repair. One ordered from France for £45, so not catastrophic. I checked all the other units and was briefly concerned that the piezos were open circuit... but then I tried them with a battery, and they all made noise, phew! So, I thought, I'm only down one drive unit, there are 9 others, what's the worst that could happen?
 
They're alive!! A decent amount of music emanated from both speakers in appropriate quantities. I put on Radiohead Kid A - decent bass, mmhmm, positive noises... let's try some Kind of Blue - sounding good, but wait... Where's the tape hiss on the left speaker?? Re-test high frequency unit, voltage ok, resistance ok, what's going on??
Duh. Treble L-pad turned down on the left speaker. Fixed!!
 
You can understand why the designer wanted to put a cover on these, they are fugly brutes. But my word, even with a little Rotel 930AX do they sound good! To do list at present is - replace the pair of 80uF electrolytics when they arrive from China, pop in the right Philips midrange, then either clean up the white covers, or find some replacement material to re-cover them.
 
cupples said:
You can understand why the designer wanted to put a cover on these, they are fugly brutes. But my word, even with a little Rotel 930AX do they sound good! To do list at present is - replace the pair of 80uF electrolytics when they arrive from China, pop in the right Philips midrange, then either clean up the white covers, or find some replacement material to re-cover them.
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Lovely job and rewarding to listen to;)
A rare speaker on these shores..
A great piece of hifi history with a fascinating background.
Found the 80ufs were way out and others,Have a peek on my thread u will see reads etc
pinkfishmedia.net

Dahlquist DQ10

Some research i have gathered on the DQ10,prior to buying a set and discovering more information,please note that this post may be updated as i find out more..... Jon DAHLQUIST-Was an aerospace engineer and was obsessed with designing the perfect speaker. Also had previously worked for the...
pinkfishmedia.net pinkfishmedia.net
 
cupples said:
I checked all the other units and was briefly concerned that the piezos were open circuit... but then I tried them with a battery, and they all made noise, phew!
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The piezos don't really make a lot of noise in this application.

While most pairs of DQ10s were black, white was available as an option.
 
I had a mint pair about 10yrs ago… they did sound better with a recap…I would check if they are mirror imaged.. I believe you can do that easily…. Just google it… I found that the do need space around them and the more power you throw at them the do sound better… great speaker!!
 
150-200W of class AB power wouldn't go wasted, more if you can manage. They respond well to an amp that can give them a good kick in the backside.
 
Here's the thing, getting that sort of current this side the pond just isn't easy or cheap. How about class D?
 
cupples said:
Well that;s the next question - what to run them with! I don't think my 300B SET is going to be happy...
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i ran a 405/1 with the dq10s and it was good also, have 909 which is better but sound per pound a 405/1 can be had for not silly money..
Looked at the big amps ,adcom stuff is relatively cheap some of it nelson pass design/ era.
The complicated output transistors and availability steered me to quad stuff as its easily repairable...
 
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