Hello All,
I was looking into building a 'kit' tube based phono pre-amp. I wanted to go with a a proven circuit design as I know that it is critical with parts and how you place them since the gain is much higher than in a line stage and hence the reason why I wanted to go with a PCB for my first time out. This is for a Moving Magnet application and will stay so as I have no interest in moving coil cartridges.
Looking on-line and on Ebay, it seems that there are numerous PCB's made for two main styles of tube based phono preamps. One is based on the Shure M-65 which is shown here:
MM RIAA Tube Phono Amplifier Board Bare PCB base on America SHURE M65 Circuit | eBay
And the other is based on the EAR-834 preamp and that is here:
E834 RIAA MM Tube phono amplifier PCB Turntable preamp Base on EAR834 Circuit[C1 | eBay
Both PCB's are around the same price, but that is irrelevant as I am more interested in the sound quality. So for those in the know and perhaps built one or both of these either of these PCB's before, which one sounds better?
From the look of it, the M65 seems simpler and uses 1 less tube. However, I do see some sand in the mix, but it could be just regulators for the tube filaments. I just know that the PCB doesn't quite match the schematic for the actual Shure M-65. The 834 definitely looks more complex as it uses 3 tubes as opposed to two, but I don't see any sand in the design.
So it boils down to what is accepted as a better design. While I am interested in input on those that have actually used these PCB variants, I am also interested in those that have used both of the original preamps or even compared the originals to these PCB variants.
Thank you,
Geo
I was looking into building a 'kit' tube based phono pre-amp. I wanted to go with a a proven circuit design as I know that it is critical with parts and how you place them since the gain is much higher than in a line stage and hence the reason why I wanted to go with a PCB for my first time out. This is for a Moving Magnet application and will stay so as I have no interest in moving coil cartridges.
Looking on-line and on Ebay, it seems that there are numerous PCB's made for two main styles of tube based phono preamps. One is based on the Shure M-65 which is shown here:
MM RIAA Tube Phono Amplifier Board Bare PCB base on America SHURE M65 Circuit | eBay
And the other is based on the EAR-834 preamp and that is here:
E834 RIAA MM Tube phono amplifier PCB Turntable preamp Base on EAR834 Circuit[C1 | eBay
Both PCB's are around the same price, but that is irrelevant as I am more interested in the sound quality. So for those in the know and perhaps built one or both of these either of these PCB's before, which one sounds better?
From the look of it, the M65 seems simpler and uses 1 less tube. However, I do see some sand in the mix, but it could be just regulators for the tube filaments. I just know that the PCB doesn't quite match the schematic for the actual Shure M-65. The 834 definitely looks more complex as it uses 3 tubes as opposed to two, but I don't see any sand in the design.
So it boils down to what is accepted as a better design. While I am interested in input on those that have actually used these PCB variants, I am also interested in those that have used both of the original preamps or even compared the originals to these PCB variants.
Thank you,
Geo
I've built an EAR-based amp, it was OK. Also built a Tubecad Tetra powered by the Tubecad PS-3 power supply, it was better.
Tetra Sans PS Phono Preamp
PS-3 Power Supply Kit
Tetra Sans PS Phono Preamp
PS-3 Power Supply Kit
Shure M65 is very similar to the PC6 used in Dynaco PAS preamp. You could buy the PC6 instead :NEW STUFFED BOARD Dynaco PAS Preamp PC-6A Phono (PC-6 12AX7) USA | eBay
As a very good alternative you can build merlin blencowes 3-tube board :
The Valve Wizard
The latter one may be built with various tube population, see the manual for details.
BTW, there is another group in this fora : https://www.diyaudio.com/forums/analogue-source/
where RIAA stages are discussed.
As a very good alternative you can build merlin blencowes 3-tube board :
The Valve Wizard
The latter one may be built with various tube population, see the manual for details.
BTW, there is another group in this fora : https://www.diyaudio.com/forums/analogue-source/
where RIAA stages are discussed.
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The EAR was just okay? Well, the Tetra looks nice and it has the cathode follower output, but it does look more involved.
Very simple and I had noted later that the M65 doesn't have a cathode follower output. It is funny that you mention the Dynaco PAS as I have one of those as well and was looking to put a better phono stage in that one. The link you pointed to was a direct copy of the original. I had heard that the phono stage in the PAS is severely flawed and needs modifications, so I would prefer to get a board that has these mods already.
This looks very interesting and simple too. Further, it looks like the EQ stage is not in a feedback loop.
Pricing looks good too, but they are in the UK and I wonder how much it would cost to ship the board to me.
Great! I will take a peek!
Thanks all for the info!
Geo
You have been misled regarding to the PAS riaa correction. It's very good if loaded with the 250k volume pot used in the pas.
Read about it ay Dynaco Tube Amplifier technical articles and upgrades ST-70 PAS 2-3 ST-35 SCA-35 EFB
Quote:
Originally Posted by Steve Morley View Post
I've built an EAR-based amp, it was OK. Also built a Tubecad Tetra powered by the Tubecad PS-3 power supply, it was better.
Tetra Sans PS Phono Preamp
PS-3 Power Supply Kit
The EAR was just okay? Well, the Tetra looks nice and it has the cathode follower output, but it does look more involved.
End Quote
The Tetra has extra supply filtering and decoupling on the board which takes up some real estate. It also has passive EQ which I think sounds better, just personal preference. It uses 6DJ8 inputs and 12AT7 outputs. Can be configured for all 12AT7 if desired.
Broskie's boards are extra thick. Price is reasonable for what you get IMHO.
Steve
Originally Posted by Steve Morley View Post
I've built an EAR-based amp, it was OK. Also built a Tubecad Tetra powered by the Tubecad PS-3 power supply, it was better.
Tetra Sans PS Phono Preamp
PS-3 Power Supply Kit
The EAR was just okay? Well, the Tetra looks nice and it has the cathode follower output, but it does look more involved.
End Quote
The Tetra has extra supply filtering and decoupling on the board which takes up some real estate. It also has passive EQ which I think sounds better, just personal preference. It uses 6DJ8 inputs and 12AT7 outputs. Can be configured for all 12AT7 if desired.
Broskie's boards are extra thick. Price is reasonable for what you get IMHO.
Steve
Interesting read, even though I didn't get through all of it, but they did mention what many say that they were put off by the PAS phono stage construction and even the line stage. So naturally I bought into that as well. In a way, there is the issue with wanting to use that pre-amp with more than just tube amplifiers. I would need a low impedance driver for it for certain.
As for the stand alone phono preamp, a low impedance output is a must as I would use it for recording my records into my computer in addition to listening. While I have mostly (and wrongfully) replaced my records with CD's. I still kept the records I couldn't find on CD. So thankfully I still have a couple hundred records left. Those I am going to keep, but I want to put the songs into my computer for casual listening.
So it looks like in the PAS, I could keep the phono pre-amp section as is as it would be loaded properly with a 250k pot, but something would still have to be done with the main output for as is, I could only use it on tube amplifiers.
Sounds pretty good from the description and it has the cathode follower output. This might be a good choice for the stand alone pre-amp.
Thanks all for the info!
Geo
I solved both tape out and line out with an external buffer:
Rebuild of Dynaco FM-1 tuner to a buffer with remote
I also know that there is a simple board that can be mounted inside the PAS powered with the filament current :
Dynaco PAS Preamp Impedance Matching Module New! | eBay
( this item has been ended, but i have seens other sources )
Dynaco-PAS-Preamp-Impedance-Matching-Module-Buffer New | eBay
Rebuild of Dynaco FM-1 tuner to a buffer with remote
I also know that there is a simple board that can be mounted inside the PAS powered with the filament current :
Dynaco PAS Preamp Impedance Matching Module New! | eBay
( this item has been ended, but i have seens other sources )
Dynaco-PAS-Preamp-Impedance-Matching-Module-Buffer New | eBay
Also this
With certification on test lab
Kit Preamplificatore Phono Riia MM Junior Audio Review nr.418
Walter
With certification on test lab
Kit Preamplificatore Phono Riia MM Junior Audio Review nr.418
Walter
That's just out of my price range. I am trying to keep it under $300. Under $200 is even better. Coming from Europe, God knows what the shipping would cost.
That is a very interesting option. At first I would be concerned about hacking into a vintage piece of equipment, but he went with an FM-1, which is mono, I believe. However, I was even more interest in what he mentioned about DAB (Digital Audio Broadcasting) now threatening to replace FM radio. I did start to read up on that, but I have not come across a date when that is going to happen. However, I did come across much opposition to it. It is one thing when they did it with TV and made all older TV's obsolete overnight, but doing it to FM is going to be VERY bad. Not only will that affect home stereos, but cars, and portables too and I don't mean the modern jobs, but the nice old boomboxes from the 80's. I have a couple of these and don't use the cassette decks anymore, but what to do with them once FM bites the dust? That isn't cool.
Already, I feel the joy of having an antique radio has been ruined because everything shortwave has moved to higher VHF bands or have gone digital as well. AM is really all talk radio now. I still have two antique radios that I have not restored yet because of this. Sure I can use a noisy AM modulator, but I think it is better to just restore the power supply and amplifier and pipe old time radio programs directly into the amplifier.
Anyway, going off on a tangent there. That does seem like a good idea, but I would rather have something self contained. I can see in that case, he needed two cathode followers, one for the tape out and one for the main. With me, I just need one. I would like to put it in the same cabinet though. I know that would mean redoing the power supply, but pulling out the tube rectifier and going solid state there would make room for the cathode follower.
Hmmmmm, that is putting sand in the audio path, but if it is transparent to the audio signal, that does seem like a viable and inexpensive option. I guess tests would have to done to compare the sound of a tube CF vs sand CF. If there is no difference, then yes, I would go that route.
This would only come into play when interfacing to modern equipment, such as my computer, but I probably would have a dedicated phono preamp for that anyway. More than likely the PAS will be connected to a tube power amplifier as I do not have dedicated SS power amps anymore. I did want to eventually build a PASS Camp Amp, which is an 8 watt per channel SS class A amplifier and that has a 47k input impedance. So yeah, that would need a follower on the PAS.
Thank you for the information. I have enough information to mull on this for a bit and see which direction I will go.
Geo
to jukingeo
The price is all execpt the box.
You can buy the pcbs if you can buy in other place the components.
For shipment I will ask, where are you?
I am pushing to explain that the kit with the certification of test lab must be considered.
For only simply reason, if you follow the indication you will get as the kit says
And under a certain price is not possible to have a quality.
The phono board has a matrix to configure the pin of filaments to use different tubes.
It has 70 um of copper
The HT pcb, is a dual mono, the two sectiona are completely separtrd, included the bridge and the ripple is zero, in practical
Plus the regulated filament board.
Walter
The price is all execpt the box.
You can buy the pcbs if you can buy in other place the components.
For shipment I will ask, where are you?
I am pushing to explain that the kit with the certification of test lab must be considered.
For only simply reason, if you follow the indication you will get as the kit says
And under a certain price is not possible to have a quality.
The phono board has a matrix to configure the pin of filaments to use different tubes.
It has 70 um of copper
The HT pcb, is a dual mono, the two sectiona are completely separtrd, included the bridge and the ripple is zero, in practical
Plus the regulated filament board.
Walter
About the FM-1 i ruined : my need was buffers to my PAS3X. It has to be an external device as the PAS has no power or place to add tubes.
With an external buffer the PASx may be kept original ( and it does sound good when driving a tube load). Two ECC82 is all that is needed to buffer both line and tape-out.
In addition i get one motorized volume control for the poweramp and a separate volume control for the tapeamp ( which is connected to a computer ). The FM-1 thus saved a PAS from modifications.
The issue was then a suitable external box and power. Instead of starting for scratch a FM-1 could be a donor giving me an undisturbed outside.
About DAB, i norway FM is dead. In sweden the DAB is built but for now FM is still alive. DAB btw is no hit, it's heavily compressed (here) and funny effects with echoes occurs in car radios.
DAB ought in my opinion be closed down just like digital TV as various Internet streaming solutions solved this better and cheaper, in addition giving access to a better Internet.
( this was off-topic, sorry )
With an external buffer the PASx may be kept original ( and it does sound good when driving a tube load). Two ECC82 is all that is needed to buffer both line and tape-out.
In addition i get one motorized volume control for the poweramp and a separate volume control for the tapeamp ( which is connected to a computer ). The FM-1 thus saved a PAS from modifications.
The issue was then a suitable external box and power. Instead of starting for scratch a FM-1 could be a donor giving me an undisturbed outside.
About DAB, i norway FM is dead. In sweden the DAB is built but for now FM is still alive. DAB btw is no hit, it's heavily compressed (here) and funny effects with echoes occurs in car radios.
DAB ought in my opinion be closed down just like digital TV as various Internet streaming solutions solved this better and cheaper, in addition giving access to a better Internet.
( this was off-topic, sorry )
Half the cost is in the board. If I am not mistaken, I think they wanted $89 for it, which is much for a small board like that.
New York
It is still a bit out of my price range.
Which is why I will not consider anything under $150. So $150 to $300 is my budget, hopefully with some kind of case.
It has 70 um of copper
The HT pcb, is a dual mono, the two sectiona are completely separtrd, included the bridge and the ripple is zero, in practical
Plus the regulated filament board.
Walter[/QUOTE]
All very nice features, but I am not going to go crazy and tube rolling on a phono preamp. On a power amp, yes, I would go a little further with that. But I only own 200 records and I mainly want to transfer that to the computer as these records I cannot get CD's for. It is also for the occasional vinyl listen. I am not a die hard record playing enthusiast.
In your situation I can see that, and certainly choosing a mostly unwanted FM-1 was good as I might have cringed if it was an FM-2 or 3 w/ stereo. But with me needing one buffer, I am aiming for nixing the rectifier tube and putting the buffer there.
I wouldn't have intentions on defacing the PAS-3 either. No drilling extra holes on the front panel.
Yeah, that is two tubes now and I definitely can see the point of an external "module", especially given that you wanted a remote control.
You have plenty more mods than I and I think I would be fine creating the cathode follower right in the spot where the rectifier is and that is good enough for me.
It looks pretty good and it matches the PAS too.
Wow, that isn't good if they are doing it in Europe already.
I am cringing just thinking of it. Radio is so much different than a TV which sits in the house. It is more portable and if you are saying you have echoing problems in cars already, then I wouldn't have it either.
THANK God I wasn't one of those fellows that got into antique TV's. I know a guy that is and when they did the digital switch over, he was cursing like crazy that he couldn't watch over the air broadcasts anymore, but he managed to adapt by adding a "line in" to his most watched TV's and his others he uses an RF modulator and pumps all the old B/W 50's programs into his old TV's.
Yeah, my fault, but what you said grabbed my attention.
Well, I guess then FET is going to be it for the PAS, I could do my own experiments to see if it affects the sound with it without it on a tube amp. But for a stand alone phone preamp, I would definitely want a tube follower.
Thanks,
Geo
Nice! Excellent pricing too. I don't have those tubes though. Can it be adapted for use of other 9 pin tubes such as in the 12A** series? I have loads of those. Mostly 12AX7's, 12AT7's and 12AU7's. I might have a couple 12AY7's floating around too.
BTW, at 1meg load resistor going into the third triode pair, could that be replaced with a 1 meg pot and essentially use the second half as a regular line pre-amp? If so, then this board would be nice as the base for an entire preamp.
Thanks,
Geo
The kit/complete price includes tubes. Pin 9 is grounded so in theory, if you feed 6V to both sides of the 12V port, you could run 6V from pins 4,5 to grounded pin 9. 12AU7 would replace 6N1, 12AX7 replaces 6N2. No other modifications would be necessary.
If you replace the 1M with a 1M pot, you'll vary the loading on the RIAA filter when you change the volume control. Also, a 12AX7 would give far too much gain for a preamp - You'd get about 40V out for 1V in.
However, if you wanted to, you could switch from phono at the 1M for a line input, and attenuate it with resistors, Then you could put a pot on the output of the board for volume - say 10k or so.
I also make a line/HP amp version of the board with 4 tubes instead of 8. There a link to the thread here: 6N3/6N6 headphone amp using PCB.
If you replace the 1M with a 1M pot, you'll vary the loading on the RIAA filter when you change the volume control. Also, a 12AX7 would give far too much gain for a preamp - You'd get about 40V out for 1V in.
However, if you wanted to, you could switch from phono at the 1M for a line input, and attenuate it with resistors, Then you could put a pot on the output of the board for volume - say 10k or so.
I also make a line/HP amp version of the board with 4 tubes instead of 8. There a link to the thread here: 6N3/6N6 headphone amp using PCB.