Hello,
I'd like to do a similar project to KYW's "El Cheapo" phonostage:
http://www.diyaudio.com/forums/attachment.php?s=&postid=335624&stamp=1077837811
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
The only thing different Is I'd like to use 6ER5 for the 1st stage and 12ATWC for output. I have these tubes on hand. This would be similar to K. Strain and G. Pimm's phonostage with 6GK5 2nd stage GL biasing. I'd like to try it without the Active-Loading though. KYW had design input years ago on Kurt Strain's phonostage, hence the El Cheapo came into fruition...
Anways, this would entail changes in values not just for the tubes but for the Riaa filter itself. I still have to read up on Kurt's tutorials here:
http://www.sonic.net/~ktstrain/RIAA_eq.htm
http://www.sonic.net/~ktstrain/Groundtutor.htm
..and KAB's filter calc. to help out:
http://www.kabusa.com/RIAA.HTM
With a help of a buddy, hopefully we could come up with something. I currently have an old model Wright phonostage that uses the same 6ER5's, it sounds best with the 12AT7WC as mu-follower output compared to the other tube types "rollable' with it. I would sell the Wright soon, as the circuit is too colored for me now having more revealing amp-speakers these days etc.
What do you guys think of the 6ER5 and 12AT7WC combo using the El Cheapo style circuit from a teccnical standpoint??? Do you think an all 6ER5 two stage circuit is a safer bet?
Thanks for any feedback or advice....
fred
I'd like to do a similar project to KYW's "El Cheapo" phonostage:
http://www.diyaudio.com/forums/attachment.php?s=&postid=335624&stamp=1077837811
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
The only thing different Is I'd like to use 6ER5 for the 1st stage and 12ATWC for output. I have these tubes on hand. This would be similar to K. Strain and G. Pimm's phonostage with 6GK5 2nd stage GL biasing. I'd like to try it without the Active-Loading though. KYW had design input years ago on Kurt Strain's phonostage, hence the El Cheapo came into fruition...
Anways, this would entail changes in values not just for the tubes but for the Riaa filter itself. I still have to read up on Kurt's tutorials here:
http://www.sonic.net/~ktstrain/RIAA_eq.htm
http://www.sonic.net/~ktstrain/Groundtutor.htm
..and KAB's filter calc. to help out:
http://www.kabusa.com/RIAA.HTM
With a help of a buddy, hopefully we could come up with something. I currently have an old model Wright phonostage that uses the same 6ER5's, it sounds best with the 12AT7WC as mu-follower output compared to the other tube types "rollable' with it. I would sell the Wright soon, as the circuit is too colored for me now having more revealing amp-speakers these days etc.
What do you guys think of the 6ER5 and 12AT7WC combo using the El Cheapo style circuit from a teccnical standpoint??? Do you think an all 6ER5 two stage circuit is a safer bet?
Thanks for any feedback or advice....
fred
Hi Jeremy,
Thanks for linking your webpage on phono designs - cool stuff... I see that you have a 6GK5 design, but I have decided not to use batteries for phono this time.
I found a full 26DHT preamp schema below using the active-loaded phono desgn, BUT it also indicates "R1: 4800" at the plates. I assume they are the measured plate resistance with the CCS loading. The question is If anyone has a schema that uses NO CCS. I have nothing against CCS it's just that I want to start with the basics first.
Anyways, I hope somone has the Non-Ccs version of the basic phono design below .. Or at least have suggestions for a 6ER5=> 12AT7WC variant, I mean like values for the last Decoupling RC filters and plate supply V after the +250V like in KYW's schema, and Output Cap and R value, etc??? Thanks!
http://www.diyaudio.com/forums/attachment.php?s=&postid=335624&stamp=1077837811
Thanks for linking your webpage on phono designs - cool stuff... I see that you have a 6GK5 design, but I have decided not to use batteries for phono this time.
I found a full 26DHT preamp schema below using the active-loaded phono desgn, BUT it also indicates "R1: 4800" at the plates. I assume they are the measured plate resistance with the CCS loading. The question is If anyone has a schema that uses NO CCS. I have nothing against CCS it's just that I want to start with the basics first.
Anyways, I hope somone has the Non-Ccs version of the basic phono design below .. Or at least have suggestions for a 6ER5=> 12AT7WC variant, I mean like values for the last Decoupling RC filters and plate supply V after the +250V like in KYW's schema, and Output Cap and R value, etc??? Thanks!
http://www.diyaudio.com/forums/attachment.php?s=&postid=335624&stamp=1077837811
An externally hosted image should be here but it was not working when we last tested it.
There won't be such a thing as a non-CCS version of Gary Pimm's design. The CCSs allow high gain from only two valves, low distortion even though a low HT voltage is used, low (and unchanging) output resistance to the RIAA network and following stage. Fundamentally, it's those CCSs that allow the design to work - use the design as the designer intended...
Konnichiwa,
Changing this circuit to a non CCS Loaded design is rather trivial.
Load the first valve with 39K Anode Load and the second with 56K.
Then change the RIAA EQ Circuit to ten times the resistor values and one tenth the capacitor values, without the "Mu-Follower" output of the CCS you cannot drive the low impedance RIAA Network.
Finally, the first series resistor needs some tuning to account for the effective anode impedance of the input valve, it looks like this is around 15KOhm (including the effect of the unbypassed cathode resistor), so that needs subtracting from the series resistor, final tuning needs to be done with measurements taken.
Doing as instructed will result in around 2 - 3db less gain and obviously the output impedance of the Phonostage is up to also around 15k, a bit high for my taste, at the levels most phonostages operate at linearity is a non-issue.
Using the ECC81 in the second stage is not that good an idea either, it too has high output impedance.
The choices I made for "Valve El Cheapo" with ECC83 in the input and ECC88 in the second stage make a good deal of sense.
You could adjust the first stage to use 6ER5 or 6GK5, but be aware that the anode impedance of the ECC83 plus it's cathode resistor form part of the RIAA EQ, so you would have to increase the series resistor in the RIAA EQ.
Sayonara
fred76 said:
Changing this circuit to a non CCS Loaded design is rather trivial.
Load the first valve with 39K Anode Load and the second with 56K.
Then change the RIAA EQ Circuit to ten times the resistor values and one tenth the capacitor values, without the "Mu-Follower" output of the CCS you cannot drive the low impedance RIAA Network.
Finally, the first series resistor needs some tuning to account for the effective anode impedance of the input valve, it looks like this is around 15KOhm (including the effect of the unbypassed cathode resistor), so that needs subtracting from the series resistor, final tuning needs to be done with measurements taken.
Doing as instructed will result in around 2 - 3db less gain and obviously the output impedance of the Phonostage is up to also around 15k, a bit high for my taste, at the levels most phonostages operate at linearity is a non-issue.
Using the ECC81 in the second stage is not that good an idea either, it too has high output impedance.
The choices I made for "Valve El Cheapo" with ECC83 in the input and ECC88 in the second stage make a good deal of sense.
You could adjust the first stage to use 6ER5 or 6GK5, but be aware that the anode impedance of the ECC83 plus it's cathode resistor form part of the RIAA EQ, so you would have to increase the series resistor in the RIAA EQ.
Sayonara
Thanks for the comments/education guys…
Hi KYW,
Just scrapped the 12AT7WC idea..
Yes, that’s why that’s the first I'd like to try out…
At least technically this is one is doable… I would try a 6ER5 input with the 180k/10uF=>39k anode-load R and a GL biased 6922 2nd stage. Apart from increasing the first series R (the 215k in 12AX7's case??) would there be other change/s in the RIAA filter or only the values itself? What are the other crucial parts in the circuit must I pay attention to for this 'version'? Like should I still use grid-stoppers for the 6ER5's (at least 100R)? Thanks again…
Regards,
fred
Hi KYW,
Just scrapped the 12AT7WC idea..
Yes, that’s why that’s the first I'd like to try out…
At least technically this is one is doable… I would try a 6ER5 input with the 180k/10uF=>39k anode-load R and a GL biased 6922 2nd stage. Apart from increasing the first series R (the 215k in 12AX7's case??) would there be other change/s in the RIAA filter or only the values itself? What are the other crucial parts in the circuit must I pay attention to for this 'version'? Like should I still use grid-stoppers for the 6ER5's (at least 100R)? Thanks again…
Regards,
fred
Hello,
there is a very helpful little RIAA calculator available free at www.beigebag.com.
This is originally from Tubecad and it calculates passive combined and split RIAA stages and even accounts for load and source resistance. I have found it to be very accurate in corresponding with the results of a respective spice simulation.
Oh, how I wish I had a working phono stage! My everlasting quest to remove all capacitors from the signal path has had me tinkering for two years now on a phono preamp which goes something like this:
EL84 ->(DC coupled)-> EL84 -> 5:1 transformer (Sowter 9040) -> Tango network (self made) -> 4:1 step-up transformer (Sowter 4383 - very good btw.) -> EL84 -> 5:1 transformer (Sowter 9040)
While it does sound good it is bitten by some stability/noise/microphonics issues. Besides it is mono...
So I am also looking for simple phono stage in order to at least listen to some records while I optimize the design. (And I can't stand the sound of the active transistor eq in my NAD 3020 - in fact I can't stand the sound of the 3020 at all - this heavy negative feedback hurts my ears after a while)
I was thinking along the lines of the original RCA circuit but it has a prohibitive output impedance of about 30K so it needs a buffer stage and a cathode follower is not compatible with my philosophy of sound. Besides I would like to reduce the size of the input resistor of the RIAA network because I feel that a lower value here would be beneficial. This is why I designed a stage around the ECC81/12AT7 like this:
It sports an output impedance of about 8K which should be enough to drive a 50K load and the network input resistor is only 100K as opposed to 470K on the RCA circuit. Its gain should be better than 40dB (100x). Now the ECC81/12AT7 is not my favourite tube but I was looking for a compromise to the shout of those high mu tubes. I really wonder how it would sound?
Meanwhile after discovering KYW's circuit, which I find very intriguing indeed, I am not so sure which track to pursue for a quick and simple RIAA? Will the ECC88 make up for the sound of the ECC83? Or is a 3 stage design the way to go? What do the experts say?
Best regards
Michael
there is a very helpful little RIAA calculator available free at www.beigebag.com.
This is originally from Tubecad and it calculates passive combined and split RIAA stages and even accounts for load and source resistance. I have found it to be very accurate in corresponding with the results of a respective spice simulation.
Oh, how I wish I had a working phono stage! My everlasting quest to remove all capacitors from the signal path has had me tinkering for two years now on a phono preamp which goes something like this:
EL84 ->(DC coupled)-> EL84 -> 5:1 transformer (Sowter 9040) -> Tango network (self made) -> 4:1 step-up transformer (Sowter 4383 - very good btw.) -> EL84 -> 5:1 transformer (Sowter 9040)
While it does sound good it is bitten by some stability/noise/microphonics issues. Besides it is mono...
So I am also looking for simple phono stage in order to at least listen to some records while I optimize the design. (And I can't stand the sound of the active transistor eq in my NAD 3020 - in fact I can't stand the sound of the 3020 at all - this heavy negative feedback hurts my ears after a while)
I was thinking along the lines of the original RCA circuit but it has a prohibitive output impedance of about 30K so it needs a buffer stage and a cathode follower is not compatible with my philosophy of sound. Besides I would like to reduce the size of the input resistor of the RIAA network because I feel that a lower value here would be beneficial. This is why I designed a stage around the ECC81/12AT7 like this:
An externally hosted image should be here but it was not working when we last tested it.
It sports an output impedance of about 8K which should be enough to drive a 50K load and the network input resistor is only 100K as opposed to 470K on the RCA circuit. Its gain should be better than 40dB (100x). Now the ECC81/12AT7 is not my favourite tube but I was looking for a compromise to the shout of those high mu tubes. I really wonder how it would sound?
Meanwhile after discovering KYW's circuit, which I find very intriguing indeed, I am not so sure which track to pursue for a quick and simple RIAA? Will the ECC88 make up for the sound of the ECC83? Or is a 3 stage design the way to go? What do the experts say?
Best regards
Michael
Fred76:
Glad you enjoyed your web visit. I have another pretty simple, but still DC-coupled design up in a different place (I've decided to colonize all of cyberspace bit by bit) at my weblog:
The Tubegeek
Before the gang starts poking holes in the design, let me make a couple of points:
1. In my system, it's only driving a couple of inches of twisted pair into a 100k volume pot, so the highish output impedance is something I'm OK with,
2. There is a battery (in series with the signal this time),
3. The whole thing (especially point #2) is a ripoff of John Atwood's very well-regarded Artemis Labs PH-1 phono stage. I wanted to see whether I could get good sound using some of his ideas while keeping things very simple.
It uses 6N1P into 6SL7 and sounds quite good to my ears. It's certainly simple enough to recommend as a project for someone looking for a quick & dirty phono.
The 6N1P uses twice the heater current of 6SL7, 600mA vs. 300mA. I have a DC supply feeding the heaters and right now I'm burning 300 mA up in a resistor paralleling the 6SL7 heater. I'm thinking about paralleling two 6SL7's instead to halve the output impedance, I just haven't had time yet to cut the hole for the additional octal socket.
Comments, hole-poking, etc., welcomed.
-j
Glad you enjoyed your web visit. I have another pretty simple, but still DC-coupled design up in a different place (I've decided to colonize all of cyberspace bit by bit) at my weblog:
The Tubegeek
Before the gang starts poking holes in the design, let me make a couple of points:
1. In my system, it's only driving a couple of inches of twisted pair into a 100k volume pot, so the highish output impedance is something I'm OK with,
2. There is a battery (in series with the signal this time),
3. The whole thing (especially point #2) is a ripoff of John Atwood's very well-regarded Artemis Labs PH-1 phono stage. I wanted to see whether I could get good sound using some of his ideas while keeping things very simple.
It uses 6N1P into 6SL7 and sounds quite good to my ears. It's certainly simple enough to recommend as a project for someone looking for a quick & dirty phono.
The 6N1P uses twice the heater current of 6SL7, 600mA vs. 300mA. I have a DC supply feeding the heaters and right now I'm burning 300 mA up in a resistor paralleling the 6SL7 heater. I'm thinking about paralleling two 6SL7's instead to halve the output impedance, I just haven't had time yet to cut the hole for the additional octal socket.
Comments, hole-poking, etc., welcomed.
-j
Hi Michael,
Thanks for the link! I don't know if you've seen Steve Bench's no C phonostage using Lundahls... You might want to check it out. I also remember the olde (r.i.p.) webpage of Mick Maloney (now Supratek of Oz) were he had design exchanges with KYW; among them I THINK are LCR type and no C phonostage/s. Thomas Mayer also had some ideas/drawings (one using DHT's in a phono!) I've seen before, I just can't remember if they are no C types. It sure has a lot of Lundahl iron ($) in it though. He must have a major discount from them by now.
Thanks for sharing your simple circuit, it just gave me an idea to try ECC81's at the input =). Maybe you could try grafting in an ECC88 output stage there just to try it out. Circa 38-45dB is actually enough for my needs. I use step-up trannies for MC.
Hi J,
Nifty blogsite =) Anyways, you guys are prolific in designing/building, the only thing I ever did was build a half-kit and tweak/modify from others suggestions. So I'm not even qualified to poke a single hole in your Atwood inspired design...
I actually did implement grid batt bias in the input of my amp but directly bypassed the coin batt w/ a small cap + grid R (not to ground). It works well w/ line level input signals but I'm not sure if the 100k series R attenuator (volume control) is a "good thing" for it as opposed to just using a fixed input R.
I'm not a real fan of Supergrass, but OTOH I just pulled out my olde "Road to Ruin" lp. It would be Joey Ramone's death anniv in a few days I think...
Thanks for the link! I don't know if you've seen Steve Bench's no C phonostage using Lundahls... You might want to check it out. I also remember the olde (r.i.p.) webpage of Mick Maloney (now Supratek of Oz) were he had design exchanges with KYW; among them I THINK are LCR type and no C phonostage/s. Thomas Mayer also had some ideas/drawings (one using DHT's in a phono!) I've seen before, I just can't remember if they are no C types. It sure has a lot of Lundahl iron ($) in it though. He must have a major discount from them by now.
Thanks for sharing your simple circuit, it just gave me an idea to try ECC81's at the input =). Maybe you could try grafting in an ECC88 output stage there just to try it out. Circa 38-45dB is actually enough for my needs. I use step-up trannies for MC.
Hi J,
Nifty blogsite =) Anyways, you guys are prolific in designing/building, the only thing I ever did was build a half-kit and tweak/modify from others suggestions. So I'm not even qualified to poke a single hole in your Atwood inspired design...
I actually did implement grid batt bias in the input of my amp but directly bypassed the coin batt w/ a small cap + grid R (not to ground). It works well w/ line level input signals but I'm not sure if the 100k series R attenuator (volume control) is a "good thing" for it as opposed to just using a fixed input R.
I'm not a real fan of Supergrass, but OTOH I just pulled out my olde "Road to Ruin" lp. It would be Joey Ramone's death anniv in a few days I think...
Hi Fred,
thanks for the pointers! Yes I have seen Steve Bench's designs and often wondered how they performed... His phono stage has a few too many diodes in the circuit for my taste But I am planning to try out his all inductor tonecontrol: http://members.aol.com/sbench101/BatteryPoweredAmps/tonestac.html.
I did also see Thomas Mayer's designs which I saved somewhere, they are very unique indeed.
Mick Maloney of Supratek/Australia who makes some very nice looking amps used to have a website up with plans for LCR and even an all LR RIAA without caps but the page is now defunct.
There is also this page from italy with an interesting articel on LCR RIAA.
This is all very inspiring really but eventually I would like to come up with a design of my own, preferably one without caps. At the moment I am looking very hard at an EF86 DC coupled to maybe an EL84 driving an output transformer. We shall see...
Bst regards
Michael
thanks for the pointers! Yes I have seen Steve Bench's designs and often wondered how they performed... His phono stage has a few too many diodes in the circuit for my taste
But I am planning to try out his all inductor tonecontrol: http://members.aol.com/sbench101/BatteryPoweredAmps/tonestac.html.I did also see Thomas Mayer's designs which I saved somewhere, they are very unique indeed.
Mick Maloney of Supratek/Australia who makes some very nice looking amps used to have a website up with plans for LCR and even an all LR RIAA without caps but the page is now defunct.
There is also this page from italy with an interesting articel on LCR RIAA.
This is all very inspiring really but eventually I would like to come up with a design of my own, preferably one without caps. At the moment I am looking very hard at an EF86 DC coupled to maybe an EL84 driving an output transformer. We shall see...
Bst regards
Michael
6ER5 => 6DJ8
How's this sample? Any changes you guys could suggest? Especially for the final RC dropper/decoupler for the 6ER5? Thanks.
How's this sample? Any changes you guys could suggest? Especially for the final RC dropper/decoupler for the 6ER5? Thanks.
An externally hosted image should be here but it was not working when we last tested it.
Re: 6ER5 => 6DJ8
Konnichiwa,
Definitly the RC filter for the first stage needs more C and less R.
For the ECC83 I made the anode voltage very low by common standards, as it is much quieter that way. The 6ER5/6GK5 should be quiet at much more anode voltage, so try 1K/22u For starters.
You then need to work out the approximate anode impedance of the 6ER5. First, to bias the 6ER5 to 2.5mA with 150V on the Anode the cathode resistor should be 620 or 680 Ohm, not 475
Ohm (just use the curves).
With that voltage and current the internal impedance of the 6ER5 is around 15KOhm, however we also need to account for the effect of the unbypassed cathode resistor. Around our operating point the valves Mu is around 70, so our 620 Ohm resistor is "amplified" by 1 + Mu to around 44KOhm, which adds to the existing 15KOhm internal impedance. We also have 39Kohm in parallel with the Valves internal impedance, so the output impedance of our first stage is around 25Kohm.
You could now use the any of the various RIAA calculators and armed with that calaculate your RIAA Network for a zero Ohm source impedance and then reduce the first series resistor by around 25KOhm, which BTW suggest around 195KOhm for the first series resistor.
BTW, the gain of complete first stage into the RIAA network is around 27, however as the RIAA itself now attenuates less than 10 (around 7 based on a quick calculation) the net gain of first stage and RIAA are around 12db. The following 6DJ8 (et al) Stage amplifies around 26 times (with a 12K resistor load, with a CCS load you get around 32 times amplification) or 28db and offers < 3KOhm output impedance. Total overall gain of the whole circuit is thusly around 40db. This is slightly lower (around 3db) than the 12AX7/6DJ8 variant.
BTW, you can keep my "semi-split" RIAA from the 12AX7/6DJ8 variant, just shift the series resistor value to the calculated 195KOhm. In the final Adjustment this resistor needs adjusting to the LF is flat at 20Hz (or whatever you want to tune to, I usually leave around 0.5db LF lift @ 20Hz).
Sayonara
Konnichiwa,
fred76 said:
Definitly the RC filter for the first stage needs more C and less R.
For the ECC83 I made the anode voltage very low by common standards, as it is much quieter that way. The 6ER5/6GK5 should be quiet at much more anode voltage, so try 1K/22u For starters.
You then need to work out the approximate anode impedance of the 6ER5. First, to bias the 6ER5 to 2.5mA with 150V on the Anode the cathode resistor should be 620 or 680 Ohm, not 475
Ohm (just use the curves).
With that voltage and current the internal impedance of the 6ER5 is around 15KOhm, however we also need to account for the effect of the unbypassed cathode resistor. Around our operating point the valves Mu is around 70, so our 620 Ohm resistor is "amplified" by 1 + Mu to around 44KOhm, which adds to the existing 15KOhm internal impedance. We also have 39Kohm in parallel with the Valves internal impedance, so the output impedance of our first stage is around 25Kohm.
You could now use the any of the various RIAA calculators and armed with that calaculate your RIAA Network for a zero Ohm source impedance and then reduce the first series resistor by around 25KOhm, which BTW suggest around 195KOhm for the first series resistor.
BTW, the gain of complete first stage into the RIAA network is around 27, however as the RIAA itself now attenuates less than 10 (around 7 based on a quick calculation) the net gain of first stage and RIAA are around 12db. The following 6DJ8 (et al) Stage amplifies around 26 times (with a 12K resistor load, with a CCS load you get around 32 times amplification) or 28db and offers < 3KOhm output impedance. Total overall gain of the whole circuit is thusly around 40db. This is slightly lower (around 3db) than the 12AX7/6DJ8 variant.
BTW, you can keep my "semi-split" RIAA from the 12AX7/6DJ8 variant, just shift the series resistor value to the calculated 195KOhm. In the final Adjustment this resistor needs adjusting to the LF is flat at 20Hz (or whatever you want to tune to, I usually leave around 0.5db LF lift @ 20Hz).
Sayonara
Hi KYW,
Thanks for the very detailed reply. I had a hunch the dropper would be 1k, although I overrated the MKP decoupler to 50uF just to be 'safe'. I would try 22uF you suggested though. I used 196k for the first series R, couldn'f find any values near enough even if I parallel R's. Taking a look at The 6ER5 datasheet, it states 8kOhm internal R @ 200V anode/10mA. Thanks for pointing out the 15kOhm 'adjustment' for a 150V anode/2.5mA... Here's an ammended schema:
This is still a bit fuzzy to me. A would get help from a buddy to figure this out. Would post another schema using the "semi-split" riaa as used in the 12AX7-6DJ8 variant. Thanks again!
Thanks for the very detailed reply. I had a hunch the dropper would be 1k, although I overrated the MKP decoupler to 50uF just to be 'safe'. I would try 22uF you suggested though. I used 196k for the first series R, couldn'f find any values near enough even if I parallel R's. Taking a look at The 6ER5 datasheet, it states 8kOhm internal R @ 200V anode/10mA. Thanks for pointing out the 15kOhm 'adjustment' for a 150V anode/2.5mA... Here's an ammended schema:
An externally hosted image should be here but it was not working when we last tested it.
This is still a bit fuzzy to me. A would get help from a buddy to figure this out. Would post another schema using the "semi-split" riaa as used in the 12AX7-6DJ8 variant. Thanks again!
Konnichiwa,
Tyohically curves of Ra vs Current & Voltage are given, if not the anode impedance is easily estimated from the Anode curves.
Simple, you can use the exact RIAA from the ECC83/ECC88 stage and only adjust the first series resistor. If the LF EQ is right all the other EQ sections will fall in place, especially as the load capacitance (ECC88 - 1Section) remains identical as well.
Sayonara
fred76 said:
Tyohically curves of Ra vs Current & Voltage are given, if not the anode impedance is easily estimated from the Anode curves.
fred76 said:
Simple, you can use the exact RIAA from the ECC83/ECC88 stage and only adjust the first series resistor. If the LF EQ is right all the other EQ sections will fall in place, especially as the load capacitance (ECC88 - 1Section) remains identical as well.
Sayonara
Hi KYW,
I just 'refined' the type of filter used by G. Pimm (included Rs in the calc.) and came up with this:
Noted... Actual measurements (breadboard) would be more accurate to fine tune R1 for the "semi-split" riaa. FWIW, with the sim I mentioned, we came up with 250k for R1, higher than 196k to get good LF roll-off... I hope you don't mind if I linked an "altered" version of your original El Cheapo schema below using a 6ER5 input valve. I'll delete the attachment asap when/if requested. Thank you....
BTW, does the current draw stay the same (30mA) with the 6ER5 for both channels?
I just 'refined' the type of filter used by G. Pimm (included Rs in the calc.) and came up with this:
An externally hosted image should be here but it was not working when we last tested it.
Noted... Actual measurements (breadboard) would be more accurate to fine tune R1 for the "semi-split" riaa. FWIW, with the sim I mentioned, we came up with 250k for R1, higher than 196k to get good LF roll-off... I hope you don't mind if I linked an "altered" version of your original El Cheapo schema below using a 6ER5 input valve. I'll delete the attachment asap when/if requested. Thank you....
An externally hosted image should be here but it was not working when we last tested it.
BTW, does the current draw stay the same (30mA) with the 6ER5 for both channels?
Hi KYW,
For a 34mA current pull I tried 320VAC=>5V4G=>10uF=>560R/100uF=>(1k/100uF x 4) and got good results with PSUD2. For 33mA still using the 5V4G, I just stuck with the first 4 filters cells (1k/100uF) in the original supply schematic and then reduced the final 1k to a 750R value...
Again, thanks for the reply above.
fred
For a 34mA current pull I tried 320VAC=>5V4G=>10uF=>560R/100uF=>(1k/100uF x 4) and got good results with PSUD2. For 33mA still using the 5V4G, I just stuck with the first 4 filters cells (1k/100uF) in the original supply schematic and then reduced the final 1k to a 750R value...
Again, thanks for the reply above.
fred
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