Cassette head preamp circuit wanted

[greenhorn]

I've ended up with another couple of decks from a deal gone sour with an online seller. Let's just say that they make my earlier technics RS-M6 look like it's in mint condition

Opening them up was like doing a post mortem. anyway, one of the problems is that one channel of the tape head preamp is shot. It's a VERY simple circuit with two transistors, but I can't for the life of me, figure out what's wrong. I've swapped the transistors, but still no luck.

At this point i thought I'd not waste more time on this, swap in a replacement DIY preamp stage (anyway the head is not original) and start troubleshooting the downstream issues.

Can anyone point me to a Low noise Tape preamp circuit, preferably easy to make on a dot pcb, without any exotic components?


I saw the TDA1522 was one feasible option. Any other recommends?

 

[omishra]

Any LA3161 based circuit?

Consider circuit before volume control in below diagram, its good sounding too.

http://www.electronicsforu.com/efyl... Tape Head Preamplifier For PC Sound Card.pdf

 

[greenhorn]

Wanted to know if discrete circuits (the ones with a two low noise transistor stages and transistor feedback) are better than the ones with these tape preamp chips (provided the supply voltage is regulated etc). Either way, the original Sendust head is missing, and a generic replacement head is there right now.

 

[reubensm]

Wanted to know if discrete circuits (the ones with a two low noise transistor stages and transistor feedback) are better than the ones with these tape preamp chips (provided the supply voltage is regulated etc). Either way, the original Sendust head is missing, and a generic replacement head is there right now.

if you are looking for convenience, the bar chip based circuit is the best. if you are looking for quality, the discrete circuit would be better. with your deck, attempt to get the service manual or draw out the circuit diagram going with what you see on the PCB, mark components separately for both channels, compare them. They've got to be similar. If the deck had been through a cowboy mechanic's hands, they might have attempted to alter the circuitry.

 

[sarith]

I've ended up with another couple of decks from a deal gone sour with an online seller. Let's just say that they make my earlier technics RS-M6 look like it's in mint condition

Opening them up was like doing a post mortem. anyway, one of the problems is that one channel of the tape head preamp is shot. It's a VERY simple circuit with two transistors, but I can't for the life of me, figure out what's wrong. I've swapped the transistors, but still no luck.

At this point i thought I'd not waste more time on this, swap in a replacement DIY preamp stage (anyway the head is not original) and start troubleshooting the downstream issues.

Can anyone point me to a Low noise Tape preamp circuit, preferably easy to make on a dot pcb, without any exotic components?


I saw the TDA1522 was one feasible option. Any other recommends?

I have a few head pre with me. Most of them IC and transistor based. I would say LA3160 is really nice if you can find one. You can use C547/48 or 1815 transistor based head pre for easy construction.

There are better sounding ones but not that easy to build (like the KIA and AN series). I have swapped KIA series IC with LA series by modifying few other components like the transistors, caps, resistors etc.

I am using one and happy with the result. (low noise, warm sound, nice bass). How about TDA1054?

 

[greenhorn]

http://diyaudiocart.com/Stereo Head Pre-Amplifier (Deluxe)
ordering this as a stop gap for now.

The current setup has 2 2SC1312's. The voltage levels are different in both the L and R channels. In the channel that doesnt work, the base and the emitter of the the first stage are at more or less the correct voltage, but the collector is .5V more (3.2V instead of 2.7) and because of this, the second stage seems to have gone into saturation because it's direct coupled - Vce is only about 1V - it should be around 6. I have the schematic, I had swapped the 2sc1312's with some BC547's I had lying around. I thought it might work with some added noise, but didnt. the resistors and continuity check out fine. Will have to see if i can get some 2sc1312's or KSC1845's - these seem to be the modern equivalent.

This is an Akai CS-M02. I got hold of the schematic, but it's in some other language. but the diagram is enough. When I got it, i found the VU meters tracking suspiciously close to each other, and noticed that i was missing some of the instruments in some music. Opened it up to find out that some mech had connected a wire from the output of One channel level pot to that of the other one!

That's just the start of it . I got a Sansui D95M with a butchered transport. Some keys wont engage, and its a funky transport - it's manual with piano keys, but it has two solenoids, one for auto stop - no idea about the other one, maybe for timer start. Thankfully the PCB is neatly marked with lines saying the function of each part. That one has unstable speed (motor and head are not original) and since the tape counter belt is missing, the auto stop solenoid has been disconnected - it keeps engaging otherwise. Let's see where this goes.

 

[sarith]

http://diyaudiocart.com/Stereo Head Pre-Amplifier (Deluxe)
ordering this as a stop gap for now.

The current setup has 2 2SC1312's. The voltage levels are different in both the L and R channels. In the channel that doesnt work, the base and the emitter of the the first stage are at more or less the correct voltage, but the collector is .5V more (3.2V instead of 2.7) and because of this, the second stage seems to have gone into saturation because it's direct coupled - Vce is only about 1V - it should be around 6. I have the schematic, I had swapped the 2sc1312's with some BC547's I had lying around. I thought it might work with some added noise, but didnt. the resistors and continuity check out fine. Will have to see if i can get some 2sc1312's or KSC1845's - these seem to be the modern equivalent.

This is an Akai CS-M02. I got hold of the schematic, but it's in some other language. but the diagram is enough. When I got it, i found the VU meters tracking suspiciously close to each other, and noticed that i was missing some of the instruments in some music. Opened it up to find out that some mech had connected a wire from the output of One channel level pot to that of the other one!

That's just the start of it . Let's see where this goes

I have used it. I have used all of their boards. All of them are good. This board gives you a low noise, good mid and not sparkling but good enough treble. Bass is not deep though. Doing mod in components makes bass better with a slight change in mid fq.

This is the head pre I was talking about. I changed the IC and few components and it sounds pretty good. (Photo with a Nokia 6303 average quality cam). I assembled it with readily available pcb.

Imageshack - jgh6.jpg

Imageshack - 6ek1.jpg

 

[greenhorn]

I think I had used one of those in a deck I made in college.

Sounded very nice with this mechanism with an original sony head. Put it into my Panasonic Hi Fi hoping it would improve the SQ - it didn't. Its still inside it Can't be bothered to go all the way to tvm to dismantle and get it heh

the board you posted, am guessing the ceramic caps in the output are the ones you had put instead with larger values than the smaller original film caps for coupling?

 

[sarith]

I think I had used one of those in a deck I made in college.

Sounded very nice with this mechanism with an original sony head. Put it into my Panasonic Hi Fi hoping it would improve the SQ - it didn't. Its still inside it Can't be bothered to go all the way to tvm to dismantle and get it heh

the board you posted, am guessing the ceramic caps in the output are the ones you had put instead with larger values than the smaller original film caps for coupling?

Actually I have moded all the caps and some resistance from the said ones in the circuit. You can use LA equivalent for a different sound. The one you have shown is crystal board. I have used most of their boards and I liked them.

I still have the crystal one in my collection . The ready made head pre is bass oriented so I started messing with the original circuit for some time and I found out the current setup.

Unfortunately head pre is not available from any other maker than online. So I collected few leftover pcbs (green ones for 80/pc). Nice mech by the way (auto reverse?). I have Sony Japan head and it sounds good.

 

[greenhorn]

traced the transport woes to a broken spring. (apart from the solidified grease)

What can be done with this? M Sealing this to the base is the only thing that comes to my mind.

This leaf spring is what pulls the sliders with the slots cut for the piano keys