Suggested Dynaco PAS mods

the thermionic watercooler

Postby jukingeo » Thu Feb 05, 2009 8:18 am

TerrySmith wrote:I never was really satisfied with the PAS phono stage, even with the curcio mods, so I repopulated an old board as per the circuit in the RCA tube manual as it's almost the same. Tubes are 6N2P-EV, eqiv to 6AX7.

The sound is much fuller, NO HUM, and the output level is a lot closer to other line inputs so I don't have to crank the volume way up.


Hello Terry,

This sounds very interesting. Which RCA book? I have several tube manuals. Hmmm, I think I packed them up for my move. Is the schematic posted on line? Is it similar to the one EWBrown posted? I would like to examine it in relation to the original circuit.

To tell you the truth I have not heard a 'stock' PAS in a very long time. Perhaps in my teens was the last time. The two PAS pre-amps I have are the original circuit and out side of some basic tests, I have not done much listening to them. The PAS-2 I have that I want to modify doesn't have a working phono section and the line stage area was recapped and some minor mods were made, but not much.

I didn't want to stick with the 'stock' PAS because of all the complaints I heard about it. I just about heard all the issues with the tone control circuit and also the poor power supply.

In terms of the work involved, I don't mind redoing the entire chassis if I have to...if it keeps me from spending the money on a new custom chassis (which is something I can't afford right now).


Slartibartfast wrote:
jukingeo wrote:
Speaking of music from the 50s, take Elvis recording at Sun Records for instance. They had at most a two channel board, so that meant two mics for him and the musicians. There is not much to work with, even with tone controls.


Sun Records used an Ampex 350 for mastering which was one of the best recording machines at that time. Most Elvis recordings are very good. However one of my favorite Elvis songs, "A Big Hunk Of Love" falls into the same category of Gimme Shelter. It is just a terrible mess. Mids and Highs are thin and the guitar and vocals are peaky. Now "Teddy Bear", which was done a year EARLIER, sounds good and more balanced.

Now your Stones example, when I said I would not listen to it, I meant I would look for a different recording of that song. This is easier to do for music of the late 60s and beyond.


Gimme Shelter wasn't remastered as far as I know, so the only 'better' recordings are usually the live versions. As for my Elvis example, "A Big Hunk of Love" was remastered, but I don't like it. The original 'performance', was better.

For critical listening in the late 50s I limit my selection to Jazz. Most of the music I like is 60s and beyond.


As I pointed out earlier, my wide range of music contains the inherit problem of having varied quality recordings.

So I have songs as poor quality as the aforementioned Elvis and Stones songs, all the way through the wonderful works of Pink Floyd and Rush (no one can argue the high quality recordings these bands produce), all the way through dance music of the early 80's and 90's.

But the time you get to club music of the 90's, the quality gets very inconsistent. You have many indy labels and there are many people producing good pieces of work, and yet really shouldn't be behind a mixing console. The end result is a good song that was recorded poorly.

So yeah, I sure can see if you limit yourself to only well made recordings, and have only certain genres that you do critical listening with, then once you get a setup you are happy with AND you have a good room for your sound system, then I would agree that you probably wouldn't need tone controls. But unfortunately I am very far from an 'ideal' situation. So tone controls will help me out a bit.

TerrySmith wrote:Here are some pics of my modded PAS3. It has slight hum in the linestage, most likely because of my wiring. There are no tone, filter, loudness, etc circuits, just a barebone linestage. Tubes in the linestage are 7AU7's.

PS: I'm trying out my new camera, whaddayou think?


Very nice indeed! It looks like you greatly simplified both the line AND phono sections. Are you using NFB at all?

If I could do something THAT simple but WITH tone controls, I would be a happy camper. Camera looks good to me!

nyazzip wrote:sorry for stirring up a hornets nest gentlemen. i can be a bit opinionated at times, and indeed i am not qualified to comment on virtually most of the things i do comment on.


I can be too, but I for one DO NOT like it when a post gets out of hand with 'bantering' and then you get the 'trolls' that come along and do nothing but start beating that 'hornets nest' further.

Anyway, I don't think it is out of hand by a long shot. I do know that there are many that prefer a very simple no tone control set up. Originally I did agree with that. Heck, I even did build a no tone control pre-amp. I got bored with it right away too and added that loudness circuit. I guess I am not a purist as I thought I would be. Sure I do still like to keep my circuits simple. But for now it is just the nature of the beast that I prefer something with tone controls...no matter how 'purist politically incorrect' it may be. I just think that I know because of my fixed room location and the varied quality of my recordings, I will be needing to do a bit of tweaking here and there.

nevertheless, it is entertaining.


So is putting pure sodium in a vat of water and watching what happens.

back to the thesis of: dynaco PAS mods which retain the tone control circuitry.
i too own a PAS 2, and one channel of the phono section is seemingly weak, and the balance pot is crap, thus i also dream about some mods some day.
for me step one is that selenium rectifier Yellow_Light_Colorz_PDT_09
cheers


I had a problem like that with a pre-amp I was working on for someone else. Recapped the darn thing and everything. But the guy insisted on keeping his NOS Mullard tubes. However, that therein was where the problem lied. One section in one tube was not fully amplifying, of which I found by swapping the tubes (seeming late in the game when it was something I should have done FIRST). The point is...just make sure you don't have a bad tube. If your PAS isn't rebuilt yet, you may have a leaking cap or way out of tolerance resistor floating around somewhere in the stage.

Geo
Last edited by jukingeo on Thu Feb 05, 2009 8:54 am, edited 1 time in total.
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby Slartibartfast » Thu Feb 05, 2009 8:46 am

jukingeo wrote:
TerrySmith wrote:
So yeah, I sure can see if you limit yourself to only well made recordings, and have only certain genres that you do critical listening with, then once you get a setup you are happy with AND you have a good room for your sound system, then I would agree that you probably wouldn't need tone controls. But unfortunately I am very far from an 'ideal' situation. So tone controls will help me out a bit.



The PAS is upstairs connected to an ST-70. For the most part the only source is a turn table. So that limits music from the late 50s to the late 80s.

Downstairs is a 2A3 amp driving a pair of LaScalas, no separate preamp. CD player for source, this allows a greater range of music.

I have found that as I get older, the less of classic rock I like. What I still like turns out to have good recordings. Newer country albums tend to be mastered well, and is there really a bad Jazz album? Yellow_Light_Colorz_PDT_11
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby jukingeo » Thu Feb 05, 2009 9:22 am

Slartibartfast wrote:
jukingeo wrote:
The PAS is upstairs connected to an ST-70. For the most part the only source is a turn table. So that limits music from the late 50s to the late 80s.


That is still wide enough in my case. I have recordings from early lousy 45 pressings all the way up to night club dance music recordings that are pressed on high quality 12" vinyl. (It is many of these recordings that I feel sound BETTER than a CD).

I did notice that on many older 50's records that they sound better with a mono needle. Less noise.

Downstairs is a 2A3 amp driving a pair of LaScalas, no separate preamp. CD player for source, this allows a greater range of music.


More then likely you have that in an optimized room. Your amp/speaker combo IS one of the more ideal setups. I am restricted to bookshelf speakers at the moment (I do intend to buy a pair of Klipsch high efficiency bookshelf speakers for my amp project. That is all I have money/room for right now).

I have found that as I get older, the less of classic rock I like. What I still like turns out to have good recordings. Newer country albums tend to be mastered well, and is there really a bad Jazz album? Yellow_Light_Colorz_PDT_11


I do listen to rock quite often. I find classic rock a 'get-away' from the terrible stuff they are playing on the radio now.

I used to be a DJ in the late 80's and early 90's. So I do like to go through all of my old records and find some really cool songs that I liked that I used to play in clubs. Many of those songs are not on CD. So that is why this time around I DO want a pre-amp with phono capabilities.

However, classic rock CAN have great recordings. Pink Floyd & Rush I regard has having excellently recorded sound. There are many great classic rock recordings in the late 70's and early 80's era.

I am not a big fan of country music, but I do have to agree that quality wise, I have not heard a terrible recording yet. There are some artists I do like. I was a big Kathy Mattea fan back in the 80's. Love The Judds. There are a couple tunes from Mary Chapin Carpenter I like. I went nuts over Patty Loveless' Jealous Bone...also an excellent recording. Of course you can't argue with the likes of Charlie Daniels :).

I will say that I do prefer rock with a southern edge though, such as CCR and Skynard.

I really do go all over with my listening genres. While I do listen to some big band music, I would say that I mostly start with the 50's, and go up through the early 90's. By the time the 90's started, I was already straying away from radio and mostly played/listened to club music. However, about the mid 90's you had what I call the 'rap infestation' and it made it's way into the mainstream as 'hip hop'. I just can't stand this stuff. The same can be said for modern soul music. Nope, nada, it wasn't like the 60's. Sorry, that is just my honest opinion.

Unfortunately my music tastes do not extend to jazz or classical. Given the nature of these genres of music, it is highly unlikely that you would get a drugged out, hungover producer behind the mixing control panel that is riding all the meters right to the point of clipping squeezing every last ounce of volume into the recording. Given the wide expanse of available jazz and classical music, I wouldn't think that those with 'golden ears' would tolerate a poor recording and it would be very easy for a listener to 'move on' to something else. Thus a jazz or classical producer that makes bad recordings, probably will not be recording for very long...or at least will not have a promising future in recording. So I would say that your chances are just that much better to get a good recording when dealing with mainly these genres. Then I probably would agree with you. If you are primarily a classical and jazz listener, then more then likely you will NOT need tone controls.

Geo
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby TerrySmith » Thu Feb 05, 2009 6:30 pm

Here is the schematic from the RC-25 manual:

Image

Image
T. Smith
User avatar
TerrySmith
KT88
 
Posts: 973
Joined: Sat Jan 31, 2004 12:51 pm
Location: Maryville TN

Postby Slartibartfast » Thu Feb 05, 2009 8:38 pm

TerrySmith wrote:Here is the schematic from the RC-25 manual:



I am in the process of building this circuit, but, using 6SN7 tubes.
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby jukingeo » Mon Feb 09, 2009 6:56 am

Hello guys,

Sorry for the slow response, but with moving week coming up, I have very little time at my computer at home. So I been doing most of my computer work at work for the time being. The movers are coming this week! Uggghh.


Slartibartfast wrote:
TerrySmith wrote:Here is the schematic from the RC-25 manual:



I am in the process of building this circuit, but, using 6SN7 tubes.


Yeah, I have that manual and have seen that circuit before. What alternations need to be done to use 6SN7's? I happen to have a BUNCH of these tubes and would like to design something around them. Hence, that was why I mentioned using octals for the line stage earlier.

Geo
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby EWBrown » Mon Feb 09, 2009 8:22 am

6SN7s would have insufficient gain for the RC-25 RIAA preamp circuit.

7025s, 12AX7s, 6EU7s or even 20EZ7s would be neded for that.

Possibly 6SL7s or 5751s could be "dragooned" into this line of service, as well.

Not saying that a phono preamp can't be designed around 6SN7s, it would take a total re-design to accomplish this. Something that is just a wee bit outside of my "comfort zone" to attempt.

/ed B
Last edited by EWBrown on Mon Feb 09, 2009 11:14 am, edited 1 time in total.
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby Slartibartfast » Mon Feb 09, 2009 8:40 am

jukingeo wrote:
Yeah, I have that manual and have seen that circuit before. What alternations need to be done to use 6SN7's? I happen to have a BUNCH of these tubes and would like to design something around them. Hence, that was why I mentioned using octals for the line stage earlier.

Geo



Here is the circuit. You can replace the AA batteries with 2.2k ohm resistors for the cathode. As far as insufficient gain goes, I am told this circuit works well into a 220k ohm load (minimum). This circuit has no feedback. The power supply was on a seperate chassis, so the phono amp would not pick up any noise from the pwr supply.

Image
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby jukingeo » Mon Feb 09, 2009 10:01 am

Slartibartfast wrote:
Here is the circuit. You can replace the AA batteries with 2.2k ohm resistors for the cathode. As far as insufficient gain goes, I am told this circuit works well into a 220k ohm load (minimum). This circuit has no feedback. The power supply was on a seperate chassis, so the phono amp would not pick up any noise from the pwr supply.



How far along are you with the circuit? I am curious to read about any tests you have done or are about to do.

I have seen the use of batteries before. Is it that great of an improvement? The thing that gets me about the use of batteries for the cathode bias is that the things do 'die'. I am assuming that you will incorporate some kind of charging circuit when the unit is powered off, correct?

Even so, Ni-Cads do wear out from constant charging. So I would consider this far from 'maintenance free', and would only consider this if the use of batteries is a night and day difference over using a conventional cathode resistor and bypass cap.

I am curious though because I have seen 'battery' circuits like this a few times before, so I would assume there must be some great benefit to having them in the circuit. But as I said, the benefits would have to far outweigh the need to replace/charge them before I would incorporate them in a design of my own. If the results are subtle, then I would stick with a standard resistor/cap on the cathode.

Geo
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby Slartibartfast » Mon Feb 09, 2009 12:01 pm

jukingeo wrote:
How far along are you with the circuit? I am curious to read about any tests you have done or are about to do.




It has been too cold to work in my garage, drilling out the top plate and paining it. Now that it appears to be warming up, I will paint it and start mounting parts. Yellow_Light_Colorz_PDT_02

This is what Joe Esmilla has to say about this circuit:

"For severaI years I was hacking a Dyna PAS chassis with various cascoded and cascaded phono circuits all employing negative feedback RIAA EQ. My research ended when I discovered this unglamorous 2-stage cascaded passive RIAA EQ phono preamp circuit at the back page of an RCA tube manual. The most important lesson I learned in this excercise is negative feedback chokes the sound! I did not alter any component values except for using Ni-mH batteries for cathode bias which I thought improved detail and definition. I strongly advice against the use of a cathode follower and make sure the circuit drives a minimum load of 220K as originally specified otherwise you will lose bandwidth at both frequency extremes. I use an Alps 250K but have also tried the cheap Alpha 250K dual log taper carbon pot sold by AES. It does not have the tracking precision of Alps but at normal volume settings the channels are balanced enough."


As for the Ni-mH batteries, they will last a long time being recharged in the amp. I have some Ni-Cads that are 9 years old and still going strong.

I will let you know when I complete the amp.
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby jukingeo » Mon Feb 09, 2009 10:10 pm

EWBrown wrote:6SN7s would have insufficient gain for the RC-25 RIAA preamp circuit.

7025s, 12AX7s, 6EU7s or even 20EZ7s would be neded for that.

Possibly 6SL7s or 5751s could be "dragooned" into this line of service, as well.

Not saying that a phono preamp can't be designed around 6SN7s, it would take a total re-design to accomplish this. Something that is just a wee bit outside of my "comfort zone" to attempt.

/ed B


I do have a bunch of 6SL7s and 12SL7's as well. So using those wouldn't be a problem. So 6SL7's could be used for the phono stages and the 6SN7's could be used for the line stages. That would be good enough fro me!

Slartibartfast wrote:
This is what Joe Esmilla has to say about this circuit:

"For severaI years I was hacking a Dyna PAS chassis with various cascoded and cascaded phono circuits all employing negative feedback RIAA EQ. My research ended when I discovered this unglamorous 2-stage cascaded passive RIAA EQ phono preamp circuit at the back page of an RCA tube manual. The most important lesson I learned in this excercise is negative feedback chokes the sound! I did not alter any component values except for using Ni-mH batteries for cathode bias which I thought improved detail and definition. I strongly advice against the use of a cathode follower and make sure the circuit drives a minimum load of 220K as originally specified otherwise you will lose bandwidth at both frequency extremes. I use an Alps 250K but have also tried the cheap Alpha 250K dual log taper carbon pot sold by AES. It does not have the tracking precision of Alps but at normal volume settings the channels are balanced enough."


As for the Ni-mH batteries, they will last a long time being recharged in the amp. I have some Ni-Cads that are 9 years old and still going strong.

I will let you know when I complete the amp.


I very much agree with the line "negative feedback really chokes the sound". I have experienced this with tests I have made with guitar amplifiers. While you can get a smoother, less distortion and wider frequency response with feedback, something just happens to the sound and it gets really sterile. Pop the NFB off and the amps jump to life.

I am still unsure about the battery thing. But given your response, I figured it is worth trying it out both ways and do a comparison.

As for the output impedance of 250k, that shouldn't be a problem going into a tube based line stage (which would follow down the path).

So thanx for sharing, I probably will give this circuit a shot once I get the amp built first.

Geo

Geo
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby EWBrown » Tue Feb 10, 2009 6:10 am

The 6SL7s (or 12SL7s) could be the gain stages as with the 7025s / 12AX7s, the plate and cathode resistors may heve to be "tweaked" a bit, to get everything out of them.

6SL7 and 5751 have identical operating characteristics, and since 5751 can often replace a 12AX7, the 6SL7s / 12SL7s are a good choice.


The 6SN7s could be worked in as a cathode follower stages for the phono preamp, .and for the line stages where large amounts of amplification are not necessary (or desired).

I've always liked the basic direct coupled VA/ CF linestage design, with 6SN7s this is good for approx 10-12 dB gain, and the CF offers a low output impedance which will drive just about any amp, tube or SS, with ease.

The "battery bias" scheme works quite well, I've tried it out myself. I'd strongly advise using solder-tab cells rather than "consumer tip" cells in battery holders, as the contacts are prone to becoming intermittent and generating noise - in a high gain stage, this would be a serious detriment.

If the cathode bias voltage is around 1.6 to 1.8VDC, then a common red LED would worj very well, as a constant voltage source. 6SN7s or 12AU7s and HLMP600s are a great combination. I've measured the operating voltage across many HLMP6000s and it is very constant, measuring at 1.65 to 1.57 volts. THe "standard common red LED" is usually around 1.8V, and some can go up as high as 2.2V.

This "LED technique" would also work with the G*S*G driver stage, with the 6SL7s.



/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby jukingeo » Tue Feb 10, 2009 8:37 am

EWBrown wrote:The 6SL7s (or 12SL7s) could be the gain stages as with the 7025s / 12AX7s, the plate and cathode resistors may heve to be "tweaked" a bit, to get everything out of them.

6SL7 and 5751 have identical operating characteristics, and since 5751 can often replace a 12AX7, the 6SL7s / 12SL7s are a good choice.


Ok, that sounds good.


The 6SN7s could be worked in as a cathode follower stages for the phono preamp, .and for the line stages where large amounts of amplification are not necessary (or desired).


However, being that you pointed that out that the 6SN7 has lower gain and really a phono stage is like a microphone stage, then I would definitely agree that the 6SN7 will not cut it (unless you use more stages).

I know this because of dealing with guitar amps. Guitars are also at mic level, but at very high impedences. Old Ampeg amps do use 6SL7's. I have seen amps use 6SJ7's also in the first stage (which is a pentode, I believe).

I've always liked the basic direct coupled VA/ CF linestage design, with 6SN7s this is good for approx 10-12 dB gain, and the CF offers a low output impedance which will drive just about any amp, tube or SS, with ease.


Yes, this was my greatest concern about the PAS pre-amp. For driving tube amps, not having a cathode follower as an output shouldn't be a problem. But what IF you want to drive an SS amp? Then you would be in deep doo doo. I guess in a way this is why I took to the SRPP (line) circuit. It is very simple, the stacked design pretty much gets the max gain out of a tube, AND tapping the signal from the top tube is akin to a cathode follower. You get SO much from such a simple circuit.

The "battery bias" scheme works quite well, I've tried it out myself. I'd strongly advise using solder-tab cells rather than "consumer tip" cells in battery holders, as the contacts are prone to becoming intermittent and generating noise - in a high gain stage, this would be a serious detriment.


Agreed. Now my guess is that you would need some kind of switching circuit to work with the power switch so that when you turn off the amp, the batteries get charged up, correct?

If the cathode bias voltage is around 1.6 to 1.8VDC, then a common red LED would worj very well, as a constant voltage source.


So what would you do here...do you just connect it across from cathode to ground?

6SN7s or 12AU7s and HLMP600s are a great combination. I've measured the operating voltage across many HLMP6000s and it is very constant, measuring at 1.65 to 1.57 volts. THe "standard common red LED" is usually around 1.8V, and some can go up as high as 2.2V.

This "LED technique" would also work with the G*S*G driver stage, with the 6SL7s.

/ed B


Can you show me some schematics using this scheme? How would this compare to using a battery?

Thanx,

Geo
jukingeo
 
Posts: 198
Joined: Wed Jan 21, 2009 11:45 am

Postby Slartibartfast » Tue Feb 10, 2009 8:47 am

jukingeo wrote:
However, being that you pointed that out that the 6SN7 has lower gain and really a phono stage is like a microphone stage, then I would definitely agree that the 6SN7 will not cut it (unless you use more stages).



Well I assume Joe Esmilla was feeding his 6SN7 phono amp into one of his SET amps. If this is the case, my SRPP preamp/driver stage will have more than enough gain, for the output stage.

As for the batteries, they would be charged while the amp is powered up.You would also start with a fresh charged set of batteries.
User avatar
Slartibartfast
KT88
 
Posts: 458
Joined: Sun Apr 15, 2007 9:40 pm
Location: Columbia S.C.

Postby EWBrown » Tue Feb 10, 2009 9:54 am

The LED connects between the cathode and ground, just like a resistor (or battery). The cathode goes to ground, the anode goes to the tube's cathode, and it does not need to be bypassed, as the LED has a low effective impedance.

In my 6SN7 based "Foreplay Clone" I borrowed the technique from the FPIII series of linestages, using a 6SN7 in a direct coupled VA / CF design.
B+ is 150VDC, the VA plate and the CF cathode resistors are 22J, 1W, the VA cathode "resistor" is an HLMP6000 (available fr0om Jameco and others) or any common 3mm low brightness red LED will work just fine.
Both halves of the 6SN7 run around 3.5 mA, the plate of the VA connects directly to the CF's grid. THe signal is than taken off the CF cathode, and run through a DC blocking cap, with a 100K to 470K resistor across the output to bleed off any DC on the output cap.

This will work with any common medium-mu twin triode, like 6SN7, 6CG7/6FQ7, 12AU7, 5963, 6189, ECC82, etc.

The schematic is similar to this one on Gary Kaufman's site:

http://www.the-planet.org/linestage2.html

Just factor in the resistor changes / mods as itemised earlier.

In fact the circuit is a lot closer to this one :

http://www.the-planet.org/images/407a.jpg


Image

Just replace the 1K VA cathode resistor with a red LED, and use a 6SN7 or 12AU7 instead of the 407A. B+ 150 to 160VDC, @ about 7 mA per channel. This may seem like a low voltage (the plate voltage is about 75V) but it operates well and sounds very good. I used a smaller output coupling cap, 1.0 uF, 400V (one of the green russian PIO caps)

I used oneof the 100K stereo ladder step attenuators from Hong Kong (on e-bay) and dispensed with the 0.47 uF input cap. THe step attenuator makes a perfectly good grid resistor, and doesn't "pop" when rotated, as it is a make-before-break switch.

DC filaments are nice, but not truly necessary, and the filaments should be "biased" at around 37-40V above ground (or 1/4 of the B+ voltage), so that the reference voltage sits midway between the two cathode's voltages of 1.6V and 75V.
That helps to reduce / eliminate any hum or instability problems.
(This applies to SRPP drivers, as well).

The B+ can be series or shunt regulated, if desired, but that isn't really necessary. Just icing on the cake ... Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_02 :o

I also built up the "407A" using WE396As, but it was very "squirrely" at first, though I did manage to tame it down with a few mods and some RFI "trickery" involving strategically located ferrite beads. I had to pick through the 396As to find two that weren't microphonic. It has far more gain than I really need for most applications, but it was an interesting "exercise". Yellow_Light_Colorz_PDT_11

/ed B
Last edited by EWBrown on Tue Feb 10, 2009 12:06 pm, edited 1 time in total.
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

PreviousNext

Return to diy hifi

Who is online

Users browsing this forum: No registered users and 1 guest