couple of questions about the 77 grey dod od

[ulysses]

hey guys

im looking at building the dod 77 grey OD. i couldnt find a schem so i traced markm's layout. 

there is no polar cap on the voltage divider - is there a technical reason it was left off? all the pics of the grey's in the gallery have 2 electrolytics??

mark, do you mind if i ask where you got the values for your layout?

cheers
ulysses

[John Lyons]

There are a couple larger threads on this here somewhere.
Try searching OD250 or '77 OD250 

I'm not sure the cap will make too much difference but the '77 values sound good.
Tungngruv is putting together a DOD "pre amp"(fet) together with a '77 OD250 that he thinks is really sounding good.
Hopefully he'll post that soon.

John

[markm]

I came up with the values from the 77 OD250 thread from here at the forum and modded my 250 layout to incorporate the changes.
Keep in mind though that the values indicated via the 77 OD250 thread are from a VERY early unit and probably differ from those that you'll find on ebay.
My layout is for the early production run and, has this circuit is fairly well-liked by those whom have built it.
It's quite different than the OD250 everyone is used to! 

[JHS]

Take the old yellow 250 schem as a basic.

In the grey 250

... diodes are 1N400..
... 1n caps are 1,5 - 2,2n
... no 10uF electrolytic cap in the bias divider
.. 4,7 or 10uF coupling cap is 22uF


For best results use a Philips uA741 as opamp and a 10nF CER I-cap give a little more grit to to sound.

JHS

[ulysses]

hey guys

thanks for those replies.

i did search the forum reading posts for about an hour - but a lot of people posted a lot of different ideas and i couldnt collate it easily..

i appreciate you summarising it for me jhs. it all makes sense now.

i will hopefully post some pics and clips later this afternoon when its built - im pretty keen to demo my amp (which i just modded with kt66's) - sounds amazing - it sounds so good i think im going to have trouble capturing it to tape properly. john, maybe you can help me as you seem to have some experience with mics- my sm57 seems to lose a lot of the bass response, is this normal? i have to mike it with a condensor with a pad to capture the real sound - prob is the sound of my marshall on 10 is pretty damn loud and the condensor has to be quite far away (1meter+) or it distorts the microphone itself - is there a reason my sm57 would be losing so much bass when close mic'd?

cheers
ulysses

[John Lyons]

Ulysses

There are some recording tips HERE for you.
A condencer mic for a tight close distortion sound is generally a bad idea as there is far to much high end and signal level.
The 57 should be fine..take a look at the link and PM me if you have any more questions.

By the way is the 57 in good shape? Sometimes if they have been dropped of beat up they sound thin.

John

[ulysses]

hey john

thanks for that reply.

yeah the sm57 is fairly new and has not been beaten around at all. i also have a badly beaten '80s sm58 - both give similar sounds.

the bass response of the sm57/58 is just no where near as real as it sounds when playing.

when i use my condensor with a 10db pad about 50-100cm away from the amp it sounds considerably better than the sm57/58 in any position. I will do an AB of the two for you and you can let me know what you think.

i will mike the condensor and the sm57 to a single session, split the channels and upload 2 different mp3's.

i will place the sm57 on a mini mic stand (about 1 foot high) specifically for recording amps. i read your artice - i will place the sm57 straight onto one of the speakers between the dust cap and the surround.

i will repost here when the samples are up.

cheers
ulysses

EDIT: thats some nice photography on your website also! did you do the panaramics with CS3? lovely scenery - is this where you live?

[ulysses]

hey john,

i uploaded the samples to my gallery (link in my signature below) - added a photo of the actual positions used.

the nt1a has a lot more room (bass) than the sm57 - i have never been able to make an sm57/58 sound like the sound from the condenser.

let me know what you think. they are similar so you might need to download them and play them in quick succession.

cheers
ulysses

edit: could only do one take becasue my kid was asleap - if you listen to the condenser track closely you may hear my wife yelling in the background 

[John Lyons]

Ulysses

Thanks for the compliments on the photos.Yes, I live there. Pretty nice views.
I use a Canon Digital Rebel and I stitched the photos together in Photoshop from about 20 shots of each scene.

Try micing the speaker as far away from the unmiced speaker as possible, you might be getting some phase cancellation.
The 57 has a high/mid range boost so it's not the most natural mic for a solo guitar sound. In context with a full band it will bring out a nice raw sound which fits nicely with other instruments, but it does boost the highs and mids in actuality.

The NT-1 will have flatter frequency response  and capture the bass better but also capture the high end better which can be edgy with a distorted guitar sound. The 57 as well as most dynamic element mics can take a beating with loud settings and still sound nice because they have a smaller range of frequencies that they pick up and the mics element compresses a little (in a good way)

For a clean sound a condencer will have a more jangly acoustic guitar sound with nice highs.
For a nice overdriven sound the 57 will smooth off the harsh edge of the sound.

I listened to the clips and they both sound nice. differernt but they sound "correct" or as I would imagine them to.
The 57 has a more forward sounding mid range which make it sound like it has less bass. It does have a less bass though...
If you want to make the 57 sound more full you can EQ out the boost. Look up the 57's Frequency response chart and cut with a about the same amount of boost that the 57 exhibits.

Try putting the mic to the left of the speaker and more towards the surround, and about 3 inches away from the grill cloth so it can breath a little.
As an alternative, try micing the amp from the back at about 1 foot away and near the top of the cabinet.
If you have a set of headphones and a friend over you can run the signal to the headphones and have the friend play the guitar as you move the mic around to different places and see how the sound changes.

John

[ulysses]

hey john,

thanks for the reply. i will try out your comments tomorrow.

as far as micing the back of the cab - thats what i did prior to getting the nt1a.

57 on the front, 58 on the back.

i was in a commercial studio with an engineer friend and he thought the 57 on the front sounded good. i said i wanted it to sound exactly like it sounds in the room - which it did not. we played around with the mics and the 58 on the back filled in the missing bass. he was surprised that it worked as he had not heard of doing it in his engineering degree and was reluctant to try it. sounded good though.

cheers
ulysses

[John Lyons]

Ulysses

To get a close room sound you should find a place in the room that you think the amp sounds good and place a mic there.
For room sounds Condensers are good mics to use. Anything further than a few feet away from the amp condencers will work well.

I didn't know you were going for a room sound... You can use both the 57 and the NT-1 to get a nice room sound.
The main thing i getting a nice room/natural sound is to make sure that the two mics are in phase. Just make sure the second mic is at least three times the distance from the amp than the first mic. When they are out of phase the bass will get cancelled and the sound will be hollow and lack bass and depth. Just like a phase shifter when stuck in one position and not oscillating in and out of phase.

Usually putting the condenser at ear level (while standing up) about 5 feet off the ground and 6 feet or so away from the amp  pointing at the cabinet works well with a close dynamic mic a few inches from the grill cloth. That should put you close to the sound you want.

Make sure the room sounds good because if it does not you will hear how bad it does sound.


John