It could either be the caps or your ears getting used to the amp even more. Both are great! My amp sounds nearly as good as it does at 2-3 hours of warm-up after about an hour after turning it on. I have had some amps where I start to listen to them and I am like, well, that sounds okay... Then all of a sudden, the switch panel in my head rearranges and it clicks, and I am like, "oh man, there it is!! 🎶"
I tend to leave whatever amp that I am using as my main amp on 24/7 as I listen off and on throughout the day. It is my one energy splurge. Otherwise, I don't use a dishwasher, dry my clothes by hanging them etc.
I am glad you decided to do the class A thing. It sounds like it is paying off 🙂
I tend to leave whatever amp that I am using as my main amp on 24/7 as I listen off and on throughout the day. It is my one energy splurge. Otherwise, I don't use a dishwasher, dry my clothes by hanging them etc.
I am glad you decided to do the class A thing. It sounds like it is paying off 🙂
Thanks, yes. I went a bit too deep on a prior reply and deleted something, but I'll share it now fwiw. While I've owned various other Class A/AB SS and other tube amps, something occurred with this upgraded amp which is unique. In one of my former KT88 based tube amps designed by Dennis Had (of prior Cary Audio), I had another 50yr local tech friend upgrade it further, and went with Gold Lyon KT88s, better caps, hexdfreds, and nice vintage RCA input tubes, really good Cardas interconnects. That amp and opt tubes were biased up fairly hot. That amp produced its own unique sound, and when hearing certain strings, chimes, bells on certain audio tracks would I hear a particular type of nice marbly tones [not sure how else to describe it], overtones, interesting decay and a nice level of engagement. When I get this now-upgraded Forte' amp nice and toasty at @3hrs on-play time, it brings forth a partial element of those same attributes in the sound. Not exactly the same, but similar attributes. Was not expecting anything like this to occur.
While my tube amps are a little smoother overall, I do like some of the additional openness and similar tone this upgraded amp now brings. Is it a factor of now running this amp in full Class-A, I don't know exactly why. In any case, it's now one of the more engaging SS amps I've owned. I like it so much, I may resale this amp down the road for what I have in it to the next lucky owner, and start looking at sourcing and building two of these same Forte' amps and run two monos to see if I can replace all of my tube amps too. I don't need more power per se yet might like to try two of these with my larger speakers, after hearing what they can do. Yes, it has moved the needle enough for me - to actually consider replacing my beloved mono tube amps with two of these same amps. It's been a really fun and interesting experiment that may take me in a new direction with my primary amps not too. 👍
To: @GKTAUDIO @Mikerodrig27
CORRECTION CORRECTION CORRECTION on my end. Wow, ugh, apologize. It's what I heard originally and thought I was shown in person when i was there. It's not the case, as to what is in my amp - as advised. Not 100kuf per cap. That was way off. Your question(s), suspicions, were wise and most appropriate. They are notably taller than stock caps though. I cannot go back and edit prior posts. JS shared this, via text today. If I open the amp up in a few weeks gonna check again myself, first hand. Ugh. Still leaving the amp and cables in place, not moving them at all - sounds way too good to move it or disturb. More listening underway.
Correction -
Upgraded from stock caps to 30,000uf on each of the four main power caps. Now 60,000uf per channel.
-------------------------
Listening report #3, well over 3-weeks now post upgrade.
Forte Class A 50w:
-more listening over long weekends and some evenings, ~80hrs now.
-smoothed out even more now, suprisingly, thought it stopped before.
-starts sounding decent at 1hr warmup. About the same at 1hr.
-really comes in a hour 3. Gets even better between 120-180min.
-pairs up really well with my Cary SLP-98 (6SN7 preamp.
Smooth, sound stage opens up nicely, and becomes more 3-dimensional at 2.0-3.0hrs warmup.
Summary:
Upgrade was absolutely worth every penny. Tube amps are still set aside, Forte' staying in primary position.
Forte Class A 50w:
-more listening over long weekends and some evenings, ~80hrs now.
-smoothed out even more now, suprisingly, thought it stopped before.
-starts sounding decent at 1hr warmup. About the same at 1hr.
-really comes in a hour 3. Gets even better between 120-180min.
-pairs up really well with my Cary SLP-98 (6SN7 preamp.
Smooth, sound stage opens up nicely, and becomes more 3-dimensional at 2.0-3.0hrs warmup.
Summary:
Upgrade was absolutely worth every penny. Tube amps are still set aside, Forte' staying in primary position.
So just to throw a curveball here, you know what would be a fun project is to build the ACA Mini. I think you mentioned that you have 92.5db sensitive speakers. The ACA Mini should be a great little amp to pair with them. I couldn't quite get an idea of what your skill set is in regards to building amps. However, that amp is intended for a first-time builder. It is also very cheap, uses nice parts and it has a cool jumper feature which you should look into 🙂
It gets pretty rave reviews among first time builders as well as the more seasoned builders.
Just something else to have kicking around in your arsenal.
Thanks for the update!
It gets pretty rave reviews among first time builders as well as the more seasoned builders.
Just something else to have kicking around in your arsenal.
Thanks for the update!
@Mikerodrig27 Fun idea. Thought about it some prior to the Forte' purchase/upgrade. Started 44 yrs ago building speakers mainly, last pair in use now. Past decade doing some small amp mods myself, nothing complex, and yet I've never built an amp start to finish. np nudged me a few yrs back about the ACA amp, and coincidentally this week we corresponded some about me doing an F5 build. Comparing bits, transformer, boards, caps, etc... Forte' seems nice enough, sounds better than expected, and the whole idea kinda stopped there I guess. Good thoughts though, thx for the idea.
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Very nice. Don't confuse the ACA mini with the older ACA. The new ACA is a simpler (no chassis) cheaper and (according to a lot of people) a better-sounding amp. A nice way to break ground building from scratch. The F5 is a very nice amp. A lot of people really love it. Some love it less than the other amp designs. It is a good idea to read about the sound characteristics on that amp.
Sounds like you are entertained. I suppose that is the ultimate goal 🙂
Sounds like you are entertained. I suppose that is the ultimate goal 🙂
"The new ACA Mini is a simpler (no chassis) cheaper and (according to a lot of people) a better-sounding amp."
One of the nifty design choices with the ACA Mini is the inclusion of a jumper, which can be plugged and unplugged even while the amp is running, to experience different distortion profiles.
Another consideration is the ACA Redux. It was created by Nelson Brock, one of the founding fathers of the actual "Amp Camp".
https://www.diyaudio.com/community/threads/aca-redux.381346/
One of the nifty design choices with the ACA Mini is the inclusion of a jumper, which can be plugged and unplugged even while the amp is running, to experience different distortion profiles.
Another consideration is the ACA Redux. It was created by Nelson Brock, one of the founding fathers of the actual "Amp Camp".
https://www.diyaudio.com/community/threads/aca-redux.381346/
@ItsAllInMyHead that ACA Mini with the LED light heat sink is a clever idea. Looking closer, realized they are single channel amps. Kinda perplexed how it works well with no transformer and very small power caps. Is it this way because it's low power, or ?
^ It uses a SMPS (power brick) just like the original ACA and the ACA Mini. So, there's no need for the big transformer or filtering caps that would normally be associated with a "linear" power supply.
The ACA mini is a stereo amplifier. One board for two channels. One thing with these small amps is that you are able to get away with a lot in regard to designing them. All good things.
6L6 did a nice build guide on it:
https://guides.diyaudio.com/Guide/ACA+Mini/21
I mention the ACA mini to people who haven't built amps before as it is easy to build and it is hard not to get excited with the results knowing you assembled it. Also, Harris parts, nice Toshiba JFETs and more importantly, a really nice circuit 🙂
It is an amp you can take the paint-by-numbers approach in regards to assembly. It drives my 89db sensitive speakers very well.
6L6 did a nice build guide on it:
https://guides.diyaudio.com/Guide/ACA+Mini/21
I mention the ACA mini to people who haven't built amps before as it is easy to build and it is hard not to get excited with the results knowing you assembled it. Also, Harris parts, nice Toshiba JFETs and more importantly, a really nice circuit 🙂
It is an amp you can take the paint-by-numbers approach in regards to assembly. It drives my 89db sensitive speakers very well.
@Mikerodrig27 thanks for the link, looks iike a sweet little amp build. I can see why it might be a fun and rewarding project to do. Would like to hear it some day. 👍
Maybe a bit of topic, but: do anyone here know if the Forte 1 or 3 can handle low impedance speakers? I'm thinking about Infinity Kappa 9.2i.
Can't get an answer anywhere to this...
Can't get an answer anywhere to this...
Hey guys,
OP here. I asked a tech to fix the Forté and it has been running well since!
I have a new issue though and it's a lot like what happened to another user here in another thread—the left channel has slight distortion on certain frequencies, like a buzz. A small tap on the left side of the amp often fixes it so I'm guessing it's probably a cold joint so I'll be resoldering everything in the next few days.
While I'm at it, I thought I could check the main caps and possibly replace them since this is an almost 40-year-old unit.
Questions:
OP here. I asked a tech to fix the Forté and it has been running well since!
I have a new issue though and it's a lot like what happened to another user here in another thread—the left channel has slight distortion on certain frequencies, like a buzz. A small tap on the left side of the amp often fixes it so I'm guessing it's probably a cold joint so I'll be resoldering everything in the next few days.
While I'm at it, I thought I could check the main caps and possibly replace them since this is an almost 40-year-old unit.
Questions:
- Besides not touching the pins unless I want to get fried, is there any other stuff I need to watch out for?
- Do I need to rebias the unit afterwards? Is it okay to not touch the bias pots before replacing them and see how it behaves afterwards or should I lower the bias before installing the new caps?
- Is there some kind of benefit in going higher in capacitance, assuming higher capacitance caps fit?
Kind of hard to say what you are dealing with until you get in there. I will tell you this. Those integrated circuits on the board were what started me on my journey with this amp. probably not a bad idea to replace them. Using larger capacitors doesn't seem to benefit anything in my experience either, although changing out caps in general is a good idea. Don't know about setting bias to lower point before replacement. Doesn't seem necc to me. You will be setting bias afterward anyway, so unless something was WAY off, I don't see the need. FWIW, my unit was completely redesigned for the rebuild, now sporting 40WPC and some rethinking of the original circuitry. Truth is, I like the original Forte' 3 design as is. If yours is in class AB, I would go so far as to say that it sounds best in this state and less so in class A. Having said that, many out there would disagree with me. I found the class AB to be more open.
Answers:
You need to discharge the caps with a resistor and leads - 100R is sufficient to pull down the voltage quickly without causing arcing. Make sure your resistor/lead assembly is insulated so you don't touch any exposed metal. Connect the common ground bar to the opposite terminal on each cap for a good 30 seconds, then measure voltage with your DMM. Don't start working until voltage is zero or less than a volt. There aren't any electrolytics on the boards to discharge, as far as I recall.
You should not need to re-bias unless the caps were so bad you were not getting full rail voltages (unlikely or the tech would have found this, most likely). However, do re-check bias, as it could have drifted since servicing, and re-check after using the amp for a few hours after re-capping.
In my experience, it is sometimes not advised to increase capacitance of the main filter caps, because it increases start-up surge, and in some cases can stress downstream components. However, I have increased the capacitance by about 50% in my unit, and have no issues with start-up or operation. I did replace the old rectifier bridges with new 35A pieces. New caps are generally smaller, so going to higher C is generally not a problem, and there is plenty of vertical space in this unit, but don't go larger in diameter - keep it the same or you may have to make a new common ground bar.
You need to discharge the caps with a resistor and leads - 100R is sufficient to pull down the voltage quickly without causing arcing. Make sure your resistor/lead assembly is insulated so you don't touch any exposed metal. Connect the common ground bar to the opposite terminal on each cap for a good 30 seconds, then measure voltage with your DMM. Don't start working until voltage is zero or less than a volt. There aren't any electrolytics on the boards to discharge, as far as I recall.
You should not need to re-bias unless the caps were so bad you were not getting full rail voltages (unlikely or the tech would have found this, most likely). However, do re-check bias, as it could have drifted since servicing, and re-check after using the amp for a few hours after re-capping.
In my experience, it is sometimes not advised to increase capacitance of the main filter caps, because it increases start-up surge, and in some cases can stress downstream components. However, I have increased the capacitance by about 50% in my unit, and have no issues with start-up or operation. I did replace the old rectifier bridges with new 35A pieces. New caps are generally smaller, so going to higher C is generally not a problem, and there is plenty of vertical space in this unit, but don't go larger in diameter - keep it the same or you may have to make a new common ground bar.
I agree with Ixnay's statement about keeping it as-is, and preferring the AB class of operation to A in this case.
One note about main filter caps - a lot of older caps had a wide tolerance range - say, -10% to +75%. That means a 10,000uF cap could measure 17,500uF in the extreme. My experience with this unit and a few others is that going with +-20% caps at say, 20-50% increased C is not problematic, and can help with "stiffness" of the rails.
One note about main filter caps - a lot of older caps had a wide tolerance range - say, -10% to +75%. That means a 10,000uF cap could measure 17,500uF in the extreme. My experience with this unit and a few others is that going with +-20% caps at say, 20-50% increased C is not problematic, and can help with "stiffness" of the rails.
I apologize but it has been a few years. I do know that it was decided to use a different IC than the original, but I do not remember the replacement IC in particular. FWIW, in my case the chip had gone bad and produced loud 'smacks' of sound unexpectantly. It would lift me right out of my chair and over to the amp to shut things down. I didn't know for some time what the trouble was until I asked an engineer friend of mine about it all. If you go this route an IC socket is advisable.
I increased that power caps with those from a Nakamichi PA5 IIRC. Not a great idea. They were much larger physically, and I had to 'expand' the chassis and rearrange things make it work. The diode bridge had to be increased as ell to accommodate the greater capacitance. You can see in this photo that the chassis has been widened by the use of thick brass extenders that worked and looked quite good.
I increased that power caps with those from a Nakamichi PA5 IIRC. Not a great idea. They were much larger physically, and I had to 'expand' the chassis and rearrange things make it work. The diode bridge had to be increased as ell to accommodate the greater capacitance. You can see in this photo that the chassis has been widened by the use of thick brass extenders that worked and looked quite good.
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