Salas,
I don't have a 5R4GY to test with, mind 5R4 sounds a bit dark. I did hear the good things about the 5R4GY, will source one to test. The 5U4G RCA sounds more vivid and balance in my system.
I read somewhere that you mentioned about adding a small telfon to C2 on version one that I have. Will a 0.047 be good??
Albert
I believe in any case that the bass response will be impacted. Need to check formulae in order to confirm which one will be impacted most however it should be minimum
Benefits of filament starvation are worth it!
Thanks
Back to rectifiers!
- AZ1 mesh: first choice, the king. Any mesh is good - and expensive!!
- 80 is very nice and cheap for a preamp, 4 pin. 5Y3 is the octal version
- 5R4GY is very nice for mid power
- 5BY5G is nice, and two are great for higher power. Medium voltage drop
- Damper diodes are good for higher power, like 6DT4 etc, in a hybrid bridge
I went through a whole stack of GZ types and 5U4 types and still preferred the 5R4GY to all of them. They were cheap but are getting a bit pricey now. Downside is the voltage drop - they have about the highest internal resistance. Also take a 4uf cap but choke input with a tiny first cap like 0.1uF is best anyway for a preamp. For low voltage drop, damper diodes with a 40uF first cap.
andy
- AZ1 mesh: first choice, the king. Any mesh is good - and expensive!!
- 80 is very nice and cheap for a preamp, 4 pin. 5Y3 is the octal version
- 5R4GY is very nice for mid power
- 5BY5G is nice, and two are great for higher power. Medium voltage drop
- Damper diodes are good for higher power, like 6DT4 etc, in a hybrid bridge
I went through a whole stack of GZ types and 5U4 types and still preferred the 5R4GY to all of them. They were cheap but are getting a bit pricey now. Downside is the voltage drop - they have about the highest internal resistance. Also take a 4uf cap but choke input with a tiny first cap like 0.1uF is best anyway for a preamp. For low voltage drop, damper diodes with a 40uF first cap.
andy
47n Teflon will be fine in bypassing C2.
Each config and pre will have its more synergistic rectifier, just watch their voltage sag to always reserve >20V Vin-Vout on the regs and trust your taste in your own system as a whole. Still we both didn't care much about 5R4 flat top, and 5R4GY is to Andy's liking too.
Slightly off topic, as I'm currently testing an 01a stage with filament bias and was concerned with the high output resistance and its capability to drive cables and amp input stage capacitance effectively. I do like the sound of 01a and will also try the 26 again in this setup.
Having read Morgan Jones latest edition and found that he measured the MOSFET follower performance being slightly better than a Russian 6c45, I though this might be a good option to include to my preamp. Has anyone tried this?
Not sure if image will upload well, but will give it a try as I am travelling and don't have my PC with me.
The MOSFET has to be a low capacitance one -hard to find but with my supply of 170v I need a 200 VDS max one. Any suggestions?
Cheers,
Ale
Having read Morgan Jones latest edition and found that he measured the MOSFET follower performance being slightly better than a Russian 6c45, I though this might be a good option to include to my preamp. Has anyone tried this?
Not sure if image will upload well, but will give it a try as I am travelling and don't have my PC with me.
The MOSFET has to be a low capacitance one -hard to find but with my supply of 170v I need a 200 VDS max one. Any suggestions?
Cheers,
Ale
An externally hosted image should be here but it was not working when we last tested it.
Hi Ale,
The Diodes-Inc (formerly Zetex of Oldham) ZVN0545 is a low capacitance n-channel, and even has a p-channel complement, the ZVP0545. They are easy to get from the catalogue-distributors.
they are 450V rated, E-line packaged (like TO92), 0,7W handling, and have maximum 4pF Cre - which is very low for a FET. Mind that this is measured at 25V D-S, at low voltages it increases sharply. Keeping at least 20V across these (same as most any FET) boosts the performance.
The Diodes-Inc (formerly Zetex of Oldham) ZVN0545 is a low capacitance n-channel, and even has a p-channel complement, the ZVP0545. They are easy to get from the catalogue-distributors.
they are 450V rated, E-line packaged (like TO92), 0,7W handling, and have maximum 4pF Cre - which is very low for a FET. Mind that this is measured at 25V D-S, at low voltages it increases sharply. Keeping at least 20V across these (same as most any FET) boosts the performance.
Thanks Rod! My anode voltage is no greater than 100V so will have a Vds>50V with an HT of 170V to ensure low Coss.
Q2 can well be a BC549 what about Q1? Any good NPN with reasonable hfe and low output capacitance that has a VCe 200v max you would recommend?
Not sure if anyone tried this setup but was probably interested in any feedback on the sound of this...
Cheers,
Ale
Q2 can well be a BC549 what about Q1? Any good NPN with reasonable hfe and low output capacitance that has a VCe 200v max you would recommend?
Not sure if anyone tried this setup but was probably interested in any feedback on the sound of this...
Cheers,
Ale
Ale, please don't forget that Q2 needs an emitter resistor to make a current-source. If you use at least two LEDs for Q2, it will be more stable.
eg: If you get about 3V on Q2 base, then emitter will have 2,4V.
Current is then 2,4/Re...... this allows you to set Re and the current to suit the circuit. If the emitter voltage is less than about 2V, stability is degraded.
Use more LEDs for Q1, too. You want about 6 to 10V across Q2 C-E for good performance.
eg: If you get about 3V on Q2 base, then emitter will have 2,4V.
Current is then 2,4/Re...... this allows you to set Re and the current to suit the circuit. If the emitter voltage is less than about 2V, stability is degraded.
Use more LEDs for Q1, too. You want about 6 to 10V across Q2 C-E for good performance.
Ops forgot about the Q2 resistor when drawing the diagram last night at the hotel.
Thanks for the tips re additional LEDs. Would you recommend swapping them for Zener diodes instead or not?
Thanks Rod for the help.
I take I may be the first one trying this setup for the DHT preamp and report the sonic results. I like the 01a very much but was a bit light on the bass and can't see it as a good stage valve due to its low anode current and high plate resistance.
Cheers,
Ale
Thanks for the tips re additional LEDs. Would you recommend swapping them for Zener diodes instead or not?
Thanks Rod for the help.
I take I may be the first one trying this setup for the DHT preamp and report the sonic results. I like the 01a very much but was a bit light on the bass and can't see it as a good stage valve due to its low anode current and high plate resistance.
Cheers,
Ale
I welcome all developments in the "26 preamp plus" field - adding an extra tube for gain and stepdown to line levels ( 600 to 1K), adding Mosfets and so on.
The problem with a 26 and a LL1660 in 4.5:1 is the gain is pretty much wiped out. For those who are depending on the gain of the preamp because they use a 2 stage amp or an amp needing a bit more gain, then the extra circuitry is pretty important.
I see this as a good line of development in reaching a good model for a 26 preamp with gain AND low output impedence. We have a good basic model already which has been tried and tested, so we could put some effort into this extended circuit. I don't know that it needs a new thread - there's most of the information on this thread so I guess we just continue.
Andy
The problem with a 26 and a LL1660 in 4.5:1 is the gain is pretty much wiped out. For those who are depending on the gain of the preamp because they use a 2 stage amp or an amp needing a bit more gain, then the extra circuitry is pretty important.
I see this as a good line of development in reaching a good model for a 26 preamp with gain AND low output impedence. We have a good basic model already which has been tried and tested, so we could put some effort into this extended circuit. I don't know that it needs a new thread - there's most of the information on this thread so I guess we just continue.
Andy
A lot of folks like LEDs, and they are probably OK.
In circuits that can support the cost, then the buried-zener reference chip, like the Burr-Brown REF10 is the lowest noise, highest stability.
the usual band-gap reference chips are much too noisy to use here.
Zener diodes are only moderately stable, and have some sample-to-sample variation. for the circuit you are using they are too noisy, and need at least some RC filtering.
I'd probably start with some cheap LEDs, then see if you prefer the sound if a REF10 is used.
In circuits that can support the cost, then the buried-zener reference chip, like the Burr-Brown REF10 is the lowest noise, highest stability.
the usual band-gap reference chips are much too noisy to use here.
Zener diodes are only moderately stable, and have some sample-to-sample variation. for the circuit you are using they are too noisy, and need at least some RC filtering.
I'd probably start with some cheap LEDs, then see if you prefer the sound if a REF10 is used.
Andy,
I personally found the cascoded MOSFET Gyrator to sound really good (not the CCS) in this setup. And is dirt cheap for anyone to build them using DN2540s
The 4P1L (or even the 71a) has a low anode resistance and its biased at 20mA so works brilliantly with either a choke or a gyrator. When tried DHT with low anode current and higher anode resistance (such as 30sp, cx112a and 01a) they are not optimised in this configuration. My 45 SE amp has a 47k input resistance and if you factor in the driver miller capacitance in addition to the cable's then they can't perform well.
Choice here is either a DHT cathode follower (with all the additional power supply complexity or a source follower as Morgan Jones recommends
We need to experiment and report the results!
I personally found the cascoded MOSFET Gyrator to sound really good (not the CCS) in this setup. And is dirt cheap for anyone to build them using DN2540s
The 4P1L (or even the 71a) has a low anode resistance and its biased at 20mA so works brilliantly with either a choke or a gyrator. When tried DHT with low anode current and higher anode resistance (such as 30sp, cx112a and 01a) they are not optimised in this configuration. My 45 SE amp has a 47k input resistance and if you factor in the driver miller capacitance in addition to the cable's then they can't perform well.
Choice here is either a DHT cathode follower (with all the additional power supply complexity or a source follower as Morgan Jones recommends
We need to experiment and report the results!
Rod,
Never used the Ref10. Worth trying them? I'd probably do a first try with LEDs and report results. Need to check which MOSFETs and bipolar have at hand first. I do have some SMD ones which may pick up if appropriate so could end up building a tiny PCB board to fit in the preamp chassis...
Cheers! Ale
Andy,
The cascoded MOSFET gyrator I used in the 26 is the same as the one I posted below for the 71a, albeit in the latter I used a BSP129 instead of the dn2540. Similar characteristics but is SMD. You should probably use the TO220 DN2540 which is dead easy to use instead. You can set the operating point with the trimpot and won't change despite the valve ages.
http://www.bartola.co.uk/valves/Valves_and_Hi-Fi_audio/Entries/2012/1/29_71a_Pre-amplifier.html
Cheers,
Ale
The cascoded MOSFET gyrator I used in the 26 is the same as the one I posted below for the 71a, albeit in the latter I used a BSP129 instead of the dn2540. Similar characteristics but is SMD. You should probably use the TO220 DN2540 which is dead easy to use instead. You can set the operating point with the trimpot and won't change despite the valve ages.
http://www.bartola.co.uk/valves/Valves_and_Hi-Fi_audio/Entries/2012/1/29_71a_Pre-amplifier.html
Cheers,
Ale
Hi BAS,
I tried the following so far:
OT (LL1660): perfect sound if matching with valve. Good bass and superb tone
Cascoded MOSFET gyrator (DN2540 and BSP129): in Mu-follower mode you can get the lowest distortion and best performance as line driver. Great tone and good bass. Dirty cheap and easy to use. Quite like that you can adjust the operating point very easily with a trimpot.
MOSFET CCS (dn2540): not as great as the Mu-follower gyrator when driving the long cables and amp's driver. Bass good but overall tone a tad worse than the gyrator.
Probably a cascoded PNP gyrator will be better in a 26 due to the low current required. I built the MOSFET version for 4P1L, 6P21S, 46, 71a and 10Y which all run at currents greater than 15mA
I should build a cascoded PNP version for the 26 to test the difference...