First board built, so far only bench tested, works fine. Bandwidth from below 2Hz to over 2 MHz (my signal generator doesn’t go higher). Will assess square wave after I have a proper PSU, my lab supplies do cause ringing.
Have built it with the large outputs, mostly Beyschlag resistors (now also part of Vishay), and a 5 pF Silver Mica cap. The bias resistors for the outputs, for Q7 / Q11, and R17 are socketed to experiment with different values.
Q9 and Q14 do get warmer than Q8 and Q10. Offset and also bias current through the outputs varies little with rails between 18 and 24 V. Offset very sensitive to P1 here, as well.
Waiting for more parts and PSU. Build will probably continue after Easter Holiday ...
When going through the thread while I was searching for something, I noticed that in my earlier post from my mobile phone the picture never made it through ... so here it is again:
There is also an addendum now: When testing the second board, I buffered the outputs of my lab supply with a WIMA MKP4 DC-LINK 20 uF capacitor on each rail. This took care of the ringing on the square waves - square waves look almost perfect now.
Also: gain continues to stay the same all the way to DC, so no falling back to unity gain at DC. Will provide caps at the output of the line stage in order to protect the inputs / transformers of my M2 and SissySIT.
Best regards,
Claas
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When going through the thread while I was searching for something, I noticed that in my earlier post from my mobile phone the picture never made it through ... so here it is again:
There is also an addendum now: When testing the second board, I buffered the outputs of my lab supply with a WIMA MKP4 DC-LINK 20 uF capacitor on each rail. This took care of the ringing on the square waves - square waves look almost perfect now.
Also: gain continues to stay the same all the way to DC, so no falling back to unity gain at DC. Will provide caps at the output of the line stage in order to protect the inputs / transformers of my M2 and SissySIT.
Best regards,
Claas
What are you considering putting on the output, brand, uF, voltage?I have similar concerns for my M2 and soon to be SissySit, regarding DC.
Thanks,
Russellc
Hi Russellc,
my budget favourite are the WIMA MKP10. This is what I normally use as coupling caps.
My M2 and SissySIT have 100 kOhms input impedance, so 0.68 uF or even 0.47 uF would be sufficient. In order to make the preamp more universal without having to think about adapting the value of the output caps, I will probably go with a higher value.
On the other hand, in my opinion, the value of the cap has to be balanced against transient behaviour at turn-on and turn-off. I know from my tube amps that large caps do cause a large voltage transient at turn-on/turn-off. This would point to a cap value as small as is reasonable without bass roll-off. Have to test if this is an issue here as well. In first lab test, I have seen transients using a 6.8 uF cap, but this has not been the final set-up, and was with just the DMM and the scope probe at the output.
I have a number of MKP10s in my drawers - 0.47, 0.68, 1.0, 2.2, 3.3, 6.8 uF ... They are mostly rated to 400V DC, but don't think the voltage rating matters much. I will go with the 2.2 uF as a start, as this would work well with amps having an input impedance down to 22 kOhms.
Once I have built up everything, I will try to get a handle at transient behaviour with a 100 kOhm ballast resistor across the output. If I don't see voltage spikes more than a few mV at turn-on or turn-off, I probably just leave it at that.
I also have a few different varieties of Jantzen MKP caps, and some Russian K42, etc. paper-in-oil caps, and one set of Russion Teflon caps, but I'm not sure if I will able to be bothered to try once the line stage is up and running ...
Best regards,
Claas
my budget favourite are the WIMA MKP10. This is what I normally use as coupling caps.
My M2 and SissySIT have 100 kOhms input impedance, so 0.68 uF or even 0.47 uF would be sufficient. In order to make the preamp more universal without having to think about adapting the value of the output caps, I will probably go with a higher value.
On the other hand, in my opinion, the value of the cap has to be balanced against transient behaviour at turn-on and turn-off. I know from my tube amps that large caps do cause a large voltage transient at turn-on/turn-off. This would point to a cap value as small as is reasonable without bass roll-off. Have to test if this is an issue here as well. In first lab test, I have seen transients using a 6.8 uF cap, but this has not been the final set-up, and was with just the DMM and the scope probe at the output.
I have a number of MKP10s in my drawers - 0.47, 0.68, 1.0, 2.2, 3.3, 6.8 uF ... They are mostly rated to 400V DC, but don't think the voltage rating matters much. I will go with the 2.2 uF as a start, as this would work well with amps having an input impedance down to 22 kOhms.
Once I have built up everything, I will try to get a handle at transient behaviour with a 100 kOhm ballast resistor across the output. If I don't see voltage spikes more than a few mV at turn-on or turn-off, I probably just leave it at that.
I also have a few different varieties of Jantzen MKP caps, and some Russian K42, etc. paper-in-oil caps, and one set of Russion Teflon caps, but I'm not sure if I will able to be bothered to try once the line stage is up and running ...
Best regards,
Claas
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One more for today:
When I go about building an amp, I usually read through all of the related threads. In order to make sense of all the information there is, and interesting modifications, etc., I put all info I find relevant, tips and hints, and my thoughts about what to buy, what to prepare and how to go about building it into an Excel sheet. Otherwise - no way I could keep track of all there is to think about in a build.
Also, I find it to be a stimulating exercise to build a mental model of an amp / a build before actually putting soldering iron to leads or drill bit to metal. (Isn't this called "Digital Twin" nowadays ? In this case, more like a bio-virtual twin)
Anyway, for Wayne's BA 2018 linestage, I have compiled the information that I find useful about the build into an Excel sheet as well; attached here. Maybe it could be of help for someone else as well.
Have fun,
Claas
When I go about building an amp, I usually read through all of the related threads. In order to make sense of all the information there is, and interesting modifications, etc., I put all info I find relevant, tips and hints, and my thoughts about what to buy, what to prepare and how to go about building it into an Excel sheet. Otherwise - no way I could keep track of all there is to think about in a build
. Also, I find it to be a stimulating exercise to build a mental model of an amp / a build before actually putting soldering iron to leads or drill bit to metal. (Isn't this called "Digital Twin" nowadays ? In this case, more like a bio-virtual twin
)Anyway, for Wayne's BA 2018 linestage, I have compiled the information that I find useful about the build into an Excel sheet as well; attached here. Maybe it could be of help for someone else as well.
Have fun,
Claas
One more for today:
When I go about building an amp, I usually read through all of the related threads. In order to make sense of all the information there is, and interesting modifications, etc., I put all info I find relevant, tips and hints, and my thoughts about what to buy, what to prepare and how to go about building it into an Excel sheet. Otherwise - no way I could keep track of all there is to think about in a build
Also, I find it to be a stimulating exercise to build a mental model of an amp / a build before actually putting soldering iron to leads or drill bit to metal. (Isn't this called "Digital Twin" nowadays ? In this case, more like a bio-virtual twin
Anyway, for Wayne's BA 2018 linestage, I have compiled the information that I find useful about the build into an Excel sheet as well; attached here. Maybe it could be of help for someone else as well.
Have fun,
Claas
Appreciate that. I'm a little nervous about ANY DC on preamp outputs, especially when M2 is being used. I know the main M2 thread suggested no more than 5 mV on transformer of M2. Also Amps like F5 that have no coupling caps. This has always made me a touch nervous as well.
Will be watching as you proceed, thanks for the response.
Russellc
I'm just a little nervous about one of the sources that might get connected to the linestage, and that might have some DC, and since Wayne's linestage also amplifies DC ...
A few years back, I nearly fried the voice coil of one of my FE208 Sigmas in a similar fashion, having connected a power amp that was also DC-coupled ... the smell of the burnt glue hang near the driver for weeks, but in the end it seems to have survived with no ill after-effects ...
A few years back, I nearly fried the voice coil of one of my FE208 Sigmas in a similar fashion, having connected a power amp that was also DC-coupled ... the smell of the burnt glue hang near the driver for weeks, but in the end it seems to have survived with no ill after-effects ...
don't be nervous .......... for instance - Boyz and Girlz at PL are doing it all the time
when made properly , it's made properly and it will work for ages properly
and this one is made by PL Boy , Full Nelson himself
Measuring at Edcor on my M2, just under 5 mV with BA3 FE. If Wayne's LS has 5 mV, (or whatever) will that be additive to Dc I am already measuring there? A lot of this I dont understand.
Russellc
M2 will not amplify DC , having that Silmic in path , remember?
though , gentle on input , autoformer will be grateful
I've been told it didnt amplify, I just thought maybe it still goes through unamplified, and was perhaps additive to M2's already existing DC at Edcor....glad to hear it isnt. Is Sissy Sit also safe from this? Really dont want to mess up those Cinemags.
Russellc
Analyze the circuit to decide whether M2 does or does not amplify DC. It's a textbook simple circuit, without tricks, stunts, weirdnesses, or unusual contrivances.
Another thing you can do is make yourself a 0.15 volt DC source from a 1.5 volt DC battery and a ten-to-one attenuator (two resistors). Apply 0.15V DC to the input of your M2 amplifier and see whether its output DC level jumps by (M2_gain x 0.15 volts).
Another thing you can do is make yourself a 0.15 volt DC source from a 1.5 volt DC battery and a ten-to-one attenuator (two resistors). Apply 0.15V DC to the input of your M2 amplifier and see whether its output DC level jumps by (M2_gain x 0.15 volts).
Sissy's block schematic is practically same as M2's
there is also Elna Silmic II in signal path ( cunningly bypassed with 1uF Philips MKC , just to look fancier and ZM sleep better) , so any DC on input will stop right on Elna
on the other hand ..... take in account that Cinemag is around 27R (by memory) for DC ; luckily , sources are always too sissy , being capable of sending some substantial DC on output , but rarely capable of sending substantial current to fry that 27R wire coil
could be calculated - what current is needed to fry tiny wire or just heat it enough to mess with enamel , but from experience I know that these circumstances are soooooo rare .......
in short - make your preamp as prescribed and chill
few mV here and there will not kill your Wabbits
Instead of saying, "not hear a difference in sound" , I should have said most will not hear a difference installing a DC blocking cap. Everything in a circuit effects the sound to some extent but most will never hear a difference in a dc blocking cap. Different coupling caps in tube amplifiers can be heard by trained ears. I myself have noticed differences between different brands of caps used as a coupling cap but very subtle if a good one is used. Splitting hairs for most.
I understand, and have addressed ( just a couple of posts up) adding caps to block DC. My questions are in order to understand the nature of how DC acts when combined with various circuits used here. I don't think anyone here is going to advocate that DC on a preamps output is a good thing.
I also understand those explaining to chill.....its not that I am unchilled, just knowing full well that DC is not something good in this regard, I'm trying to understand better, so I ask. Previously the notion of DC on a preamp's output would have indicated a big problem....I have been well advised that in these quantities, it is no biggie....now was wondering if it was additive to M2's DC right before the Edcor. Knowing that beyond 5 mV is considered bad for little Edcore and mine is just under that. Yes, I know Mark's M2x has a cap to prevent this, but mine is original schematic which does not. Yes I could graft one on, but without risk, I can ask so I did.
Thanks for the responses, I was shy to use this linestage for M2 because of that, as was the member above I responded to about type of cap and so forth. Even more shy with SissySit, but Zenmod has assured me its not an "additive" problem.
Again thanks for the answers,
Russellc
I also understand those explaining to chill.....its not that I am unchilled, just knowing full well that DC is not something good in this regard, I'm trying to understand better, so I ask. Previously the notion of DC on a preamp's output would have indicated a big problem....I have been well advised that in these quantities, it is no biggie....now was wondering if it was additive to M2's DC right before the Edcor. Knowing that beyond 5 mV is considered bad for little Edcore and mine is just under that. Yes, I know Mark's M2x has a cap to prevent this, but mine is original schematic which does not. Yes I could graft one on, but without risk, I can ask so I did.
Thanks for the responses, I was shy to use this linestage for M2 because of that, as was the member above I responded to about type of cap and so forth. Even more shy with SissySit, but Zenmod has assured me its not an "additive" problem.
Again thanks for the answers,
Russellc
it is good to ask
then think
then ask again
then think again.
I'm doing it all the time ........ only forgetting sometimes to think
Appreciate patience and answers. I like to read whole thread on a project, and sometimes wait for the thread to develope.
I make notes on anything I don't understand, problems others have solved, part substitutions,, etc. To that end, hoping it will answers someone else's concerns, as another member just a few posts back expressed similar concerns.
I remembered to think, it didn't help. My bad.
Russellc