Great, I can hardly wait to get it finished...
Model 1120 Full Rebuild/Upgrade
- Thread starter hirscwi
- Start date
Great, I can hardly wait to get it finished...
The axials are mostly Vishay 138AML with some Vishay 021AML and Nichicon TVX - and the Sprague Atom in one location. All from Mouser.
Leestereo
Super Member
The LM334Z mod can be used to incorporate a true constant current source (CCS) for just about any differential input amplifier that just uses a resistor to feed the differential pair. I would expect the effect to be subtle under most listening situations; the originator of this modification, Dan Mattis of DRM Audio Kits, reported: "a noticeable improvement in the stability of the stereo image and depth". When I did this mod on the Kenwood M1 (http://www.audiokarma.org/forums/showpost.php?p=8034327&postcount=4), it was at the same time as all of the other improvements, so I wasn't able to evaluate the LM334Z modification separately. Theoretically, in instances of high power demand on the output stage, the CCS is likely to be beneficial by isolating the input stage from power fluctuations and hence preventing induced distortion.There is a differential pair on each channel that used a resistor as a current source (R305, 306). Based on a thread by Leestereo, I wanted to replace these resistors with a true current source, the LM334Z IC. With guidance from Ben, I calculated the setting resistor as follows: 20.6V drop across R305 (22k ohm) is .936 mA. Using the formula in the LM334 datasheet, the value for the Setting Resistor is 67.7mV/.936mA = 72ohm. The setting resistor goes between the center leg of the TO-92 package and the V- leg (need to refer to datasheet - it's on the right facing the flat side). This IC/resistor then fits where the R305, 306 were, with the V+ leg to the higher voltage side (in this case, the emitters of the diff pair). Once I got over the worry about screwing things up, this is an easy mod and I'll probably use it in other locations that have a differential pair. There are also other likely places for a true current source. Maybe Ben will chime in with reference to the work he did relative to this modification. It should bring some stability. I've been informed that it will allow me to determine how much change the conductor has in his pocket during quiet passages
Main Amp Board
This was the most time-consuming board because almost all of the resistors and capacitors were replaced.
Before starting I cleaned off the burn residue using denatured alcohol and a small artists brush. Some charring remains - actual burning of rht PCB!
Notable changes were:
C501, 502 - High pass filter - were 10mfd electrolytics replaced with 2.2mfd ECW films. These wre a tight fit - can be seen at the top corners of the bard in the photos.
C505, 506 50mfd/40V electrolytics replaced with Vishay Atoms 100/40
C509, 510 50mfd/6.4V replaced with Vishay Atoms 50/20
C515, 516 Low pass filter - were 150pf replaced with 100pf WIMA FKP3 (lead spacing = 7.5mm)
C517,0518 were .1/250 mylar films replaced with Pansaonic ECW .1/250V polypropylene films because there was not room for the Janzens used on the tone board
R507 and R508 were replaced with the LM334Z IC constant current source. The 33ohm setting resistor is soldered between the center leg and the "V-" leg (the leg on the right with the flat facing up);. Use a clip-on heatsink on the LM334 leg during the resistor installation. The "V+" leg of the LM334 is connected to the emitters of the differential pair. (The V+ leg is the on the left facing the flat of the case). These can bee seen near C501 and 502 in the top of the photos.
All resistors were replaced with metal film 1% - typically Vishay RN60 series.
Next up assembly and adjustment...
This was the most time-consuming board because almost all of the resistors and capacitors were replaced.
Before starting I cleaned off the burn residue using denatured alcohol and a small artists brush. Some charring remains - actual burning of rht PCB!
Notable changes were:
C501, 502 - High pass filter - were 10mfd electrolytics replaced with 2.2mfd ECW films. These wre a tight fit - can be seen at the top corners of the bard in the photos.
C505, 506 50mfd/40V electrolytics replaced with Vishay Atoms 100/40
C509, 510 50mfd/6.4V replaced with Vishay Atoms 50/20
C515, 516 Low pass filter - were 150pf replaced with 100pf WIMA FKP3 (lead spacing = 7.5mm)
C517,0518 were .1/250 mylar films replaced with Pansaonic ECW .1/250V polypropylene films because there was not room for the Janzens used on the tone board
R507 and R508 were replaced with the LM334Z IC constant current source. The 33ohm setting resistor is soldered between the center leg and the "V-" leg (the leg on the right with the flat facing up);. Use a clip-on heatsink on the LM334 leg during the resistor installation. The "V+" leg of the LM334 is connected to the emitters of the differential pair. (The V+ leg is the on the left facing the flat of the case). These can bee seen near C501 and 502 in the top of the photos.
All resistors were replaced with metal film 1% - typically Vishay RN60 series.
Next up assembly and adjustment...
Attachments
Re-assembly
I forgot to mention that I cleaned the heatsink and replaced teh mica insulators and new grease (sparingly) and then re-soldered the legs of the outputs into the amp board.
Putting this back together was very easy. Simply reverse the steps from the service manual. The only tricky part was getting the wire to the thermal switch routed without getting it pinched.
The trickiest part was setting the bias - it's very difficult to adjust the trim pots because of their placement. They need to be accessed from the side. A non-metallic screwdriver helps, but I made the adjustments with the power disconnected to be on the safe side (I wanted no magic smoke after all these efforts). Given the nice layout of this model, this difficulty is surprising. But minor.
The offset did not need to be set - amazingly it was under 3mV for both channels with no adjustment.
I took Randy's advice and cleaned the wire connector terminals with Simichrome polish (pins) and Deoxit 100 for the plugs (female connectors).
Amazingly enough, it worked perfectly the first time on the DBT. I was pleasantly surprised given the extensive amount of work - I thought surely I'd get something wrong...
The service manual give an amazingly complete protocol for testing the performance of the unit so I will put it through it's paces, but first I wanted to give it a bit of a shakedown. The photo shows it happily playing in my office system. That's a B&O Beogram table on top. I like it for the office because it's a semi-automatic and uses the very excellent Soundsmith SMMC3 cart.
Next up, listening impressions
I forgot to mention that I cleaned the heatsink and replaced teh mica insulators and new grease (sparingly) and then re-soldered the legs of the outputs into the amp board.
Putting this back together was very easy. Simply reverse the steps from the service manual. The only tricky part was getting the wire to the thermal switch routed without getting it pinched.
The trickiest part was setting the bias - it's very difficult to adjust the trim pots because of their placement. They need to be accessed from the side. A non-metallic screwdriver helps, but I made the adjustments with the power disconnected to be on the safe side (I wanted no magic smoke after all these efforts). Given the nice layout of this model, this difficulty is surprising. But minor.
The offset did not need to be set - amazingly it was under 3mV for both channels with no adjustment.
I took Randy's advice and cleaned the wire connector terminals with Simichrome polish (pins) and Deoxit 100 for the plugs (female connectors).
Amazingly enough, it worked perfectly the first time on the DBT. I was pleasantly surprised given the extensive amount of work - I thought surely I'd get something wrong...
The service manual give an amazingly complete protocol for testing the performance of the unit so I will put it through it's paces, but first I wanted to give it a bit of a shakedown. The photo shows it happily playing in my office system. That's a B&O Beogram table on top. I like it for the office because it's a semi-automatic and uses the very excellent Soundsmith SMMC3 cart.
Next up, listening impressions
Attachments
Addenda...
Here are a couple of notes that I forgot in the thread:
The small, pF capacitors are silver mica types. They generally do not need to be replaced unless they have been subjected to DC voltage (for extended periods of time). They are considered excellent capacitors. They are not typically used in lower priced consumer gear due to their high cost (the 1090, for example, did not have any of this type). It's not surprising that Marantz liberally used silver mica capacitors in critical positions in their US-made products; these were always high quality components that were really designed states-side (the "Designed in the USA" for the made in Japan product line was most likely referring to a design approval and maybe small design changes).
The ERO MKT cylindrical capacitor is a polyester/Mylar type (MKS and MKT denote polyester). Polystyrene capacitor are typically <10nF. I suggest that you consider replacing the ERO film caps since they do not have a good longevity reputation. In general, you can replace a polyester capacitor with a better film but IMO the law of diminishing returns is more apparent here than replacing an electrolytic with a film. Polypropylene is readily available and relatively cheap due to economies of scale.
Here are some numbers for dissipation factor (DF), smaller is better:
Polyester (PETP) .5%
Polycarbonate .05%
Polyphenylene sulfide (PPS) .05%
Polystyrene .05-.02%
Polypropylene .025-.01%
Teflon (PTFE) .025-.01%
The yellow rectangular capacitors are also polyester/Mylar types. No need to replace unless you want to use and can find a polypropylene of the same size and capacity.
C405/C406 can be increased up to 220uF, space and regulator "speed" are considerations. The "speed" reference is for a capacitor on the base of a pass transistor; a large capacitor here "slows" down the transistor's ability to regulate the voltage, the upper limit is 330-470uF .
C413, C414, C415 are part of the relay circuit, replacements should be close to original values, modest increases to current standard values is OK, e.g., 180uF instead of 150uF
Here are my calculations for the setting resistor needed for these LM334Z. I used the datasheet to make these calculations and the voltages from the schematic.
R217, R218:
-20.5V - -.85V = 19.65V drop across 22k resistor is .893 mA
R(setting) = 67.7mV/.893mA = 76 ohm
R305, R306:
-21.5V - -.9V = 20.6V drop across 22k resistor is .936mA
R(setting) = 67.7mV/.935mA = 72ohm
R507, R508:
-44V - -.65V = 43.35V drop across 20k plus 220ohm resistors is 2.1mA through both – or approximately 2.08 through R507, 508
R(setting) = 67.7mV/2.08mA = 33ohm
Here are a couple of notes that I forgot in the thread:
The small, pF capacitors are silver mica types. They generally do not need to be replaced unless they have been subjected to DC voltage (for extended periods of time). They are considered excellent capacitors. They are not typically used in lower priced consumer gear due to their high cost (the 1090, for example, did not have any of this type). It's not surprising that Marantz liberally used silver mica capacitors in critical positions in their US-made products; these were always high quality components that were really designed states-side (the "Designed in the USA" for the made in Japan product line was most likely referring to a design approval and maybe small design changes).
The ERO MKT cylindrical capacitor is a polyester/Mylar type (MKS and MKT denote polyester). Polystyrene capacitor are typically <10nF. I suggest that you consider replacing the ERO film caps since they do not have a good longevity reputation. In general, you can replace a polyester capacitor with a better film but IMO the law of diminishing returns is more apparent here than replacing an electrolytic with a film. Polypropylene is readily available and relatively cheap due to economies of scale.
Here are some numbers for dissipation factor (DF), smaller is better:
Polyester (PETP) .5%
Polycarbonate .05%
Polyphenylene sulfide (PPS) .05%
Polystyrene .05-.02%
Polypropylene .025-.01%
Teflon (PTFE) .025-.01%
The yellow rectangular capacitors are also polyester/Mylar types. No need to replace unless you want to use and can find a polypropylene of the same size and capacity.
C405/C406 can be increased up to 220uF, space and regulator "speed" are considerations. The "speed" reference is for a capacitor on the base of a pass transistor; a large capacitor here "slows" down the transistor's ability to regulate the voltage, the upper limit is 330-470uF .
C413, C414, C415 are part of the relay circuit, replacements should be close to original values, modest increases to current standard values is OK, e.g., 180uF instead of 150uF
Here are my calculations for the setting resistor needed for these LM334Z. I used the datasheet to make these calculations and the voltages from the schematic.
R217, R218:
-20.5V - -.85V = 19.65V drop across 22k resistor is .893 mA
R(setting) = 67.7mV/.893mA = 76 ohm
R305, R306:
-21.5V - -.9V = 20.6V drop across 22k resistor is .936mA
R(setting) = 67.7mV/.935mA = 72ohm
R507, R508:
-44V - -.65V = 43.35V drop across 20k plus 220ohm resistors is 2.1mA through both – or approximately 2.08 through R507, 508
R(setting) = 67.7mV/2.08mA = 33ohm
Listening Impressions
I've had this up and running in my office system for several days, using custom Tekton monitors with 7" SEAS main driver and Usher tweeters.
I am very pleased with the sound of this unit. It is very clean at all ranges. The midrange is very realistic sounding and clear. The top end is clear without being too bright and the bass is very tight. Without conducting an A-B test, I'd say it's as good or better than any Marantz I've heard (I suppose that will generate some reaction). But for me, it's an enjoyable sound. I started this as much as an experiment to see if I could incorporate all the updates that I'd leared on AK. It turns out to have been a really fun project and I am quite happy with the sound. Now I just need another room to leave it set-up...
If anyone cares to replicate this project, I'd be glad to provide them with the information that I used, including all the excellent guidance from Leestereo.
I've had this up and running in my office system for several days, using custom Tekton monitors with 7" SEAS main driver and Usher tweeters.
I am very pleased with the sound of this unit. It is very clean at all ranges. The midrange is very realistic sounding and clear. The top end is clear without being too bright and the bass is very tight. Without conducting an A-B test, I'd say it's as good or better than any Marantz I've heard (I suppose that will generate some reaction). But for me, it's an enjoyable sound. I started this as much as an experiment to see if I could incorporate all the updates that I'd leared on AK. It turns out to have been a really fun project and I am quite happy with the sound. Now I just need another room to leave it set-up...
If anyone cares to replicate this project, I'd be glad to provide them with the information that I used, including all the excellent guidance from Leestereo.
catrafter
Marantz Specialist
Thanks for the kind words, Ben.
It compares very favorably to my MAC4100 (which sounds virtually identical to my MAC4200). I'm sure that a critical, trained ear might be able to discern some differences but they all sound very excellent. And the Marantz was about 1/3 of the cost. I do want to try a comparison with my model 18. It makes me think I want to try the predecessor to the 1120 (but I'm not sure just which model that is) - need to do some research.
Thanks for the kind words. It was a fun project. Something a bit more than just re-capping.
Hipocrates
Super Member
Inspiring work... kudos!
Thank you.
Wdhilliard
New Member
I am now doing this same project and have found some of your advice to be a great help. So, thanks! One question: In some of your pictures, you can see a 3-conductor gray wire (red, white, ground) soldered across some leads on the back of the interconnect board. My unit has the same. It seems that they cut the small ground traces on the bottom of the board and ran this wire across. However, from the pictures of the potentiometer on the front, you do not seem to have the same bypass that I have on the front switches. Did you end up removing the wire on the back of the interconnect board? Any idea why this was added in the first place? Poor grounding maybe? There is no mention in the service manual.
macman007
Mcintosh..Made In USA
Interesting older thread and read. I'm looking for an electrical basket case with excellent cosmetics to try some of these mods on. I've lived with a Model 1200 and 1120 since they were brand new in the box. Both were played for many years, mostly with the 1120 playing thru a pair or ESS Tempest Lab Series 1's while the 1200 got the better ESS AMT 1C's. Still have the 1200, 1120 and all the ESS speakers, both sets.
I have always liked the sound of the 1120,..though different in some ways from the 1200, and not a powerhouse, it could easily fill a mid size room with high quality music at realistic levels, provided the speakers are reasonably efficient. Deep, taut bass, and clean HF's with a midrange neither too forward or recessed, accurate and real for want of better terms. The 1120's sources were a B&O 3000 radial TT and Teac A2300S for many years. Those individual components complimented the sum total of the high quality sound which got me more than a few eviction threats from my landlord when I was in my teens and 20's.
They just don't build 'em like the 1120 and 1200 anymore, both built like a brick outhouse, ...for comfort AND speed...
..unlike much of the current crop of paperweight HT Receivers and the like..
I have always liked the sound of the 1120,..though different in some ways from the 1200, and not a powerhouse, it could easily fill a mid size room with high quality music at realistic levels, provided the speakers are reasonably efficient. Deep, taut bass, and clean HF's with a midrange neither too forward or recessed, accurate and real for want of better terms. The 1120's sources were a B&O 3000 radial TT and Teac A2300S for many years. Those individual components complimented the sum total of the high quality sound which got me more than a few eviction threats from my landlord when I was in my teens and 20's.
They just don't build 'em like the 1120 and 1200 anymore, both built like a brick outhouse, ...for comfort AND speed...
..unlike much of the current crop of paperweight HT Receivers and the like..
Traverso
Member
Hello Hirscwi,
I like to start an upgrade of my currently used 1120 see pic.
My first task was to improve a rusty casing done now.
Would you provide me with the details regarding mod and upgrades made to enhance this amplifier.
I should receive soon the Jim's audio ps part.
Thanks a lot
Alain
I like to start an upgrade of my currently used 1120 see pic.
My first task was to improve a rusty casing done now.
Would you provide me with the details regarding mod and upgrades made to enhance this amplifier.
I should receive soon the Jim's audio ps part.
Thanks a lot
Alain
