Hmm, 100W class A at 8ohm (per mono block) with 32VDC (out of the 24VAC secondaries) just can't be done. 2x35V transformer will give around +/-45VDC under load. Bias will need to be 2.5A. I think this is what I am going with... 800VA, might increase and go with 1kVA. 2x 115VAC primaries, 2x 35VAC secondaries.
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600VA transformers in monoblocks will still get the job done nicely. You get no additional power from bigger transformers.
Yes, if the goal is 100wpc then you’ll need 35V or more secondaries. Cascode V3 front-end. Higher voltage capacitors, etc…
You mention bigger cases than the 5U, if so you could consider daisy-chaining another output board per side and have more devices to share the load.
Will be a neat build!
Yes, if the goal is 100wpc then you’ll need 35V or more secondaries. Cascode V3 front-end. Higher voltage capacitors, etc…
You mention bigger cases than the 5U, if so you could consider daisy-chaining another output board per side and have more devices to share the load.
Will be a neat build!
Thanks, Dirk.
6L6, is there an example somewhere of daisy-chaining output boards?
I suspect they go of course in parallel, to each + and - side of each mono block.
Will need to order more boards then.
Ordered a matched octet of Jfets for cascoding in the FE boards and all the other transistors and diodes as well as the boards. Two of the four FE boards will remain unused.
6L6, is there an example somewhere of daisy-chaining output boards?
I suspect they go of course in parallel, to each + and - side of each mono block.
Will need to order more boards then.
Ordered a matched octet of Jfets for cascoding in the FE boards and all the other transistors and diodes as well as the boards. Two of the four FE boards will remain unused.
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to starcat #1309
Hello starcat,
if you want to build a balanced version of the F5TV3, then you will need
2 frontend - boards per monoblock and minimum 2 N-channel- and 2 P-channel-
outputboards per monoblock.
If I understood the F5T-article of Nelson Pass right?
Or you check EUVLs approach to a balanced F5T.
But I think you only want to add a balanced input?
Cheers
Dirk
Hello starcat,
if you want to build a balanced version of the F5TV3, then you will need
2 frontend - boards per monoblock and minimum 2 N-channel- and 2 P-channel-
outputboards per monoblock.
If I understood the F5T-article of Nelson Pass right?
Or you check EUVLs approach to a balanced F5T.
But I think you only want to add a balanced input?
Cheers
Dirk
Attachments
I am not sure I understand your question. A monoblock is not balanced by nature. It's just whether you choose to have each amp channel in its own chassis. Many people build monoblocks for standard First Watt clone amps as an example. Most are not balanced.
If you're trying to say that one balanced monoblock takes roughly the same number of parts as a stereo amp, and that you could easily convert a stereo amp to a balanced monoblock, then you're correct. However, you do wire them just a teeny bit differently.
See page 13 in the article for the schematic for a single channel of single ended V3. See Dirk's post and the article for the balanced config.
What do you want to build? You can certainly build the F5T v3 in a balanced configuration.
Either way, if you build the balanced version using common XLRs for your inputs, the hookup is. Pin 1: GND (or chassis) Pin 2: +In Pin 3 -In.
Is that what you're asking?
If you're trying to say that one balanced monoblock takes roughly the same number of parts as a stereo amp, and that you could easily convert a stereo amp to a balanced monoblock, then you're correct. However, you do wire them just a teeny bit differently.
See page 13 in the article for the schematic for a single channel of single ended V3. See Dirk's post and the article for the balanced config.
What do you want to build? You can certainly build the F5T v3 in a balanced configuration.
Either way, if you build the balanced version using common XLRs for your inputs, the hookup is. Pin 1: GND (or chassis) Pin 2: +In Pin 3 -In.
Is that what you're asking?
I have ordered two sets of the F5T PCBs which gives me 4 FE boards and 8 output boards. Should be set for the balanced mono blocks, right?
Optional, I could order one set more if I want to daisy chain the output boards (for 4 more output boards, 2 per mono block).
I have ordered as well an octet of the 8-11mA Toshiba JFETs, which gives me 2 devices per FE board. Optional, I would need another octet in order to cascade them in a balanced configuration (4 devices per FE board, total of 4 FE boards = 16 JFETs for cascaded balanced), right.
Trafo it looks like it will be a custom 800VA per mono block with 2x 115VAC primaries and 2x 35VAC secondaries. Going for 45VDC rails and 2.4-2.5A bias in order to reach 100Wpc. CLC instead of CRC in the PSU with 3.3mH 14AWG air chokes.
Still deciding on external vs. internal PSU. I tend more to go external.
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I don't really need that much power (100wpc in pure class A is more than enough),
I need the slew rate of the balanced amp, particularly as all my equipment and amps is balanced as well.
My calcs showed however 100wpc with 45VDC rails?!
Edit:
I have not yet ordered the custom toroids.
I need the slew rate of the balanced amp, particularly as all my equipment and amps is balanced as well.
My calcs showed however 100wpc with 45VDC rails?!
Edit:
I have not yet ordered the custom toroids.
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Yes, for a standard F5 turbo V3. (schematics on p.13 https://firstwatt.com/pdf/art_f5_turbo.pdf ). But that's not balanced.
Once you build it as balanced as in the form of template on p15, your voltage swing doubles.
Once you build it as balanced as in the form of template on p15, your voltage swing doubles.
Dennis, I see your point and you are right on doubled power output for balanced. With 45VDC rails it gets to 200Wpc, maybe more.
So, the question is what secondaries to order for the toroids?
I could lower rail voltage or lower bias to output devices and stay with 45VDC, if I need less power. What do you think?
Edit: I will fully populate the F5T v3 PCBs, so not lowering output device count and opt for cascoding JFETs.
So, the question is what secondaries to order for the toroids?
I could lower rail voltage or lower bias to output devices and stay with 45VDC, if I need less power. What do you think?
Edit: I will fully populate the F5T v3 PCBs, so not lowering output device count and opt for cascoding JFETs.
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The calc is actually simple. A single-ended stereo F5T v3 using 2 FE and 4 output boards gets 100Wpc with an 800VA transformer and 45VDC rails. If that single-ended stereo amp is converted to balanced, it still uses the same 800VA transformer and rails and the same number or FE and output boards (but for a single channel, i.e. using both available channels for amplification of the + and - of the signal as balanced doesn't reference GND). Effectively doubling voltage swing, output power and slew rate.
I tend to increase the 800VA to 1kVA however, in order to be at least 5x the output power.
I tend to increase the 800VA to 1kVA however, in order to be at least 5x the output power.
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