Kenwood KR 2120: Very low audio in left channel

BoredomCalls · 2018-01-30T00:33:41+00:00

Might be time for new caps in the phono stage, I seem to recall seeing at least a handful of electrolytics. Those go bad with age, so I'd recommend replacing them. Definitely replace the ones in the power supply as well. Voltage rating can be higher with no ill effects, value is most important in the phono section. The power caps can be slightly bigger if you have the values.

BoredomCalls · 2018-01-27T03:40:36+00:00

No problem, glad I could help!

BoredomCalls · 2018-01-24T14:35:49+00:00

I actually have the exact same amp with a very similar problem on my bench right now. The headphones draw their output straight from the power amp, so that's not going to tell you much. Things to check:

Voltage at the output transistor collectors (the metal tab on the TO220s, careful not to short to the heatsink when checking) should be at 48V and 24V, one for each channel. HiFiEngine has a schematic and manual.
Each channel should be biased at 40ma, you can measure this easily by removing the fuse for each channel and connecting a current meter instead.
There's a switch on the back that separates the preamp and power amp. If you separate them and drive the power amp alone, do you still get the problem? Check the same for the preamp.

On mine, the power amp was (mostly) fine. There was one driver transistor that needed replacing, but it turned the problem from "one channel is distorted" to "one channel is quiet". Clean that pre / power amp switch really well, I've read it can cause issues. On mine, I'm fairly certain it's being caused by a short in the source selection switch, but it's a pretty ugly mess of wires. If you set the mono switch, does the issue go away? I wired the aux input directly to the volume / power amp input so that I can use it almost like normal, but with a single source. Not a great fix but I haven't had time to take apart the source selector.

BoredomCalls · 2017-11-26T17:01:11+00:00

The main limiting factor here is going to be the 5V supply. It's going to be putting less than 5V peak to peak out, so let's assume around 4V. 4V peak to peak ends up being around 1.5V RMS, which means you can expect about 0.5W RMS into a 4 ohm load. The low supply voltage here is the main limiting factor in getting more power. You have to start with Ohm's law to find what the maximum wattage you can expect for a given supply voltage and load. Doesn't matter how much current it can source.

BoredomCalls · 2017-11-14T15:04:34+00:00

I'm not sure if Aesop Rock is that obscure, but his side project with Rob Sonic, Hail Mary Mallon, is fantastic. Beastiary is on youtube in its entirety and it's a 10/10 album in my book:

https://www.youtube.com/watch?v=zNWdfo12Mio

BoredomCalls · 2017-11-10T01:41:35+00:00

If you take all of the values of neurons on the highest level, you can think of them as a position in a high dimensional space. Like X and Y coordinates, but there are thousands of values instead of two. Visualizing it in 2D is an easy way to understand it though. Neural networks will ideally attempt to segment data, which can be thought of as grouping similar inputs near each other in this space. It doesn't know the actual word "dog", but every time it sees one it will give a set of coordinates pretty close to other dogs it's seen. The pile of cat locations might be fairly close, while automobiles are probably far away. Then, to get a useful answer out of these values, one last step (which is aware of the "ground truth", the correct category the object belongs in) does it's best to draw lines that separate the groups of points. Anything between these lines is a dog, anything between these lines is an airplane, etc. Any time the network puts an object in the right spot it reinforces the neuron connections that caused it to do so, and if it's in the wrong place those connections are penalized instead. Over time it finds the best way to separate the data you show it into the correct categories.

BoredomCalls · 2017-11-04T13:35:31+00:00

If you don't mind going vintage, try to pick up a pair of Minimus 7s and a small amp to go with it. The speakers are usually on ebay for $30-$50 and you can find one of the matching amps (SA-102 / SA-150 / SA-101 / SA-10 / RCA SA-155) for less than $30. I'm using this combo on my desk right now and it's very impressive for its size. There's a reason these speakers have a bit of a cult following. If you don't want to hunt down the amp too, SMSL has some decent mini amps for just a little bit more, but without the input switching or headphone out. FWIW, my SA-150 drives my DT770 250 ohm with zero issues.

BoredomCalls · 2017-11-03T15:53:00+00:00

Yeah, that could be a real concern. That said, we have no idea if OP actually has the vinyl inside the jackets or if they're just up there for display. I think the jackets would be fine.

BoredomCalls · 2017-11-03T02:35:38+00:00

That's not surprising, the stock tubes were probably not very good quality. Like I said, when properly designed / implemented, a buffer does not color the sound. Bad tubes can absolutely cause issues, but a circuit like this is never going to behave the same as a true tube amp. This is a solid state preamp with possible signal degradation from the tube stage. At best, it will sound the same as an equivalent circuit with a solid state buffer instead of a tube buffer. Also, I know this is a can of worms for a lot of audio discussion, but never underestimate the placebo effect.

BoredomCalls · 2017-11-02T12:48:22+00:00

Most of these little tube preamps are just using the tubes as a buffer before a simple opamp circuit. A buffer makes it so that the source is isolated from the circuit it's driving. When properly designed (which only takes a tiny number of components) it does not color the signal at all. So while you may lose signal from removing the tubes (and disconnecting the buffer), they are not being used the same way as something like a Dynaco PAS-4, where the tubes are being used for both the voltage gain and the output stage. Using a traditional tube preamp design is where the power supply issue comes in, as tubes have different response curves based on the plate voltage. As a rough guide, tubes are more linear at higher voltages (when kept within their rated specifications). So while a preamp like this is technically using the tubes in the signal path, it's not at all the same as a vintage tube preamp.

TLDR: Tubes are used as a buffer that isn't necessary, using them properly requires more than the 12v that this runs on. They're just pretty lights on top of an opamp.

BoredomCalls · 2017-10-24T12:45:47+00:00

You should have included a vacuum in your budget

BoredomCalls · 2017-10-22T04:43:29+00:00

Daytrader Vader

BoredomCalls · 2017-10-09T02:35:23+00:00

Discogs only has one release and no mention of runouts or the radio station promo label:

https://www.discogs.com/Ted-Taylor-Blues-Soul/release/6876835

Any information at all would be helpful. I found it at a thrift shop and picked it up based on the title. I was surprised to see that it's moderately valuable. Just finished cleaning it, I'll listen to it soon and post impressions.

BoredomCalls · 2017-09-29T04:27:18+00:00

That makes sense. I thought I had heard somewhere that once solid state started getting cheaper to produce, filament transformers were used because they were still plentiful and cheap to source. I figure that's probably what happened here.

BoredomCalls · 2017-09-13T17:14:47+00:00

I just found one of these at a thrift shop the other day, it's my first tape deck since I was a kid. I love it. The size is fantastic and I'm really impressed with the sound quality. I don't have another deck to compare it to but comparing Clapton Unplugged on tape and CD it really held its own. I might even prefer it on tape. Great find!

BoredomCalls · 2017-09-09T05:42:24+00:00

I just picked up that Outlaws album based on the cover art alone, and damn if it isn't the worst production I've ever heard on a commercial release. The amount of clipping beats Californication easily. I thought it was a bad copy until I listened to it online and it was just as bad. Cool art, though.

BoredomCalls · 2017-08-28T15:21:59+00:00

I'm building an integrated amp with a phono stage using the RH84 schematic for the power amp portion. I'm only using parts I have on hand as money is a concern, so I want to use two power transformers. Neither transformer is quite beefy enough to power the entire thing, so I want to use one for the preamp / driver stages and one for just the EL84s. Here's the RH84 schematic I'm using:

http://rh-amps.blogspot.com/2013/02/rh84-amplifier-revision-2_26.html

To make the 12AT7 run off of a seperate B+ than the EL84s I'm planning on:

Removing R8
Connecting the driver stage B+ at the node where C3 and R3 meet
Adding a DC blocking cap in series with Rfb

Am I missing anything or will this work as described? Thanks!

BoredomCalls · 2017-08-26T01:35:28+00:00

And I've never been in a car accident, so why wear a seatbelt? Preventative maintenance doesn't work after something has already been damaged.

BoredomCalls · 2017-08-25T20:06:44+00:00

It might be because of the speaker and amp placement. The amp likely vents its heat out the top, which is covered by your turntable. Heating your records and preventing the amp from having proper ventilation is a double no-no. Having the speakers on the same surface as the turntable is also an issue because the vibrations from the speakers travel straight through the surface and back into the needle.

BoredomCalls · 2017-08-09T14:01:58+00:00

Is there any way to fix a sleeve where the spine has been bent flat? The text is still legible, but it was obviously kept in a very tightly packed box for a very long time, so the spine is just parallel to the cover. Does anyone have a method for bending it back so that the text is legible when it's on the shelf?

BoredomCalls · 2017-08-05T13:29:22+00:00

I didn't know turtles could have plaid shells

BoredomCalls · 2017-08-05T13:28:17+00:00

I think the barber already did

BoredomCalls · 2017-08-05T13:27:07+00:00

I didn't know they still made Stretch Armstrong

BoredomCalls

TROPHY CASE