Hello everyone,
I have been listening to my uncle's set up since I was very young and yesterday I grabbed the opportunity to buy it. I'm in heaven. I have been an audio lover since forever, but this is the first time with what can be considered an excellent system. I'm in love!
The amp is a Forté Audio Model 3. I have been reading a lot and I'm usually a fan of the DIY on a lot of stuff, but my knowledge is limited. I had never heard about amp bias until yesterday and I know some components might need changing since this is a 25 year old amp.
It's not that it sounds bad, but I want to ensure that I'm getting the most out of it and that it's running in the most optimal way to guarantee durability.
Now, I'd like to ask if you could guide me towards what I should do so I can decide if it's something I could do alone or if I need to look for a tech. I have a multimeter, a soldering iron and all the tools I think I'd need minus the parts and knowledge so let's hope there is an e
"explain like I'm 5" version somewhere ahahah.
Thank you in advance!
I have been listening to my uncle's set up since I was very young and yesterday I grabbed the opportunity to buy it. I'm in heaven. I have been an audio lover since forever, but this is the first time with what can be considered an excellent system. I'm in love!
The amp is a Forté Audio Model 3. I have been reading a lot and I'm usually a fan of the DIY on a lot of stuff, but my knowledge is limited. I had never heard about amp bias until yesterday and I know some components might need changing since this is a 25 year old amp.
It's not that it sounds bad, but I want to ensure that I'm getting the most out of it and that it's running in the most optimal way to guarantee durability.
Now, I'd like to ask if you could guide me towards what I should do so I can decide if it's something I could do alone or if I need to look for a tech. I have a multimeter, a soldering iron and all the tools I think I'd need minus the parts and knowledge so let's hope there is an e
"explain like I'm 5" version somewhere ahahah.
Thank you in advance!
I found some photos here:
Forte Audio Model Three - 200/400wpc - Can be wired for 50wpc Class A Photo #2303408 - Canuck Audio Mart
It already has one of the best BJT's for audio. The (around 0.1uF) yellow film capacitors look good. The input sound-coupling capacitor also looks good.... you could try different flavours here (teflon, oil, copper, silver...), to suit the sound to your taste / the rest of your system.
Check the collector (emitter) grey resistors; make sure there's no discolouration. If you REALLY want to remove the PCB's (to replace the sound coupling input caps, for example), make sure the solder joints are sound - especially around these resistors.
Other than that, you could replace the input hook up wiring with solid core copper/silver wires - unshielded. That will also colour the sound... a fair bit... this will open the sound-stage (removal of the capacitance). Again, depending on your taste and the rest of the system - you may like the end result. You could experiment....
Make sure you have a fresh set of mica insulators and especially -> make sure there are no shorts between the transistor collectors and heatsink... once you mount the PCB's back in.
Check the DC wires are tightly screwed at capacitor terminals.
If you are really happy with the sound AND your knowledge is limited.... why risk it?
I uploaded some pictures, I hope they're good enough. I see @Extreme_Boky also found some pictures if that helps.
Thank you!
PS: Dusting it is definitely on the to-do list, but I don't have a can of compressed air around so that'll have to wait until tomorrow. It looks awful.
I mean, almost everything you mentioned I would have to search and study about, so I understand what you mean. If all is good (apparently), then I shouldn't worry about it. I just read everywhere that bias adjustment should be done hence why I thought about opening a thread asking for help about that specifically and anything else I should do.
In the mean time, I noticed a buzz on the speakers. It's quiet, but it's there. And the issue is on the Forté since I don't even need the preamp turned on for the speakers to buzz. Any idea what could be causing it? I know buzz is a PITA to solve mainly because it's hard to know where it comes from, but maybe there's an obvious answer?
There are some pictures attached, btw. Feel welcome to have a look.
Thank you so much for the help!
Attachments
I have the same amp, and have re-capped it and adjusted it. It does not hum or buzz when operating properly.
Based on your comments, you have little to no experience working on electronics, so my suggestion is that particularly high-amperage, high-ish voltage gear like power amps, you should first practice with low-power circuits. These devices contain transformers, circuits, and capacitors that can harm or kill you if you don't know the proper procedures. Making one critical mistake could be dangerous to you immediately, or later if something you worked on or missed fails and causes a short or fire.
The hum may be related to the PS reservoir caps or other electrolytic caps on the boards, or it may be another issue. Either way, you should have not only some experience, but proper tools to conduct the work. No one wants to see you light yourself up.
Based on your comments, you have little to no experience working on electronics, so my suggestion is that particularly high-amperage, high-ish voltage gear like power amps, you should first practice with low-power circuits. These devices contain transformers, circuits, and capacitors that can harm or kill you if you don't know the proper procedures. Making one critical mistake could be dangerous to you immediately, or later if something you worked on or missed fails and causes a short or fire.
The hum may be related to the PS reservoir caps or other electrolytic caps on the boards, or it may be another issue. Either way, you should have not only some experience, but proper tools to conduct the work. No one wants to see you light yourself up.
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Yeah... maybe get someone to re-cap it for you. The amp seems to be in its original condition, so -> definitely replace the DC-rails filter capacitors; they have probably dried-out. I wouldn't think that the amp in its original form would buzz at all... you could also decide if you want to use a choke here... or at least a resistor (like DIYAudio store power supply... 4x0.47ohm / 3W => single resistor: 0.12ohm / 12W)
Another cap I'd replace is the input (sound-coupling/DC blocking) capacitor. Try AuriCap XO (very neutral), or silver-in-oil capacitors (if you want to colour the sound a bit towards warmish... but the bass definition may suffer)
Once again, maybe get someone from DIY audio forums who lives near-by to do the above for you...???
Another cap I'd replace is the input (sound-coupling/DC blocking) capacitor. Try AuriCap XO (very neutral), or silver-in-oil capacitors (if you want to colour the sound a bit towards warmish... but the bass definition may suffer)
Once again, maybe get someone from DIY audio forums who lives near-by to do the above for you...???
Thank you for chiming in!
I understand what you're saying and I thank you for taking the time to give some sound advice.
Even though I don't have the theoretical knowledge, I know my way around soldering and using a multimeter hence why I think I'd be comfortable changing some things up. But only if I have someone telling me exactly what I should be doing.
The hum is definitely closer to 120hz than 60hz. I unplugged everything (even TV, TV box, PS4 etc) and the hum still remains. It's really quiet, I almost need to touch the speaker with my ear to hear it, but it's definitely there and I fear that when I connect my sub to the system it gets worse. I might be wrong, but I'm pretty sure I can also hear the same type of hum coming from inside the amp. Is this indicative of something?
All I would be able to do is swap some capacitors and measure the voltage to adjust bias, but I'd need to know the correct values. Is this information available?
Like I said above, I have done this kind of work on video game consoles and receivers so I know my way around soldering these components. The issue is the theoretical part. Unless I'm watching/reading a tutorial pointing to which ones I'd need to replace, I'm pretty much blind.
I wish I could get someone from here to do it for me, but I'm from Portugal, a fairly small country. Is there any way to search for someone who would be able to do it for me? On top of that, I just dropped good money (at least for me) to buy this setup so I'm not able to spend too much on top of it 🙁
"Reviving" a former thread to keep it together in one place - with a request for review by experts and gurus here on DIY.
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Recently acquired a Forte'3 amplifier as a long-time lurker. I did search and read all available Forte 1,1a,2,3 thread I could find here and elsewhere.
Amp is unmodified stock. Nice condition, needs health check, possible tune-up. Some of it I can do myself, basic stuff, or can take it to Jon Soderberg, not too far away.
While most prefer to convert the model 3 to 50w Class-A like Forte' 1, I may also keep it in stock 200w-8ohm 400w-4ohm configuration. This amp will be for or testing and listening very casually to larger speakers I build and will retire with. Was thinking if I could simply get 10w of Class A and the rest Class AB, I'd be totally happy with this. Will be rotating this Forte 3 in/out place of my tube mono amps. I tend to listen at low volume levels. These speakers I designed and built are 93db sensitivity @1m1w, generally between 4-5 ohms at best. I never crank it up. Trying to decide, your input matters.
REQUEST:
What are some of the Recommended Maintenance & Upgrade tips and considerations for Forte' 3:
Thanks in advance for your thoughts and replies. Much appreciated.
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Recently acquired a Forte'3 amplifier as a long-time lurker. I did search and read all available Forte 1,1a,2,3 thread I could find here and elsewhere.
Amp is unmodified stock. Nice condition, needs health check, possible tune-up. Some of it I can do myself, basic stuff, or can take it to Jon Soderberg, not too far away.
While most prefer to convert the model 3 to 50w Class-A like Forte' 1, I may also keep it in stock 200w-8ohm 400w-4ohm configuration. This amp will be for or testing and listening very casually to larger speakers I build and will retire with. Was thinking if I could simply get 10w of Class A and the rest Class AB, I'd be totally happy with this. Will be rotating this Forte 3 in/out place of my tube mono amps. I tend to listen at low volume levels. These speakers I designed and built are 93db sensitivity @1m1w, generally between 4-5 ohms at best. I never crank it up. Trying to decide, your input matters.
REQUEST:
What are some of the Recommended Maintenance & Upgrade tips and considerations for Forte' 3:
- Must-Have?
- Nice-To-Have?
Thanks in advance for your thoughts and replies. Much appreciated.
Looking at the pictures above, I don't see anything that sticks out. Check the large power supply caps with a tester for ESR and if what the capacitance of them is. Chances are they are probably still fine. Otherwise you can replace them with modern equivalents or even larger ones. The screw terminal caps of that size can be pricey so that is the only reason I suggest testing them.
If you want to do a little upgrade, add a snubber circuit to the transformer. The link leads to something called the Quasimodo. It is a tool to reduce transformer ringing which makes for a healthier transformer and a better-sounding amp. You populate a little board, hook it up to your transoformer, and use a oscilloscope to test while turning a trimmer pot to find the values you need for the snubber. You can buy little pcb boards that fit onto the bridge rectifiers that are in the amp.
Those single turn pots can be kind of hard to use. They can also get some crud in them. You can pull the pot, measure the resistance accross the two outer leads and replace it with a multiturn side adjust pot so you can adjust it from the top and not fumble around with a screw driver inside.
Check DC offset accross the binding posts of the amp with the RCA shorted. Should idealy be less than 50mv.
Check the bias procedure of the amp. In most cases with pass stuff, you set it to 45-50 degrees celcius on the top of the heatsinks. When it gets uncomfortable to touch.
Lastly, I have an amp from a similar era as yours. I converted it to class A. It sounds much better. Stronger too!
If you want to do a little upgrade, add a snubber circuit to the transformer. The link leads to something called the Quasimodo. It is a tool to reduce transformer ringing which makes for a healthier transformer and a better-sounding amp. You populate a little board, hook it up to your transoformer, and use a oscilloscope to test while turning a trimmer pot to find the values you need for the snubber. You can buy little pcb boards that fit onto the bridge rectifiers that are in the amp.
Those single turn pots can be kind of hard to use. They can also get some crud in them. You can pull the pot, measure the resistance accross the two outer leads and replace it with a multiturn side adjust pot so you can adjust it from the top and not fumble around with a screw driver inside.
Check DC offset accross the binding posts of the amp with the RCA shorted. Should idealy be less than 50mv.
Check the bias procedure of the amp. In most cases with pass stuff, you set it to 45-50 degrees celcius on the top of the heatsinks. When it gets uncomfortable to touch.
Lastly, I have an amp from a similar era as yours. I converted it to class A. It sounds much better. Stronger too!
I'd like to learn and evaluate about any benefits of NOT changing the Forte 3 from a 200/400 Class A/AB amp to a 50w Class-A amp like many do.
Background Info:
The preference would be to keep this particularly Forte 3 amp in its original stock 200/400 power configuration.
My speakers are designed to handle and consume higher power, up to ~400w rms. I will not turn it up much.
I also run dual dual 12" Scanspeak powered Stereo subwoofers on this system, below 50hz. Extra bass is not required.
Usage may not always involve dedicated sitting/listening right in front of the speakers.
Walk-around listening over long weekends. Fire it up early Thursday mornings and let it run til vey late Sunday nights, is the plan.
Summer time usage during warmer months will be a likely use-case scenario. This amp will get put in place of my big tube amps.
Not running the amp extra hot and wide open with standing current all of the time - is something I'm thinking I'd like to avoid.
I'd like to see if the amp can be optimized and made to operate quietly in its original configuration - IF that is remotely possible?
Low volume listening will be regular usage.
I'd like for this amp to last another 20 years if that's possible.
I will convert it if it's overwhelmingly necessary.
Are there other [less obvious] benefits of keeping it as-is and not converting it to full-time class A egg cooker operation?
- What are they?
Background Info:
The preference would be to keep this particularly Forte 3 amp in its original stock 200/400 power configuration.
My speakers are designed to handle and consume higher power, up to ~400w rms. I will not turn it up much.
I also run dual dual 12" Scanspeak powered Stereo subwoofers on this system, below 50hz. Extra bass is not required.
Usage may not always involve dedicated sitting/listening right in front of the speakers.
Walk-around listening over long weekends. Fire it up early Thursday mornings and let it run til vey late Sunday nights, is the plan.
Summer time usage during warmer months will be a likely use-case scenario. This amp will get put in place of my big tube amps.
Not running the amp extra hot and wide open with standing current all of the time - is something I'm thinking I'd like to avoid.
I'd like to see if the amp can be optimized and made to operate quietly in its original configuration - IF that is remotely possible?
Low volume listening will be regular usage.
I'd like for this amp to last another 20 years if that's possible.
I will convert it if it's overwhelmingly necessary.
Are there other [less obvious] benefits of keeping it as-is and not converting it to full-time class A egg cooker operation?
Personally, I've kept mine AB for the same reasons you are considering. It sounds great as-is, though it's been completely re-capped and adjusted. However, it's not as loud as my other "200 wpc" amplifiers - something that makes sense considering the 65 vdc rails, compared to up to 86 vdc in my other amps. Running even higher current through the 35 year old output devices to bias into Class A is not what I want to do, even with using a lower voltage tap on the transformer. I experimented with biasing the amp so that the heat sinks were at 50C and just found the sound to be almost indistinguishable from that when set at a lower bias - heat sinks at 45C, so back down it went.
It's a very articulate amp, but lacking some of the bottom end punch of my other 200 wpc amps, so I've been considering using it in a bi-amp configuration, with the Forte handling the mids/treble.
It's a very articulate amp, but lacking some of the bottom end punch of my other 200 wpc amps, so I've been considering using it in a bi-amp configuration, with the Forte handling the mids/treble.
@GKTAUDIO Super helpful, exactly the type of thinking and response I was looking for. Thank You.
It also makes a point on why I might want to "avoid" running higher current through 35+ year old opt devices, with no spares on hand.
I'm okay with slightly less optimized sound in trade for extended amp longevity since this is not my primary amp setup - my tube mono amps are.
It also makes a point on why I might want to "avoid" running higher current through 35+ year old opt devices, with no spares on hand.
I'm okay with slightly less optimized sound in trade for extended amp longevity since this is not my primary amp setup - my tube mono amps are.
Sounds like you're down to just checking the caps and replacing as needed and calling it a day. Snubber again is a great little upgrade if you decide to look into it.
Have you checked the DC offset and where the bias is (temperature)?
Have you checked the DC offset and where the bias is (temperature)?
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Thank You both. Should have the amp in hand soon and set up this weekend for a first listen. May pop the cover the next week.
Speaking Binding posts - too, eh?
The Forte 3 amp arrived safely today. Very nice condition visually, as in it appears to be very low use. All of the front/rear labels, decals, are amazingly nice. However, can't use it as-is with my Cardas speaker cabling with banana connector ends. Argh. The stock speaker connector barrels on the amp are larger, as in way too loose to use as-is, and would cause speaker damage if I tried it. My cable work with all of my other amps. These are just old school speaker connectors on this amp - likely old news to all of you here. Looking now to see which of the Cardas speaker binding posts to use - would like to find bananas to seat deep into the pocket, if you guys know which ones to get?. New Cardas site too: http://www.cardas.com/binding-posts
Change of plans later today, not going to wait and/or try different things myself. Decided to put it in the hands of a pro. It will have new Cardas binding posts on it in a week. Just dropped the amp off with Jon Soderberg tonight. He lives 15m from me. Made a decision to replace a bunch of stuff, new/big power caps, bias adjusters, binding posts, some other stuff. I understand more now, and will go ahead and convert it to full Class-A 50w-4ohm/100-8ohm. He shared a bit with me about how/why, different tap on transformer too. I felt the temp on amps running while I was there - not any warmer than my prior dual mono amps. He will set it up close to the same as it would have been in Class A/AB at 47-50c temp on heat sink fins.
Sound stage will move back a tad with full Class A similar to how my tube amps work now, vs. a little forward in Class A/AB mode. Just seeing the difference in the four main power caps moving up to 100,000uf each was helpful to see for the Class A conversion. He's local so I went for it. We'll see how it turns out. I do want to see how close I can get it to compete with my mono tube amps and how it sounds compared to new Pass 🙂
Sound stage will move back a tad with full Class A similar to how my tube amps work now, vs. a little forward in Class A/AB mode. Just seeing the difference in the four main power caps moving up to 100,000uf each was helpful to see for the Class A conversion. He's local so I went for it. We'll see how it turns out. I do want to see how close I can get it to compete with my mono tube amps and how it sounds compared to new Pass 🙂
Very cool. Jon is a very capable guy. You are lucky to live so close to him.
Yes, class A seems like and obvious upgrade to me. Report back when it's all done. It'd be interesting to hear your listening impressions!
Yes, class A seems like and obvious upgrade to me. Report back when it's all done. It'd be interesting to hear your listening impressions!