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Post by PinkFloyd on Feb 5, 2008 15:29:28 GMT
I have always wanted a shot of one of these so when I saw this one on e-bay going pretty cheap I just had to hit the bid button. I haven't had a good listen to it yet (have been too busy poking about inside it!) but initial impressions with Pink Floyd - Meddle suggest it's "not bad". I'll leave her to warm up for a good while before doing any further listening as she hasn't been used for years apparantly. The heart of the amp is the LM8177 Dual Audio Power Amplifier which outputs a whopping 2 watts. There's not really much more to it apart from a sprinkling of caps and resistors. Build quality is very good and the amp is actually quite a bit bigger than I thought it would be. From the board I can tell that this amp dates back to 1992 so is a relatively "vintage" headphone amp. 2 sets of inputs, 2 headphone sockets (handy) a dual ALPS volume / balance pot and a tape monitor switch. Specs: • Amplifies line level output to drive upto two pairs of headphones • Output 2 Watts R.M.S. per channel • Channel separation : 60 dB • Input impedance : 10K • Signal to noise : 70 dB • Volume control • Balance control • Connects to tape loop or Pre-Amp output • 12 volt D.C. 500 mA power supply required • Gold plated phono sockets • Size (mm): 160 (w) x 55 (h) x 120 (d) • Made In England Well, without further ado here's the pRon:
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Post by PinkFloyd on Feb 5, 2008 15:30:57 GMT
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Post by PinkFloyd on Feb 5, 2008 20:53:22 GMT
Tell you what this thing drives the Sennheiser HD-414 with utter ease (and they are a REAL bugger to drive!) and what a cracking pair of 'phones the 414 are when driven correctly! Very AKG-K501 like in presentation but with a touch more bass.... superb 'phones with this particular amp.
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leo
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Post by leo on Feb 5, 2008 21:21:34 GMT
The chip looks like a headpnone amp version of those Gainglone speaker amps I'm not normally big into swapping just things like capacitors but if this chip is similar to those Gainclones the parts used has quite a big impact on performance.
I'd try a 1000uf FC cap soldered straight onto the chips rail pin to ground, theres quite a lot of track length from that green cap. Low leakage types on the feedback instead of the noisy Novers and worth looking at the Bias too
Those orange Rubycons are already low leakage, seem to be the signal DC blockers on the output
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leo
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Post by leo on Feb 5, 2008 21:23:50 GMT
Those caps will probably be tired now anyway due to age ;D especially the big green decoupling and feedbacks
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Post by PinkFloyd on Feb 5, 2008 21:41:54 GMT
The chip looks like a headpnone amp version of those Gainglone speaker amps I'm not normally big into swapping just things like capacitors but if this chip is similar to those Gainclones the parts used has quite a big impact on performance. I'd try a 1000uf FC cap soldered straight onto the chips rail pin to ground, theres quite a lot of track length from that green cap. Low leakage types on the feedback instead of the noisy Novers and worth looking at the Bias too Those orange Rubycons are already low leakage, seem to be the signal DC blockers on the output The orange caps are 100uF Marcon types Leo and, yes, they appear to be output caps. 100uF is pretty crap for any 'phones under 300R so I may fit 470uF non polars here. With 100uF the cut off frequency if using 32R 'phones will be 49.74Hz but with 470uF it will be 10.58Hz..... may even end up slotting in a couple of 1000uF non polars here. The noVers are definitely getting whipped out, horrible bloody things, will probably replace with the blue Panasonics or maybe ELNA RE2. The green ELNA is 1000uF / 35V I may replace with something like a 3300uF Panasonic NHG and definitely solder onto the chip direct. Not much else to do really as the chip is boss here. It's a bloody decent little amp though and anybody looking for a first time / budget amp should not discount this puppy. Can be picked up on ebay for about £20 - £45 and with a recap is a very good amp for little money.
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leo
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Post by leo on Feb 5, 2008 21:52:31 GMT
Marcon, I'm not familiar with those , they look a lot like the Rubycons. Anyway should be fun to have a play about with, 2w into 8R's that chip can drive a little pair of speakers
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leo
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Post by leo on Feb 5, 2008 22:20:57 GMT
I reckon a nice supply for this wouldn't half improve things, just looked at the PSRR.
Those low ESR FC's should really help in this case, is the wallwart a AC to DC non regulated?
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Post by PinkFloyd on Feb 5, 2008 22:45:01 GMT
I reckon a nice supply for this wouldn't half improve things, just looked at the PSRR. Those low ESR FC's should really help in this case, is the wallwart a AC to DC non regulated? I'm using a 12V / 500mA uniross regulated wart at the moment, the amp didn't come with a wart which is why I got it so cheap.
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Post by canjunkie on Feb 5, 2008 23:14:25 GMT
Just joined and barely 48 hours in you've had me rummaging around the loft! I found my circa 1988 QED Headphone amp (no model number - that's what they called it!). Housed in a pressed steel two piece case the insides are on first glance almost identical to the MB45 except: 1. Has a DC thru output 2. Full tape monitor loop It wasn't sold with a PSU - I'm currently using a 12V 1000Ma wall wart. I'll sort out some pics if anyone wants a look. I've just swapped it with my XcansV2/X-PSU and straight from cold (very cold in the loft actually) and its not exactly disgracing itself. Definitely more 'in head' and not as smooth and detailed as the MF but you're not wrong - bearing in mind I think it set me back less than £30 new you're right Mike what a bargain! But that Xcans upgrade kit looks oh so tempting.............
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Post by PinkFloyd on Feb 5, 2008 23:43:16 GMT
Just joined and barely 48 hours in you've had me rummaging around the loft! I found my circa 1988 QED Headphone amp (no model number - that's what they called it!). Housed in a pressed steel two piece case the insides are on first glance almost identical to the MB45 except: 1. Has a DC thru output 2. Full tape monitor loop It wasn't sold with a PSU - I'm currently using a 12V 1000Ma wall wart. I'll sort out some pics if anyone wants a look. I've just swapped it with my XcansV2/X-PSU and straight from cold (very cold in the loft actually) and its not exactly disgracing itself. Definitely more 'in head' and not as smooth and detailed as the MF but you're not wrong - bearing in mind I think it set me back less than £30 new you're right Mike what a bargain! But that Xcans upgrade kit looks oh so tempting............. Hi there, welcome aboard mate! Pictures would be appreciated, the more the merrier, it's always interesting to have a look at the more obscure (old) ones.... I haven't seen one naked picture of the QED on the net so decided to upload a few myself.... that's what it's all about man It would be worth your while soldering in some fresh caps, as Leo says the originals will be pretty dry by now and way out of tolerance... it's surprising just how good old amps can sound if they are treated to a fresh set of caps.
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leo
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Post by leo on Feb 5, 2008 23:59:31 GMT
you've got a wide range of voltages suitable, could even try rectification etc in the amp case and use a nice external AC traffo supply, lower some of that PSU filth getting to the chip
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Post by PinkFloyd on Feb 6, 2008 0:00:47 GMT
you've got a wide range of voltages suitable, could even try rectification etc in the amp case and use a nice external AC traffo supply, lower some of that PSU filth getting to the chip Just listening to it now with the Golden Graham PSU1 and will also try my Calex job.....
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leo
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Post by leo on Feb 6, 2008 0:28:44 GMT
Be interesting to see what you think how the regulated supply compares against the raw supply, sometimes raw can sound better with the power op-amps especially if you have good cap filtering
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Post by canjunkie on Feb 6, 2008 0:49:12 GMT
OK - sleep is for whimps! I suppose I shouldn't complain about my cold loft - me bein' a damned southern softie! Here are a few pics. That Tape monitor switch is definitely showing signs of age - I've had to wobble it to restore the music! I think replacing the caps & sorting out some cleaner volts 'n' amps is worth a try. At worst it'll give me some soldering practice since I haven't done any serious PCB work for a while. I'll let you know how I get on when I get some time to heat the 'iron up! Then there is that Kit for the X-Cans............. In the meantime the old dear could do with a good clean up!
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Post by PinkFloyd on Feb 6, 2008 16:11:51 GMT
Right..... got to work on replacing the old caps and jesus christ what a TREMENDOUS improvement!! Not sure if it's just pot luck with the caps I selected or if there was method in my madness but this amp is absolutely rockin' now! Close your eyes and you'd think you were listening to some huge 3kW power amp..... seriously..... the dynamics are huge, the bass is DEEP, this amp slams like a piledriver. I am not imagining this and will be sending her down to Nigel for a second opinion.... that little LM1877 chip is one hell of a good performer. So what have I done to her..... let me think....... ah yes...... removed the two 100uF electrolytic output caps and replaced with 1000uF non polar types. Swapped out the 470uF cap for a Philips 046 series 470uF bypassed with a 100nF WIMA, strapped a mama honker RIFA PME 271M 470nF Class X2 capacitor across the DC input, fitted a 1000uF ELNA RE2J direct to chip / ground and bypassed it with a 470nF film cap, removed the two 1uF electrolytics and replaced with 2 x 1uF film caps, replaced the two 10uF caps with Panasonic blues, replaced the 1N4002 diode with a UF4007 bypassed with 100V / 100nF WIMA MKS4. I then reflowed all the joints on the board, cleaned the headsockets, cleaned the phono sockets and washed the board with Isopropyl. Very simple but [glow=red,2,300]OH SO EFFECTIVE[/glow]! Stock: With new caps:
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insomniac
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Post by insomniac on Feb 6, 2008 17:54:37 GMT
Great job you've done there Mike, looks the part. What did you use to clean the phono's and headphone socket?
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leo
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Post by leo on Feb 6, 2008 18:19:44 GMT
Looking good Mike, let us know how it sounds once it had some run in. This chip will be limited to what you can do but it makes sense to squeeze as much out of it as you can, it'll appreciate the recap anyway
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Post by PinkFloyd on Feb 6, 2008 19:57:38 GMT
Looking good Mike, let us know how it sounds once it had some run in. This chip will be limited to what you can do but it makes sense to squeeze as much out of it as you can, it'll appreciate the recap anyway Sure as hell has appreciated the recap! I can't believe the quality of sound that's emerging from that little chip.... I think this is definitely a keeper, especially to drive my high impedance 'phones (Senn 414 are 2Kohm and it drives them very well) not at all bad for £40
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Post by canjunkie on Feb 6, 2008 22:41:37 GMT
Nice Job Mike! Looking at the the MB45 with a much clearer head I notice it still has the monitor loop - they just used stack sets - 0/10 for observation for me then! After seeing comments like yours on the improvement in SQ I'd be a mug not to dust off the soldering kit! Any chance of a quote on putting a kit together? (The only concern I have is that the RIFA might foul the lid on my '88 version.) Can't wait to get home to see how its warmed up!
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Post by ticktockman on Feb 6, 2008 22:58:42 GMT
Well this got my attention as I to have a Qed circa 1988 up in the loft(somewhere). My question is would the little devil have the grunt to drive ergo2's as I have a pair( which I love to bits) that frankly have never shown their true colours with any headphone amp I have had in my possession. In fact the only thing that made them sing(sort of) was driving them off a Leak stereo20 through a "can opener" type of device made for me way back when. You do look a prat in them but they sound so good it is almost worth the ridicule
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Post by PinkFloyd on Feb 6, 2008 23:03:04 GMT
Any chance of a quote on putting a kit together? (The only concern I have is that the RIFA might foul the lid on my '88 version.) Cheap as chips canjunkie... PM me. You have PLENTY of room over toward the left (or right if looking at the rear of the amp) to fit a Mama Honker RIFA PME271.... you've got a lot of board estate there and could park tons of caps at funky angles. The PME271 will dissolve a load of junk before it enters the amp.... look at this puppy as a giant "prison" where all those nasty EMI / RFI people go to... with the PME271 on board you are effectively crook free... Sandy and leo may tell you different but, believe me, your best form of defence is at the front door. Once the bastards get in you have to deal with them..... PME271M disables the bastards at source.
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Post by PinkFloyd on Feb 6, 2008 23:18:34 GMT
My question is would the little devil have the grunt to drive ergo2's as I have a pair YES!!!! most definitely!!The Ergo amp employs a very similar module to the QED.... do a search for "Ergo model 1 amp"
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Post by canjunkie on Feb 6, 2008 23:43:16 GMT
Cheers Mike - PM Sent. I'm with you mike - The PS is the rock on which any piece of electronic kit should be built - but is rarely seems that way - even in so called professional (including broadcast) gear! If you accept that 'rubbish in rubbish out' applies to your signal path, surely the same must be true of the 'volts 'n' amps' that are driving the thing! In fact I'm glad I flogged my scope when I got out of engineering - some of the readings I got from PSU's varied from 'interesting' to frightening! And that was when they were allegedly within spec. Trying it on my home kit would have probably made me cry!
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leo
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Post by leo on Feb 6, 2008 23:48:46 GMT
Filtering as much as that shite on the raw supply you can is going to help, the Rifa is made for filtering
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