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jeffs last won the day on March 29

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TO-247L Transistor

TO-247L Transistor (17/21)



  1. The 901s and m1.5t is a good combo. I had it for a while and it can go big ......... problem is the 901s are not very good at lower levels (just my opinion). The front plastic bezel on the m500 can be polished with a succession of Novus 1/2/3 polish, from coarsest to finest, depending on the level of damage. There's probably a thread if you do a search
  2. If you look at the service manual, the bulb looks replaceable. Item 53 in this diagram The schematic is not all that easy to read, but it looks like it's a 10V bulb? It's supplied by the top of the 3 regulators shown below. First step would be to find this lamp and put a voltmeter across the 2 terminals to make sure you have 10V. 99% likelihood it's the lamp, but make sure. Could be a shorted cap on the output of the regulator, or a bad regulator. Never seen one of these so take it apart, out if you can, take a pic and post it.
  3. you might need cap head screws (hex drive)? The heads are smaller in diameter. I've made this work in the past but no longer have that setup. My custom rack rails inside is 17 7/8".
  4. I assume both pieces have the factory notched faces. Reply is based on that. I've made my own racks and have a bit of control over width. I've used Sanus racks that had a bit of adjustability in the width. I could get clearance in those situations. Can you angle it in on one side and rotate to get clearance Clarence? .... or are the screws right where the rails are so you can't get past them? A pic would be great but I know you don't have those privileges yet ....
  5. The spring action is fine. They have a decent amount of throw before they latch. You really need elf fingers as the button itself is quite small. Resting fingers on the top of the unit and pressing with a thumb tip works fine. I detailed this in a different thread, but don't remember where. I basically copied the C-1 gain stage which includes balance. It's easier to show using the C-19 schematic - which is more-or-less the same: So - here's the issue with this, while you do need only a single pot (3 connections) for balance, it's less than ideal. In the default state, with the 50K pot shown, it basically puts 25K ohm in parallel with each volume pot. Not really much of an issue. When the pot is turned all the way to one side, it puts 50K in parallel with one sides volume pot, and ZERO ohms in parallel with the other side. So - you see the 820ohm resistor? It serves as the minimum load that the previous stage will see with the pot twisted all the way. Without it, the previous stage is presented with a ZERO ohm load. In the case of the C-19 shown, the previous stage is an internal op-amp, followed by 1K ohm, so that op-amp would be presented a 1.82Kohm load. Not really an issue. In the case of the C-1, I think the 820 ohm is the same but the 1K changes to 1.5K, so the presented load with balance turned all-the-way would be 2.32Kohm..... however, there is no internal op-amp, so this low load is presented to whatever is connected to the preamp input. It's less than ideal, but is it a problem? It's hard to say but I've never had an issue using a C-1 preamp and I like them quite a bit. I've also never run a unit with balance turned all the way to one side. I will say that once I gave this some thought, I chose to NOT use the balance connections on 2 of the units I built, it's only on one. In the case of my manual unit, I used a C-1 20K ohm takeout 2-gang volume pot. In the case of the remote volume units, the volume pots are 50Kohm 2-gang motorized.
  6. Top: simple 2 channel preamp with SH. Volume and SH functions remote controllable. Middle: simple 2 channel preamp with SH. Manual volume and SH switching. Bottom: SH only. SH switching via remote control. Input1, Input switch, Input 2, Preamp out, line level out. One unit has balance control under the input switch. Almost 200 mounted components, all surface mount except electrolytics. Tedious work but at least my hand is still stable enough to do it. This was my winter project. Mostly for fun and to keep up on a few skills.
  7. My point was that there were NO Topping amps on your linked list. As far as my "vote" goes, don't twist my post to fit your poll. You clearly did not read my reply in its entirety. I've probably owned more Carver vintage amps and preamps than anyone on this site. My list includes 58 amplifiers. I don't count preamps, but I'd guess it's between 20-25. It would be interesting if anyone could top these numbers. Granted - some of these were flips, but none of them were consigned repairs. I purchased, repaired, tested and listened to every one of them. I'm often asked to repair/refurbish other peoples gear and I politely decline. It's not what I do. I currently own 7 amps and 2 preamps, plus a few units that I have gifted to my adult children. I expect these numbers to stay static as I'm not interested in acquiring more gear. There are always exceptions. I've owned ZERO amps of any other make since 2014 or so. I was gifted a vintage Denon integrated which I never intended on keeping and sold after repair. I don't count that one. These are facts. I'm not sure how you equate this to me preferring cheap gear that tests great.
  8. I'm confused as to what point you are trying to make here? Your question is in regards to audio amplifiers? Correct? I followed the link that you provided. I reviewed the "categories" of the items listed. Only ONE listing was for an "Amplifier". No price is shown as this is a "Wanted" listing! All of the other "Topping" listings are for items such as DACs, preamps, Headphone Amps, etc. Fact is, people buy stuff and no longer have a use for it, for a variety of reasons. The result of only 30 listings of Topping products across the board actually seems quite low to me, based on what I would guess is a very high sales volume. If you turn your search to "Carver" you will find At least as many listings for gear. By your logic, Carver gear must be no good since customers are "parting ways" ........ I thoroughly enjoy most of my Carver gear of the 80s. I occasionally replace a unit which means I have one to sell. Does not mean that I didn't appreciate it, just that I no longer need it. I think Topping makes very good DACs at reasonable prices. I have no knowledge of their other products. A while back I was using a low-end Schitt DAC on my desk/bench. It sounded decent, but the digital noise from the computer USB was beyond noticeable. I also had a low-end Topping DAC available .... sounded great, had more features, and was dead quiet. I couldn't sell the Schiit fast enough. The opinion was based solely on my personal experience. I have never bought or sold a product based on a review on ASR ... or anywhere (actually I once bought a pair of speakers based on reviews .... mistake). Just my opinion: In todays economy, people's discretionary spending dollars are limited, probably more so than in the past 15 years, maybe longer. Personally, I've cut way back. Every purchase of this type is going to be thoughtfully considered. Table of Topping gear categories as listed on USAM, per your link:
  9. If you use a C-1 in it's simplest form using a line input with no switches engaged, that's pretty much what you get ..... except ..... The problem with this circuit is the way balance is implemented. It's really less than ideal. If you leave tone control out, the input is essentially connected to the left side of R335. The preamp input impedance becomes R335+R336+ (20K volume in parallel with 25k( 1/2 of the balance pot)= 13.42K. Already somewhat low but acceptable. If you turn the balance pot all the way to one side, the volume pot is shorted to GND on the other side. The input impedance on the opposite side becomes R335+R336= 2.32K .... So the input impedance is dependent on balance pot position. Otherwise the C-1 simplest path is more-or-less just a volume pot followed by a simple gain circuit (18.6dB).
  10. Welcome. The PM100 and PM300 are indeed the same amplifier. I've never owned a 300. It might have a different main pc board? No upgrades that I know of. I believe the PM100 shares a main PC board with the m200t? They do have different output transistors. I do remember a m200t upgrade thread. I think the general conclusion was that it didn't add much. Not sure how applicable it would be. The 1U height of the PM100/300 is going to make modifications challenging.
  11. PC board quality has come a long way. You have to try really hard to get low quality boards these days. Even low-cost boards from the hi-end Chinese houses are very good. You can dial in everything - pay as you go. Copper weight, layer thickness, board material, etc. 20-25 years ago if you went low end - it was pretty bad. Not going to name names, but some of the Carver amps built in the first 1/2 of the 90s have very poor quality PC boards. Corners were cut in that timeframe.
  12. I would agree. It's probably the worst amp to start your Carver repair journey. One bright spot is that the amps are mostly completely independent channels, including power. If one channel works, you have a reasonable reference. It's not a commonly discussed amp so I would not think there are any threads regarding repair. I fixed a PT1800 a long time ago ... have stayed away from these amps since. The PC boards are dual sided. For me, this significantly adds to the repair challenge.
  13. If the DC is high yet reasonable (under 60mV or so), check the input AC coupling capacitors for shorts. Many models this is 470uF, but others have 220uF. For which model? The m1.5t does not have a thump fix bulletin. It's one of only a few models (m400 series) that does not have a power switch. It's "instant on" as soon as it's plugged in.
  14. I ripped most of my CDs onto a Mac years ago. At that time, no special software was required, ripping was part of the "iTunes" application. My 2010 Mac also had an optical drive. Most (all?) Macs have not had an optical drive for many years .... maybe you have an external one? Additionally, iTunes is a thing of the past, but I would think the Apple Music app has ripping capability? Apple Music has fully replaced iTunes.
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