In my opinion the advantages do not justify the added complexity and cost.
I'd only use monoblocks for a very heavy amplifier, some single ended OPTs can be 5 to 10kg each.
If you build an amp from a schematic but use a different OPT then there's a distinct possibility you will need to change the feedback resistor and capacitor value's because every OPT is different even if it has similar specs, IE primary Z, power OP, etc. This change might not be that much though and won't really effect the sound that you hear. Think of tweaking the FB components as like a tuning up a car engine: without the tuneup the car will still work, so don't worry about it too much.
Monoblocks do have better stereo separation but as mentioned it's a lot more work to build monoblocks. The problem with monoblocks is getting the power supply & power transformer far enough away from the sensitive parts of the amp as space is often tight.
Regarding what amp to build, the schematic you posted in post # 1 wouldn't be the first one I'd recommend to a beginner. Choosing the right design for a first amp can be very tricky, try sitting down for five minutes and list what you want from the amp. Cost is often the greatest constraint, but for a beginner look for an amp design that has good back up, where the designer is still about and active. There's a few on this forum that are simple to build and have been built lots of times by members and that has good feedback/reviews.
Andy.
Monoblocks do have better stereo separation but as mentioned it's a lot more work to build monoblocks. The problem with monoblocks is getting the power supply & power transformer far enough away from the sensitive parts of the amp as space is often tight.
Regarding what amp to build, the schematic you posted in post # 1 wouldn't be the first one I'd recommend to a beginner. Choosing the right design for a first amp can be very tricky, try sitting down for five minutes and list what you want from the amp. Cost is often the greatest constraint, but for a beginner look for an amp design that has good back up, where the designer is still about and active. There's a few on this forum that are simple to build and have been built lots of times by members and that has good feedback/reviews.
Andy.
I have spent over eight pages trying to sus out the details of this, never seeming getting a complete answer. I am not about to start that again.
Can you please tell me if this is a good option? https://www.ebay.com/itm/314399041893
I almost put a bid on it this morning, then had second thoughts.
I know this, though the analogy is better. Could take it a step further and say tuning for different styles of driving (different styles of music) can be a benefit. The idea I have, never heard back if a reasonable one, is to put in a resistor and the a potentiometer, either with or without a switch (a lot of folks have had better results with no feedback loop).
Turns out we were told wrong, notice the two channels are connected at R5.
Why more work? Is it vastly more?
I am not seeing the issue with size, the board is 8"/20cmx17"/43cm, if need more space, add another one or two. Just checked, the cabinet is 15,25"/38,7cm x 27,5"/69,8cm. Hmmm... 🤔
I was recommended a layout program, reminds me still need to do that.
Mind me asking why?
Power supply, there is a way to simplify.
I did this twice, only the second time recommended a Dynaco ST-35, which now can't be built as the OPTs are NLA, and the Tubelab PP.
Well, I could over and over switch a design based on help, then get none, happened once and not sure want to go through that again. Eight pages of trying to pry a couple of answers out has made me shy to go with the Tubelab PP. How to we at least alleviate if not remove this?
Your right forum's etc can be frustrating sometimes when you ask a question and don't get an answer or get an answer that is unintelligible.
Re the scope, buying an old scope is a minefield, owning a vintage scope can be just as challenging. I wouldn't buy that scope for various reasons.
Re variable FB, yes, it's a thing where a pot is subbed for the fixed R in order to vary the FB and thus vary the sound.
Didn't notice R5, but it isn't an issue, you'd have to change a few value's, IE RR2 & 3 and tweak the PSU/s to build monoblocks. Monoblocks are more work because
1) you have to make or buy two enclosures
2) You need two mains tfmr's and need to build two power supply's.
3) Room can be an issue, two monoblocks take up more room, most people haven't got a big space to put massive amps so as a builder you try and keep them small. Hence space can be tight and the build can be trickier as a result as everything is more squashed together. Also sometimes monoblocks are built to keep weight down with higher power amps, thus bigger mains tfmr etc, etc, room is tighter.
I'm talking in general here, your build may be different.
The design could be problematic because of the use of an RF triode/pentode the ECL80 and because it's has a high gain stage. Notice the RC stabilising networks? C9/C7 & R8, that shows the designer had stability issues and needed to roll off the frequency response to stop a stage oscillating. Also the first stage is direct coupled to the cathodyne phase splitter. These aren't big issues and if the design works you may have no trouble at all, the design is just less straight forward than triode front end RC coupled to a long tail pair with AC heaters all round. To be honest I'm probably nit picking and being over cautious.
Is there a way to simplify the power supply? It depends, you could use silicon rectifiers, big caps and no choke, but if you already have the mains tfmr stick with the original design.
Your right, finding a first design can be tricky, as mentioned I was being over cautious, stick with this design, if you can get PCB's that makes life easier & go for the simplest method of construction. It can take a year to build an amp, it's easy to get discouraged and get bogged down, the quicker and easier you can put it together the better your chances of finishing it.
Have fun, Andy.
Re the scope, buying an old scope is a minefield, owning a vintage scope can be just as challenging. I wouldn't buy that scope for various reasons.
Re variable FB, yes, it's a thing where a pot is subbed for the fixed R in order to vary the FB and thus vary the sound.
Didn't notice R5, but it isn't an issue, you'd have to change a few value's, IE RR2 & 3 and tweak the PSU/s to build monoblocks. Monoblocks are more work because
1) you have to make or buy two enclosures
2) You need two mains tfmr's and need to build two power supply's.
3) Room can be an issue, two monoblocks take up more room, most people haven't got a big space to put massive amps so as a builder you try and keep them small. Hence space can be tight and the build can be trickier as a result as everything is more squashed together. Also sometimes monoblocks are built to keep weight down with higher power amps, thus bigger mains tfmr etc, etc, room is tighter.
I'm talking in general here, your build may be different.
The design could be problematic because of the use of an RF triode/pentode the ECL80 and because it's has a high gain stage. Notice the RC stabilising networks? C9/C7 & R8, that shows the designer had stability issues and needed to roll off the frequency response to stop a stage oscillating. Also the first stage is direct coupled to the cathodyne phase splitter. These aren't big issues and if the design works you may have no trouble at all, the design is just less straight forward than triode front end RC coupled to a long tail pair with AC heaters all round. To be honest I'm probably nit picking and being over cautious.
Is there a way to simplify the power supply? It depends, you could use silicon rectifiers, big caps and no choke, but if you already have the mains tfmr stick with the original design.
Your right, finding a first design can be tricky, as mentioned I was being over cautious, stick with this design, if you can get PCB's that makes life easier & go for the simplest method of construction. It can take a year to build an amp, it's easy to get discouraged and get bogged down, the quicker and easier you can put it together the better your chances of finishing it.
Have fun, Andy.
I do try and remember it takes two to tango. I know sometimes I don't come across clear, partly as add other stuff (working on that, a new friend has comprehension difficulty and asked me to simplify).
Thank you for providing an answer. 🙂 If a vintage scope is shown to be working, then would that be an option or is new the only option?
Is it not interesting how we can have an idea and then find out someone already thought of it?
Please correct me if I am incorrect, my understanding is the resistor must be at least 12kΩ (not 10kΩ of the original) to prevent melting speaker wires and maybe damaging the drivers. So you leave the 12kΩ in and adding to it reduces the amount fed back. I did read the text recommended, only explained what feedback is, not how to design it.
Here is an example of me not being clear. I been stuck on this idea of building monoblocks, the thread on it I think said it was, and how many folks have seen it and no one said you blithering idiot, that is a stereo design.
Now if that is the difference, don't see why one couldn't switch it and see if they can tell the difference between monoblocks and stereo. Who says monoblocks must be built on separate chassis? There are monoblocks which share a power supply. Or is the power supply also separate with umbilical cords?
Regarding number three, there is a possibility of them going into an upright console gutted when stereo came out.
The next section in the recommended book is on tubes, will have to look out for what "RF" means.
The ECL80 is neat having two in one, though if understanding correctly, this is causing problems. Is there a better tube to look for when selecting your first? Ask for others.
So the ECL80 boosts the signal more than other pre amplifier tubes?
No, because I don't even know what this means...
This is on the original design by Audio Note. I looked and not finding the frequency response.
I don't know what this is. Additionally, why is this an issue?
Those who have built it are very satisfied. I have seen specifications and looked great (too much to do to go hunt them down...)
Again, no clue what this means...
This has DC heaters?
I rather this so I have a heads up.
All that matters is B+ is supplied with 300 to 325 volts, correct?
Look at all those resistors and capacitors, gobs of them don't exist in a tube rectifier power supply was my observation I was trying to say.
Good to know, thank you. 🙂
Yes it's an option, you can't beat a good a good analogue scope. First check you can get a service manual for the scope. Second do some research on it, does it have unobtainable parts inside? Is it easy to work on? For instance some Tek scopes are a devil to work on and have custom IC's that you can't get any more. So, do a search on EVVblog forum, something like "Bongo 4000 scope problem" .
It depends on the open loop gain of the amp in question. Open gain is the gain of the amp before applying FB. If the amp has high open loop gain you need a bigger FB R, lower gain, lower R. That's in general. I think I posted how to find the FB R by using a pot in one of my posts.
Re monoblocks, mono means one, it's the separate power supply's that make the difference. Yes, you can build monoblocks with one supply using umbilical cords, I built such an amp, see -
RF = radio frequency 20khz and up, AF audio frequency = 20hz to 20khz, roughly speaking. Valves design to run at RF can be prone to oscillation, ECC81's, ECC88's etc can be oscillate when you don't want them to. You can stop this by using grid stoppers and RC networks but it makes a beginners first build potentially more difficult.
RE the ECL80, it's a pentode and triode, the designs first stage is very high gain, it's a pentode with a big anode R. pentodes have higher gain, the bigger the Ra, the higher the gain. The desiner did this because the cathodyne PS (phase splitter) has two low OP's.
Stabilising network is to stop a valve self oscillating: you can add a resistor and cap to roll off the gain at a frequency a tad below were it is oscillating, this is what the designer did I think. It's a big subject, if you watch some of my terrible videos on my channel I explain it somewhere.
I'll answer the rest of your questions tomorrow if I may, it's been along day. Hope that this post answers some of them, Andy.
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Thank you for this information, it is appreciated; ditto on the rest. 😀
Unable to find it.
Ah, ha.
I happened on your channel by accident, watched the ones on mercury vapor.
Regarding a 100 to 120 watt amplifiers, that is crazy. What do you do with all the power?
Regarding monoblocks, it named on the channel, PS Audio has a video and calls those with a shared power supply a dual monoblocks. It also makes the point that separating the channels has more benefit than separate power supplies. Doesn't matter, don't seem building monoblocks anyway.
Unless want oscillation, like a computer (op-amp) or radio (if understanding the one video on a one tube radio correctly). Maybe if have the time and more desire, just for curiosity look for a list. Or is it all ECCs?
Hopefully resting well. Yes, more than. If get a chance be appreciated and enjoyed.