Sony TA-F7 Channel Imbalance

smithyy

New Member
I recently received a Sony TA-F7 that I couldn't believe just how poorly packaged it was. There was literally no padding in the box. Before shipped the seller said that it was in perfect working order.

This is a superb sounding amp but there seems to be some channel imbalance and crackling (along with some cosmetic damage now too). Fiddling around with the position of the knobs, particularly if I balance the muting switch to be in the middle this imbalance disappears only to return again after some time - sometimes a few minutes later, sometimes an hour. RCA connections are also loose. Not in the sense that the cables don't fit, but in the way that the board moves when I attach them.

I'm not technical at all (as you can probably tell) and was always planning to send this off to be serviced in any case, but what could be the likely issue here?

Also, does anyone know who might be able to service this within the UK or Europe? I know there's a couple on this forum who specialise in Vfet amps but they tend to be very much booked up.
 
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Hi Smithyy,

Nice amp you have there, where in the uk do you live? I've had one come through the bench for a restoration a number of years ago and I seem to remember them having pre out power in jacks? If I'm right you could verify the power amps are working ok by connecting a different preamp or CD player with volume control to the power amp in sockets making sure the pre or cd volume is turned right down before the Sony is switched on.
 
The first thing I would check is that all the switches and pots are clean. That's usually the most common cause of intermittent sound/unbalance coming from the preamp: I had a TA-8650 with no sound at all due to a dirty muting switch. As mentioned above, if the power amp does not present those symptoms when connected directly to an external source, then it's very likely it's just dirty contacts in the preamp.
And definitely yes, have it serviced because those are prone to failure, and you're probably well aware of how rare they are and how unobtanium the vfets transistors are.
 
There's a lot of screws on this thing, I couldn't figure out how to remove the front panel. I cleaned what I could and behaviour seems to be a lot more consistent than before, so it probably just needs a good clean.
 
These second gen best amps aren't prone to the same failure as the 1st gen ones, there pretty bullet proof in the power amp department, the only thing i would recommended to change were the drivers iirc, new silpads and change the single iirc electro cap in each channel maybe the trim pots aswell if any other work is being completed. With the preamp it does suffer from those alps slide switches guming up with dirt and oxidizing and I would replace the fusible resistors as these seemed prone to premature failure. For the low current supply card there's a couple of caps that cannot be low esr as it upsets the amp, I'd have to check the schematic to be sure on which ones, I remember using panasonic nhg for here. I didn't have to deal with the Eva input board but I remember that the rear panel would probably have to come off if you suspect any damage here.
 
I've been comparing the TA-4650 to the F7 over the past few days quite extensively. The 4650 has been restored while the F7 is stock, though I'm not sure it would change its character too much in any case.

I've come to the conclusion that the F7 is definitely the "better" amp. It's harder hitting, has a wider soundstage, more dynamic, more detailed. Yes, but the 4650 simply sounds more real to my ears - probably due to it being a pure Vfet design. While it may not have as wide of a soundstage it does have better depth, which is I think is the main reason for this.

I think the TA-8650 may be the ultimate Vfet amp for my preferences judging by this.
 
Have you tired connecting the preamp of the 4650 to the power amp of the TA-F7? I'd be curious to do that as well, I might try one of these days.
My experience with restoration of these V-FETS is that caps in the audio path impact the sound quite significantly. I had a TA-5650 that I recapped with Nichicon FG and another one that I recapped with Elna Silmic II, and I definitely preferred the latter> I was frankly quite surprised at the difference, I didn't think it would be so noticeable.

The TA-8650 is so far my favorite of the bunch, although I still think the TA-4650 and 5650 are really little hidden gems that sound better than almost anything else at their price. I have not come across a TA-N7 yet, everyone says great things about those.
 
I've yet to try that. No Vfets in the preamp section, but it'd still be interesting to hear.

In what sense did they impact the sound? Tonality as well as technicalities?

From what I've read the second gen units have a slightly different sound to the first gen, which seems consistent with what I'm hearing. That's why I'm not sure the overall character will change. The F7 is undoubtedly better in most aspects but it's not as sweet.
 
Unlike what TVK claims, The preamp of the TA-4650 does have the same 2SK63 small signal vfets that are also in the preamp section of the TA-5650. (they're Q102-152 in the preamp circuit, if you want to check).

I'd say mostly tonality, Silmic II in my opinion for the 5660 give it more presence and depth, compared to Nichicon FG. From that, now I always use Silmic II when I get to recap a VFET.
 
The only v-fets found in the 5650 pre-amp section are in the phono amp, so other inputs would not benefit from them.
 
And I think it's only quite recently there were identified as actual v-fets. The ones in mine are 2sk79, apparently the same transistor but with in a different package.
 
That's interesting, I did not know they can also have different names and packages. Typical old Sony... :D
 
Power-amp stage wise: the weakest point in the N7B and F7B are the cascode transistors in series with the VFETs, and all of the fusible resistors that drift enormously out of spec.
Besides that the cascode transistors fade out over time, they were originally already applied at the edge of their 'safe operating area'.
Besides the fading fusible resistors (they increase in value, and in some case look like an open circuit, potentially killing the VFETs), those fading cascode transistors are the cause why so many owner/rebuilders are facing very low maximum achievable bias current (voltage), and the sound quality decreasing as well consequently. Hence, replacing those TO-220 cascode transistors and all fusible resistors is a must.

Proven and liked subs for the cascode transistors are OnSemi D44H11/D45H11 (H11 is 80V, do not take the H8 version which is 60V only) , readily available at Mouser.

The original SIL pads under the VFETs are all prone to drying out and cracking: they should be removed by decent new SIL pads.

Myself I replace any speaker output relay in an old amp; too many times the worn-out contact surfaces influenced the sound substantially.

The F7B pre-amp is another story (i.e. a b***h)
Even when all the switches are in off or unused position, the sound still goes through all those switches, aka the Sony tortuous path (as in the TA-8650/5650/4650)
Any and all of these switches should be dismantled and cleaned; spraying contact cleaners don't do much, most of the inner contacts are unreachable like that.
Plus that they often used a lubricant around the sliding internals to give that smooth movement feeling; but that stuff goes acid after 4 decades and is often a cause for more contact quality trouble, while spraying cleaners inside actually makes more mess by thinning that lubricant and making things even worse (if not over time....). Truly fully dismantling of all those switches is the only cure for long term reliability and direct sound quality.

oh yeah, and the N7B and F7B have those double 'suicide' diodes that MUST be changed out.

The RCA connectors of the F7B are a known weak point; resoldering (reflowing) here and there is recommended.
 
Hello! I'm new here. I restoring Sony TA-N7B. Have the questions for those who have more experience with this:
- what other options are there for replacing cascode transistors, besides OnSemi D44H11/D45H11? Or are they the best today, like were 10 years ago?
- where I can buy high-quality replacement of the fusible resistors? For example, Farnell offers a maximum of 200 ohms, while 330 ohms are needed. And, is it possible to replace a 1/4 W fusible resistor to a 2W resistor with the same resistance? I really don't want to buy this on Ali.
- speaker output relay, what type did you use?
- what do you think if to replace the silicone pads to mica?
I would be grateful for help.
 
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